A surprising chemical finding from ALMA could help detect and confirm protoplanets

Scientific article

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) to study the protoplanetary disk around a young star have discovered the most convincing chemical evidence to date for protoplanet formation. The discovery will provide astronomers with an alternative method to detect and characterize protoplanets when direct observations or imaging are not possible. The results will be published in a future issue of The Astrophysical Journal Letters.

Soul Communications.- HD 169142 is a young star located in the constellation Sagittarius of great interest to astronomers due to the presence of its large circumstellar disk, rich in dust and gas that can be seen almost head-on. Several protoplanet candidates have been identified over the past decade, and earlier this year scientists from the University of Liège and Monash University confirmed that one such candidate, HD 169142 b, is in fact a similar giant protoplanet. to Jupiter. The discoveries revealed in a new analysis of archival data from ALMA may now make it easier for scientists to detect, confirm and ultimately characterize protoplanets forming around young stars.

“When we look at HD 169142 and its disk at submillimeter wavelengths, we identify several compelling chemical signatures of this recently confirmed gas giant protoplanet,” said Charles Law, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and the lead author of the new study. “We now have confirmation that we can use chemical signatures to find out what kinds of planets might be forming in the disks around young stars.”

The team zeroed in on the HD 169142 system because they believed that the presence of the giant protoplanet HD 169142 b would likely be accompanied by detectable chemical signatures, and they were right. Law’s team detected carbon monoxide (both 12CO and its isotopologue 13CO) and sulfur monoxide (SO), which had been previously detected and thought to be associated with protoplanets in other disks. But for the first time, the team also detected silicon monosulfide (SiS). This was a surprise because for ALMA to be able to detect SiS emission, silicates must be released from nearby dust grains in massive shock waves caused by gas traveling at high speeds, behavior that usually results from outflows. powered by giant protoplanets. “SiS was a molecule that we had never seen before in a protoplanetary disk, let alone in the vicinity of a giant protoplanet,” Law said. “The detection of the SiS emission caught our attention because it means that this protoplanet must be producing powerful shock waves in the surrounding gas.”

With this new chemical approach to detecting young protoplanets, scientists may be opening a new window on the Universe and deepening their understanding of exoplanets. Protoplanets, especially those still embedded in their parent circumstellar disks, such as in the HD 169142 system, provide a direct connection to the known exoplanet population. “There is a great diversity of exoplanets and, using chemical signatures observed with ALMA, this gives us a new way to understand how different protoplanets develop over time and ultimately connect their properties to those of exoplanetary systems” Law said. “In addition to providing a new tool for the search for planets with ALMA, this discovery opens up a wealth of exciting chemistry that we have never seen before. As we continue to examine more disks around young stars, we will inevitably find other interesting but unanticipated molecules, such as SiS. Discoveries like this imply that we are only scratching the surface of the true chemical diversity associated with protoplanetary configuration.”

Additional Information

This research will be published in The Astrophysical Journal Letters as “SO and SiS Emission Tracing an Embedded Planet and Compact 12CO and 13CO Counterparts in the HD 169142 Disk» by Charles J. Law et al.

The original press release was published, in English, by the National Radio Astronomy Observatory (NRAO)an ALMA partner on behalf of North America.

He Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomical facility, is a partnership between the European Southern Observatory (ESO), the US National Science Foundation (NSF) and the National Institutes of Natural Sciences of Japan (NINS) in cooperation with the The Republic of Chile. ALMA is funded by ESO on behalf of its member states, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council of Taiwan (NSTC), and by NINS in cooperation with Academia Sinica. (AS) of Taiwan and the South Korean Institute of Astronomical and Space Sciences (KASI).

The construction and operations of ALMA are conducted by ESO on behalf of its member states; by the National Radio Astronomical Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) is in charge of the general direction and management of the construction, as well as the commissioning and operations of ALMA.

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