Venus could have oceans, an oxygen atmosphere, and life. It is possible that microorganisms still live there. The RIA Novosti correspondent, having attended a joint seminar with NASA at the Space Research Institute of the Russian Academy of Sciences, dedicated to the choice of the landing site for the Venera-D mission, figured out what this planet was like immediately after the formation of the solar system.
Venus as an exoplanet
How did life originate in the solar system, and is it elsewhere in the universe? This is one of the hottest questions in astronomy right now. Scientists are looking for celestial bodies like Earth, where there may be traces of liquid water. Meanwhile, nearby is a planet very similar in size and mass to ours - Venus.
It is believed that the Earth and Venus formed in the same region of the protoplanetary disk, from the same material, but then their development went in different ways.
The earth is enveloped in an atmosphere that contains almost 20 percent oxygen, a moderate greenhouse effect and the presence of oceans make the surface conditions comfortable for life to flourish. Venus is surrounded by a shell of carbon dioxide, on the surface - almost five hundred degrees Celsius due to the giant greenhouse effect and a pressure of 92 atmospheres.
To the surprise of scientists, it turned out that the conditions on fifty exoplanets, comparable in size to Earth, should be more similar to those of Venus.
Venus is slightly out of the habitable zone - this is how the orbits are called, where the radiation of the star is not so strong as to destroy liquid water. It receives more energy from the Sun than it receives from its star, a red dwarf, one of the most promising exoplanets for searching for traces of life - TRAPPIST-1d, located on the border of the habitable zone.
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Since in the foreseeable future we will not receive information about the conditions on exoplanets directly (all data will be either indirect or obtained remotely), Venus is the best option for studying the evolution of planets and their habitability conditions.
As Michael Way of NASA's Goddard Space Research Institute pointed out, Venus is very important for astrobiological research. There is a consensus among scholars in this regard. It is necessary to understand how its atmosphere was formed, what is the history of the surface, what were the temperature conditions in the past.
All questions about the habitability of Venus rest on the question of the existence of liquid water on it. Indirectly, this possibility is evidenced by the unusual ratio of the content of deuterium and hydrogen, many times higher than the Earth's, discovered for the first time by the American probe "Pioneer" in 1978 and confirmed by the European apparatus "Venus-Express". This can be explained if the planet had very large oceans in the past, but they evaporated, and light hydrogen left the atmosphere as a result of the dissociation of water molecules.
When did the oceans evaporate, and for what reason? The answers to these questions can only be given by a future mission to Venus, which will collect information about volatile elements in the atmosphere and on the surface, Way believes.
Photo of Venus in the optical and ultraviolet range, taken by the cameras of the * Akatsuki * probe.
Too sour
The Venera, Pioneer, and Vega spacecraft have shown that there are three cloud layers saturated with sulfuric acid in the atmosphere of Venus. The upper one is well observed from the Earth by remote sensing methods, including in the ultraviolet range, in fact, in the rays of the Sun. Below it are the middle and bottom layers, which are not directly visible due to the fact that the top layer is opaque.
“What substance, besides SO2, absorbs solar radiation in the atmosphere of Venus? Gas, particulate matter, or something else? - asks planetary scientist Sanjay Limaye from the University of Wisconsin in Madison (USA).
There are two assumptions: a chemical imbalance in the atmosphere and microorganisms in the clouds. If methane could be found there, it would be a strong signal in favor of the second version. On Earth, this gas is mostly of biogenic origin.
Many types of microorganisms on Earth feed on sulfur compounds instead of oxygen. If such bacteria were aboard Soviet and American probes that visited Venus's atmosphere, they could adapt to life in its sulfur clouds, Limaye believes.
Oleg Kotsyurbenko, Doctor of Biological Sciences, from Ugra State University, spoke about the parameters of the cloud layers of Venus. Unlike a hot surface, the temperature in the atmosphere is not high. At an altitude of fifty kilometers, it is only 50 degrees Celsius - quite acceptable for the habitation of terrestrial microbes. The pressure there is two atmospheres or less. In such conditions there are thermophilic, acid-loving (acidophilic) bacteria, habitual inhabitants of hot springs, solfatara in the craters of volcanoes, the bottom of the sea.
They could survive in the Venusian clouds and create self-sustaining communities, says Kotsyurbenko. The only problem: pH 0.3 is too low for terrestrial organisms.
Microorganisms in the bowels of the Earth live at higher temperatures than in the sulfur clouds of Venus / Illustration by RIA Novosti. Alina Polyanina.
Young Venus as the cradle of life
In the pre-satellite era, naturalists thought that Venus was similar to Earth, that there was an oxygen atmosphere, clouds of water vapor. David Grinspoon recalls the disappointment that befell scientists in 1967 when the Mariner probe transmitted information about the planet's gas envelope. It became obvious that she was completely unfit for life.
In 1997, the scientist submitted the manuscript of the book "Venus revealed" to the publishing house, where he spoke about the possibility of the existence of acidophilic bacteria in sulfur clouds. They feed on the energy of chemical or photoreactions supported by volcanism.
The unknown UV absorber is possibly a photosynthetic pigment, a product of their metabolism, Grinspoon suggested. Microbes multiply with the help of spores, which can survive the harshest conditions and serve as a seed for the formation of aerosol particles of sulfuric acid. They affect the reflective and emissive properties of clouds, and possibly even their dynamics.
Sulfur clouds on Venus / Illustration by RIA Novosti.
Such ideas seemed to the editor too speculative, undermining the credibility of the book as a whole, and he asked to remove them, but the author refused.
Grinspoon believes that clouds on Venus are much longer and more stable than on Earth, aerosol particles in them exist for months and do not fall down. In the upper layer, submicron particles are formed and slightly larger ones - they are referred to modes 1 and 2. The largest drops, the so-called aerosol mode 3, are in the lower layer, their diameter reaches seven micrometers.
In the upper layer there are particles of unknown nature, absorbing almost half of the heat received by the planet from the Sun. Perhaps these are compounds of sulfur or chlorine, but so far no candidate fits the observed spectrum. In addition, the absorption capacity of the layer varies greatly in time and space. All this awaits its explanation, and the hypothesis of microorganisms exists on an equal basis with others.
On early Venus billions of years ago, conditions could have been even more favorable than on Earth. Maybe this planet became habitable first?
"When did Venus lose water?" - this is the key question, according to Grinspoon.
He paints this picture. While the bowels of the planet were active, a molten ocean of magma existed there, volcanoes poured out lava on the surface, there was water, its vapors formed a water-oxygen atmosphere.
In the early stages, Venus, Earth and Mars could exchange material, including biological. And when Venus began to lose water about three or two and a half billion years ago, its inhabitants adapted to life in sulfur clouds.
"For the first two billion years, the Earth could have two neighbors with oceans on the surface and life," the scientist suggests.
Tatiana Pichugina