Undeniable (34 page)

A smile comes from deep within. If it's not genuine we can tell, albeit not consciously, and often not right away. Will a future generation of women smile wonderfully, because good smilers are more likely to attract a man who can support them as they successfully reproduce, ensuring that both her own and the man's genes get passed into the future? Is it more likely that the woman's genes will be passed on if she's just tougher in childbirth? Or is it just that whatever genes anyone has stand a better chance of going forward if she or he lives in an industrialized society where appendectomies (like mine) are routine?

Another consideration: Any distinctive genetic traits—good or bad—that happen to be in a population with access to effective health care will get passed on. Health care takes away certain selection pressures, and may introduce others. Unselected genes get passed on generally because that society or tribe is passing so many more of its members into the future. Are these effects strong enough to show up in some future detailed research study? Will they noticeably influence our evolution overall?

Whatever the future holds for humankind, I very much hope we are all in it together, that we all continue to remain one species with wisdom enough to preserve as many other hominids and other creatures, the Ivans and Vips of the world. I hope we keep using our big brains to understand and appreciate the extraordinary process by which we came to be (and hope to remain) the top species on the planet.

 

34

ASTROBIOLOGICALLY SPEAKING: IS ANYONE THERE?

I intensely remember lying on the grass in my front yard in Washington, D.C., when I was perhaps nine years old. The sky was a lovely bright blue. My father, influenced by his time staring at the sky in a POW camp during World War II, was fascinated with the stars. He had let me look through his old telescope a few times; the experience left me with a vague sense that there
had
to be other worlds going around those distant points of light. On this particular day, I had just been to the National Art Gallery and seen some paintings by Van Gogh. I was intrigued that his sky was often not blue. I turned these ideas over in my mind. I remember imagining another boy like myself, living on another world, and wondering what the sky might look like there. Would it be green? Pink?

What was once the stuff of childhood daydreams is now the next frontier in evolutionary science. Since 1995, astronomers have found nearly two thousand confirmed planets around other stars. Some of these planets are similar to Earth in size and mass. About two dozen of them orbit in the habitable zone, the distance from their stars where temperatures are potentially suitable to our kind of life. Extrapolating broadly, there may be 50 billion habitable planets in our galaxy. Nowadays, there is an entire field of science known as astrobiology—the study of life among the stars.

Asking about life elsewhere is really another way of asking about living things in general. It's equivalent to asking, “Just what does it take to be a living thing?” It forces us to reexamine all of the evolutionary ideas we've discussed so far from the bottom up. At the most basic level, life clearly needs chemicals of some sort. Any realistic living thing we envision would be made of atoms and molecules, just like you, me, birds, and trees. (Sure, there are living things made of pure energy or dark matter or other exotic things in science fiction stories, but that's not the kind of hard scientific speculation I'm talking about here.) From there, things rapidly get more ambiguous.

When I was in school, it was generally agreed that in order to live, you had to have sunlight. Everyone still agrees you need a source of energy, and sunlight is a great one, but now scientists understand it is not the only possible one. In my lifetime, we have discovered hydrothermal vent ecosystems at the bottom of the sea, where sunlight does not penetrate. These systems are powered in a way that scientists had not considered until they saw it in action. The animals down there rely on certain bacteria that help them metabolize the chemical energy in hydrogen sulfide and water, and the extraordinary amount of heat energy that streams up from the ocean floor. The bacteria in turn produce chemicals for giant tubeworms, bright white crabs, and unusual huge clams as they all make a living.

In recent years, the deep-ocean hydrothermal vents have been studied extensively. As I write, it's looking likely that the organisms there got their start on the surface. They are probably all descendants of surface creatures; they are all to the right or downstream on the Timeline of Life from other clams, crabs, and worms. If so, that finding contains an important message: Life's biochemistry is flexible enough that it can switch from one kind of energy input to another. But the process had to begin somewhere. In order for the whole metabolism of life we know to get going, the chemicals need some initial energy input. Maybe life started in a hot sea and made its way to the surface. Researchers press on.

According to one particularly compelling hypothesis, the energy input in question was electromagnetic radiation in the ultraviolet range. For you Latin buffs,
ultra
means “above” in Latin. So, ultraviolet is at an energy level above the violet or purple that's visible to our eyes. The ultraviolet hypothesis points to at least two ways to explore the origin of life. First, we could check our climate computer models, and especially our computer models of how stars evolve, and see if it is reasonable that Earth was well irradiated with ultraviolet light from the Sun in life's earliest days, say 3.5 billion years ago. Second, we can study whether there is something in the genes or DNA of the ocean vent creatures that gives us a clue as to their origin and the need for their ancestors to have used ultraviolet light for their early metabolism. If this proves to be true, it would mean that living things there now started on the surface and made their ways to the ocean depths. It's a fascinating bit of research that could inform the way we look for life on other worlds, which may lead to that discovery of life elsewhere.

In coming years, we can also expect more experiments that attempt to study the origin of life directly by re-creating nature's experiment and synthesizing self-replicating molecules in the laboratory. It will then be a reasonable question: Is it alive?

Whether we are seeking out new forms of life in nature or trying to create them ourselves, here's something they almost certainly will need: liquid. Life requires some solvent to transport molecules from one place to another as it extracts energy from them, or uses them to make other chemicals move around. Astrobiologists have studied all kinds of possible life-sustaining liquids: ammonia, chlorine, liquid methane, alcohols of different varieties, and so on. They've explored their properties at different temperatures and pressures. In the end, they keep coming back to water. It is just a very effective, very versatile solvent. It also has the advantage of being very abundant.

Our solar system is loaded with water, if you know where to look. Jupiter's moon Europa has a saltwater ocean under its enormous shell of water ice. Asteroids are often made up of a great deal of ice. The giant asteroid Ceres—so big that it has been reclassified as a dwarf planet (lame expression, oh well)—seems to have a surface made of wet clay. We'll know soon enough, since the Dawn spacecraft is headed there in 2015. Pluto and its moon Charon, along with the smaller satellites Nix, Hydra, Kerberos, and Styx, are undoubtedly rich in ice. Big news coming here, too, as the New Horizons probe will be flying past the Pluto system on July 14, 2015. The whole swarm of worlds beyond Neptune, known as the Kuiper Belt, is probably full of frozen water. By the way, instead of thinking of Pluto as the last of the traditional planets, I like to think of it as being the first of a new class of objects called the
Plutoids
. Water even shows up in the most unlikely places. It's present in frigid, shadowed craters at the north pole of the otherwise searing-hot planet Mercury, and forms a frost in the polar craters of the Moon.

In any consideration of life on other worlds, a wonderful evolutionary question emerges right away. How different would any type of alien life really be? You have to figure that it would not have DNA. Or, would it? It would not have cell membranes and organelles that metabolized chemical energy. Or, would it? They, if there are any of them, would not have five fingers and toes on each of four appendages. Or, would they/it? They/it would not have a water-based brain closely connected to chemical, stereo-aural, multi-channel-tactile, and stereo-optical sensors (taste, smell, hearing, touch, and sight). Or, would they/it, etc.? Would the process of evolution converge on common designs and problem solving for the contingencies of life, or would everything be different?

If there is life elsewhere in the solar system it might actually have a lot in common with life on Earth. Think about the enormous asteroid that struck Earth 66 million years ago, when the ancient dinosaurs vanished. As it kicked up a huge cloud of rock and dust, some of that material escaped Earth entirely and began migrating through the solar system. The same thing happens on other planets. Over billions of years, the planets exchange quite a bit of material. This is not speculation; this is fact. Planetary scientists have found pieces of Mars and the Moon here on Earth, and may have identified fragments of Venus and Mercury as well. Could life have made the journey from Earth to Mars, or vice versa? This idea has come to be called transpermia, sending life across interplanetary or even interstellar space.

It's also possible there is a completely different type of life out there on one of these other worlds in our solar system. Then we could study it and gain great insight into nature and the process of evolution. Along the way, such a discovery would lead to profound changes in our beliefs as citizens of planet Earth. But we'd have to send spacecraft and researchers way out there to conduct an investigation, and we'd have to be exceedingly careful about avoiding contamination in either direction. It's a delicate business this dealing with aliens.

Scientists and the lay public alike are taking these ideas increasingly seriously. After they landed on Mars in 2004, NASA's
Spirit
and
Opportunity
rovers sent back conclusive proof that water once flowed almost everywhere on that world. At that point, the famous gambling houses in Britain such as Ladbrokes and the William Hill Company stopped taking bets on whether or not life will be found on Mars. In 2004, the betting closed at 16-to-1, down from 1,000-to-1 forty years ago. Ladbrokes is the same gambling house that paid out £10,000 to a gentleman who successfully wagered just £10 that humans would land on the Moon before the end of the decade of the 1960s. This sort of wagering is more than just human entertainment. It shows the kind of support a government or commercial space company can expect from the public in the search for life elsewhere. As the CEO of the Planetary Society, I hope that excitement persists, and inspires the kinds of missions needed to get concrete answers.

At this point, I hope you're asking yourself, “Where is the most logical place to look for alien life?” As Earthlings, we cannot help but look at Venus and Mars. These two worlds closely resemble our own, astronomically speaking. They are similar distances from the Sun. Earth is about 13,000 km in diameter. Venus is about 12,000 km. Mars is about 7,000. Neither neighboring world is quite as big as ours, but for an astronomer, it's the same order of magnitude—rounding to one significant digit, they're all three about 10,000 km across. Earth turns in 24 Earth hours. Venus takes 243 days, but Mars spins once around in 24 hours 40 minutes; a Mars day is virtually the same as Earth's.

We are getting to know Mars quite well. As of this writing, the
Opportunity
rover is still roving. It was designed to run ninety Martian days—just over three months—but it is still running, ten years later. That's like buying a car with a three-year warranty and finding it running 120 years down the road, with no maintenance, no oil changes, no tire rotations, and without new brake pads. It is an amazing example of your tax dollars at work. Meanwhile, the bigger, newer
Curiosity
rover is hard at work exploring another part of the planet.

Venus is a whole other ball of rock. It looks great from here. When I was a kid, science fiction movies filled with lovely Venusian women were a staple; earlier, some scientists seriously imagined Venus as a steamy jungle planet populated with dinosaurlike creatures. Upon closer inspection, though, Venus proves to be utterly inhospitable. Its surface is hot, astonishingly hot, around 460° C (840° F). That's intense enough to melt lead. Your fishing weights would just turn to pools of shiny metal. Venus is kept that way by a thick, dense atmosphere that's full of carbon dioxide. It's the greenhouse effect gone wild—runaway, as it is oft described. In fact, the models of climate change here on Earth were developed in part by scientists, James Hansen especially, who were studying the atmosphere of Venus. They observed that visible light passes the atmosphere, hits the surface, and then is reradiated as heat that is then trapped by carbon dioxide. This process has a big influence on whether or not a planet is habitable.

The carbon dioxide in the Venusian atmosphere was cooked out of carbon-bearing chemicals, the carbonates, in the Venusian rocks. It is so hot there that the oxygen (O) broke away and bonded with carbon (C) in the air. Any water that was once on Venus has been bonded with sulfur to make sulfuric acid (H
2
SO
4
), giving rise to sulfuric acid clouds. On Venus, it rains acid. But the acid rain never hits Venusian ground, because the heat is so intense that the raindrops evaporate before they can make it to the surface. Venus is a good approximation of hell. A few Soviet space probes managed to land there and look around, but even the hardiest lasted just a couple of hours. This is not a promising place to look for life, though some researchers have suggested that sulfur-loving microbes could possibly survive in its clouds.