Astronomers have obtained the first unequivocal observations that moon formation is taking place around an exoplanet in the PDS 70 system, some 370 light-years away from here, in the constellation Centaur.
PDS, in this case, is not Paulo Maluf’s old party, but it is still from Brasil-sil-sil. It is the acronym for Pico dos Dias Survey, a catalog of young stars identified by the Pico dos Dias Observatory, in Brazópolis (MG), from 1989 onwards.
The PDS 70 system, in particular, has had great prominence. The two known planets, PDS 70b and c, were discovered by direct observation with the VLT (Very Large Telescope), also in Chile, in 2018 and 2019. And last year an international group used the Hubble Space Telescope to measure the accretion process (growth) of the most internal of them, the PDS 70b. Here’s why the system is so appealing to astronomers: at some 5 million years old, it’s young enough that planet formation is still ongoing.
Now, the new observations, made with the Alma radio telescope set and led by Myrian Benisty, from the University of Chile, bring an additional element to the interest in the system: the clear detection of a disk of gas and dust around one of the planets, PDS 70c, reproducing the planetary formation on a microscale. The researchers estimate that there is enough mass there to form three Earth-like moons, and the disk itself is huge, comparable to the Earth-Sun distance, 150 million km.
With the finding, researchers will be able to study “in real time” how moons form around giant planets, an investigation that should also help explain how the planets themselves are born. And, furthermore, the result confirms that the moon formation process is indeed common, as would be expected.
Unlike the formation of planets, which for a long time had a single known example, the generation of moons was offered to astronomers right away as a common process, given that all giant planets in the Solar System bring evidence that something like this has happened, 4.5 billion years ago. Of course, many of the moons of Jupiter, Saturn, Uranus, and Neptune are merely asteroids or gravity-captured comets, but some of them, larger and arranged in orbits over the planetary equator, suggested a local origin, from a disk of gas and dust. –a miniature version of the birth of planets around the Sun.
Still, we have very little evidence of mature exomoons. Data from planet-hunting satellites so far has proved insufficient to detect them with conviction (although there are strong candidates like the bizarre Kepler-1625b, but that’s talk for another day). With the new study, accepted for publication in the Astrophysical Journal Letters, the conclusion remains that we just need to look better.
This column is published on Mondays in Folha Corrida.
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