Venus is one size and one mass close to those of the Earth and the presence of a thick cloud cover suggested for a time that it was covered with swamps, as explained by the famous Carl Sagan in a chapter of his equally famous book: Cosmos. Alas, it was Sagan himself who during the 1960s showed that on Venus there had to be a greenhouse effect generating hellish temperatures. In fact, as early as 1958, radio astronomers had picked up signals from theatmosphere of Venus suggesting a temperature of around 600 kelvinsclose to the point of merger Lead.
Sagan’s theory was not based on pure speculation because certain observations suggested that the Venusian atmosphere was mainly composed of gas carbonic. I’astronomer Rupert Wildt (to whom we owe the determination of the composition of the atmosphere of Jupiter in the 1930s and the models of the interior of the gas giants post-war) had already concluded, as early as 1940, that there must be a strong greenhouse effect. According to him, the temperature of Venus even had to reach the boiling point of water.
The hypothesis, and that of the high concentration of CO2 were confirmed by the first probes to approach the planet, namely Mariner 2 for the United States and Venera 4 for Soviet Russia, respectively in 1962 and 1967. Today, the pressure on the ground is estimated at 90 atmospheres (90 times that of the Earth, therefore) and the temperature at some 750 kelvins (i.e. approximately 480°C) for the hottest regions.
From Magellan to Parker Solar Probe
It will be necessary to wait for NASA’s Magellan mission to make a huge leap in the knowledge of the topography of Venus between 1990 and 1994. The first maps were rudimentary and only radar waves, like those emitted by the Arecibo radio telescope or the Pioneer Venus 1 probe, had made it possible to see under the global cloud layer of Venus. Everything changed with the Magellan radar because not only the cartography became complete, but with a resolution horizontal less than 100 meters.
However, we know much less Venus than Mars and many discoveries remain to be made there, such as the clear and direct demonstration ongoing volcanic eruptionsor what is more speculative with the recent debate regarding the possible discovery in its atmosphere of phosphine molecules and what it entails, of microscopic life forms in its upper atmosphere. Several new missions to Venus are therefore planned as NASA’s Veritas and Davinci+ or ESA’s EnVision.
Many of the images presented showing Venus in space and taken by probes close to the planet are in false color and are not taken in the visible. The well-known image of Marinate 10 was taken in the ultraviolet, like those of Pioneer Venus Orbiter or Venus express that we often present. In this video, NASA explains the new images of Venus taken by the probe Parker Solar Probe. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © NASA’s Goddard Space Flight Center
Today, images of Venus’s floor through its cloud cover come to us from an unexpected source, NASA’s Parker Solar Probe. Parker Solar Probe.
Let us recall that the objective of this probe is above all to make observations delivering information making it possible to penetrate the secrets of the heating of the crown of the Sun and those of solar wind. However, this requires passages around Venus to benefit from the technique ofgravity assist which allows you to make changes in trajectory and speed while saving fuel.
Mission members Parker Solar Probe then had the idea of taking advantage of these passages to use the probe’s wide-field imager, the Wide-Field Imager or WISPR, to observe from space in the visible face nocturnal of Venus.
We know that the surface of the planet is increased to several hundred degrees Celsiusthis means that it must begin to radiate like a bar of iron heated. Part of the spectrum of the radiation must be in the visible spectrum and in the part of the near infrared which borders it.
The first observation was made in July 2020 and the second in February 2021. NASA had already delivered some images of it, but today it is adding a video accompanied by the publication of an article in the famous newspaper Geophysical Research Letters.
Perhaps not very spectacularly but strikingly all the same, the hottest and therefore the brightest regions are clearly visible by contrast with those colder and less luminous of the surface of Venus seen through its atmosphere. We therefore see the continental regions, the plains and the plateaus of Venus. Aphrodite Terra, the largest mountainous region of the Venusian surface, is thus revealed in the visible under the WISPR. It appears to be dark but its contours are very similar to those that we were able to draw by radar with Magellan, as NASA clearly shows in the images below presented on Twitter. We also see the plateau of Tellus Region and the plains ofAino Planitia.
The discovery in 2020 was made by serendipity as the saying goes. The planetary scientists wanted to see if they could get information on the speed of clouds of Venus when they were surprised to see details of sister Earth’s topography in WISPR images.WISPR was designed to see fine detail in the atmosphere and solar wind. Some scientists had therefore thought that they might be able to use WISPR to image the tops of clouds veiling Venus and make new discoveries.
As the images taken by WISPR were taken in the visible, they complement those taken by Magellan in the domain. radio with regard to the geology from the surface of Venus. Indeed, depending on the rocks and minerals which constitute them, the spectra of the light emitted or reflected are not the same. By looking at different parts of these spectra we can therefore characterize the rocks, and since these rocks are the product of several processes that we would qualify as geodynamics on Earth – such as the volcanism and the tectonic plates – the new data could turn out to be talkative about the functioning and history of the planet. Planetary scientists have played this game both with the Moon than even today with Mars.
We could thus have clues to constrain the models explaining why, and when, Venus has become hell unlike the Earth and while they have masses and probably similar average compositions.
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