Unless you’ve been living in a cave — which actually seems more alluring every day here in the age of coronavirus, fading democracy, and accelerating climate change — you’ve heard that we’ve found possible signs of life in the Venusian atmosphere.
We’ve been combing the Universe for life somewhere, anywhere, for a long time. And now it may turn out that it’s been right next door all along. It would be perhaps the single most profound discovery of any kind humanity has ever made, an absolute drop-everything moment:
So, we need to take a step back and breathe a minute. First of all, what other evidence, or at least logical support, do we have for life up in the clouds of Venus, and second, when can we go back and get more tangible observations to find out once and for all what’s going on up there?
I wrote a little while ago about how the detection of phosphine in an exoplanet’s atmosphere would be a proverbial smoking gun for the presence of life. So the fact that we are seeing it in the atmosphere of Venus is awfully tantalizing. No, not exactly proof, but the kind of thing that’s going to gnaw at us until we find out what it’s doing there. Venus isn’t a thousand or a million light-years away like some hypothetical exoplanet, either, so now we’ve got no excuse. We need to get back there, with the appropriate instruments, and resolve this as soon as we can.
Let’s not get singularly hung up about the phosphine, either. There has been speculation for many reasons about life up in the clouds of Venus since at least 1967, when Harold Morowitz and Carl Sagan envisioned “spherical hydrogen gasbags” the size of ping-pong balls floating around in the lower cloud decks, photosynthesizing to build larger molecules out of CO2 and using mineral nutrients blown up from the surface. They didn’t have tons of observational data to go on, but they knew that temperatures and pressures at the Venusian cloud bottoms are actually similar to those on Earth. They also knew that ultraviolet (UV) light gets absorbed by the clouds, so UV radiation under that cloud cover wouldn’t present a significant obstacle to life.
These days we do have a good bit of observational data from the Japanese Akatsuki and American MESSENGER missions. We know, for example, that there are variations in light absorbance in the UV range, more so than at other wavelengths:
Up close, these absorbance patterns can change rather rapidly. Features a couple of miles wide can change in just a few minutes, while planetary patterns change over days and weeks. The images below were taken 12 minutes apart through a 365-nm (UV) filter by Akatsuki in 2016, and you can see some examples of wispy movement within the ovals:
We don’t know what exactly is absorbing the UV this way; molecules like SO2 and FeCl3 probably have something to do with it. But lots of biological molecules absorb in the UV range, too: nucleic acids (260 nm), protein (280 nm), iron-containing proteins (350-450 nm), and natural sunscreen pigments (310-360 nm). It doesn’t prove these are biological particles, of course, but it is consistent with that notion.
One important thing that would need to be present up in the clouds to support life is water. And it is present, but not a heck of a lot of it. There’s only about 40 parts per million (though some estimates put it closer to 200 parts per million). Plus the sulfuric acid concentration is very high, on the order of 80 to 90 percent:
MIT professor Sara Seager, who is part of the international team that announced the phosphine finding, puts this challenge into perspective:
The atmosphere is, for example, 50 times drier than the driest places on Earth. The cloud droplets are made not of liquid water but of concentrated sulfuric acid. The acid environment is billions of times more acidic than the most acidic environments on Earth. Earth-life components including DNA, proteins, and amino acids would be instantly destroyed in sulfuric acid. Any life in the Venusian clouds would have to be made up of building blocks different than Earth life, or be protected inside a shell made up of sulfuric acid-resistant material such as wax, graphite, sulfur, or something else.
But still, there’s that darn phosphine…
The finding is so astonishing because phosphine should not be present in Venus' atmosphere. Phosphine needs lots of hydrogen and the right temperatures and pressures to form -- conditions found on Jupiter and Saturn but not at all on Venus. My team at MIT exhaustively searched all known chemistry and did not find any way for phosphine gas to be easily produced on Venus. Planetary processes including volcanoes, lightning, meteorites entering Venus' atmosphere are also "no goes" in that some might produce the tiniest amount of phosphine but not nearly enough to match the observations.
There are microbes on Earth that can thrive in strong acid and that build things from CO2 with the help of electrons they get from reduced iron, lots of which is found on Venus, such as Ferroplasma acidophilum:
And there are bacteria found up in the clouds on Earth as well. One 2003 study found viable cells at Earth altitudes from 21 km to 41 km, similar to where we’d be looking for them above Venus. Another in 2013 took samples at heights of 2 km to 7 km and sequenced ribosomal RNA to find out what was in there, and it was a lot:
Periodic dessication, or drying out, as might be necessary in a Venusian cloud life cycle, doesn’t stop life on Earth either. Heck, a new species of crustacean was just found living in intermittent pools in the hottest place on Earth, the Dasht-e Lut, a desert in Iran. Its eggs can stay dry and dormant for decades, and as soon as some water pops up, bam! Desert shrimp!
Of course, the only way to show one way or another whether life is in the Venusian clouds is to go back there with the right instrumentation and find out. Akatsuki is still zooming around Venus, orbiting it once about every 10 days…
...but it only does flybys and isn’t equipped to attempt any sampling.
So the question is, what’s the soonest we can get back to Venus and explore the clouds? The answer is around 2023, and there are at least two missions in the works.
One is DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus), a proposal that’s been on NASA’s radar since 2015. In light of the phosphine story, they almost have to approve it now. They would give the green light in 2021, we’d have a launch as soon as November 2021, setting up a June 2023 arrival. DAVINCI+ would drop a balloon sensor down through the Venusian atmosphere and take measurements and images. We’d definitely get a better understanding of chemical composition and conditions as a function of altitude, but it’s not clear we could definitively resolve the life question this way.
But there’s another potential answer for 2023 that is designed to answer the life question. It’s the brainchild of a private New Zealand company called Rocket Lab, which has had a Venus mission planned for some time, but still has wiggle room to put just the right instruments onboard, such as spectrophotometers and even microscopes, so that life can be targeted as directly as possible. Rocket Lab is seeking advice from phosphine researchers such as Sara Seager, whom we met above, to make sure they do the right experiments. They’re no slouches; they were just awarded a contract to accompany a NASA satellite to the Moon in 2021. So they may indeed have the chops to pull this off. They’d put a 660-pound satellite into orbit around Venus, and from it drop an 82-pound probe through the atmosphere. They could actually launch several missions, at a cost of just $10-$20 million each, in a relatively short amount of time.
There are claims that India will try to launch a Venus mission called Shukrayaan-1, with a 100-kg instrument payload — so, quite well-stocked for good science — around 2023 as well, but information on the reality of this timeline is still a little spotty. You suspect that the Indian government will try to fast-track this now, and let’s hope they get it up there.
Northrop Grumman has designed a mission to send a sort of hovercraft called VAMP through the Venusian atmosphere with any number of instruments that could remain active for up to a year. Nobody cared about this back in 2015 when they proposed it, but I think they’ll get funding now! They claim the flight time for the mission need only be 3-6 months, so 2023 wouldn’t be at all unreasonable for this one either:
While it’s true that 2020 has been a trying time in so many ways, and will continue to be, as the last couple of days have graphically demonstrated, we’ve been given a ray of hope and something very exciting to look forward to.
We might find life on another planet, and well within our lifetimes! That would change everything, wouldn’t it? We were all so thrilled a year ago with the first image of a black hole, as indeed we should have been, but how would we react to the first microscope image of an organism that lives on another planet?
Stay tuned….