Death from the Skies! (26 page)

Nasty.

There are other types of viruses too. Some use RNA, not DNA. Others attack bacteria and not tissue cells. And not to make you uncomfortable or anything, but your body is currently
brimming
with these viruses. Most are completely harmless. Some do cause a variety of issues—for example, they can throw off your body’s ability to regulate its systems, resulting in illnesses from mild to severe—but most don’t kill. They have to attack in ferocious numbers to do that, or be particularly virulent, like Marburg (which has a mortality rate of about 25 percent) and the more famous Ebola (with its truly terrifying 80 to 90 percent mortality rate).

The structural simplicity of viruses is both a blessing and a curse when it comes to an invasion from space.

Because they are such simple structures, viruses are resistant to many of the problems a more complicated microbe might have with exposure to space. Prolonged periods of vacuum, low temperatures, and even some radiation may not prove an obstacle to them. Embedded deep in a rock, they could fall to Earth intact, only to be opened like a cursed pharaoh’s tomb by a hapless scientist.

But if they got under his skin, they might starve to death.

That’s because viruses are generally adapted to attacking
one specific kind
of organism. A virus that can infect a plant can’t harm a butterfly, and one that is adapted to attacking bacteria (called
bacteriophages
) can’t hurt a human. Viruses are too simple to change radically, and the DNA or RNA snippet in the virus is like a key to a lock. A car key won’t work in a house door.

So even though any hypothetical space-borne virus might survive all the way into the lab of a scientist, it’s incredibly unlikely that it would swarm and multiply and turn us all into raging zombies.
⁶⁵

So in reality, viruses aren’t a big threat. They would find us completely incompatible for their purposes, and would quickly die out.
⁶⁶

Score one for life on Earth.

Interplanetary bacteria are another horror movie staple, and while they have some advantages as invaders over viruses, they’re also unlikely to be much trouble to us Earthbound creatures.

Unlike viruses, which are programmed to fit certain types of cells or proteins, bacteria are less choosy. And while viruses use our own cells’ machinery against us, bacteria consider us more as a flophouse. Like an unwanted guest, they can eat your food, mess up the place, and, of course, overstay their welcome.

The main difference between a virus and a bacterium is complexity. Bacteria are cells in their own right, and are considered alive. They can ingest food, excrete waste, and reproduce on their own. Give them a warm, wet environment with the nutrients they need, and they’ll do all three of these functions with abandon.

Our bodies make excellent sites for what bacteria need. Our bodies are loaded with bacteria, as with viruses. Bacteria are in your gut, in your skin, and living on your eyelashes. They’re everywhere, and in fact it’s been estimated that there are ten bacteria in your body for every single human cell!

You’re outnumbered.

The vast majority of bacteria inside you are benign. They either don’t do anything harmful or exist in numbers too small to do any damage. Many are beneficial to us; without them we’d die. They help us digest our food, for example; they also create vitamins and boost our immunity to more harmful types of bacteria. They even help us digest milk.

An excellent example of such a bacterium is
Escherichia coli,
more commonly known as
E. coli.
This little ovoid bug lives in huge numbers inside your intestines, and has the underappreciated job of helping you process your waste matter.
⁶⁷
Normally, they live happily in your gut, doing whatever it is they do. But that’s not always the case.
E. coli
eats and poops too, and some strains of the bacterium exude a toxic chemical brew. In low doses your body can handle it. But if you get too much in your system, it can make you quite ill. Food poisoning, for example, can be caused by eating food that has been contaminated by
E. coli.
If the infection is bad enough, it can be fatal.
E. coli
can also get out of your intestines (through a hole or herniated region) and into your abdomen, causing peritonitis.

The list of possible problems bacteria can invoke is lengthy (diarrhea, vomiting, nerve damage, cramps, fever . . . you get the picture), but usually we live in an uneasy truce with the bugs inside us.

The bacteria inside us have, of course, evolved along with us so they can maintain this symbiotic relationship. A hypothetical bacterium that evolved on Mars, say, or some other planet would not enjoy this luxury. Still, the effect of an alien bacterium on us really depends on what it needs, and, pardon the expression, what it excretes.

If all it needs is a warm place with water and some nutrients, then any port in a storm, as they say. Your intestines will look just as good as any other place. And if the bacterium multiplies, and the colony emits a toxin, then that can be trouble.

But is that likely?

In reality, almost certainly not. The very complexity that makes bacteria more versatile and therefore more adaptable than viruses is also their Achilles’ heel: it makes them more fragile. Their internal machinery is unlikely to survive the journey through space, and their entry into our atmosphere.

Moreover, the conditions alien bacteria need to survive would make Earth look pretty unfriendly. The chemistry of the surface of Mars, for example, is very different from Earth’s. Its thin atmosphere means it’s hit by a high level of UV light from the Sun. There is very little if any water on most of the surface, and some readings indicate rather high levels of hydrogen peroxide, a chemical that tends to destroy terrestrial bacteria (which is why it’s used to clean wounds, though it should be noted that it is produced by some forms of life on Earth—notably the bombardier beetle, which uses it to ward off predators). Any bacterium that evolved to survive on Mars would most likely find Earth to be a very difficult environment—too wet, too hot, too
alien.

Of course, not all life on Earth likes the same things we do. Some bacteria like extreme cold, some like it hot, others eat sulfur, and some like the extreme pressures found deep underwater or underground. These
extremophiles
are abundant on Earth, and may exist on Mars as well. But even if they are there, deep under the Martian surface, it’s unlikely they’d get scooped up and carried away by an asteroid impact.

Looking to other worlds in the solar system for potential bacterial breeding grounds is even more futile. Europa, a moon of Jupiter that is covered in ice, may harbor a vast water ocean under its surface. It’s an excellent candidate to look for life beyond Earth, but it’s a low-probability location for anything that’ll think our environment is cozy. The ice on Europa is probably ten miles or more thick; any impact that could loft a subsurface ocean-dwelling microbe into space would also be powerful enough to vaporize said microbe.

Another potential home for life is Titan, one of Saturn’s moons. Titan is aptly named: it’s over 3,000 miles in diameter (about the size of Mercury) and sports a thick atmosphere of nitrogen, argon, and methane. It rains there, but the drops are liquid methane! It’s
cold
on Titan, about −300 degrees Fahrenheit. Any water on the surface is frozen into a solid harder than terrestrial rocks. And while biochemists have speculated that life could arise in such a weird environment, it would be utterly alien to us. Any bug capable of living there would find itself in the equivalent of a blast furnace on Earth.

It seems that as incubators go, we’ve struck out of potential bugs in the solar system. Any alien microbes that would have evolved for Earthlike conditions almost certainly wouldn’t survive the trip.

Of course, this assumes that any form of life Out There is just sitting back and waiting for a ride. Maybe, though, the more sophisticated types would prefer to drive.

The question was asked so succinctly by the physicist Enrico Fermi in the early 1950s, over lunch with some other scientists. They were discussing the recent spate of flying saucer sightings and considering interstellar travel, human or otherwise. When the topic turned to aliens, Fermi asked, “Where are they?”
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The question, simple though it is, has a rich backstory. The basic idea is that by now either we should have detected intelligent life in our galaxy or it should have come visiting. Since neither has occurred,
⁶⁹
asking where the aliens are is a reasonable thing to do.

Let’s assume that for aliens to come knocking, their circumstances must be something like ours: Sunlike star, Earthlike planet, development and evolution of life over billions of years, discovery of technology, then the capability to travel between the stars. How likely is all this to happen?

For that we can turn to the Drake Equation. Named for the astronomer Frank Drake, it categorizes all the necessities of advanced life and assigns probabilities to them. If you fill in all the terms correctly what pops out is the number of advanced civilizations in the galaxy (where “advanced” is defined as being able to send signals into space—which is how we’d know they’re out there).

For example, the Milky Way Galaxy has roughly 200 billion stars in it. About 10 percent of these stars are like the Sun: similar mass, size, and so on. That gives us 20 billion stars to work with. We’re just now learning how planets form around other stars—the first planet around a Sunlike star was discovered in 1995—but we’re finding that stars like the Sun are rather likely to have planets. Even if we assign a ridiculously low probability of there being planets around another star (say, 1 percent), there are still hundreds of millions of stars out there with planets. If we assign a ridiculously low probability of these planets being Earthlike (again, say, 1 percent), then there are still millions of Earthlike planets. You can continue to play this game, estimating how many planets can support life, how many have life, how many have life capable of technology . . . each step in the chain is a little less firm than the last, but even the most pessimistic view of this series indicates we shouldn’t be alone in the galaxy. The estimates of the number of aliens out there vary widely, literally from zero to millions.

That’s not terribly satisfying, of course. The lower estimate is sobering. Maybe, just maybe, we really
are
alone. In all the galaxy, in all the vast trillions of cubic light-years of emptiness, ours is the very first planet to harbor creatures that can ponder their own existence.
⁷⁰
This is a humbling and in some ways frightening possibility. And it’s possibly true.

Another possibility is that life might be common, but “advanced” life is rare. Books have been written on this topic, and it makes for an interesting argument. Maybe once life gets to a certain stage, it tends to go navel-gazing and never develop or care about technology (alien psychology is a difficult topic to get too deeply into). And I hope that by the time you get to this point in this book, I’ve made it clear that civilization-ending events occur uncomfortably often over geologic time scales. Maybe every civilization eventually gets wiped out by some natural event before it can develop space travel advanced enough to prevent it.

I don’t think that’s a good answer, actually. We are within years of being able to prevent devastating asteroid impacts on Earth. We know we can properly shield ourselves from solar events. Our astronomy is good enough to pick out nearby stars that might explode, so if we saw one ticking away we could devote ourselves to getting away from it. All of these advances are quite recent, happening in a blink of the eye compared to how long life has existed on Earth. It’s almost impossible for me to imagine a civilization intelligent enough to explore the heavens yet not advanced enough to preserve its own existence.

I’m suspicious of the other end of the estimates of the Drake Equation as well, that there are millions of aliens out there as advanced as we are or more. If that were true, I think we’d have unequivocal evidence of them by now.

Remember, besides being vast, the galaxy is
old.
The Milky Way is at least 12 billion years old, and the Sun only 4.6 billion. If we imagine a star like the Sun forming just 100 million years earlier—a drop in the bucket compared to the age of the galaxy—then it’s not hard to imagine an alien civilization rising many millions of years before humans did. We know that life arose easily enough on Earth; it got started as soon as the bombardment period ended and the surface of the Earth calmed down enough for long-term growth of life to occur. This implies strongly that life takes hold given the smallest opportunity, which in turn means it should be abundant in our galaxy. And, despite a list of disasters epic and sweeping, life on Earth has managed to get this far. We are intelligent, we are technologically advanced, and we are a space-faring species. Where will we be in a hundred million years?

Given that stretch of time and space, an alien species really should have knocked on our door by now.

They should have at least placed a call. Communicating across the vastness of space is easier than actually going there. We’ve been sending signals into space since the 1930s. These are relatively faint, and an alien would have a hard time hearing them from more than a few light-years away, but we’ve leaked out stronger signals as time has gone on. If we wanted to target a specific star, it’s not hard to focus an easily detectable radio signal to any star in the galaxy.

The reverse is true as well: any alien race with a strong urge to chat with us could do so without too much effort. The Search for Extraterrestrial Intelligence (SETI) is banking on just that. This group of engineers and astronomers is combing the sky, scanning for radio-wave signals. They are almost literally listening for aliens. The technology is getting so good that the astronomer Seth Shostak estimates that within the next two dozen years, we’ll be able to examine the million or two interesting star systems within a thousand light-years of Earth. This will go a long way toward our discovering whether we are alone or not.