Just 30 years ago, we had not discovered a single planet outside our solar system. Now we know of more than 3,000 of them, and we know nearly every star in the night sky has at least one planet in its orbit. “Even people who are not terribly interested in science know that we’ve found that planets are as common as fire hydrants — they’re everywhere,” says Seth Shostak, the senior astronomer at the SETI Institute. “One in five or one in six might be a planet similar to the Earth.”
That doesn’t mean we’ll ever find an exact replica of Earth, but maybe we don’t have to. Our study of other planets and moons in the solar system shows us many worlds possess the ingredients necessary for life — an atmosphere, organic compounds, liquid water, and other necessities. (The moons orbiting Jupiter and Saturn, for example, feature whole subsurface oceans.)
And even though these places are extremely harsh environments, that doesn’t mean as much as we might once have thought it did; recent discoveries on Earth itself demonstrate that life is much tougher than we thought. We’ve found organisms in blisteringly hot geysers in Yellowstone National Park, in the darkest crevices under the most ungodly pressures in the deep ocean, in dry hellscapes like the Atacama Desert in Chile (an analogue for Mars). These “extremophiles” don’t need a warm and fuzzy paradise to call home — in fact, they have already evolved to live in environments as harsh as those on other planets. Some, like tardigrades, can even survive the bleak vacuum of space itself. If there’s life in most of those places, “it’s going to be pond scum,” says Shostak. “But it’s alien pond scum. It shows that biology is all over.”
And where there’s biology, there may well be intelligence, and our increasing understanding of evolution also tells us life can evolve faster than we ever anticipated. Millions of years is a long time for us, but it’s the blink of an eye on the cosmic scale. Blink too fast, and you’ll miss that pond scum turning into an intelligent civilization sending out messages every which way, looking for friends.
And we’re now at the point where we could one day find those messages and send a reply. New technology gives us a better chance to actually make contact with extraterrestrials. Our radio telescopes can scan more of the night sky for an intelligent message than ever before. Our optical telescopes and observatories can peer farther into space and look for new planets, moons, and perhaps even signs of something altogether artificial (see “Tabby’s Star”). Our ability to parse volumes of data in mere seconds means we could conceivably survey much of the galaxy in just a few decades. That’s why, in the past few years, Shostak has continually bet a cup of coffee with everyone he knows that humans will find aliens by around 2029. “We’d have to be dead above the neck if we weren’t interested in this,” says Penelope Boston, the director of the NASA Astrobiology Institute. —Neel Patel