A new study indicating the presence of a gas associated with microbial life on Venus had NASA chief scientist Dr. James Green "grinning from ear to ear."
Green said the discovery of the compound phosphine in Venus's atmosphere is "our first indication of potential life on Venus." (NASA was not directly involved in this study, which was published Monday in the journal Nature.) The discovery could even reshape a proposed NASA mission to Venus.
Green spoke during Westminster College's annual Hancock Symposium lecture series Wednesday. He has been NASA's chief scientist since 2018, having been with the space agency since 1980 and directed its Planetary Science Division from 2006-18.
"Dr. Green has had his hands in hands in every significant space mission since 1980," Westminster professor David Schmidt said while introducing Green.
As such, the search for extraterrestrial life has long been of interest to Green — even before Monday's big announcement, he was already planning to speak on the topic. But the new study, in which scientists at MIT, Cardiff University and other institutions found significant amounts of a gas possibly produced by living microbes, came as a surprise.
As Green explained during his lecture, scientists have identified several ingredients necessary to produce life as we know it beyond Earth. Carbon, water ("If we see water on Earth, we find life," Green said) and energy (usually in the form of sunlight) must be present. Additionally, they must have been present for the many millions of years scientists hypothesize it takes for life to evolve — the fourth ingredient is time.
Venus is closer to the sun than Earth, though similar in size, and its dense atmosphere is packed with carbon dioxide. Previous studies by NASA, the European Space Agency and other entities indicated that in the past, much of its surface was covered with liquid water — which may have persisted for up to 2 billion years.
"This was really quite exciting because it means Venus could've been habitable in its past because of its amount of water," Green said.
Computer modeling suggests that by about 800 million years ago, the sun had evaporated enough of the oceans to disrupt the water cycle. Water vapor lingered in the atmosphere to be stripped away by solar winds. Its atmosphere now full of greenhouse gases like carbon dioxide, the planet sweltered — today, at the surface, it's hot enough to melt lead and 90 times the atmospheric pressure of Earth and the very air is acidic.
"This makes it really difficult for us to believe that life as we know it could exist on surface of Venus," Green said.
But high in the atmosphere, 30-37 miles above the surface, temperatures are a much more hospitable 30-200 degrees F. The atmospheric pressure is more reasonable, too. According to a news release from MIT, scientists have speculated that if there's life on Venus, it might be found in that habitable band of atmosphere. A NASA study Green selected for funding discovered bacteria and other microorganisms living high in Earth's own atmosphere — the first indication such a thing was possible. A separate NASA-funded study spotted unexplained dark streaks in the same area of the atmosphere, composed of particles about the size of Earth bacteria.
Using two telescopes, the scientists involved in the MIT/Cardiff study found a significant of one unique and stinky gas right in that habitable zone.
"(They've observed) an exciting compound — one phosphorous and three hydrogen molecules — called phosphine, which could be associated with anaerobic life," Green said. "This is that next step, and an exciting next step."
On Earth, phosphine is produced in three main ways: in labs, in small amounts through certain extreme events (such as lightning strikes and volcanic activity) and by microbes that thrive in oxygen-free environments. In a previous study, one of this study's authors concluded if phosphine shows up on a rocky planet, it's a near-sure sign of life there.
MIT's team looked at alternate explanations but determined "there is no explanation for the phosphine detected in Venus' clouds, other than the presence of life," according to the news release.
"It's very hard to prove a negative," study co-author Clara Sousa-Silva wrote in a statement. "Now, astronomers will think of all the ways to justify phosphine without life, and I welcome that. Please do, because we are at the end of our possibilities to show abiotic processes that can make phosphine."
Green was more reserved.
"Either this discovery tells us this is life or some exotic chemistry we don't quite understand," he said.
Both possibilities intrigue him.
A proposed NASA mission announced in February, DAVINCI+, could provide an opportunity for further study. The mission concept, designed by NASA's Goddard Space Flight Center, aims to study the past and present of Venus's atmosphere by dropping a probe all the way to its surface. It'll sniff for chemicals along the way.
DAVINCI+ is among four finalists in the agency's Discovery Program and is competing against three other missions for funding; a decision is expected by summer 2021.
As that mission is still in the developmental phase, NASA may ask its developers to plan a closer look at the atmospheric region found to contain phosphine, Green said.
"It could change their approach, maybe at that time period (in descending through the atmosphere) they were planning to be in a low-data rate mode, now they're in a high data-rate mode," Green said. "It could completely change their sampling."
There's plenty of research scientists can do right here on Earth, too. Green envisioned sending high-altitude balloons back up into Earth's upper atmosphere to study whether the live microorganisms spotted there are actually spending their whole life-cycle high in the sky, including reproducing.
Though this discovery on Venus is promising, Green has his eyes on Mars.
"We've been seeing all kinds of indication of even what we call extant life, life today, that might exist on Mars," he said.
One promising indication: Every Martian summer, the planet gets gassy, with the amount of methane gas present at the surface increasing dramatically. The Curiosity rover also detected spikes in molecular oxygen, which increases each spring and summer by up to 30 percent before dropping again in the fall. On Earth, both gases are produced by microscopic organisms (in addition to other sources).
"That tells us life may be underground during the summer — the soils heat and therefore loosen up such that the methane can leak out," he said. "We have all kinds of circumstantial observations that perhaps Mars has microbial life too."
And Mars has water in abundance, both in its past when two-thirds of its northern hemisphere was beneath an ocean, and in the present, in underground aquifers and frozen glaciers.
"Life could've started there," Green said.
NASA, which will land on the planet in February 2021, holds great promise for identifying evidence of past life on Mars.
"What we need is the rock record, which may hold information about life in the past, in our labs to study," he said. "That's what Percy is doing it will land in an area in Jezero Crater right at a river delta that into an ancient ocean, where sediments built up over hundreds of millions of years — where we believe there's a great opportunity to perhaps find life."
On Earth, river deltas are full of silt and microbial life; ancient river deltas often hold fossils, too. Perseverance will take rock core samples that future scientists can analyze, searching for tiny fossils and other indicators of life.
"On Earth, there's 5,000 or so minerals," he said. "Three hundred of them or more are only made because of life. The rock record tells us about life, in addition to how the planet evolved."
Jupiter's moons Europa and Enceladus, with huge oceans of water below the surface, are also promising candidates for study, Green said. He feels planetologists are close to a breakthrough.
"We have so many circumstantial sets of measurements that it's hard for me to believe that there's not some sort of life element to this whole thing," he added. "It might be just a handful of years, maybe no more than 10, to answering the question of whether we're not alone."
Later in his lecture, Green discussed NASA's work in tracking space objects that could potentially pose a threat to earth, how studying other planets provides insights into climate change here on earth and the importance of exposing young people to science at an early age, among other topics.
To watch a recording of Green's full talk for Westminster College's symposium, visit youtu.be/ZBGeduI44wM.