The first transit planet’s chemical fingerprint ‘reveals its birthplace

Astronomers have found evidence that the first exoplanet identified that orbits its star could migrate to a close orbit with its star from its original birthplace farther away.

An analysis of the planet’s atmosphere by a group of scientists from the University of Warwick identified the chemical fingerprint of a planet that formed much farther from its sun than it currently is. This confirms previous thinking that the planet after its formation moved to its current position, only 7 million km from its sun or the equivalent of 1/20 the distance from the earth to our sun.

The conclusions will be published in the journal today (April 7) Earth by an international team of astronomers. The University of Warwick led the modeling and interpretation of the results, which is the first time that up to six molecules have been measured in the atmosphere of an exoplanet to determine its composition.

It is also the first time that astronomers have used these six molecules to definitively determine the place on which these hot, giant planets form thanks to the composition of their atmosphere.

With new, more powerful telescopes soon to be available online, their technique can also be used to study the chemistry of exoplanets that could potentially house life.

This latest research used the Telescopio Nazionale Galileo in La Palma, Spain, to obtain high-resolution spectra of the atmosphere of the exoplanet HD 209458b, while passing through it on four different occasions before its host. The star’s light is changed as it moves through the planet’s atmosphere and by analyzing the differences in the resulting spectrum, astronomers can determine what chemicals are there 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 the atmosphere of HD 209458b. The unexpected abundance of carbon-based molecules (hydrogen cyanide, methane, acetylene and carbon monoxide) indicates that there are about as many carbon atoms as oxygen atoms in the atmosphere, double the carbon expected. This indicates that the planet has gas rich in carbon during formation, which is only possible if it orbits much further from its star when it originally formed, probably at a similar distance to Jupiter or Saturn in our own solar system.

Dr Siddharth Gandhi from the Department of Physics at the University of Warwick said: “The most important chemicals are carbon and nitrogen-containing species. If these species are at the level we detected them, it is a sign of an atmosphere that is enriching is in carbon compared to oxygen.We used these six chemical species for the first time to narrow down where it would originally originate in its protoplanetary disk.

“There is no way a planet would form with an atmosphere as rich in carbon as it is within the condensation line of water vapor. If the atmosphere contains all the elements in the earth, it is very hot (1,500 K) same ratio as in the parent star, oxygen must be twice as abundant as carbon and usually bound with hydrogen to form water or to carbon to form carbon monoxide.Our very different finding is consistent with the current notion that hot Jupiters such as HD 209458b far from their current location. “

Using models of planetary formation, the astronomers compare the chemical fingerprint of HD 209458b with what they would expect for a planet of this type.

A solar system begins life as a disk of the material that surrounds the star and collects to form the solid core of planets, which then collects gaseous material to form an atmosphere. Near the star where it is warmer, a large amount of oxygen remains in the atmosphere in water vapor. As it cools, water condenses further into ice and is trapped in the core of a planet, leaving an atmosphere composed more of carbon- and nitrogen-based molecules. Therefore, planets orbiting near the sun are expected to contain atmospheres rich in oxygen, rather than carbon.

HD 209458b was the first exoplanet identified using the transit method by observing it as it passed in front of its star. Many studies have been conducted, but this is the first time that six individual molecules have been measured in the atmosphere to create a detailed ‘chemical fingerprint’.

Dr Matteo Brogi of the University of Warwick team adds: “By scaling up these observations, we will be able to see what classes of planet we have there in terms of their location and early evolution. It is really important that we does not work under the assumption that there are only a few molecular species that are important in determining the spectra of these planets, as has been done regularly before, it is useful to detect as many molecules as possible if we are going to test the technique on planets with conditions suitable for the habitat of life, because we will have to have a complete portfolio of chemical species that we can detect. ‘

Paolo Giacobbe, researcher at the Italian National Institute for Astrophysics (INAF) and lead author of the article, said: “If this discovery were a novel, it would start with ‘In the beginning there was only water …’ because the vast majority of the derivation on exoplanet atmosphere of near-infrared observations was based on the presence (or absence) of water vapor, which dominates this region of the spectrum.We wondered: is it really possible that all the other species emanating from the theory, does not leave a measurable trace? The discovery that it is possible to detect it, thanks to our efforts to improve analytical techniques, offers new horizons to explore. ‘