Was Carl Sagan right about life on Venus? India can help find out more

Harold Morowitz and Carl Sagan speculated in 1967 that the clouds of Venus aka Shukra may harbour life. The recent exciting detection of phosphine from these clouds strengthens the possibility that micro-organisms may indeed be floating around in them. Galileo’s discovery through his telescope of the Moon-like phases of Venus solidified our understanding that Venus and Earth both orbit the Sun. Venus came to be regarded as something of a twin of the Earth, with roughly similar size, mass and solar distance. Radio images of spacecraft that travelled to Venus in the `60s revealed, however, that it was blistering hot on the surface. So much so that even metals could only be molten, and it had a crushingly high-pressure cloudy atmosphere. This was in contrast to Mars, with its Earth-like temperature, pressure and seasonal variations.

Why then did Venus hit the global headlines in the context of the eternal human question of “are we alone?” There are many methods to search for extraterrestrial life. One is to listen for orderly, seemingly deliberate radio signals that could possibly be from sentient and technologically-able life-forms in our Milky Way or beyond. A second method is to search for planets that could harbour life as we know it. Over 4,000 `exo-planets’ have been discovered around other stars several of which are in the ‘Goldilocks zone.’ That is, at a distance from their host star that is not too close/hot nor too far/cold but just right to allow water to exist in liquid form and, therefore, harbour life of a familiar kind. Then there is in situ investigation, i.e., spacecraft landing on the planets (such as Curiosity-Rover to Mars). Robotic instruments on these crewless landers sample the planet’s atmosphere and surface material for evidence of life-nurturers like water, for “biosignatures” or chemical compounds that can‘t be generated by astrophysical or geo-chemical processes and, therefore, must be generated by life-forms, and, of course, for life-forms themselves.

A fourth method, that ties in with the second, is to search for molecules of volatile “biosignatures” that float around in the planetary atmospheres, using telescopes. When these molecules are back-lit, even by the feeble light from the heated planetary surface, they absorb some of this light at specific wavelengths that are dependent on their make-up, amounting to a fingerprint stamped on the light. Phosphine is a molecule with a phosphorous atom bonded to three hydrogen atoms. It is very hard to make by natural processes, except under exceptionally high pressures and temperatures, in, for example, the core of Jupiter. However, living micro-organisms in oxygen-less environments on earth are also known to generate phosphine, and it is, therefore, a clear, though relatively neglected biosignature.

One of phosphine’s molecular fingerprints on light occurs at a wavelength of 1.123mm and is in the range of current cutting-edge telescopes. So astrobiologist Jane Greaves and her team pointed the JCM Telescope in Hawaii at Venus in 2017, motivated by the speculation that its clouds could harbour life, and, sure enough, they found the fingerprint! They calculated that the implied amount of phosphine simply could not be produced by any known chemistry, and is, therefore, suggestive of micro-organisms in the clouds of Venus. A second observation, using the more sensitive and sharper-visioned ALMA telescope in Chile in 2019, confirmed the finding. The estimated quantity of phosphine (20 parts per billion) seems almost nothing. But that amount is at least 10,000 times higher than can be produced by any known abiotic chemistry: Volcanic, lightning-induced, solar wind-induced or delivered by meteorites.

What next? Search for additional fingerprints, for starters. Then go the in situ way. Can Isro’s Shukrayaan help make headway? If conducted in the spirit of collective intellectual advancement rather than competitive nationalism, then yes, it can. Science knows no borders, and expanding the horizons of life as we know it is science that is transformational for humankind.

Prajval Shastri is an astrophysicist from Bengaluru whose core research interest is the empirical investigation of giant black holes that are found in the centres of distant galaxies.

The views expressed are personal

Source: Read Full Article