Astronomers using the Multi Unit Spectroscopic Explorer (MUSE) spectrograph on ESO’s Very Large Telescope have directly imaged two still-forming gas giants — one of which was previously unknown to scientists — that are gravitationally carving out a large gap within a protoplanetary disk surrounding the young star PDS 70.
PDS 70 is a K7-type pre-main sequence star at a distance of about 370 light-years.
Also known as V1032 Cen, the star is only 5.4 million years old, slightly smaller and less massive than our Sun.
It hosts two infant planets, named PDS 70b and c, and a protoplanetary disk in which a large region from 20 to 40 AU (astronomical units) is cleared of dust.
PDS 70b is located within the disk gap at a distance of about 21 AU from its star, similar to the orbit of Uranus in our Solar System. The planet has a mass of between 4 and 17 times that of Jupiter.
PDS 70 c, the newly-discovered planet, is located near the outer edge of the disk gap at 34.5 AU from the star, similar to Neptune’s distance from our Sun.
It is less massive than PDS 70b, weighing between 1 and 10 times as much as Jupiter.
The two planetary orbits are near a 2:1 resonance, meaning that the inner planet circles the star twice in the time it takes the outer planet to go around once.
“This is the first unambiguous detection of a two-planet system carving a disk gap,” said Dr. Julien Girard, an astronomer with the Space Telescope Science Institute.
“This new observing mode was developed to study galaxies and star clusters at higher spatial resolution,” said Dr. Sebastiaan Haffert, an astronomer at Leiden Observatory.
“But this new mode also makes it suitable for exoplanet imaging, which was not the original science driver for the MUSE instrument.”
“We were very surprised when we found the second planet.”
The findings were published online this week in the journal Nature Astronomy.
S.Y. Haffert et al. Two accreting protoplanets around the young star PDS 70. Nature Astronomy, published online June 3, 2019; doi: 10.1038/s41550-019-0780-5