Life on Venus? Six Carnegie Scientists Respond
The September 2020 announcement that scientists found phosphine gas on Venus set off a buzz of excitement across the scientific world, leaving one question in the minds of many spectators: Did we just discover signs of life on Venus?
Planetary Scientists: even if it's just anomalous chemistry, it's still super-interesting!
Planetary scientists writing next batch of Venus mission proposals: LIFE! LIFE!! LIFE!!! LIIIIIIIIIIIIFE!!!!!!!!!!!!!!!!
— Larry R. Nittler (@LarryNittler) September 14, 2020
Life in the Clouds
Life would be hard-pressed to make it big on Venus.
Despite being pretty similar to Earth in size and rocky composition, the planet’s dense CO2 atmosphere exerts 93 bar of pressure on objects at the surface—the same pressure you would experience 3,000 ft underwater here on Earth. The CO2 is also responsible for the extreme greenhouse effect that accounts for Venus’ blazing 564°C surface temperature— hot enough to melt lead (327.5°C) and more than enough to vaporize any water that may have once flowed on the surface.
Even considering the harsh conditions, humanity is suddenly alight with the hope that life may exist on our sister planet.
Cosmos presenter and astronomer Carl Sagan was one of the first to propose that something like microbial life could exist suspended in the atmosphere of the planet, where the hellish temperatures and pressures of the surface give way to more temperate conditions.
Fifty-three years later, research—led by former Carnegie scientist Sara Seager and including the newly hired Carnegie scientist Peter Gao—suggested a mechanism that could allow the hypothesized microbes to live floating in the sulphuric acid droplets of Venus’ clouds.
It’s this highly acidic outer atmosphere where an international team of scientists (including Seager) recently found phosphine (PH3). On Earth, this rare gas is only created industrially or by microbes that live in oxygen-free environments. Seeing as the team couldn’t identify a clear nonliving pathway that would create phosphine in Venus’ atmosphere, could finding phosphine mean we’ve spotted signs of alien life?
The resounding answer from the scientific community—including the authors of the paper itself—is: “We’re going to need way more data.”
So, Did We Find Evidence of Life on Venus?
We asked six Earth and Planets Laboratory scientists to respond to the question of life on Venus from the perspective of their own work.
Update: On October 27, 2020, researchers from the NASA Goddard Space Flight Center announced that they could not reproduce the phosphine findings. The scientists called for a correction or retraction of the original report.
No, astronomers found evidence for a rare gas, phosphine, in Venus' atmosphere and no good explanation for why it is there.
On Earth, phosphine can be produced by certain microorganisms, so one possibility for Venus is that similar organisms are making it high up in a sulphuric acid cloud layer. But this is a long-shot.
It may be that the detection is wrong—though they did a meticulous job and detected it with two different telescopes—or that it is made by some chemical process nobody has thought of yet.
But it is really super interesting and worth a lot more investigation.
I think it's way too early to tell.
First, the authors emphasize that this detection is of a single transition and that researchers should try to observe other phosphine spectral signatures. They felt confident enough to publish these results, which is a high bar, but point out that further observations could give different results.
Second, the authors wrote about their process to rule out several abiotic pathways to produce phosphine, but point out that there could be other geophysical or photochemical processes that are not yet known or well-characterized from which the phosphine originates.
The paper does say, ‘This could be unknown photochemistry or geochemistry, or possibly life.’
Since life is an extraordinary claim, I'd want to have more smart atmospheric scientists and geochemists pursue the first two before believing it is life.
Just because scientists can't think of a way to generate phosphine efficiently abiotically doesn't convince me it can't happen. Nature is very clever, and many phenomena have been observed first not predicted first—hot Jupiters, for example.
This is an unconfirmed detection of a molecule that is associated with life on Earth but is also associated with quite a few other processes including the manufacture of electronics and UV-resistant coatings. It is produced by volcanic eruptions and weathering of volcanic ash on Earth and is present in the upper troposphere of our own atmosphere as part of Earth’s phosphorus cycle. We’ve also detected and used phosphine gas as an atmosphere dynamics tracer on Jupiter and Saturn for decades.
These exciting measurements need to be confirmed and non-life (abiotic) formation conditions entirely eliminated before such a signature could be considered a potential biosignature.
At the same time, other evidence of biological signals should be undertaken to provide separate and confirming observations of a possible biogenic source.
So, yes, the discovery is exciting, but it is the start of a journey of robust scientific inquiry.
No! To find life on another planet, we have to be able to rule out all abiotic processes that could lead to a false positive, as the authors acknowledge throughout the whole paper.
Impacts on Future Research
Carnegie Earth and Planets Laboratory Director Richard Carlson thinks that Venus would be "a MAGNIFICENT target for planetary studies." According to Carlson, there are myriad questions a mission to Venus could help answer. In an email on the subject, Carlson listed off several of these questions, "Is it made of the same stuff as Earth? Why doesn't it have a magnetic field?" He continued, "Has it ever had plate tectonics? Are there granites on the surface that would suggest the presence, at least at one time, of water in the interior? Why has weathering of the surface not reduced the CO2 content of the atmosphere." The list, according to Carlson, goes on.
Carlson is not alone in thinking Venus should be on the planetary research map. In the wake of the new finding, NASA Administrator Jim Bridenstine tweeted: “It’s time to prioritize Venus,” in the same tweet he said, “The discovery of phosphine, a byproduct of anaerobic biology, is the most significant development yet in building the case for life off Earth.”
It turns out that even with the uncertainty (or maybe because of it), the potential to find life on Venus could be tantalizing enough to kick off a new age of Venusian exploration.
Considering the potential research implications for planetary scientists, we asked our staff scientists to explain how this finding might impact their research at the Earth and Planets Laboratory.
To me, this is the beginning of many decades of research aimed at understanding the atmospheres of other planets. The most important part of this research paper, to me, is that it will motivate NASA to send a probe to Venus.
Only by going to Venus we will be able to figure out why there is phosphine in the atmosphere. And if we can’t figure out the atmospheric chemistry of Venus, it will be unbelievably hard to understand the atmosphere of an exoplanet.
My research is aimed at experimentally determining key variables so that the models calculated for these atmospheres are more accurate.
I also am constantly advocating for more communication amongst different disciplines and this paper is a great example of why that is important.
What excited me most about this work was the new energy and attention it injects into studies of chemical pathways on potentially habitable planets (even if in just parts of their atmospheres)! I'm learning to appreciate more the critical importance of experimental lab work here on Earth for interpreting the very complex chemistry in, but very limited observations of, atmospheres of exoplanets (planets outside our Solar System), which is ultimately what I'm interested in understanding.
Planets like Venus that are within our Solar System offer the prospect of testing predictions based on theory and experiments with in situ measurements, which is impossible for more distant worlds.
It's almost like this paper is presenting a grand challenge to experimentalists--what else could be causing this signal? I can't wait to see what they find, and how it might apply to planets like Venus around stars other than the Sun.
If a spacecraft sent to Venus could prove that the phosphine was produced by microbes, that would be a revolutionary discovery.
Even still, it might not mean much for the detection of life on exoplanets, because of the extremely low abundance levels on both Venus and Earth -- if inhabited exoplanets have similar abundances, there is little hope of detecting such a faint signal with any space telescope currently under consideration.
Not directly at all, except that I am keenly interested in the chemical diversity of planets throughout the galaxy.
Alycia Weinberger | Astrophysicist
I'm in favor of doing as complete molecular surveys of planets and exoplanets as possible, so that we're open to discoveries we don't expect.
That's one reason why I'm trying to build MagNIFIES (a Near-Infrared Spectrograph for the (Giant) Magellan Telescope, which would cover 1.07 - 5.3 micron wavelengths simultaneously at high spectral resolution.
Andrew Steele | Astrobiologist
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