Earth and Venus were supposed to be sister planets. But what would you do if your sister turned out to be a toxic wasteland so hot that she could melt lead and so high-pressure that she could smash submarines?
News this week that there may be signs of life on the second planet from the sun came as a surprise not because scientists had never contemplated such a possibility but because they had. Venus is about as big as we are, about as dense and, judging only by its distance from the sun, about as habitable. It is also our nearest neighbor — which is why, when humans finally sent a probe beyond our own planet, Venus was the obvious destination.
Unfortunately, as David Grinspoon of the Planetary Science Institute put it in an interview, Venus is “an easy place to get to and a hard place to get to know.”
The welcome wasn’t what we’d hoped for. Humankind’s initial overtures came in the Soviet Union’s Venera missions in the dawn of the 1960s. After a couple of tries, the Russians landed a probe on Venus’s surface, though “landing on” in that case really meant “crashing into,” presumably as a molten mess. Subsequent probes, fortified for unforgiving climes, conveyed an unlikely vacationland with surface temperatures of 860 degrees Fahrenheit, sulfuric acid rain in the clouds and an atmosphere 90 times more crushing than ours.
In short, a bummer. We had traveled to the heavens and found a hell. Some writers had imagined jungles and oceans; few had predicted formaldehyde dust. Exploratory efforts refocused on less hostile destinations nearby, plus farther reaches of the solar system that at least had the distinction of being mysterious and distant. Venus was both too similar and not similar enough.
The search for extraterrestrial life has long been full of contradictions. Even as we seek confirmation that we’re less special than we assume, we conduct our search in a way that assumes we’re awfully special. We’re pursuing an Earth-like environment, whether that’s Mars after a little dusting or the moons orbiting gas giants such as Saturn and Jupiter. At the same time, we secretly hope there’s no place like home.
There’s a scientific reason for our geocentrism: We don’t have any other data. Unless this whole shebang is a simulation run by aliens, we can be confident that the conditions on Earth support life — because, well, we’re here. So we assume we’re more likely to find life elsewhere by looking for those conditions that sustain us here than we are by flailing around madly in the Milky Way.
Imagination is always rooted in reality; where there’s nowhere to start from, there’s nowhere to go. Ask any kid to draw an alien. Those little green guys are usually just like us, but with antennae.
Which is why reports of potential life on Venus are different. The astronomers haven’t encountered any little green guys with their telescopes, but they also haven’t encountered any subsurface oceans or mold-friendly mountains, either. What they’ve encountered is in the clouds: a chemical called phosphine that they’ve determined shouldn’t exist on a rocky planet such as Venus unless there are microbial organisms around to keep it there. They say — and astrophysicist Carl Sagan hypothesized this, too, over 50 years ago — that these organisms are likely to live high above the ground, in a Goldilocks-like sweet spot for pressure and heat but chock full of acid nonetheless.
Phosphine itself is, in fact, poisonous to humans, besides being foul-smelling. And the whole chock-full-of-acid-thing is a far cry from anything like earthiness. Some scientists say organisms that survive in that soup could rely on a sort of protective shell that shields them from the acidity that would otherwise scorch into oblivion any of the DNA, amino acids and other building blocks of life. Others say that life on or above Venus is simply implausible, and that the researchers themselves have acknowledged there may be some “anomalous and unexplained chemistry” to explain the presence of the phosphine.
It may turn out there’s nothing vital on Venus after all. Still, the frenzy surrounding the very thought is worthwhile. Maybe any DNA-based critter would be scorched into oblivion in the Venusian winds, and maybe an anomalous and unexplained chemistry does explain the phosphine — but maybe that chemistry is life of a kind, too, only one made of building blocks far different from those we know.
We’ve been searching for the conditions for life as we know it because we’ve been searching for life as we know it. This week’s dispatch from our sister planet suggests a different kind of life that remains unknown to us. In which case, the question isn’t merely whether there’s extraterrestrial life in this universe. The question is bigger: What is life, anyway?