Venus is one of the four rocky planets in our Solar System. There is a stifling temperature. And not a drop of water can flow there today. there is no doubt. But for researchers, the planet’s past remains a mystery. Some people imagine oceans for him. Others claim that Venus never knew the conditions necessary for the formation of such bodies of liquid water. Jérémy Leconte, researcher at the Bordeaux Astrophysics Laboratory, takes stock for us.
Today,is a dry planet. Desert. Yet scientists wonder if it could not, in its past, have been able to shelter an ocean. Look a little more like Earth. « Non », concludes a carried out by researchers from the CNRS and the University of Versailles Saint-Quentin.
Before telling how these French scientists got there, it is good to remember that another study, published a few years ago by American researchers, had imagined a. The climate simulations launched from there, with a similar to the one we know on our Earth, had then shown that these oceans tended to evaporate, forming protectors, who reflect the of . “In the so-called substellar zone, that is to say at the point where the Sun heats the strongest, especially, explains Jérémy Leconte, researcher at the Bordeaux Astrophysics Laboratory. A bit like what happens on Earth, at the level of , in short ”.
The work of French researchers does not really contradict one another. “Our colleagues explain that if oceans existed on Venus, they were able to maintain, emphasizes Jérémy Leconte. We, we wondered if oceans could even have formed. And our answer is no ”.
What are the chances of forming an ocean on Venus?
“When they form, the planets literally cover themselves with an ocean of. A magma which degasses a lot and maintains a very thick atmosphere consisting in particular of (CO2) and of (H20). L’ is intense, describes us the . If the planet cools down enough to allow water vapor to condense and rain to fall, oceans can form ”. This is what has been played out on our Earth.
theon which the French researchers rely reveals that on Venus, things did not happen at all as envisaged by the scenario imagined by the American study. “The only place on the planet where it wasn’t too hot was on the night side. And in addition, very high in the atmosphere, on the side of the . From loaded with water vapor were able to get there from the day side. They then formed clouds, but which remained localized on the night side. They could not therefore have a protective effect. They could not participate in refreshing Venus. Worse, they formed a kind of heat shield that even kept the planet from cooling down. The rain could not fall. No ocean could form. “
There is very little chance that Venus could have formed an ocean.
“If we imagine having oceans on Venus like a coin toss, the American study only told us that if the coin falls on the edge, it has a good chance of staying there. Very well. But we, we say … that the coin has very little chance of falling apart “, continues Jérémy Leconte.
Extract information about other planets
Astrophysicists now wish to understand what this study may have as an implication concerning the. They would like to better fix the limits within which there can be liquid water. “Knowing that there was never an ocean to form on Venus gives us a precious indication, Jérémy Leconte points out. Our work leads us to consider that if our Earth had been born around a star such as our Sun today, it might never have been able to cool enough to form oceans. Thus, an exoplanet located at the same distance from its star as us from ours does not necessarily harbor oceans. It is enough that his star has changed little – as is the case with , host stars of most known exoplanets – so that this planet has never been able to cool itself sufficiently ”.
Answering the question of potential past oceans on Venus could also provide crucial information about the future of our planet. “Studies have already shown us that the Earth could, within a billion years – a period of time which remains to be defined more precisely –, lose his oceans, explains the astrophysicist. In the past, Venus received a little lessof the Sun. Due to the very nature of our star, which is gaining in over time. A bit of what our Planet receives today. In the future, the Earth will receive more energy from the Sun, much like what Venus receives today. Thus, by studying the past of Venus, we can hope to clarify if and when our Planet risks losing its oceans. “
To confirm their results, the French researchers will nevertheless wait for the data that can be collected on site by the missions that will soon be launched to Venus. “We know there is water vapor in the atmosphere of this planet. But surprisingly few. Hardly enough to imagine oceans a few centimeters deep. We believe that there was a lot more water in the atmosphere of Venus at some point in history. But that she ended up escaping into space, leaving behind enoughto shape this oxidized atmosphere that we know him », explains Jérémy Leconte.
“One can imagine that the new missions to Venus will be able to measure the chemical composition of its atmosphere and even the isotopic composition of some of its elements. This is, for example, one of the goals of the DAVINCI + mission (). With the idea of dating the escape of water. If it happened late in the life of the planet, we can imagine that Venus sheltered an ocean and that it was when it evaporated, when the Sun got too warm, that the water is of its atmosphere. If it happened earlier, it could be further evidence that Venus was never able to harbor an ocean. It is these kinds of clues that we will now have to collect. “
The Veritas mission (Nasa) and the( ), as for them, will carry out, by infrared, mineralogical measurements of the surface of Venus. However, some need water to form. Detecting their presence would be a strong indication of the lasting presence of liquid water on the planet’s surface. “In this case, we would have to explain not the stability of the oceans – remember, this was done by the American study –, but how the water vapor was able in spite of everything to condense to form it at the beginning of the history of Venus ”, slips us Emmanuel Macq, researcher at the University of Verseilles Saint-Quentin, also author of the study, by way of conclusion.