2023-06-26 06:00:15
An international team led by Stefan Pelletierdoctoral student at the Trottier Institute for research on exoplanets (iREx) from the University of Montreal, announces the publication in the journal Nature of a detailed study on the exoplanet (An exoplanet, or extrasolar planet, is a planet orbiting around a…) ultra-hot giant WASP-76b.
The giant exoplanet WASP-76 b, which was studied by UdeM astronomers, is an extremely hot world that orbits very close to its giant star.
Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani
Thanks to the “MAROON-X” instrument installed on the Gemini North telescope, the team was able to identify 11 chemical elements in the atmosphere (The word atmosphere can have several meanings:) of the planet and measure their abundance. Among these elements are components of rock whose abundance has not yet been measured for the giant planets of the solar system (The solar system is a planetary system composed of a star, the…) such as Jupiter or Saturn.
“It’s extremely rare for an exoplanet hundreds of light-years away to teach us something that would otherwise be impossible to know about our own solar system,” he said. Stefan Pelletier. This is the case with this study.”
Another look at a singular planet
WASP-76b is a strange world. It reaches extreme temperatures due to its proximity to its host star, a massive star located 634 light-years away in the constellation Pisces: approximately 12 times closer than Mercury is to the Sun. With a mass similar to that of Jupiter, but almost six times greater in volume, WASP-76 b is very sparse. Since its discovery en 2013 par le Programme Wide Angle Search for Planets (WASP), many teams have studied it and have detected different elements in its atmosphere. In particular, in a study also published in the journal Nature in March 2020, a team found the iron signature on the planet and speculated that iron rains might be taking place there.
Stefan Pelletier, aware of these studies, wanted to obtain new independent observations about WASP-76 b using the high-speed optical spectrograph MAROON-X resolution installed on the Gemini North 8-meter telescope. This telescope is part of the Gemini International Observatory, located in Hawaii and operated by the National Optical-Infrared Astronomy Research Laboratory (NOIRLab) of the National Science Foundation (NFS).
“We knew that the new and powerful MAROON-X spectrograph would allow us to study the chemical composition of WASP-76 b with an unprecedented degree of precision for a giant planet”, explains the professor Björn Bennekeco-author of the study and research director of Stefan Pelletier at the University of Montreal (The University of Montreal is one of the four educational establishments…).
The Gemini North telescope, shown here, was used by Stefan Pelletier and his colleagues to assess the atmospheric composition of the ultra-hot exoplanet WASP-76b.
Crédit: International Gemini Observatory/NOIRLab/NSF/AURA/P.Horálek (Institute of Physics in Opava)
A composition similar to that of the Sun
We know with great precision the abundances of almost all the elements of the periodic table present inside the Sun. However, this is only true for a small amount of elements present in the giant planets of our solar system, whose composition remains poorly defined. This gap hampers our ability to understand the precise mechanisms that govern the formation of these planets.
Due to WASP-76b’s proximity to its star, its temperature is well over 2000°C. At these temperatures, many elements that would normally form rocks on Earth (such as magnesium (Magnesium is a chemical element, with symbol Mg and atomic number 12.) and iron) are vaporized and present in gaseous form in the upper atmosphere of the planet. Its study therefore makes it possible to obtain unprecedented data on the presence and abundance of elements that enter into the composition of the rocks of the giant planets. Indeed, in colder giant planets such as Jupiter, these elements are found at lower altitudes in their atmosphere and are therefore impossible to detect with current technological tools, however efficient they may be.
The direct product of the Big Bang
The abundances of many elements measured by Stefan Pelletier and his team in the atmosphere of the exoplanet, such as manganese, chromium, magnesium, vanadium, barium and calcium, correspond very closely to those of its host star. as well as those of our own Sun. These abundances are not the result of chance: they are the direct product of the Big Bang, followed by billions of years of stellar nucleosynthesis (In the field of astrophysics, stellar nucleosynthesis is the term which…), of so scientists measure roughly the same composition in all stars. However, this differs from the composition of rocky planets like the Earth, whose formation is more complex. The results of this new study indicate that the giant planets could retain an overall composition reflecting that of the protoplanetary disc (Stars are formed from a cloud of gas and dust whose central part…) from which they arise. are formed. However, other elements are found to be depleted in the planet relative to the star, a result which Stefan Pelletier found particularly interesting.
“The elements that seem to be missing in the atmosphere of WASP-76 b are precisely those that require higher temperatures to vaporize, such as titanium and aluminum, he explains. On the other hand, those that corresponded to our predictors, such as manganese, vanadium, or calcium, all vaporize at slightly lower temperatures.”
The interpretation of the team of scientists is that the composition observed in the upper layers of the atmospheres of giant planets may be extremely sensitive to temperature. Depending on the condensation temperature of an element, it will be present in gaseous form in the upper part of the atmosphere, or condensed in liquid form in the deeper lower layers. When in gaseous form, the element plays an important role in the absorption (In optics, absorption refers to the process by which the energy of a photon is taken up by…) light and can be observed by astronomers. When it is condensed, it cannot be detected by astronomers and therefore completely disappears (Completeness or completely automatic, or by Anglicism completion or…) from their observations.
“If this discovery is confirmed, it would mean that two giant exoplanets with slightly different temperatures from each other could present very different atmospheres, explains Stefan Pelletier. A bit like two containers of water, one at -1°C where the water is frozen, and the other at +1°C where the water is liquid. For example, calcium is observed on WASP-76 b, but it may not be on a slightly colder planet.”
First detection of vanadium oxide on an exoplanet
Stefan Pelletier’s team obtained another interesting result, namely, the detection of vanadium oxide. This is the first time that this molecule has been detected with certainty on an exoplanet. This molecule arouses the interest of astronomers, because they know that it can have a strong impact on the hot giant planets. “This molecule plays a role similar to that of ozone in the Earth’s atmosphere: it is extremely effective in warming the upper atmosphere, explains Stefan Pelletier. Temperatures therefore increase according to altitude, instead of decreasing like c is usually the case on colder planets.”
Other discoveries
One element, nickel, is significantly more abundant in the exoplanet’s atmosphere than astronomers had expected. Several hypotheses could explain this fact. One is that WASP-76 b may have accreted material from a Mercury-like planet. This small, rocky planet in our solar system is enriched in metals like nickel due to the way it was formed.
The team also found that the asymmetry in iron uptake between the eastern and western hemispheres of WASP-76b, reported in previous studies, is also present for many other elements. This means that the underlying phenomenon causing this asymmetry is likely a global process such as a temperature difference or the presence of clouds on one side of the planet and not the other, rather than the result a condensation in liquid form as previously suggested.
Next steps
Following these exciting results, Stefan Pelletier and his team wish to learn more about this exoplanet and other ultra-hot giant planets, in particular to validate their hypothesis concerning the very different atmospheres which could prevail on planets whose temperature differs slightly. They also hope that other researchers will take what they have learned about this giant exoplanet and apply it to improve our understanding of the planets that make up our own solar system and their origin.
“Generations of researchers have used the abundances of hydrogen and helium measured on Jupiter, Saturn, Uranus and Neptune to compare theories of the formation of gaseous planets, summarizes the professor Björn Benneke. In the same way, the measurements of heavier elements such as calcium or magnesium on WASP-76 b will make it possible to better understand the formation of gaseous planets.”
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