2. Astronomers spy phosphine on Venus
Venus is a sizzling world thought by many to be inhospitable to life. Surface temperatures are hot enough to melt lead — almost 900 degrees Fahrenheit (480 degrees Celsius) — while the pressure at ground level is more than 90 times that of Earth at sea level. But that hasn’t stopped some, including Carl Sagan, from proposing that life could exist in the more temperate clouds of our sister planet. And now, there could be evidence to support that hypothesis — albeit controversial evidence.
In a paper published September 14 in Nature Astronomy, researchers presented observations of an inexplicable surplus of the rancid gas phosphine in the clouds of Venus. On Earth, microbes produce most phosphine, though it can also be created abiotically under great temperatures and pressures. Measured at a level of some 20 parts per billion, the researchers behind the new paper say no known geological activity or exotic catalysts — such as lightning or meteorites — can explain the strength of their observed signal.
“We are not claiming we have found life on Venus,” said co-author Sara Seager, an MIT planetary scientist, in a press conference. However, she added, they can’t explain the phosphine’s origin.
Many find the unexplained biosignature, or potential evidence for past or present life, tantalizing. However, others remain skeptical. Chemical compounds each have a unique spectrum, or fingerprint, that depends on the wavelengths of light they absorb. Although the researchers detected this fingerprint of phosphine with two independent telescopes at different times, they only saw it at a single wavelength — one that sulfur dioxide happens to absorb as well.
“As a geochemist, I always worry about detection from one peak,” says Justin Filiberto of the Lunar and Planetary Institute. “A single line is a coincidence, not a detection,” adds astrobiologist Kevin Zahnle of NASA Ames Research Center in California. Still others are concerned about the quality of the noisy data itself, which means many groups are already reanalyzing it.
But if the detection holds up, “it demands follow-up,” says Bethany Ehlmann, a planetary scientist at Caltech who was not part of the discovery team. “The top three destinations to look for life in the solar system are Mars, Enceladus, and Europa — and now we should perhaps add Venus to the list.”
Editor's note: Since the publication of this story, new research has come out that suggests the detected signal may have been from sulfur dioxide instead of phosphine.