A pair of nascent planets directly seen around a young star

Astronomers have directly imagined two exoplanets gravitationally gravitating in a large space in a disk forming a planet surrounding a young star. Although more than a dozen exoplanets were directly imaged, it is only the second multi-planet system to be photographed. (The first was a four-planet system orbiting the HR 8799 star.) Unlike HR 8799, the planets in this system continue to grow by accumulating disk elements.

"This is the first unambiguous detection of a two-planet system digging up disk space," said Julien Girard of the Institute of Space Telescope Sciences in Baltimore, Maryland.

The host star, known as PDS 70, is located approximately 370 light-years from Earth. The 6 million year old star is slightly smaller and less massive than our Sun and continues to gas. It is surrounded by a disk of gas and dust that has a large free space of about 1.9 to 3.8 billion kilometers.

PDS 70b, the most internally known planet, is located in the disk space at a distance of about 2 billion kilometers from its star, similar to the orbit of Uranus in our solar system. The team estimates that it weighs between 4 and 17 times more than Jupiter. It was detected for the first time in 2018.

PDS 70c, the newly discovered planet, is located near the outer edge of the disk space about 3.3 billion kilometers from the star, a distance similar to that of Neptune to our Sun. It is less massive than planet B, weighing between 1 and 10 times more than Jupiter. The two planetary orbits are approaching a resonance of 2 to 1, which means that the inner planet surrounds the star twice during the time required for the outer planet to go around once.

The discovery of these two worlds is significant because it provides direct evidence that planet formation can extract enough material from a protoplanetary disk to create an observable space.

"With equipment such as ALMA, Hubble or large adaptive optics ground telescopes, we see discs with rings and empty spaces.The open question is to know if there are planets here. case, the answer is yes, "said Girard

The team detected the PDS 70c on the ground using the MUSE spectrograph located on the very large telescope (VLT) of the European Southern Observatory. Their new technique was based on the combination of the high spatial resolution provided by the 8 meter telescope equipped with four lasers and the average spectral resolution of the instrument that allowed it to "capture" the light emitted by the camera. hydrogen, sign of accumulation of gas.

"This new mode of observation has been developed to study galaxies and star clusters at higher spatial resolution, but this new mode also makes it suitable for exoplanet imaging, which is only a matter of time. 39; was not the original scientific engine of the MUSE instrument, "said Sebastiaan Haffert of Leiden Observatory senior author on paper.

"We were very surprised when we found the second planet," added Haffert.

In the future, NASA's James Webb Space Telescope could be able to study this system and other planetary nurseries using a similar spectral technique to reduce the wavelength of light from hydrogen. This would allow scientists to measure the temperature and density of gas in the disc, which would help us understand the growth of gaseous giant planets. The system could also be targeted by the WFIRST mission, which will feature a demonstration of high performance coronagraphic technology capable of blocking starlight and revealing a lower light from the surrounding disk and companion planets.

These results were published in the June 3 issue of Nature Astronomy.