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Does the atmosphere of Venus shelter life ?

– News of June 9, 2019 –

Until the early 1960s, we thought that Venus could have sheltered life. Observed from afar, it is indeed the planet most similar to the Earth. The first flyby by Mariner 2 and the intensive exploration of the Soviet program Venera showed that the habitability of the planet Venus was not as promising as we thought, at least at ground level.

The conditions in the atmospheric layers located at about fifty kilometers of altitude are less hard. The temperatures are only a few tens of degrees Celsius and the atmospheric pressure similar to the Earth. A population of micro-organisms could survive there. On Earth, many bacteria living in different layers of the troposphere have been discovered.

When Venus is observed in ultraviolet, the cloud layers located at this altitude have a strong contrast. They are covered with dark spots. This could be populations of bacteria that absorb ultraviolet light as a source of energy. In any case, this is the assumption that was supported in an article published in september 2018. Of course, a chemical process with no relation to life could also explain this absorption of ultraviolet light.

The past habitability of the planet Venus is difficult to determine. According to some models, there were hospital conditions during the first two billion years of its existence. But these are just models. Our knowledge of Venus is very incomplete compared to the planet Mars. The arrival of new orbiters and landers can trigger new discoveries. The search for extremophiles living in the Earth’s upper atmosphere could also guide us in this quest.

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A giant ocean could be the cause of the hellish conditions on Venus

– News of May 28, 2019 –

The Soviet space probe program Venera has taught us that the planet Venus is a real hell. Ground temperatures exceed 450° Celcius, atmospheric pressure is 90 times higher than on Earth, and the upper atmosphere of Venus is obscured by clouds of sulfuric acid. Yet Venus may not have always looked like this. The planet Mars is highly suspected of having seas and rivers. Venus may also have had a lot of water in the past.

Several billion years ago, the solar system may have briefly hosted 3 blue planets. We know that on the planet Mars the absence of magnetic field eventually erode the atmosphere, which has caused the disappearance of liquid water on the surface. The story of Venus is less well known because the planet has some characteristics difficult to explain, starting with its speed of rotation. The planet Mars and Earth do a complete turn in about 24 hours, while it takes more than 240 days for Venus to complete its rotation, which is also in the opposite direction of most other planets of the solar system .

Several hypotheses have been formulated to explain this. The planet Venus may have been suddenly slowed down by a giant impact. An international team, however, offered a different explanation. In a study published May 22, they looked at the impact that a giant ocean would have had on Venus’ rotation rate. On Earth, the oceans slow down the rotation of the planet by 20 seconds every million years. This is due to friction between the ocean currents and the ocean floor. If we imagine that Venus had an immense ocean, then it had to undergo a similar effect, perhaps even more important.

Thanks to a simulation, the researchers showed how this ocean would have almost put Venus at a standstill after only 10 to 50 million years. Because of endless days, the oceans of Venus boiled in the sun. Their evaporation would have generated a greenhouse effect that would have self-powered. A few billion years later, Venus has traces of this climate change. Although this is only a hypothesis, it shows how fragile the conditions for life are. It only takes one small parameter to change to generate a butterfly Effect.

It is also a valuable hypothesis to characterize the exoplanets. Even if this scenario did not take place on Venus, it remains possible on the ocean-planets that we might discover during the next decades. Meanwhile, to learn more about the history of Venus, we will have to launch other exploration missions. Indian and Russian missions are being prepared. They will deploy orbiters, atmospheric balloons and landers.

On Venus, a greenhouse effect has been self-sustaining until CO2 depletion

– News of February 17, 2019 –

On the planet Earth, a large part of the CO2 is trapped in the Earth’s crust by sedimentation, in limestone for example. Only a very small part of this gas is released into the atmosphere. On Venus, it was probably the same a few billion years ago. But Venus is closer to the sun than Earth. The initial temperatures were therefore probably a little higher. But the crust of telluric planets tends to release its carbon dioxide because of high temperatures. A little more CO2 in the atmosphere causes temperatures to rise slightly, which releases even more CO2 trapped in the crust.

As a result, all the CO2 of Venus is present in gaseous form in its atmosphere. The atmosphere of Venus has become 90 times denser than the atmosphere of Earth, and there are extreme temperatures. If all of the carbon dioxide in the Earth’s crust is released into the atmosphere, Earth would also become hell.

The atmosphere of Venus does not contain water at all. Increasing temperatures are thought to have evaporate water until it reaches the upper layers of the atmosphere. Venus does not have a magnetic field to protect itself from solar winds. The water molecules were therefore broken by the ultraviolet radiation of the sun. Hydrogen has escaped into space and oxygen has formed new molecules with the other elements present in the planet’s atmosphere.

Unlike Mercury or Mars, Venus is massive enough to trap heavy molecules like CO2. Even without a magnetic field, it is able to maintain a thick atmosphere. Small differences in the initial conditions of the planets of the solar system can make them live a completely different destiny.

The essentials about Venus

Venus has an atmospheric pressure almost 100 times stronger than on Earth. Our closest neighbor is a permanent reminder of the terrible power of greenhouse gases. But it has not always been like that. Several billion years ago, Venus was probably similar to our planet, and perhaps fertile for life. The atmosphere of Venus makes it appear as a white ball. As a result, it reflects light well. Venus is the third brightest object of the sky seen from the Earth, after the sun and the Moon. Venus is even sometimes visible in broad daylight. The days on Venus would seem very long because they last longer than the terrestrial years. Venus is often referred to as the twin sister of the Earth.

Sources

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