The First Transiting Exoplanet’s “Chemical Fingerprint” Reveals its Distant Birthplace. The Positive Side

Astronomers also discovered evidence that the first exoplanet to be discovered transiting its star could have moved from its original birthplace farther out to a similar orbit with its star.

Six different chemicals have been found in the atmosphere of the first transiting exoplanet discovered, according to an international team led by the University of Warwick.

It’s the first time such a large number of molecules have been counted, indicating that there’s more carbon in the atmosphere than oxygen.

This chemical fingerprint is representative of a planet that originated far farther from its sun than the current position, which is just 7 million kilometers away from the star.

First transiting exoplanet's 'chemical fingerprint' reveals its distant  birthplace | EurekAlert! Science News

When more powerful telescopes become available, the results of this study can be used to test techniques for detecting signs of potentially habitable planets.

Astronomers also discovered evidence that the first exoplanet to be discovered transiting its star could have moved from its original birthplace farther out to a similar orbit with its star.

A team of scientists from the University of Warwick analyzed the earth’s atmosphere and discovered the chemical fingerprint of a planet that developed far farther away from its sun than it is now. It supports the previous speculation that the planet traveled to its current location after formation, which is just 7 million kilometers from its sun, or 1/20th the distance between the Earth and our Sun.

An international team of astronomers published their findings in the journal Nature today (April 7, 2021). The findings were modeled and interpreted by the University of Warwick, and they are the first time that as many as six molecules in an exoplanet’s atmosphere have been calculated to determine its composition.


It’s also the first time astronomers have used these six molecules to pinpoint the exact place where these hot, giant planets shape by studying the composition of their atmospheres.

Their methodology may also be used to research the chemistry of exoplanets that could potentially host life, with modern, more efficient telescopes coming online soon.

The Telescopio Nazionale Galileo in La Palma, Spain, was used in this latest study to obtain high-resolution spectra of the atmosphere of the exoplanet HD 209458b as it passed in front of its host star four times. As the star’s light travels through the planet’s atmosphere, it changes, and astronomers can tell what chemicals are present and how abundant they are by observing the variations in the resulting spectrum.

In the atmosphere of HD 209458b, astronomers discovered hydrogen cyanide, methane, ammonia, acetylene, carbon monoxide, and small quantities of water vapor for the first time. The concentration of carbon-based molecules (hydrogen cyanide, methane, acetylene, and carbon monoxide) means that there are about twice as many carbon atoms in the atmosphere as there are oxygen atoms, implying double the carbon required. This indicates that the planet accreted carbon-rich gas preferentially during formation, which is only plausible if it orbited far away from its star when it formed, most likely at a distance comparable to Jupiter or Saturn in our own solar system.

“The main chemicals are carbon-bearing and nitrogen-bearing species,” said Dr. Siddharth Gandhi of the University of Warwick’s Department of Physics. If these animals are present at the levels we’ve detected, it’s a sign of a carbon-rich atmosphere relative to oxygen. For the first time, we’ve used these six chemical species to pinpoint where it would have evolved in its protoplanetary disc.

“If a planet is within the condensation line of water vapor, it is impossible for it to form with an atmosphere so rich in carbon. At this planet’s extremely high temperature (1,500K), if the atmosphere contains all of the elements in the same proportions as the parent star, oxygen should be twice as abundant as carbon, mostly bound to hydrogen to form water or to carbon to form carbon monoxide. Our unexpected discovery supports current theories that hot Jupiters such as HD 209458b evolved far from their current location.”

Chemical Fingerprint

The astronomers compared HD 209458b’s chemical fingerprint to what they would expect to see for a planet of that kind using models of planetary formation.

A solar system starts with a disc of material surrounding the star that collects to form planets’ solid cores, which then accrete gaseous material to form an atmosphere. A significant proportion of oxygen exists in the atmosphere as water vapor closer to the star, where it is cooler. When it gets colder farther out, the water condenses into ice and is trapped into a planet’s center, leaving an atmosphere dominated by carbon and nitrogen-based molecules. As a result, planets orbiting near to the sun are predicted to have oxygen-rich atmospheres rather than carbon-rich atmospheres.

By observing it as it passed in front of its star, HD 209458b became the first exoplanet to be discovered using the transit process. Many experiments have been conducted on it, but this is the first time that six individual molecules in its atmosphere have been analyzed to establish a precise “chemical fingerprint.”

First transiting exoplanet's 'chemical fingerprint' reveals its distant  birthplace : space

“By scaling up these observations, we’ll be able to tell what classes of planets we have out there in terms of their formation position and early evolution,” says Dr. Matteo Brogi from the University of Warwick team. It’s important that we don’t make the mistake of assuming there are only a few molecular species that matter when determining the spectra of these planets, as has been done in the past. When we move on to testing this technique on planets with conditions conducive to life, we’ll need a complete portfolio of chemical species we can identify, so we’ll need to detect as many molecules as possible.”

“If this discovery were a novel, it would begin with ‘In the beginning, there was only water…’ because the vast majority of the inference on exoplanet atmospheres from near-infrared observations was based on the presence (or absence) of water vapor, which dominates this region of the spectrum,” said Paolo Giacobbe, a researcher at the Italian National Institute for Astrophysics (INAF) and lead author of the paper. Is it really true that all of the other organisms predicted by theory don’t leave any detectable traces? The realization that it is possible to detect.

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