It has been almost 30 years since the first exoplanet was discovered around a famous main sequence star. We now know thousands of them, and with James-Webb, we hope to make important discoveries about their structure. atmosphereatmosphere These exoplanets when they have. Obviously, in the near future, we hope to discover biosignatures this way but it will not be easy because the concept of biosignature is not self-evident. Indeed, how can we be sure that the composition of a particular environment is really influenced by life forms and not by purely abiogenic processes as exobiologists say in their string?
In the meantime, we continue to make interesting discoveries about exoplanets, as just demonstrated by a group of researchers led by him. AstronomersAstronomers Canadians and those who used the Hubble Space Telescope to determine Planetary transitsPlanetary transits Part of the composition of the atmosphere of a planet with a radius about twice that of Earth, placing it in the sub-series.NeptunesNeptunes.
For the record, let’s recall that the super-meanssuper-means Having a mass between one and ten times that of Earth, a sub-Neptune is a planet that has a smaller radius than Neptune but has a greater mass. Finally, a mini-Neptune is a planet less massive than Neptune but similar to Neptune in that it has a dense atmosphere of hydrogen and helium.
In this case, the sub-Neptune observed with Hubble is called GJ 9827 d. As its name suggests, it is part of the surrounding planetary systemthe starthe star GJ 9827, a Red DwarfRed Dwarf at 97 light yearslight years No the sunthe sun in ConstellationConstellation No FishFish. She the doorthe door No. 9827 in the Gliese-Jahreiss catalog (named after astronomers Wilhelm Gliese and Hartmut Jahreiss) which attempts to list all stars at distances below 25. parsecparsec of the earth.
Planetary atmospheres have spectral signatures that represent their chemical composition, but also their composition in clouds and “haze”. Thanks to several techniques, it is possible to determine the physicochemical characteristics of exoplanet atmospheres. These techniques include: spectroscopic transits, secondary transits or eclipses, direct spectroscopic observation of the planet, or observation of the planet at different phases around the star to measure temporal and seasonal variations. Discover exoplanets through our 9-episode web series available on our YouTube channel. Playlist proposed by CEA and University of Paris-Saclay as part of the H2020 Exoplanets-A European research project. © CEA
An atmosphere made up almost entirely of water vapor?
As explained in an article published in The Astrophysical Journal Letters And which can be found in open access on arXiv, as well as a press release from the Trottier Institute for Research on Exoplanets, GJ 9827 d may be an example of a new type of planet with an atmosphere composed primarily of water vapor.
This conclusion was reached by members of a team led by scientists from the University of Montreal and commented in this press release by a member of the research team, Professor Bjorn Beneke.AstrophysicsAstrophysics at UdeM and Pierre-Alexis Roy, student of Björn Benneke and lead author of the study.
To detect the presence of water vapor in the atmosphere of GJ 9827 d, the telescope was used over three years to observe 11 transits of the exoplanet in front of its star. Light passing through the atmosphere of GJ 9827 d then betrays the linesabsorptionabsorptionBarcode types of chemical compounds exist and can be detected by Hubble’s instruments.
Let us point out directly that, even if the radius of GJ 9827 d is twice that of Earth, it orbitorbit Since its discovery by the idle Kepler space telescope in 2017, we know it in just 6.2 days. NASANASA. The exoplanet’s atmosphere is therefore much hotter, with an average temperature of about 430 degrees Celsius, on the order of Venus’s hell.
Presentation of findings regarding GJ 9827 d. To get the most accurate French translation, click on the white rectangle at the bottom right. English subtitles should appear afterwards. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © NASA’s Goddard Space Flight Center
A mini-Neptune that might have migrated?
This discovery has been described by Bjorn Beneke in these words: “ This will be the first time we can directly demonstrate through atmospheric detection that planets with water-rich atmospheres exist around other stars. This is an important step towards better understanding the diversity of the atmosphere Rocky planetsRocky planets “
However, the AstrophysicistsAstrophysicists It is not yet known whether the extended, hydrogen-rich atmosphere of GJ 9827 d contains a small amount of water vapor, or whether it is mainly water, light hydrogen or helium, having temporarily abandoned the planet’s attraction. Already, like a vapor of a LiquidLiquid Hot, in this case GasGas of an exoplanet’s atmosphere by the radiation of a red dwarf.
There is also uncertainty regarding two possible scenarios for the origin of GJ 9827 d.
In the first, with a water-rich atmosphere, the exoplanet initially looked like Neptune with a high ice content surrounded by an atmosphere of hydrogen and helium. It would then have migrated, which would have led to the evaporation of the early atmosphere and to meltto melt For Björn Beneke in this case ice, “ It is possible that the planet GJ 9827 d is half water and half rock: a small core of rock surrounded by a thick layer of water vapor. “
In the second, GJ 9827 d’s atmosphere would contain only traces of water vapor because it formed closer to its star and therefore has less water content.
” Until now, we have not been able to detect such environments directly small planetsmall planet. We are gradually succeeding in this technical challenge. As we study dwarf planets, we expect to find worlds without hydrogen, with similar atmospheres. VenusVenusDominated by carbon dioxidecarbon dioxide », concludes Björn Benneke.
Apparently, James-Webb will participate in this research.
