The Universe is out to get you

 kw: book reviews, nonfiction, science, popular treatments, humor, space, mortality

"Nobody gets out of this alive." A common proverb. Scientist Paul M. Sutter, in his book How to Die in Space: A Journey Through Disastrous Astrophysical Phenomena, has advice for delaying the end, "Don't go into space." After reading this book, almost anyone will be convinced that a surefire way to reduce one's "alive time" is to get off the Earth, out of the atmosphere, beyond the Van Allen belts, and ultimately to exit first the Earth's magnetosphere, then the heliosphere, and finally enter interstellar or even intergalactic space. Each step adds new risks.

The book's four sections, each with four chapters, detail all the interesting, amazing, and terrifying things that happen to a human who has left behind the cherishing and nurturing embrace of our mother planet. Now, there are a lot of things right here on Earth that can kill us. Sooner or later, one of them will happen to each and every one of us. Space just provides new and improved methods of attaining an early demise. The galaxy really is out to get you.

If the book were a dry catalog, it wouldn't be worth reading. Happily, Dr. Sutter's humor keeps it light. He really doesn't want you to die an early death (a later one will do just fine, thank you!). His tone is appropriate to a class filled with ready-to-be-bored sophomores, most of whom will ignore all the warnings anyway. So as you read, relax and let your inner adolescent enjoy.

The book got me thinking. Just how many layers of protection are provided, not just by the Earth with its atmosphere and biosphere, but by the solar system itself? The heliosphere is produced by one dangerous phenomenon—solar wind—but protects Earth from certain interstellar and intergalactic risks. For example, at any one point near the Sun, its magnetic field is about as strong as a refrigerator magnet. But a refrigerator magnet is a couple of centimeters across, while the Sun's surface is about 10,000 times as large as the surface of the Earth. The Earth's magnetic field strength is less than 1% of that. The solar magnetic field diverts most non-solar cosmic rays. The much smaller magnetic field of Earth, including the Van Allen belts, diverts many of those that the heliosphere allows through. Even then, thousands of cosmic rays pass through any particular square cm of earth, or of you, each second. Without these two magnetic bubbles, cosmic ray intensity would be about equal to that of visible light, or roughly a kilowatt per square meter. But since cosmic rays are penetrating (average energy per particle is about 100,000 times the energy of the photons in a dental X-ray), you'd be warmed throughout, kind of like being in a cosmic microwave oven, with the proviso that these are not microwaves, but super-gamma-ray energies, so they also damage proteins and DNA.

Some stars, and particularly dying ones, have magnetic fields millions or billions or trillions of times as strong as that of the Sun. Suppose an intrepid interstellar traveler wishes to see a magnetar, which is a super-magnetic neutron star. It's only a few km in diameter, but weighs about as much as the Sun, perhaps up to twice as much. Let's ignore the high gravity environment for a moment. You get close enough to see the magnetar as something larger than a simple, blazing point, say a distance of 10,000 km. Have you seen the videos of scientists levitating a small frog in the field of an MRI magnet? Flesh is weakly magnetic. 10,000 km from a magnetar, the billion-times-MRI field would shred your body like a blender. Let's also consider gravity. At the surface of the Sun, if you could stand on it, gravity is about 28 G's. Fighter pilots wearing special suits can briefly tolerate 6 G's. You'd die, fast. And your distance from the Sun's center is 700,000 km. Remember the inverse square law? Do the math if you like. At 10,000 km from a neutron star (magnetar or not), gravity would be about 137,000 G's. In fact, getting to a distance of 10,000 km from any one-solar-mass "compact object", whether it's a neutron star, white dwarf, or black hole, would be the same. Big grease spot.

"All things in moderation." That is what the Earth, in its magnetospheric and heliospheric cocoon, provides. We need a little gravity. The 1-G field we are suited to, plus-or-minus 10% or so, is best. Extreme gravity goes from bad to catastrophic. How about low G? Zero gravity is bad for astronauts; lots of recent reports tell us just how bad. Early osteoporosis, for example. Even the 1/6 G of the Moon isn't enough. Stay on the Moon for a few years, and it will never be safe for you to return to Earth. Even Mars, with 3/8 G, may not be good enough to keep human bodies healthy long term. Sorry, ice skaters that want to skate a Martian canal. Do try to make it a short trip! And the only ice-covered area on Mars you'll find is near one of the poles, where it's cold enough to freeze carbon dioxide. You can't skate on frozen CO2. Most outer space temperatures are extreme in the other direction, at least if you're close enough to some kind of star to be able to learn much about it.

It's not just heat that does one in. Most hot things in the Universe also produce copious penetrating radiation, of several kinds. Outside Earth's magnetosphere, solar wind is a fierce drizzle of protons and alphas (He nuclei) and electrons, with particle energies similar to dental X-rays, dense enough to give a fella radiation poisoning rather soon, in days or even hours. Solar flares emit gamma rays (photons) at much higher energies and densities. Astronauts in space stations receive warnings of solar flares, and hide in specially shielded areas, so they'll live through it. Earth's magnetosphere has no effect on gamma rays. But let's consider a rather quiet star that happens to be larger than the Sun, such as Sirius. The Dog Star weighs in at 2 solar masses, but is 25 times as bright. Where the Sun's light is about 1/3 UV and shorter wavelengths, for Sirius the proportion is 2/3, and a lot of that is at short wavelengths indeed. It might seem good news that the habitable zone (where water on a planet would be liquid most of the time) is 5 times the size of the one in the solar system. In that liquid-water zone you would get sunburnt twice as fast, and unless you had a really robust ozone layer, you'd need to worry about more than UVA and UVB. UVC and UVD are progressively more damaging, verging on the kind of damage X-rays do. In orbit around a planet that is orbiting Sirius, you would need a huge amount of shielding just to be safe from the much stronger stellar wind. And lots of stars are progressively bigger, brighter and more dangerous than Sirius.

The author catalogs everything out there that is "out to get us". It's an impressive list; I've just skated the surface here, just vamped on topics that came to me as I wrote. The author's humor keeps it light, so a reader will hardly mind that the subject is death, dying and other kinds of mayhem. Very enjoyable, actually.

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Coda: I have to deal with an issue. Dr. Sutter explains the onionskin model of the core of a large star, describing the successive crises as first hydrogen is consumed, then after the core heats up by 10x or so, helium is burned until it runs low, and so forth. When he gets past carbon, which fuses to produce neon (plus an alpha particle) at some horrendous temperature in the billions of Kelvins (same size of degree as °C, but shifted by 273), he oversimplifies. He states that neon burns to produce oxygen. Is it going backward? It's more complicated than that. The neon shell contains some alphas, produced by carbon fusion, and under intense bombardment by gamma rays, some of the neon is split to oxygen plus alpha (helium), while the rest captures the alphas to produce magnesium and then silicon. Silicon then fuses to produce nickel, but a lot of other reactions also occur, so that all the even-numbered elements in between are also produced. His point is that the nickel isotope so produced is unstable and emits an alpha to yield iron. That's the end of the chain. No more fusion energy is available; other processes that occur in supernovae and during collisions of neutron stars produce all the other elements. See the Stellar Nucleosynthesis article in Wikipedia for a more comprehensive discussion.