Astronomer Discovers New Way to Measure the Distance to Other Galaxies

A research astronomer at Mount Wilson Observatory has discovered a new way to measure the distances to other galaxies.

E. P. Hubble is a former college athlete and US Army Officer who somehow ended up in the stargazing business. Shortly after his discharge, he was hired by Mount Wilson and soon developed his innovative trick.

Hubble’s technique builds on the work of previous scientists, and uses a special type of variable star. Early on, astronomers recognized the bright star Delta Cephei changes brightness about every five and a half days. Over time, quite a few similar stars have been discovered, with different periods and of different brightnesses.


The brightness of Delta Cephei varies regularly over several days.

Source: ThomasK Vbg

For a long time, it wasn’t clear if brightness related to period, because how bright a star looks from Earth (known as its apparent magnitude) depends both on the star’s intrinsic luminosity (or true magnitude) and how far away it is. Since scientists couldn’t measure the distance to any of these stars, called Cepheid variables after the nearest specimen, the relationship between their brightness and period was a mystery.

That is, until an assistant astronomer named Henrietta Leavitt started studying them.

Leavitt focused on stars in the Small Magellanic Cloud, an irregular region near the edge of the Milky Way. The Cloud is so far away that its size is negligible compared to its distance from the solar system. Leavitt reasoned that brighter Cepheid variables in the Small Magellanic Cloud would be be more luminous not just in appearance but in fact, so she could determine whether that had anything to do with the period.

As it turns out, brighter Cepheid variables have a longer period, while smaller ones have a shorter period. With a little math, astronomers can work out the true brightness of a Cepheid variable from how long it takes to complete a full cycle.

Leavitt’s supervisor at Harvard College Observatory, Harlow Shapley, realized that this relationship could determine true distances in space. Shapley used a statistical analysis of Cepheid variables to determine their true distance in space, as indicated by the Doppler shift of their spectral lines.

Hubble was the first astronomer to apply this tool to measuring galactic distances. He made a dedicated search for Cepheid variables in other galaxies, the Andromeda Galaxy in particular.

The results were shocking. All the galaxies where Hubble found Cepheids turned out to be much further away than scientists had previously thought. Several other teams have already confirmed the findings, but it will probably take astronomers and physicists a years to figure out all the implications.

Happy Amazing Breakthrough Day!


Some Things That Affect Spacecraft Orbits

The derelict Chinese space station Tiangong-1 is expected to re-enter this weekend. The precise time and location aren’t easy to predict, and this has caused some concern among various members of the public. A space station is much bigger than a normal satellite, and it’s conceivable that larger pieces could cause major property damage or even injuries on impact. So why don’t we know where it will hit?

The answer is actually pretty complicated, because there many, many things which affect the paths of even simple, Earth-orbiting satellites. Some are immediately obvious, like drag from the upper atmosphere and Lunar perturbations. A lot are more subtle, like interference from Earth’s magnetic field. In this post I’d like to briefly explain all the significant factors, without going into too much math. Hopefully this will emphasize to specialists and laymen alike the value of responsible debris mitigation and the importance of safely disposing old spacecraft before ground controllers lose contact.

Atmospheric drag is, of course, the largest force affecting satellite orbits, and the reason Tiangong-1 is re-entering. As I explained in my last post about orbital mechanics, there is no clear upper edge to the atmosphere. Below about 500 kilometers, the atmosphere is still sufficiently thick to de-orbit most debris. Satellites above this altitude can remain in space for decades without any maintenance, and geosynchronous orbiters will last centuries or even millennia.

Low Earth Orbit is the natural regime to place crewed spacecraft, since the debris risk is dramatically lower. (The radiation hazards are also significantly higher in the medium orbits, and our current manned capsules can’t easily punch through the Van Allen belts.) This is fine as long as the spacecraft is operational and performing orbital maintenance maneuvers. The International Space Station has to perform these regularly.


ISS altitude over the last year. Discontinuities between decay regions represent maneuvers to raise the orbital height.


Atmospheric drag on spacecraft is governed by a simple equation, which will be extremely familiar to even underclassmen aerospace engineers:

F_D = \frac{1}{2} m C_D \rho A V^2

In essence, this equation states that drag force F_D on the spacecraft is equal to half the product of the spacecraft mass m, cross-sectional area A, atmospheric density \rho and the square of the relative velocity V^2, all multiplied by a fudge factor C_D. We call the fudge factor the drag coefficient, and for satellites it tends to fall between 2.1 and 2.3, though higher values are common depending on the spacecraft configuration and materials used.

Density is the biggest unknown factor. It varies based on the altitude, time of day, time of the year, and how active the Sun has been lately. A number of these factors also affect relative velocity, because the atmosphere isn’t still. Upper atmospheric winds can be significant, often hundreds of meters per second.

Altitude plays a role, because different gases have different masses.  Mass is related to velocity via kinetic energy and the ideal gas law, which essentially states that the velocity of a particle, for a given internal energy, with be greater if the particle has a lower mass. Essentially, heavier gases like molecular oxygen and nitrogen will hug the planet, while lighter gases such as hydrogen and helium can easily climb into the thermosphere.

Additionally, the amount of solar and cosmic radiation is higher the further one rises. Collisions with energetic particles cause molecules to break into their components, so the frequency of atomic oxygen and nitrogen increases dramatically. This affects the effective density of the upper atmosphere and therefore the drag force. Since the amount of solar radiation is highly variable over the short term and changes with the eleven-year solar cycle, the numerical density of the upper atmosphere isn’t at all constant.

Solar radiation was ultimately responsible for the failure of a previous space station: Skylab. Initially NASA expected it to remain on-orbit till the early 1980s, when the space shuttle could have pushed it higher. The sun was particularly active during that era, however, and by the mid-1970s it was clear that the station would re-enter much earlier. A special mission would have saved it, but NASA never seriously planned one and Congress never allocated any funds. Skylab disintegrated over Australia on July 11, 1979. Despite widespread concerns, there was very little damage and no one was hurt, though one jurisdiction fined NASA $400 for littering.


Skylab photographed by the last departing crew in February 1974.

Source: NASA

Temperature changes over the course of the day and year also affect the upper atmospheric density. Warm gases move faster and rise higher, and which can be seen in aggregate as an increase in pressure. Warm air near the surface displaces upwards, effectively increasing the size of the atmosphere. This can significantly increase the drag which a satellite experiences.

Generally speaking, day is warmer than night. Summer is warmer than winter, though of course that depends on which part of Earth you’re considering. (Remember that seasons are caused by axial tilt, not the eccentricity of our path around the Sun.) Advanced density models take all of these factors into consideration—date, time of day, latitude, longitude, altitude, and multiple indices of solar activity.

Atmospheric density is the biggest effect that astrodynamicists have to consider, especially for satellites in low orbits, but there are several other major forces which can cause significant accelerations, particularly upon smaller objects. From Newton’s Second Law, the acceleration a force has on an object is directly related to the mass of the object in question. Space stations have high masses, so only large forces can affect them. Cubesats have much lower masses, and can see large perturbations from forces that space station controllers happily ignore.

One of the larger effects we have to worry about is Earth oblateness, usually abbreviated as J_2. This is a low-order model of Earth’s shape, which is actually really complicated. High-fidelity models often reach high two-digit orders, though these are only needed for the most precise of missions.

The effect of J_2 is to reduce the inclination of an orbit, while also causing the orbit to change its orientation around Earth. The essential mechanism is that, because Earth is not exactly a sphere, when the spacecraft is north of the equator, it will be experienced an unbalanced force pulling it south, which the reverse occurs when it passes below the equator again. Over time, the satellite trajectory will approach an equatorial orbit, precessing around the pole.

We can define a J_2 value for every planet, because their non-sphericity is caused by rotation. Other gravitational effects may also be present, though these can usually be neglected. Luna is a notable exception. The internal mass distribution of our moon is so irregular than only a handful of orbital inclinations are stable. We learned this the hard way when Apollo astronauts left hand-launched microsatellites in orbit. One lasted for over a year, while other crashed within weeks.

This alludes to another important point: anything the size and density of a planet is not going to be perfectly rigid. In addition to ocean tides, gravitational effects from the Sun and Luna also cause internal tides, as the solid material within the planet bends slightly. These are called solid Earth tides, and affect satellite orbits about an order of magnitude more than the ocean tides. Usually these can be neglected, but precision gravity models need to taken them into account.

Accelerations of about the same order of magnitude (\approx 10^{-12} \ \textrm{km}/\textrm{s}^2) arise from general relativity. Because the spacecraft is travelling around a deep planetary gravity well, there will actually be a small but measurable change in velocity over time due to the spacecraft’s velocity through space. Mathematically, this is stated as:

a_r = -3\frac{\mu}{r^2}\frac{v^2}{c^2}

where a_r is the relativistic acceleration, \mu is the standard gravitational parameter for the body in question, r is the distance of the spacecraft from the body, v is the instantaneous velocity of the spacecraft, and c is the speed of light. This acceleration will get smaller the further the spacecraft is from the primary body, and the slower it is moving (which, incidentally, spacecraft in higher orbits tend to do).

Generally, the position effects of relativity will be on the order of a centimeter, so orbit determination on larger scales can neglect that easily. Spacecraft in higher orbits probably won’t be affected, though spacecraft in very low orbits may see significant effects if they remain in space for a long time. The planet Mercury, orbiting so close to the massive Sun, experiences a dramatic relativistic acceleration. Astronomers once suspected that another planet lurked close to the Sun, perturbing Mercury’s orbit in a more typical way, until Einstein’s theory closely predicted the observed variations.

The Sun and Luna cause the greatest gravitational perturbations to Earth orbiting satellites, dragging the satellite slightly astray as it swings around our green planet. If we want to be really precise, though, we need to consider accelerations from other worlds, as well. Astrodynamicists rarely find a case where any besides Venus and Jupiter can be worth the trouble (and even those rarely). Venus is important because it is close to Earth, while faraway Jupiter is merely massive. Mars is nearly as close as Venus during much of its orbit, but is so much less massive that we neglect it entirely.

There’s one final type of force which affects orbits directly: radiation pressure. This can be somewhat counter-intuitive, because the majority of the radiation in question comes in the form of massless photons. F = ma would seem to break down. Massless though they be, photons carry momentum. The rigorous definition of Newton’s Second Law of Motion is really that force is the change in momentum, which is the product of mass and velocity. We simply assume that mass remains constant in most applications.

Since photons carry momentum, however, they can produce a force directly. It’s not much, but when you consider how many photons are streaming through space each second, it turns out to be significant. The radiation flux from the Sun is usually around 1376 \textrm{W}/\textrm{m}^2, while the reflected radiation from Earth is around 459 \textrm{W}/\textrm{m}^2. Dividing by the speed of light, we find the two radiation pressures.

The force F_s from this pressure P_s is a function of the cross-sectional area of the spacecraft and the angle \alpha between it and the incoming photons:

F_s = P_s\cos\alpha

The same equation can be used to calculate the effect of Earth radiation pressure, though the incidence angle will necessarily be different.

At this point, let’s return to the question of Tiangong-1. We’ve seen a great many reasons why it is challenging to make long-term predictions about its orbit. However, there is another problem which affects derelict spacecraft in particular: we don’t know its orientation in space. Now a large spacecraft can be imaged by radar, which gives us some idea about its orientation, but that will not work for smaller satellites. To make matters worse, it turns out Tiangong-1 is rotating, so its orientation will be different depending on when we look.

“What causes this rotation?” you might be wondering. I’m glad you asked. There are four major disturbance torques that attitude control engineers have to consider, though several of the above forces can also cause smaller torques.

At low altitudes, the largest torque by far is aerodynamic torque T_a. Recall the drag force equation I introduced above. Any offset between the center of the cross-sectional area and the center of mass will produce a moment arm L, over which the the force can act to induce rotation:

T_a = F_D L

We again find ourselves facing the fact that we may not know the cross-sectional area. If the precise forces and and orientation are well-known when ground controllers lose contact, we can model its rotation forward for a time, but not long enough to predict the re-entry of Tiangong-1.

But that’s not the end of it. There’s also force from Earth’s magnetic field, which will align any magnetized object with it, including spacecraft. The magnetic torque $T_m$ is a function of the residual magnetic dipole M on the spacecraft, the Earth’s magnetic field strength B, and the misalignment \theta between the two:

T_m = MB\sin\theta

The magnetic field strength is a function of altitude r and latitude l, as follows:

B = \frac{B_0 r_0^3}{r^3}\sqrt{3sin^2l + 1}

where B_0 is the magnetic field strength at sea level (3\times 10^{-5}\ \textrm{T}) and r_0 is the average radius of Earth (about 6,370\ \textrm{km}).

Finally, the spacecraft orientation leads to torques due to the small gravity gradient between its highest and lowest components. Measuring gravity gradient torque T_g requires very accurate information about the moment of inertia distribution, which is often difficult to determine without detailed blueprints. It is also a function of altitude above the planet, because gravitation force (and therefore torque) drops off with increasing distance, and the angle \theta off vertical”

T_g = \frac{3\mu}{r^3}\lvert I_z - I_y\rvert\theta

where I_y and I_z are the moments of inertia about the y– and z-axes, respectively.

As a general rule, the aerodynamic and magnetic torques dominate at lower altitudes, but may be significant for higher orbits or with special spacecraft configurations. These have to be determined on a case-by-case basis.

So that’s why we don’t know exactly when or where Tiangong-1 will re-enter. There’s a lot of variables involved, many of which are difficult to estimate, and often are strangely coupled at higher orders. There are many things which can be improved if we’re willing to spend enough money, such as building better atmospheric and gravitational models or tracking debris more regularly. Ultimately, though, there’s no substitute for responsible disposal at the end of a spacecraft’s mission, either into a stable graveyard orbit or by de-orbiting at a safe location.

…and all of this assumes that the spacecraft generates no thrust. Imagine how complex it gets when we consider outgassing!


  • Brown, C. D., Dukes, E. M., Elements of Spacecraft Design, edited by J. S. Przemieniecki, AIAA Education Series, AIAA, New York, 2003.
  • Knipp, D. J., Understanding Space Weather and the Physics Behind It, 1st ed., McGraw Hill, New York, 2011.
  • Moe, K., Moe, M. M., “Gas-surface interactions and satellite drag coefficients,” Planetary and Space Science, Vol. 53, No. 8, 2005, pp. 793–801
  • Montenbruck, O., Gill, E., Satellite Orbits: Models, Methods, and Applications, 1st ed., Springer-Verlag, Berlin, 2000.
  • Vallado, D. A., Fundamentals of Astrodynamics and Applications, 4th ed., Microcosm, Hawthorne CA, 2013.

Book Review: Artemis

Andy Weir made it big with The Martian, a survival story about an astronaut abandoned on Mars. The Martian is a very individualized book, focusing mostly on the exploits of a single person, with brief interludes to small teams at NASA and in space.

Artemis is a very different sort of story. Like The Martian, it is set at some unspecified point in the future, probably still the mid-to-late 21st Century. But instead of an astronaut alone on a planet, Artemis is the tale of a smuggler trying to pay off her debts in the first Lunarian city. It may only be about 2000 people, but they’re packed in tight. That itself is a very different sort of setting.

It’s also a different sort of conflict. Mark Watney was trapped on Mars essentially by accident. Jasmine Bashara is paying a much more dangerous game: industrial sabotage for one of the richest people on the Moon, who wants to steal a government contract from even richer people on the Moon. Well, what passes for a government contract. Artemis doesn’t really have a coherent political structure, or even a real currency. Transactions are conducted in soft-landed grams, or slugs, which are basically a credit with the megacorporation that set up the lunar colony in the first place.

That turns out to be a significant plot point. Slugs aren’t real currency, and aren’t monitored as such. Criminal organizations from Earth exploit this little fact to launder money on Luna, with marginally-profitable aluminum production as a front. They aren’t happy when Jasmine destroys several of their ore collectors. Barely making it back into the city, she’s suddenly on the run from—not the law, exactly, but definitely from the mob. Her employer is brutally murdered and she realizes her family is in danger. She goes into hiding and asks her estranged father to do the same.

As Jazz tries to figure out what’s going on, she realizing that money-laundering was just the beginning. That story could be told anywhere, but this is Artemis, the only city outside Earth’s gravity well. The real MacGuffin in a new technology, worth at least billions of dollars, that can’t be manufactured in a high-gravity environment. If the cartels get control of its production, then Luna will be in their pocket, forever.

She assembles an unusual team to finish the job of taking down Sanchez Aluminum. An ESA scientist, the chief of the EVA guild (which tried to prevent her from making it into the city), an ex-friend (who let her back in despite his better judgement), and her father, a career welder. With the tacit blessing of Artemis’ chief executive, they plot to shut down the Sanchez Aluminum facility directly.

It’s a relatively simple plan: scare the staff out of the smelting facility, breach the dome’s hull, trick the control system into thinking the smelter is undertemperature, and let it overheat trying to compensate. Once the facility is out of commission, Sanchez Aluminum will lose their power-for-oxygen contract, killing their profitability. Jazz’s erstwhile employer had a large reserve of oxygen and machinery built up, and his orphaned daughter will step in with the same offer to take over supplying the city in exchange for unlimited free power.

Okay, maybe it’s not a that simple of a plan. And, this being fiction, something has to go wrong. Most of the Sanchez Aluminum employees evacuate per plan, but one doesn’t. Loretta Sanchez, mastermind of the company, thinks she can resolve a little toxic gas alarm by herself. Jazz realizes that Sanchez has no idea what’s about to happen to her prized smelter, and barely manages to force her into the jerry-rigged airlock.

As they head back for the city, they realize there’s a problem. No one is answering the radio. Sanchez runs through the possible products of the smelter explosion and figures out that a massive amount of chloroform has entered the city’s air supply, incapacitating the entire population. Contrary to the movies, chloroform kills after about an hour of exposure. They’re on the clock.

The next thirty minutes are complication-tastic and I won’t try to summarize them. Long story short, Jazz has to head outside to open up the oxygen tanks, and can’t do it in the tourist pressure suit she donned in haste. (They’re called hamster balls for a reason.) She punctures the suit to get leverage, fully expecting to die in the process.

She wakes up in the city medical center, with the sort of radiation and heat burns one would expect after being exposure to the vacuum of space and lunar surface. Her EVA partners managed to get her inside before hypoxia did permanent damage, and the city is more-or-less saved. No one died of chloroform poisoning, and the low gravity prevented any fatal injuries.

The mob may have been deactivated in Artemis, but Jazz is still on the hook for a variety of crimes. The head administrator intends to deport her to Earth, which wouldn’t quite be a death sentence, but not exactly a good outcome for our protagonist.

Jazz manages to strike a deal. She’s the dominant smuggler in Artemis, and always keeps careful control over what comes in. Without her, less scrupulous characters will step in to satisfy demand. In exchange, she gives the city a “‘Deport-Jazz for Free’ card”, a confession to her various offenses which they can use if she breaks an official rule again.

By this point, she’s paid off her debt: a new workshop for her father with the equipment and material stock destroyed in a fire Jazz started during her irresponsible teenage years. That costs about half the fee she’d earned for taking down Sanchez Aluminum. Artemis takes the rest, in the form of a “voluntary donation” since they don’t technically have fines. From an economic standpoint, she’s back to square one.

Socially, it’s a different story. A lot of Artemisians are unhappy with her, but she’s also earned a lot of trust back from her friends and family. It’s also strongly implied that she’s going to start dating her scientist friend, though that isn’t definite.

I’ve seen some criticism of Weir’s decision to write a female narrator. Some have even gone so far as asking whether he’s talked to a woman. According to the acknowledgements, he has, and I’m willing to give him the benefit of the doubt of this. Just because a particular male-written female character feels unnatural to you doesn’t mean she’s unbelievable. Personally, I find plenty of male-written male characters unrelatable.

There’s a lot of different ways to be a human. The space of possible minds is bigger than anyone can possibly imagine, and our experiences are not universal. It’s totally absurd to demand that someone raised in a totally different culture and community to duplicate my own mental architecture. Sure, there’s general principles to get right, but details? Impossible. It’s called speculative fiction for a reason, and seeing coherent mind-models different from my own is part of why I enjoy it.

Some may be tempted to compare Artemis to The Moon is a Harsh Mistress, but I would caution against that. Yes, they’re both stories about lunar communities coming into their own, but Artemis has dramatically less social and political theorizing. Displaying some trace of economic comprehension doesn’t automatically make it a libertarian novel, just a more satisfying one.

In the end, Weir managed to write a science fiction thriller without firing a single raygun, blaster, or bullet. Instead, he manages to tell a very human tale through very real science. I know some people find that tedious, but I enjoyed it. The worldbuilding is adequate, though of course I have a hundred questions about Artemis and society on Terra that will probably never be answered. But if Weir does decides to set another book there, I’m guaranteed to read it.


Book Review: Introduction to Objectivist Epistemology

Introduction to Objectivist Epistemology is what it says on the tin: an introduction. The original book was extremely short, barely 100 pages. An additional essay by Leonard Peikoff and extensive discussion transcripts are included in the second edition. The transcripts come from a series of workshops conducted between 1969 and 1971, discussing Objectivist epistemology with about a dozen (anonymous) professors.

I would advise against reading the appendices on a first pass through the book. It’s not that they’re bad, but they contain a lot of high-level material that takes a long time to process usefully. Fully comprehending the basic concepts put forth in the main text is higher priority. The appendices are included to help flesh out the information academically. Lay readers can probably skip them entirely.

The basic concept which Rand is trying to get across is measurement omission. By this, she means the process of noticing similarities between the essential aspect of concretes, and thus developing general categories that omit the non-essential characteristics of the concretes. This, Rand argues, is the crux of concept-formation.

Objectivist concept theory is very similar to the reductionist model. Unfortunately, I don’t think Rand spends enough time explicitly arguing against the idea of things having essences. A lot of Objectivists still get hung up on “but it is a X?” questions rather than one would naively expect. This is a metaphysical matter, but a relevant one. Rand is very clear in all her works that epistemology follows from metaphysics. Getting epistemology right is a lot easier you’re your metaphysics is right, though developing an accurate metaphysics requires a functional epistemology.

Spending more time on philosophical development would have been valuable. Instead, the details of concept formation—what concepts are valid, what concepts aren’t, how to tell the difference, and so on—are the bulk of the book. This is, possibly, more practical, and Objectivism is a philosophy for living on Earth.

Still, I’m not sure that practical philosophy can achieve wider acceptance without stating the case clearly, in language that serious lay readers can understand. The appendices cover a lot of important ground, but not in the most efficient manner. Writing summaries probably would have been more efficient, but ARI Objectivists tend to tread carefully when it comes to interpreting what Ayn Rand really meant. Naturally, they opted for edited transcripts over new material. This gives a better insight into the ensuing philosophical development, but makes untangling final conclusions slow and laborious work.

Nevertheless, I would recommend Introduction to Objectivism Epistemology. It covers a number of useful ideas for developing a personal theory of knowledge, and warns against several common pitfalls. The main body of the text is interesting and readable, but the appendices are a bit more challenging. Non-academics should probably just skim for material that looks interesting and avoid reading those sections in their entirety.


Annual Themes

The last few years have seemed to have a pattern for me.

Before 2014, I don’t think I was the same person as afterward. I was very young, and only beginning to develop some kind of adult wisdom when I arrived at college. Feeling the brain develop is a strange sensation from the inside, and the process didn’t really finish fast enough. I spent the latter half of 2014 struggling with the consequences.

New Year’s Eve of that year was one of the first halfway-decent mental health days that I’d had in many, many months. It wasn’t a grand victory or anything—I cleaned (one corner of) my room, and piled up a few books to read. But it was something. 2015 felt like I was, slowly, becoming myself again. Or maybe for the first time.

In 2016, I adjusted to that role, but it didn’t go particularly well. Academically, I did alright, but found myself struggling again. I tried to blog regularly and failed. I read more, though hardly enough. My relationship peaked and ended. Mom and Dad decided to move. By December it felt like my life had mostly fallen apart around me.

This year began with uncertainty. I didn’t know how I was going to do in school, and my personal life might as well’ve been nonexistent. Classes proved interesting, but my performance left a lot to be desired.

I disappointed some of my classmates, and only after getting some scathing peer evaluations did I really shape up. I pulled my first all-nighter since 2014 on May Day. This fall I put in a lot more effort and hopefully rebuilt some part of my reputation.

2017 was the year that I learned how to try. 2018 is the year I actually try.

Talking about your specific goals is generally a poor idea, so I won’t delve into the details of what I’ll be trying to do. I’m hesitant to even announce my intention to try, but since one of the major items is a group effort with people I respect, there will be some accountability for it. Even so, I’m already a bit behind. There were things I’d planned to do over winter break, and I haven’t completed as many of them as I’d wanted. I need to get to work, and talking about it won’t help. So stop “trying” and just try.

Book Review: A Canticle for Leibowitz

A Canticle for Leibowitz was one of the last science fiction books about nuclear war published while surviving such a conflict was relatively plausible. ICBMs weren’t really a thing yet, so most of the bombs would have to be delivered by submarines, intermediate-range missiles, and airplanes. The death toll probably would have been a lot lower than it would have been later.

Miller speculates on what might come afterwards, and presents an all-too-plausible hypothesis. Once the dust settles and people start assembling a post-war society, the survivors decide to blame the engineers and scientists for the war, rather than the public’s elected officials. Technical types are killed en masse, to the point that “Simpleton” is the new comrade and mere literacy is a carefully-guarded secret.

A few professionals escape detection, often seeking refuge with the Catholic Church. The church apparatus survives and is now headquartered in North America, though it’s not clear from the text whether this is a relocation from Rome or a new establishment. The Church can’t protected everyone, but they take in many of the persecuted intellectuals and shield them from public wrath. This particular plot point seems implausible today, but strikes me as reasonable if World War III had happened in the early 1960s.

One of these professionals is Isaac Leibowitz, a Jewish electrical engineer who developed weapons systems for the military. He converts to Catholicism after the war, and with permission from New Rome, founds an Albertian Order in the southwest to hide and preserve ancient knowledge until such time as humanity wants it once again. Before the work is complete, however, he is captured and killed in the great Simplification. To the members of the abbey, Leibowitz a saint. Outside of it, no one knows his name.

The story begins in the 2500s, as Brother Francis of Utah performs his Lenten hermitage as an inductee to the Order. He is visited by a Wanderer, who frightens Francis, but who marks a rock that would make a good keystone for the stone structure which Francis is building to protect himself from wolves. After the wanderer leaves, Francis removes the stone, and causes an unexpected cave-in. That pile of rubble covered the opening to a fallout shelter. In the antechamber, Francis finds a human skeleton, and a toolbox that belonged to the Blessed Leibowitz himself. Francis’s amazement is doubled when the toolbox contains an actual blueprint, the first found in readable condition for centuries.

Unsurprisingly, this does not ease along Francis’s induction. Eventually, though, he is inducted, and the evidence satisfies New Rome that Leibowitz should be canonized. Investigators conclude that the skeleton belonged to Leibowitz’s wife. Proving that she died before he took the monastic vows was the last hurdle before his Sainthood.

As a monk of Saint Leibowitz, Francis becomes a scribe. His skill develops, and he soon begins to copy the writings he found in the cave, culminating in the blueprint. No one understands it, but it must be dutifully preserved regardless. Once the copy is made, Francis does research in the archives, and decides to produce a more dramatic, illuminated copy.

The Illuminated Blueprint is a success, and the Abbot decides to sent both the copy and original to New Rome. Francis is sent, travelling alone, and is robbed by mutants along the way. The mutants take the illuminated copy and hold it for a ransom that Francis could never pay. Discouraged, he continues with the original to New Rome.

Meeting the Pope, however, reassures him. The Pope points out that the mutants left the original holy relic, so the illuminated copy provided a great service. As Francis prepares to return to the abbey, the Pope further gifts Francis the gold necessary to pay the ransom. However, Francis is skilled as he approaches the robber’s lair. The Wanderer is watching, though, and denies the mutant murderer a meal. Eventually, the Wanderer returns Francis’s corpse to the abbey.

The second part of the book takes place six hundred years later, as humanity approaches a renaissance. The plot of this section is much less dramatic and memorable, focused on the scientist Thon Taddeo’s visit to the abbey from Texarkana. The monks barely beat Taddeo to the reinvention of the electric lightbulb, initiating a long dialogue on the conflict between science and religion.

War is brewing between the southern city-states. Taddeo gathers as much information as he can, and soon must depart. The abbey prepares to defend itself and take in refugees from the nearby town, on the condition that able-bodied men fight alongside the monks. We’re not told if the abbey even needs to defend itself in the coming wars. The section ends with a cynical Poet, tolerated by the long-suffering monks, dying in the sun after trying to save some harmless refugees from blood-thirsty cavalrymen.

The final part of the book picks up in 3781, as humanity prepares for atomic war once again. The first several pages break dramatically from the narrative style of the rest of the book, and the final part is punctuated with a few press conference transcripts from the Atlantic Confederacy’s Defense Minister. I think this is an artefact of the book’s history as a fix-up. More introduction was necessary when these final chapters stood by themselves, and that introduction was probably longer at the time.

In practice, we’re quickly shown a world with atomic spacecraft, interstellar colonies, and temperamental translation computers. Leibowitz is popular as the patron saint of electricians, and mostly forgotten for his work in booklegging.

The Atlantic Confederacy and Asian Coalition have, for undisclosed reasons, found themselves in a cold war. It builds slowly. An atomic accident—possibly a test—occurs in the Asian Coalition. The Atlantic Confederacy considers this violation of international law an act of war, and fires a warning shot over the Pacific.

Observers in the abbey watch the atmospheric radiation count rise and become worried. Realizing that the future likely holds nuclear war, they activate an old plan to “borrow” a starship from the government and carry the core teaching of the church to the extrasolar colonies.

Further bombings occur, destroying Texarkana and a number of Asian space stations. The World Court enforces a 10-day ceasefire, which both sides agree to. The Church mobilizes their survival plan, collecting the Leibowitzian monks with space experience to depart for Alpha Centauri.

At this point, Miller could have ended the book. Terra is about to erupt in nuclear flames once again, and the Church is prepared to survive. Honestly, I was feeling fairly sympathetic towards Catholicism after reading such believable, devoted characters. But Miller respects his readers too much for that. He pushes us.

During the ceasefire, millions of refugees leave the outskirts of Texarkana, suffering from radiation sickness. The Atlantic Confederacy’s government is still functional at this point (one wonders if ours would be, if Washington, D.C. (and just D.C.) were destroyed). The Green Star, their version of the Red Cross, sets up voluntary euthanasia camps to let those terminally afflicted die quickly without further suffering.

The abbot won’t stand for this. As a devout Catholic, he can’t assist in the matter, or even suffer it to continue. The majority of the population is Catholic, in the way that Americans are Christians, and the abbot tries to put the literal fear of God into them. The abbot desperately tries to stop a sick woman from taking her child to the camp, despite the fact that both are clearly terminal cases. He almost succeeds, before being stopped by the Green Star officials. Seeing the Church overwhelmed by worldly forces is enough to break the streak, or so the abbot thinks.

He doesn’t have much time to ponder the matter before war erupts again. A nuclear explosion destroys the rubble, trapping the abbot in rubble. As he lays dying, he’s visited a mutant woman he’s known for years, except something is different. Her second head, which everyone assumed was braindead, is awake, while her first head appears to be unconscious. The abbot had previously refused to baptize the second head, and desperately tries to rectify this error as his final act. Amazingly, she refuses, and instead gives communion to the abbot, implying that she is holier than him. She wanders off and the abbot slips into the final night. Meanwhile, the monks board their starships, ready to take the Church to the stars.

It’s an interesting book. Walter Miller was a Catholic convert, and clearly believed it very strongly. Still, I can’t imagine that a truly merciful God would care so much about self-destruction if a) you’re dying painfully of a hopeless disease and b) the entire world is about to be destroyed. Perform your own miracles, I guess. We’re conscious, I promise, but we aren’t omnipotent. A-bombs are a long way from the alpha and the omega.

Despite the depressive ending, it’s a book worth reading if you’re interested in moral theology or the material implications of nuclear war. The story is fast-paced and exciting, with a simmering suspense underneath it all. A Canticle for Leibowitz definitely earned its place in the canon of post-apocalyptic science fiction.


How To Make An Astronautical Engineer

Like quite a few aerospace engineering majors, I’m not really here for the aircraft material. Now, planes and helicopters are interesting in their own right, and the overlap between the two fields makes perfect sense historically. My disinclination to the aeronautical courses (which, at my school—and most others—represent the bulk of the curriculum) stems mainly from the fact that that’s not where I want to spend my working years, and college is too damn expensive to waste my time and my parents’ money on irrelevant material.

The major argument for the current arrangement is that space-focused students represent a minority of the department’s undergrads. While this is generally true, it is also misleading: the lack of astronautics classes deters many interested high-schoolers from applying. To magnify the distortion, a lot of the kids who do enroll jump ship for propulsion and fluid dynamics once they realize how few options are open to them.

In seeking a more balanced plan of study, let’s take things to extremes and consider what a dedicated astronautical engineering curriculum would look like. A few such departments do exist, sometimes even operating alongside aerospace engineering programs at the same institution. As the opportunities to work in strictly space-related roles expand in the coming decades, it may be worthwhile to rehabilitate aeronautical engineering as an independent major while astronautical engineering comes into its own.

Before we begin, I’d like to discuss a few issues with engineering curricula in general.

First, the approach to teaching math and science generally is deeply flawed. It makes absolutely no sense to teach so much algebra, trigonometry, vector geometry, and so on before so much as showing the poor kids a derivative. Supposedly our math curriculum was designed to churn out aerospace engineers after the Sputnik Crisis, but fear must have clouded their judgement, because hiding the beauty of mathematics behind semesters of drudgery seems to scare off more students than it’s worth. The fact is, it’s easier to buckle down and work on a problem when the kid appreciates its applications.

This is closely related to another criticism, which is that students get very little experience with the subject matter of their major until basic math and science requirements are complete. This is not only unpleasant for the student, but dangerous. It may be that the student will absolutely hate the field of engineering they’ve chosen to study, but won’t find out until two years of college tuition have already been sunk. By that point, it may be financially impossible to change majors.1

None of that would be a problem if public schools were capable of turning out educated adults, but it would seem that they aren’t, so it is. The same goes for reading, composition, and oral communication, to say nothing of economics, ethics, and epistemology.

But it’s not clear to me that you need multivariate calculus to learn the history of spaceflight. I would recommend integrating some sort of dedicated, big picture class into every semester of the underclassman curriculum.2 Considering how many of us arrived at our capstone class here without a coherent concept of airplane dynamics, this seems like a good addition to the baseline program. The vast majority of the curriculum I propose, though, would consist of substitutions. Only one or two classes would I remove outright.

Before we talk about that, though, let me zoom out for a moment and explain the major areas of aerospace engineering. (If you already know this, bear with me—I’m not writing solely for aerospace engineers, or even engineers generally.)

The five major areas of aerospace engineering are aerodynamics, controls, propulsion, structures, and design. (One could make the case for spinning out a separate focus on hardware from design and structures, but this is not generally recognized. A bit more on that later.) Design is somewhat distinct from the other areas as a synthesis that cannot stand alone. The degree to which this is true, of course, depends on just how abstract the dividing line between design and subsystem application is. In many cases, the entire question is quite fuzzy, which is fine. A lot of the best work happens in that region.

By number of workers, structures is the biggest area of aerospace engineering. On the order of 70% of aerospace engineers will work in structural analysis at some point in their careers. Oddly enough, this is one of the areas I have the most difficultly explaining to my non-engineer family members. Structures is….structures. It’s all the structure that holds an airplane together. It’s the frame of your house keeping the roof from caving it, it’s the frame of your chair keeping you off the ground. The aircraft structure holds the engines to the wing and the wing to the fuselage and the fuselage together.

Propulsion is easier to see: it’s the engines pushing the plane through the sky. These can be propeller or jets of various types, and less frequently, rocket engines. Spacecraft propulsion, of course, is almost entirely based on different forms of rocketry, though there are proposals to use jet engines to carry launch vehicles part of the way through the atmosphere.

Aerodynamics is the art of minimizing drag on the vehicle as it moves through the atmosphere, and—for aircraft—transforming a portion of the longitudinal force from the engine into lift. This is a bit more difficult to visualize,3 but relatively straightforward. It would have a much smaller role in an astronautical engineering curriculum, but a role nonetheless.

Controls is considerably more abstract. It combines aerodynamics, propulsion, and avionics to maintain static or dynamic stability for the vehicle, and make it do what the operator wants. Interestingly, this is both were hardware applications and systems engineering come in. It’s all about making the actuators, computers, and cabling play nicely together.

All of these fields would appear in an astronautical engineering curriculum, one way or another. With that out of the way, let me break down the approximate manner in which I would assemble it.

Firstly, I would substitute epistemology and economics for the worldly perspective requirements. Composition and oral communications would stay, though doing those in-house is obviously desirable.

Basic science and mathematics would necessarily stay, though I would personally prefer to see the course content described properly. For instance, instead of call it Physics I & Physics II, I would describe them as Mechanics and Electrophysics. The same goes for structural analysis—what we know here as Aerospace Structures I & II would be Determinate Structural Analysis and Indeterminate Structural Analysis, i.e. finite element analysis. That doesn’t necessarily communicate more information to freshmen, but it hardly communicates less. The rest of the structures curriculum is mostly fine—statics & dynamics, materials, and so on.

Propulsion would see significant changes away from air-breathing and towards vacuum-capable systems. Beginning with fluid mechanics and thermodynamics, we would explore spacecraft aerodynamics, rocket propulsion, and finally spacecraft propulsion. Aerodynamics is necessary for the controls curriculum, which would begin with basic orbital mechanics before moving on to spacecraft flight dynamics (including attitude control) and then move on to astrodynamics. A propulsion prerequisite might be useful, depending on the precise plan-of-study.

In the spacecraft systems focus area, we would begin with programming and electrophysics before moving on to circuits, spacecraft hardware, and instrumentation. These are some of the areas where I feel least confident in my engineering education thus far—despite spending a little time assembly a model airplane kit and the lab section of our electronics class, we didn’t really get much hands-on experience until the senior manufacturing project in Aerospace Materials & Processes. A dedicated hardware course might be worth the trouble.

Finally, the design courses. In most curricula, the various sequences culminate in a senior capstone. I question this approach. My current situation in airplane design is feeling dozens of disparate threads coming together immediately after the report block where I needed to understand them. I would vastly prefer to have this process happen earlier, so senior design could focus on skillful application.

My solution to this is to maintain some sort of integrating coursework throughout the undergraduate experience. My suggestion is to begin with an introduction to astronautics as a freshman seminar. This could progress to a history of spaceflight in the sophomore year. As a junior, I’d recommend an introduction to space system design and space mission architecture.

All told, my proposed curriculum looks something like this:

Astronautics Curriculum

Note the suggested technical electives listed. Students could spend their senior year taking these alongside the spacecraft design capstone. The full list would be much more extensive; these are just a few obvious areas which might be interesting to focus in on. Advanced spacecraft propulsion, structures, or astrodynamics classes would also be offered.

I may enumerate a semester-by-semester plan of study after a bit more thought, but right now I’m not sufficiently certain which classes should go in which semester. Balancing the workload is important, in my experience, to avoid burnout in otherwise perfectly capable students. Just as the high school can’t be depended on to teach students mathematics, we can’t rely on them to teach coping and study skills. A carefully-curated ramp up will be necessary.4


Perhaps that will change by the time that such a curriculum is widely needed, though. In any case, dedicated astronautical engineering won’t be a common major for several decades, at least. I’m writing this mainly to satisfy my own curiosity, but also to discuss what the nascent programs should be doing in the meantime. As you may have noticed, I think developing practical, economic spaceflight is very important. We aren’t there yet, not by a long shot, but I’d like to hit the ground running when the powers that be get the message.

Till then, however, it’s all about squeezing what astronautics material I can from a pretty aeronautical-focused program. Speaking of which, I should probably go finish that spacecraft telecommunications homework.


1You will recall that I flunked out after two years of school. I returned at a different institution in the same major, and after another year found myself doubting the decision. If I could do it over, I would probably tell myself to study in engineering physics or mechanical engineering to pursue a more manageable and personally-relevant plan of study. By the time I’d realized this, however, I was absolutely not going to ask my parents to finance another two years of university just because I’d been ignorant going in. By now I’m entirely committed.

2Here at the University of Kansas, I would recommend dusting off that Global History of Aerospace Technology class, and getting it approved to fulfill the Cultural & Diversity Awareness goal. This would be such a logical and productive use of engineering credit hours that I cannot possibly expect it to be accepted by the Mickey Mouse departments.

3One of my structures professors once described aerodynamics as one of “the magic subjects” in comparison to his own field. I politely refrained to telling him that I found aerodynamics relatively transparent next to structures, which then even more than now felt like black magic. My suspicion is that this stems primarily from my extremely visual thinking style, which translates better to aerothermodynamics and orbital mechanics than to structural analysis.

4This is another point of criticism towards the program here: just when you think you’ve gotten the hang of things, the airplane of your academic performance slams into the concrete wall of junior year.

Asimov on Entropy

Isaac Asimov’s science book View From A Height dedicates an entire chapter to explain concept of entropy. Assuming you have a decent background in the physical sciences, it does an excellent job, even better, I daresay, than my thermodynamics professor managed. So far the whole book has been a worthwhile read, but that essay in particular may be instructive to those interested in the topic.

Asimov concludes the chapter by presenting a very appealing hypothesis:

[E]ven if the universe were finite, and even if it were to reach “heat-death,” would that really be the end?

Once we have shuffled the deck of cards into complete randomness, there will come an inevitable time, if we wait long enough, when continued shuffling will restore at least a partial order.

Well, waiting “long enough” is no problem in a universe at heat-death, since time long longer exists there. We can therefore be certain that after a timeless interval, the purely random motion of the particles and the purely random flow of energy in a universe at maximum entropy might, here and there, now and then, result in a partial restoration of order.

It is tempting to wonder if our present universe, large as it is and complex though it seems, might not be merely the result of a very slight random increase in order over a very small portion of an unbelievably colossal universe which is virtually entirely in heat-death.

Perhaps we are merely sliding down a gentle ripple that has been set up, accidentally and very temporarily, in a quiet pond, and it is only the limitation of our own infinitesimal range of viewpoint in space and time that makes it seem to ourselves that we are hurtling down a cosmic waterfall of increasing entropy, a waterfall of colossal size and duration.

This is an intriguing idea. It suggests an alternative possibility for the fate of the cosmos than “eternal coldness”. Presuming that black holes don’t end up consuming all the matter in the universe, and proton decay turns out to not occur, then it might be possible to square a sort of steady-state theory with the existence of entropy.

Entropy isn’t merely disorder—though disorder is certainly a part of it. The Second Law of Thermodynamics tells us that energy does not spontaneously flow from cold areas to hot areas. Only by applying work can we force the flow in the opposite direction. Work, however, can only be extracted from the flow of energy from a hot reservoir to a cold one. Thermal efficiency is based on the temperature difference between the two reservoirs:

\eta_{th} = \frac{T_H - T_C}{T_H}

Where \eta_{th} is the thermal efficiency, and T_H and T_C are the temperature of the hotter and cooler reservoirs, respectively. As an example, if a warm reservoir is at 500 K and a cooler reservoir is at a mere 350 K, then the maximum thermal efficiency of a work-extracting cycle between these two reservoirs is 30%. (But don’t take my numbers for granted. Check it yourself!)

Note that the absolute quantity of energy in either reservoir is irrelevant. We are only concerned with their relative values. Work cannot be extracted by placing two equally hot reservoirs in contact, even if both are at 10,000 °C.

It is, of course, theoretically possible that random motion of individual particles might provide a very small about of usable work. However, this is exceedingly unlikely. Asimov gives an extreme example: could water in a pot freeze while the fire beneath grows hotter? Theoretically, yes. The laws of statistical thermodynamics do not forbid it. But even if the entire universe were filled with such pots, and we waited for eons and eons, we would not realistically expect to see a single pot significantly cool, let alone freeze.

As time goes on, we will approach universal thermal equilibrium. Extracting useful work, of any form, will become impossible. Work is energy, and life depends on a continuous source of energy, so all forms of life will perish.

This, naturally, can be a bit frightening to think about, especially if you are very young when you learn about it, as I was. A cosmological expiration date seemed like a very serious problem, because it meant that all of our efforts would necessarily be in vain. If the universe ends end regardless, social morality seems farcical. Rank hedonism looked like the only alternative, so my early attempts to reject

Objectivism helped me out of that trap, though its presumption of an inexhaustible universe remains problematic. But that doesn’t matter if morality is not social but personal, and the purpose of existence is Apollonian joy rather than a greater obligation.

Still, the possibility that the universe, even after heat death, can randomly reorganize will offer hope to the last mind that joy won’t go out of existence forever. A silent eternity would pass, and then…something. A universe appears again from darkness.

Doesn’t that sound familiar?

I’m tempted by this hypothesis not merely because it offers hope for the universe, but also because it helps get around one of the frequently-asked unanswered questions about the Big Bang: what happened beforehand?

So far, we don’t know. Did time even exist before the Big Bang? Did conservation of mass-energy already apply? I haven’t studied the astrophysics to pretend to answer such questions.

Random reordering gets around this issue. The universe we know is a ripple is the wider open of equilibrium particles. Entropy is maximized. Everything is in the lowest possible energy state. By chance, some of this matter happened to organize itself. Net entropy will now continue to increase, so I think this is allowed.

Since the time for a “dead” universe to randomly form an orderly patch of significant size must be incredible, it would be no surprise if the photonic evidence of previous ordered periods had been entirely absorbed or diffused. Photons, being massless, don’t decay, but in such a long period would no doubt either be absorbed by the near-equilibrium particles. The remainder would be spread out over such a large area that the number of photons are simply swamped by more recent light. No instruments could possibly detect them.

But just because a hypothesis would be personally comforting does not forgive a lack of evidence. We should seek contradicting evidence for all hypotheses, regardless of our feelings toward them. Falsification is how science works.

Does random reordering fit the evidence we’ve already gathered about the early universe?

I’m little more than a layman, but generally speaking, the answer is: not really.

We have a pretty good picture of everything that happened more than a second after the Big Bang, and for a good while before that. A lot is based on astronomical data, such as the cosmic background data gathered by COBE, WMAP, and Planck. The remainder comes from particle accelerator experiments, from which physicists can build up models that extrapolate back even further.

The current theories don’t look very much like the result of randomly reshuffling baryons or leptons. It looks like a lot matter being created ex nihilo, with somehow antimatter being in the slight minority. Possibly a reshuffling at a much lower scale occurred, well after proton decay and whatnot evaporate the particles we’ve come to expect—I have an idea about how that might work, but I won’t burden you with more unwarranted speculation.

More study is clearly needed: better space telescopes and more powerful particle accelerators to give us data, faster supercomputers to process it, maybe some mathematical breakthroughs. It will probably take awhile to get a better estimate on the odds, but until then, I would put a low prior on the likelihood that our universe is a temporary reprieve from heat-death.


Full-sky image of the cosmic microwave background, gathered over nine years by the Wilkinson Microwave Anisotropy Probe.

Source: NASA/WMAP Science Team

However, there is a bigger philosophical question here: a reorganization hypothesis does not explain the origin of the universe, it just moves the cosmological problem up a step. Our universe being a mere ripple on a larger heat-dead ocean doesn’t tell us where that ocean came from. Did that universe have a Big Bang? Is it cyclical? Is it Steady-State? We still have to answer the same questions, and now we have less data!

(Of course, if it does turn out to be true, then we’ll just have to make do with less data. But that’s a methodological question.)

Trying to explain why there is something at all isn’t necessarily a hard question, but to explain why existence started to exist 13.8 billion years ago is a bit trickier. At this point, perhaps the simulation hypothesis is a decent pseudo-explanation. You can’t make very many predictions with it, so I wouldn’t call it a real explanation. That said, it does manage to constrain our anticipation to some degree. And there is some evidence for it.

Whatever reality is, we’ve still got at least some distance further to walk on the path to Truth. It’s tempting to take a short-cut through speculation and a priori arguments, but those are distractions. If we want to be sure, we have to do things right. Proposing hypotheses is part of that process—but so is rejecting them. As tempting as random reorganization is, I’d be happy to reject it with a little counterevidence.

Cassini and Me

Early this morning, while I lay sleeping, the Cassini spacecraft plunged into Saturn’s upper atmosphere. It had been in space over twenty years, and at Saturn for over thirteen.


The last image transmitted by Cassini, about 15 hours before impact.

Like the Galileo spacecraft before it, mission controllers intentionally configured Cassini to deorbit when it reached the end of operational life. Once the supply of maneuvering fuel is exhausted, there’s no way to control a spacecraft’s trajectory. Cassini would, eventually, crash into one of Saturn’s moons.

This isn’t a problem in-and-of itself—we don’t have much compunction about littering the Solar System with terrestrial debris. But we wouldn’t have any control over which moon, and that is a problem.

One of Cassini’s big discoveries was that Enceladus has liquid water plumes coming from its south pole. Both Enceladus and Titan (which is loaded with organic and pre-biotic molecules) could be potential abodes for life. Given that we can’t perfectly guarantee our spacecraft are sterilized of Terran microbes, disposing of Cassini in Saturn’s atmosphere is better than risking planetary contamination. The final, ring-grazing orbits concluded with a fly-by of Titan, a distant interaction robbing Cassini of just enough mechanical energy to send it into clouds below.

I agree with that logic, but the decision is bittersweet. In many ways, Cassini was the first probe that I followed through its entire science mission. I was paying attention when Cassini arrived, when the Huygens lander touched down on Titan, when the plumes were found on Enceladus, when the hexagonal storm was spotted at Saturn’s north pole. The other real contender for that title would be the Mars Exploration Rovers, Spirit and Opportunity, but the latter is still operating. Cassini, as of this morning, is over.

chesley bonestell titan

This famous Chesley Bonestell painting of Saturn from the surface of Titan greatly anchored my expectations for the Huygens probe.

The joy of discovery, however, is far from finished. Unless NASA finally comes around to nuclear propulsion or outer-planet aerocapture there won’t be many more Saturn probes in my lifetime, but most of Cassini’s results still haven’t reached my eyes. Even the Huygens probe, which only operated for a few hours during descent and landing, probably has some pictures I haven’t yet laid my hands on. And that’s before we consider the data from other instruments.

Space science, you see, isn’t just about snapping the prettiest photographs—though that’s certainly a part of it. We’re gathering information to test existing models of reality, and to begin the process of building new ones. Some will be refinements to our existing ideas, and some will be new notions entirely. When a scientist in twenty years has an idea about the way gas planets or their moons behave, they’ll have a wealth of information waiting to validate it with.


Artist’s rending of Cassini at Saturn. Note the high orbital inclination.

But there’s a lot of scientific value in those beautiful images Cassini sent back to us, too. Every kilo counts, and we didn’t cart those cameras to Saturn for the hell of it. We sent them to understand the planet’s atmosphere, its rings, its moons. We’ve learned so much we didn’t even know to ask about in 1997. Those pictures give us a better perspective on the science, and on our place in the universe.

Even the picture I’ve been using a personal motif the last couple years, of Earth seen from under the rings, is a Cassini image. Space exploration lets us see the view from a height, of our planet, of ourselves, and of our universe. This mission had to end, but it didn’t have to happen in the first place. We didn’t have to expand our knowledge and perception, because there’s no cosmic law dictating humanity choose wisdom over ignorance. We chose to send Cassini-Huygens to Saturn, and I’m very glad that we did.

Book Review: Life in the Universe

Life in the Universe was the assigned textbook for the astronomy class I took in the fall of 2015. The course is titled the Quest for Extraterrestrial Life, and is sometimes taught by retired astronaut Dr. Steven Hawley. Another professor taught it that semester, but I really can’t complain about that—my issues with the course mainly came from the fact that it was open-enrollment. The majority of the term covered material I already knew, and we never got to the more interesting questions. But that’s my fault for dabbling in astrobiology.

The textbook is great for this purpose, however. Bennett and Shostak don’t assume much prior knowledge of astronomy, chemistry, or biological science. The first several chapters are a crash course on the history of the field and the relevant background material. For those who want to learn more about science and don’t know where to be begin, this book might be a good introduction.

But the book does get into the minutiae of estimating the odds of alien neighbors. It looks at the habitability of the planets and major moons of the Solar System, both now and in the past, and then moves on to discuss (what was then) the state of exoplanet research.

What makes a planet habitable is a complicated question. Even on our single planet, where every organism shares the same general biochemistry, environments in which one species thrives can be instantly fatal to another. We have to constrain the search space.

Bennett and Shostak look primarily at carbon-based life using water as its solvent, i.e. life as we know it. They offer justification for this focus, but I’m not entirely convinced. It’s especially weird when contrasted with their willingness to argue that we should take an optimistic stance towards the possibility of life overcoming any given obstacle.

To be clear, lifeforms which use something other than carbon as a base-structure would have more trouble evolving. Carbon is wonderful because it can easily bond with up with other molecules, and is conveniently small. Science fiction writers sometimes swap out our biochemical components with elements from a row down on the periodic table, ignoring the fact that those elements are larger and thus less electronegative. In layman’s terms, such molecules aren’t going to form as easily and will be less stable. That’s not so good for life.

Similarly, using other solvents than water presents some issues, because water has an unusually wide liquid temperature range, even for other polar molecules. This is a product of hydrogen bonding, polarity, and molecular weight. Almost any other conceivable solvent trades off at least one of these.

The same problem repeats for all the other chemicals in our bodies. There is good reason to focus on “life as we know it”. What I find harder to justify is the assumption that life won’t encounter very many major obstacles on the path to intelligence.

First and foremost is the fact that evolution doesn’t move in a straight line. Intelligence was not an end-goal for evolution. Even once intelligence developed, there wasn’t any rule that said we should develop modern technology. That has been the general trend since the development of farming, but by no means inevitable. Suppose a second round of glaciation had hit around 8,000 BCE. Agriculture would have been abandoned, and later selection pressures might have bred the genes for intelligence out of the population. Who knows how many species that’s happened to in the history of Earth, let alone across the galaxy.

Life isn’t pursuing complexity—complexity is often a cost which requires immediate justification. Inventing a wing is easy; evolving a wing is hard, because each intermediate step needs to provide a positive benefit to the organism, too.

Second, abiogenesis. We have just one example of life developing, and we’re not entirely sure how it happened. We have a good picture of the biochemistry that was probably involved, much of which would have occurred before the first cells came into existence. We’re pretty sure it involved RNA replicators, but that’s still an unclear picture.

On Earth, life developed about a billion years after planetary formation, which is pretty early in the grand scheme of things. This suggests that life can emerge from non-life pretty easily in the conditions that existed on Earth about 3.5 billion years ago.

But how common are those conditions? What percentage of rocky planets in the habitable zone will have that sort of environment for a sufficiently long time for life to develop? What percentage of those planets will stick around long enough for complex life to evolve? Intelligent life?

This is where I found the book’s analysis lacking. It took three billion years for life on Earth to develop complexity and we still don’t entirely know why that changed so suddenly. There’s a number of possible explanations: a mass-extinction eliminating competition, planetary glaciation eliminating competition, development of eyes or teeth causing runaway competition, the evolution of aerobic organisms, the formation of the ozone layer making surface environments more habitable—the list goes on. It’s not even clear that the Cambrian Explosion was an explosion. Perhaps it’s just an artifact of an incomplete fossil record.

At least weak evidence exists, however, of complexity being a hard step along the road to intelligence. The fact that so many explanations have been suggested to me suggests that perhaps multiple factors were actually at play.

I would go so far as to postulate that an additional term should be added to the Drake Equation to account for this fact, but that post will have to wait a few months at least.

The book concludes with a discussion of the Fermi Paradox. For those who don’t know, the Fermi Paradox comes from a question asked by the famous nuclear physicist: “Where is everybody?” Considering all the evidence that Bennett and Shostak had marshalled above, why can they not point to any real examples of extra-terrestrial intelligence?

enrico fermi

Italian-American physicist Enrico Fermi

Many answers are possible, which they explore in reasonable detail. Perhaps the strongest argument is that interstellar travel is extremely difficult (and we haven’t sent enough interplanetary probes to effectively assess the likelihood of non-intelligent life in our Solar System). The aliens are out there, but they won’t be coming here. Odds are that we won’t be going there, either.

These are intriguing ideas, which I’d hoped to learn a lot about. Life in the Universe is a decent introduction to them, but once again doesn’t discuss the topic in adequate depth. I would recommend it, then, as only an introductory text. There’s probably better astrobiology books out there, and I look forward to reading them.

The single most frustrating aspect of the book, however, was the authors’ expectation that readers wouldn’t take the material seriously. Almost every chapter has a dedicated section for taking pot-shots, fair or not, at some famous works of science fiction. Now there’s certainly a degree to which we must remove misconceptions before the truth can succeed, but there’s also a risk of anchoring. I’m not convinced that the trade-off was worth it.

Even in the final chapter, by which point the reader is, presumably, sufficiently credulous to believe what the relevant PhDs are saying, they’re still on the defensive, even about phenomena as real as anti-matter. It was frankly embarrassing to read, but fits pretty well with the mood of the class. One of the rewards of reaching higher-numbered courses is that everyone takes the material halfway seriously. I don’t suppose I’ll ever study astronomy at that level, but who knows. The future is long and full of possibilities.