The ‘chemical fingerprint’ of the first transiting exoplanet reveals its distant birthplace

The 'chemical fingerprint' of the first transiting exoplanet reveals its distant birthplace

Astronomers have found evidence that the first exoplanet to be identified in transit through its star could have migrated into a close orbit with its star farther from its original birthplace. Analysis of the planet’s atmosphere by a team that includes scientists from the University of Warwick has identified the chemical footprint of a planet that formed much further away from its sun than it currently resides. It confirms the earlier thought that the planet has moved to its current position after forming, just 7 million km from its sun or the equivalent of 1/20 of the distance from Earth to our Sun.

The findings are published in the journal Nature by an international team of astronomers. The University of Warwick led the modeling and interpretation of the results that mark the first time that up to six molecules have been measured in an exoplanet’s atmosphere to determine their composition.

It is also the first time that astronomers have used these six molecules to definitively pinpoint the location where these hot giant planets form thanks to the composition of their atmospheres.

With new and more powerful telescopes coming online soon, his technique could also be used to study the chemistry of exoplanets that could potentially host life.

This latest investigation used the Nazionale Galileo Telescope on La Palma, Spain, to acquire high-resolution spectra of the atmosphere of exoplanet HD 209458b as it passed in front of its host star on four separate occasions. The star’s light is altered as it passes through the planet’s atmosphere, and by analyzing the differences in the resulting spectrum, astronomers can determine which chemicals are present and their abundance.

For the first time, astronomers were able to detect hydrogen cyanide, methane, ammonia, acetylene, carbon monoxide, and low amounts of water vapor in HD 209458b’s atmosphere. The unexpected abundance of carbon-based molecules (hydrogen cyanide, methane, acetylene, and carbon monoxide) suggests that there are roughly as many carbon atoms as there are oxygen atoms in the atmosphere, twice the expected carbon. This suggests that the planet has preferentially accumulated carbon-rich gas during formation, which is only possible if it orbited much farther from its star when it originally formed, most likely at a distance similar to Jupiter or Saturn in our own solar system.

Dr Siddharth Gandhi from the Department of Physics at the University of Warwick said: “The key chemicals are species that contain carbon and nitrogen. If these species are at the level that we have detected them, this is indicative of an enriched atmosphere. in carbon compared to oxygen We have used these six chemical species for the first time to determine where it would have originally formed on its protoplanetary disk.

“There is no way for a planet to form with an atmosphere so rich in carbon if it is within the line of condensation of water vapor. At the very hot temperature of this planet (1,500 K), if the atmosphere contains all the elements del In the same proportion as in the parent star, oxygen should be twice as abundant as carbon and mostly bonded with hydrogen to form water or carbon to form carbon monoxide. Our very different finding is consistent with the current understanding of that hot Jupiters like HD 209458b formed a long way from their current location. “

Using models of planet formation, the astronomers compared HD 209458b’s chemical fingerprint with what they would expect to see on such a planet.

A solar system begins life as a disk of material that surrounds the star that comes together to form the solid cores of the planets, which then accumulate gaseous material to form an atmosphere. Near the hottest star, a large proportion of oxygen remains in the atmosphere as water vapor. Further afield, as it cools, the water condenses to become ice and locks into the core of a planet, leaving an atmosphere more made up of carbon- and nitrogen-based molecules. Therefore, planets orbiting close to the sun are expected to have atmospheres rich in oxygen, rather than carbon.

HD 209458b was the first exoplanet to be identified using the transit method, observing it as it passed in front of its star. It has been the subject of many studies, but this is the first time that six individual molecules have been measured in its atmosphere to create a detailed “chemical fingerprint.”

Dr Matteo Brogi from the University of Warwick team adds: “By expanding on these observations, we will be able to know what kinds of planets we have in terms of their location of formation and early evolution. It is really important that you do not work under the assumption that There are only a couple of molecular species that are important in determining the spectra of these planets, as has often been done before. Detecting as many molecules as possible is useful when we move on to testing this technique on planets with favorable conditions to host life, because we will need to have a full portfolio of chemical species that we can detect. “

Paolo Giacobbe, a researcher at the Italian National Institute of Astrophysics (INAF) and lead author of the paper, said: “If this discovery were a novel it would start with ‘At first there was only water …’ because the vast majority of the inference about atmospheres of Exoplanets from observations in the near infrared were based on the presence (or absence) of water vapor, which dominates this region of the spectrum. We ask ourselves: is it really possible that all the other species expected from the theory do not leave any traces? measurable? Discovering that it is possible to detect them, thanks to our efforts to improve analysis techniques, opens up new horizons to explore “.

Investigation report: ‘Five carbon and nitrogen carrier species in the atmosphere of a hot giant planet’

related links

Warwick University

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