2020 has been a shit year for most of us here on Earth. But it may turn out to be a landmark year for science, and the search for life outside of Earth.
The search for extra-terrestrial life has mostly focused on Mars and the icy moons of the outer solar system.
For decades, the focus of the search for extraterrestrial life has focused on Mars, the outter solar system (such as the moon Titan and Europa), and searching for non-natural radio signals from other stars. But a recent review of data from the Pioneer 13 space probe has revealed that the probe detected one of the tell-tale indications of life in the atmosphere of Venus way back in 1978. The review of Pioneer 13's data was prompted by the recent discovery (by scientists using a land-based telescope) of a chemical called phosphine in the atmosphere of Venus. The findings were published in the journal Nature Astronomy a month ago, on September 14.
Phosphine is a class of gas that can be produced from atmospheric chemistry under high pressure, or as a by-product of anaerobic biology. Phosphine has also been detected in the atmosphere of gas giants such as Jupiter, where the incredibly high pressure and energy of Jupiter's interior atmosphere produces the compound, which then floats up to the upper atmosphere, where it reacts with other chemicals and oxidized (or dissolves). The atmosphere of Venus, however, lacks the higher pressure of Jupiter that would be continually-creating phosphine. As such, the chemical cannot be produced in Venus' atmosphere, in the quantities detected, by the same mechanisms that produce it on Jupiter. Another explanation is required, and the only other known way to produce this type of phosphine is through anaerobic biological processes.
Venus has been discounted as a potential candidate for life due to its toxic atmosphere and runaway greenhouse effect -- a reality that may be part of our own future here on Earth if we don't get our carbon and methane emissions under control. The surface of Venus is famously hot enough to melt lead. The atmosphere is also largely toxic, and much thicker than Earth's, leading to pressure that has crushed and melted every spacecraft or probe that humans have tried sending to the surface. If the atmosphere and surface of Venus are too inhospitable for a spacecraft, then surely it's too inhospitable for any form of life as we understand it.
The Pioneer 13 probe may have detected a bio-signature
in Venus' atmosphere back in 1978.
Or is it?
The surface of Venus and lower atmosphere is too hot, pressurized, and dominated by toxic sulfuric gas for life to likely exist. The outer atmosphere is also an unlikely host for life, since it is being constantly bombarded by lethal cosmic radiation. There is, however, a band of potentially safe atmosphere in between those two extremes. In this layer of the atmosphere, it is hypothetically possible for floating microscopic organisms to exist. It's also possible that larger organisms that float like balloons could exist at this altitude; though, that's a much more extreme and unlikely possibility.
Physicist Heinz Haber first proposed the idea in 1950. The idea was further expounded in 1967 by Carl Sagan and Harold Morowitz. After the phosphine observation last month, scientists such as Sara Seager from MIT have proposed newer models for how such life could hypothetically exist.
We need to temper our expectations. It is possible that the phosphine could be produced by some kind of chemical or geological process that we aren't currently familiar with. Natural processes that we do know about are certainly producing small quantities of the stuff at or near the surface, from which it floats up into the atmosphere and breaks down quickly. Perhaps some kind of hereto unknown volcanic reaction could be producing the additional quantities? Or a novel reaction of lightning or cosmic rays in the atmosphere?
We'll need to do further study of Venus to confirm the observation of high quantities of phosphine.
Either way, exploring Venus more thoroughly is going to be a source of new science. We'll either discover a new mechanism of producing this particular substance, which would allow us to maybe rule it out as a strong biosignature for future exoplanet exploration. Or we'll rule out other explanations, leaving us with life as the only likely explanation. Or we'll make the most exciting discovery of all: the direct observation of extraterrestrial life for the first time.
In any case, space agencies around the world should be turning their attention to our closest cosmic neighbor, Venus, and I hope to see the U.S. government (and other governments around the world) invest in sending further probes to the planet. NASA was already considering new missions to Venus. The proposals did not include life-detecting instruments, but this recent discovery will likely prompt NASA researchers to add such an instrument to whichever mission ends up being greenlit. Forget Mars! Suddenly, Venus is the place to be!