Atlantis Dispatch 001:
in which ATLANTIS contemplates the meaning of “past" life.
March 8th, 2021
…begin transmission…
Perhaps you, too, can’t stop watching Perseverance land on Mars. It’s not just the unprecedented footage of the new rover, slowed by the pleated red and white parachute, nailing its landing against the ream of imaginable mishaps. It’s the vocal track, too, with Swati Mohan’s final call-outs from Mission Control: “Touchdown confirmed. Perseverance is safely on the surface of Mars, ready to begin seeking the signs of past life.” Perhaps the moment makes your heart swell. De Capo! De Capo!
And rightly so. Percy landed on the most challenging terrain that NASA has targeted. It’s no wonder scientists refer to the time between entry, descent, and landing as “the seven minutes of terror.” When Percy’s capsule hit Mars’s atmosphere, it slowed from 12,000 mph to 1,000 mph, released that seventy-foot, supersonic parachute, and then its Skycrane, to slow the rover further and set its 2,260 lb body on the surface of the red planet. Since there’s a transmission lag of about eleven minutes, the rover did all of this autonomously, by its own pre-programmed lights.
Now that the rover has turned on its cameras and is sending images and sounds back to us, what exactly are we looking for? Mohan said, “signs of past life.” What does that mean? Perseverance landed in the Jezero Crater, the site of an ancient river and body of water the size of Lake Tahoe — a place regarded as a prime site for ancient microbial life. The rover will use its many tools, including SHERLOC, a scanning device that can detect organic matter and minerals, PIXL, an x-ray spectrometer that maps the chemical compositions of rocks, and SuperCam, a laser that homes in on rocks to study their composition at a distance. Basically, Percy is looking for signs of life, aka biosignatures, in dust and pebbles.
Yeah, ok, but how exactly will scientists recognize these biosignatures? If you’ve been paying attention to the great phosphine freak-out, you no doubt know that this is a pretty big challenge. Back in September 2020, a group of astronomers announced that they had observed telescopically large quantities of phosphine in the Venusian atmosphere. On our planet, phosphine is associated with life, so the researchers posited that they’d found life on Venus. By November, however, many in the scientific community had challenged the findings, arguing that measurement errors were behind the data, and later, the group recalibrated their data and walked back their estimate, while still affirming their original discovery.
The dispute caused a few scientists, including SFI External Professor Sara Walker and SFI Professor Chris Kempes, to return to theoretical fundamentals. In the wake of the Venus controversy, Walker tweeted this Borgesian gem: “until we can prove a planet is devoid of life, we won’t be able to prove whether a planet has life either.” In a conversation about astrobiology, Kempes remarked that there are many false positives in the field, and we would do well to look for more general principles to be able to know the signs of life. “Without complete theories for life,” Kempes said, “we have no way of identifying false positives and false negatives.”
So what is a rover to do? If the chemical biosignatures of life, like phosphine, have other causes than life in different planetary environments, how will we know for sure if Percy spots biosignatures on Mars?
Mars has a few things going for it. For one, it’s a lot like Earth. So when we look at Mars, we are looking at a planet that bears striking similarities to Earth’s early geology. So far, we haven’t found life on Mars, but that doesn’t mean it didn’t exist in the past, or that we couldn’t bring it there in the future.
Future life, you say? Yup. Percy is charged also with examining whether Mars is habitable, which — let’s be clear — is very different from saying that it has life. It’s more like asking whether or not it could support a pretty robust lifeform, while (for now, at least) leaving the question of “present” life in the regolith.
But what if Percy were to stumble on extant life, like Marvin the Martian? Well, sorry, Marvin, but she’d obviously shoot her lasers at you and eviscerate you, in order to understand you, learn about you, and help us learn about ourselves. All in the name of science!
More seriously, even if Percy stumbles upon some less easily identifiable form of life than Marvin, her lasers are focused on past life and future life, not so much on present life. Have we given up on the search for extant life? Does that mean we’re seeking signs of past life, and the possibility for future life, because we know, deep down, that if we found present life, we’d likely take over, anyway? Is that what Mohan meant by past life? Probably not, but let’s be real: our roving Martian scientists, Percy and Curiosity, while totally adorable are not Jane Goodalls. They’re Francis Bacons.