VENUS — A POTENTIAL HARBOUR FOR EXTRATERRESTRIAL LIFE
Space
For ages, a glittering jewel that would pop up in the sky near dawn and dusk had remained the subject of mankind’s tales. It was Venus — a sister planet of Earth and the brightest object visible to the naked eye in Earth’s sky after the Sun and Moon. Fascinated by its magnificence, Jane Greaves — a radio astronomer at Cardiff University in Wales — set about to assess her molecular identification abilities on it’s yet-mysterious world.
In 2017, Greaves observed Venus with the James Clerk Maxwell Telescope (JCMT), situated on Mauna Kea in Hawaii, looking for bar code — like patterns of lines in the planet’s atmosphere that would suggest the presence of various chemicals. While casting around, she noticed a line linked with phosphine, and the data showed that the molecule existed at around 20 parts per billion in the planet’s atmosphere, a concentration between 1000 and a million times greater than in Earth’s atmosphere.
“I was stunned,” she remarks.
Can’t figure out yet as to why? If no, keep reading then.
Phosphine is a comparably simple molecule, consisting of a phosphorus atom bonded to three hydrogen atoms. It is an odourless gas when pure, but by the time it reaches concentrations where humans can smell it stinking of garlic or rotting fish, it is likely to lead to lungs impairment. Here on Earth, it is essentially always affiliated with living creatures either as a by-product of metabolic processes or of human technology, such as industrial fumigations and methamphetamine labs. In addition, since it is so challenging for it to be made through ordinary geological and atmospheric action, phosphine has been signaled out by scientists as a potentially unambiguous signature of life.
Following the revolutionizing discovery, the researchers and their colleagues made follow-up observations of Venus using the more powerful Atacama Large Millimeter / submillimeter Array (ALMA) in Chile last year, only to re-encounter the existence of phosphine in the planet’s atmosphere. They then tried to hunt for every possible pathway leading up to the molecule’s weird presence, including volcanic activity, lightning, strikes and even meteorites breaking up in the planet’s atmosphere.
“I think the best route we could find fell short by a factor of about 10,000,” Greaves remarks.[2]
Eventually, after racking their brains trying to come up with abiotic explanations for it, the researchers felt compelled to recognize one other possibility which later emerged in Nature Astronomy: the molecule could be made by life on Venus just as life is the main way it is produced on Earth.
Feeling taken aback, right? Let’s look at the argument.
Phosphine has been detected by the researchers precisely in a relatively clement region in the planet’s atmosphere. This is an atmospheric layer located about 50 to 60 kilometers above the Venusian surface with temperatures between 0 and 50 degrees Celsius and pressure equal to that of sea level on Earth. Although the presence of sulfuric acid clouds develops extremely acidic conditions, there are terrestrial organisms that will happily endure such tremendous acidic conditions in hot springs or other environments. Hence, all these conditions render this atmospheric layer habitable. Furthermore, since the 1960s, astronomers have perceived that Venus’s clouds are not reflecting as much of the sun’s ultraviolet light as they should be, which may be a consequence of something anonymous in the atmosphere preferentially absorbing that light instead. This observation led the late astrobiologists Harold Morowitz and Carl Sagan to propose that energy-hungry photosynthetic organisms might be the culprit.
“I’ve always thought that it’s as plausible to have life in the clouds of Venus as it is to find it in the subsurface of Mars,” says David Grinspoon, an astrobiologist at the Planetary Science Institute, who was not involved with the study.
Probably thinking that there is definitely life on Venus, right? You may be surprised to learn that yet an almost equally good case can be made for Venus being hostile to life.
Microbes have been found drifting around in Earth’s atmosphere but none have been known to spend their whole lifecycle solely there. In the end, they have to land on the surface. However, this behavior of such microbes does not seem practicable on Venus, for its surface seems too inhospitable a place to make for a good reservoir. Besides, the Venusian area concerned is 50 times more arid than Chile’s Atacama Desert, the driest place on our planet, and though it is fact-based that living things have uncovered ways to flourish in aqueous environments tinted with minute amounts of sulfuric acid, the conditions are reversed on Venus: its cloud layer is largely composed of sulfuric acid with just a few traces of water. Moreover, the biggest issue might be the detection of phosphine itself. There are noisy ripples that make determining a specific line somewhat difficult and, on top of that, these ripples are more pronounced on Venus’s spectrum in the team’s data. Thus, it is quite plausible to infer that these wavy structures could have imitated a phosphine’s signature, says Bruno Bezard, a spectroscopist at the Paris Observatory.
“I don’t see a strong argument to say that it’s not a ripple.” he states.[3]
Conceivably, Venus is an underexplored planet. Despite it being literally next door, it holds many mysteries that still need to be unveiled. In order to reject all non-living explanations for the existence of phosphine in its atmosphere, scientists and researchers will have to carefully examine the results and extend their knowledge regarding the planet, including its biology, geology and atmospheric physics. For this purpose, missions are being planned to send on Venus. Yet for now, it can be said that this phenomenon seems to have sparked a renewed interest in exploring our sister planet next door.
[1] “Venus Might Host Life, New Discovery Suggests — Scientific American,” accessed November 10, 2020, https://www.scientificamerican.com/article/venus-might-host-life-new-discovery-suggests/.
[2] “Venus Might Host Life, New Discovery Suggests — Scientific American.”
[3] “Venus Might Host Life, New Discovery Suggests — Scientific American.”
Credits:
- Fig.1 provided by Wikimedia Commons, https://creativecommons.org/licenses/by-sa/4.0/legalcode
- Fig.2 provided by P. Horálek/ESO on Flickr, https://creativecommons.org/licenses/by/4.0/legalcode
