The Debate on Phosphine in the Atmosphere of Venus Continues

Venus’ inhospitable clouds are visible in this newly processed image from the Mariner 10 spacecraft. Credit: NASA/JPL-Caltech.

The reported detection of the chemical phosphine in Venus’ atmosphere last September based on observations from the James Clerk Maxwell Telescope and the Atacama Large Millimeter Array (ALMA) inspired additional interest in our neighboring planet. With a crushingly thick atmosphere composed primarily of carbon dioxide and a surface temperature of almost 900°F (480°C), Venus is often considered completely inhospitable to life. The detection of the molecule phosphine (PH3), which on Earth is mostly known to be produced by biological sources, suggested that similar microbial processes may be occurring on Venus, possibly in the upper reaches of its atmosphere where temperatures are less hostile to life as we know it.

However, a new report by Alex Akins of NASA’s Jet Propulsion Laboratory and a team of researchers at the University of Washington and Georgia Tech comes to a different conclusion. The initial detection, reported by a team led by Jane Greaves of Cardiff University, was based on observations of an absorption feature at 266.94 GHz, a frequency near which both phosphine and sulfur dioxide (SO2) absorb radio waves. Based on the apparent lack of detection of other absorption features of SO2 in Venus’ atmosphere, the Greaves team concluded that the feature at 266.94 GHz was caused by phosphine.

The Akins team re-examined the same data using a revised set of calibration procedures for the ALMA telescope and were not able to detect the same 266.94 GHz absorption feature. The Akins team also modeled the atmosphere of Venus to examine how the spectral signal of SO2 might be “diluted” (less detectable) in its atmosphere. They determined that there could be considerably more SO2 in the atmosphere that would not be detected based on the configuration of the ALMA telescope at the time of the Greaves team’s observations. Thus, SO2 cannot yet be ruled out as the potential source of the purported absorption feature near 266.94 GHz. The debate over the presence of phosphine reinforces the need to continue studying Venus with telescopic observations, atmospheric modeling, and perhaps dedicated spacecraft in the future to better understand its potential for life. READ MORE