It is commonly believed that the atmospheres of newborn exoplanets should contain the same chemical elements as the protoplanetary disks that gave rise to them. However, a new study of the PDS 70 system refutes this claim.
Planetary atmospheres and gas-dust disks
Scientists have recently questioned the claim of what the atmospheres of newborn exoplanets should look like. We are talking about both those Earth-like worlds and Jupiter-like gas giants.
All planets form from gas-dust disks that surround the newborn luminaries. Therefore, it has been thought up to now that the atmospheres of worlds which have just been formed should repeat in their chemical composition the one from which they originated, because what other gases could there be than those surrounding the planet’s embryo?
At the same time, this statement was not actually based on any observations. Because we have too little observation of the Universe, and therefore have not had the opportunity to determine the chemical composition of both the disk itself and the planets that formed from it.
The only way we can do this is to study those protoplanetary disks where new worlds are already forming and see how it really is. But it’s not easy, because they are predominantly very far away from us. Therefore, it is extremely difficult to separate the light from the planets and the dust that surrounds them.
PDS 70 system
And here comes a recent study published in the Astrophysical Journal Letters. The authors describe how they have managed to perform a spectral analysis of light from the protoplanetary disk in the PDS 70 system and the worlds forming in it.
The PDS 70 system is only 366 light-years away from us in the direction of the constellation Centauri. Its age is estimated at 5 million years. Two Jupiter-like planets orbit in the protoplanetary disk: PDS 70b and PDS 70c.
The first of them was investigated by scientists. Thanks to the photonics technology developed by the authors, they were able to isolate the spectrum of the planet itself and distinguish the signal from water and carbon monoxide in it. Using it, it was possible to calculate the composition of the atmosphere.
Scientists compared the carbon and oxygen ratios on the planet to what is observed in the disk itself, expecting them to match. However, it turned out that this ratio is much lower in the planet’s atmosphere.
The authors themselves suggest two possible scenarios for how this could have happened. According to the first one, the planet formed before the protoplanetary disk was enriched with carbon. Another explanation is that the planet may have grown mainly by absorbing large amounts of solid materials in addition to gases. While the spectra show only gases, some of the carbon and oxygen may have first been extracted from the solid, trapped in ice and dust.
Provided by phys.org
