Image of HD 169142 system showing the sign of the formation of the planet HD 169142 b (around 11 o’clock), as well as a shiny arm that rotates due to the strong interaction between the planet and the disc as it is. The signal from the star, 100,000 times brighter than the Earth, was removed by a combination of layers of light and image processing (mask in the middle of the image). Viewing at different times shows the world moving around time. Image taken by ESO’s VLT/SPHERE instrument. Words: V. Chrisitaens / ULiège
Located 374 light years from Earth, HD169142 b has been confirmed as a protoplanet by a team of researchers from the University of Liège and Monash University.
An international team of researchers – including Valentin Christiaens from the University of Liège – has just published the results of an analysis of data from the SPHERE instrument of the European Southern Observatory ([{” attribute=””>ESO), which confirms a new protoplanet. This result was made possible thanks to advanced image processing tools developed by the PSILab of the University of Liège. The study is published in the Monthly Notices of the Royal Astronomical Society (MNRAS).
Planets form from clumps of material in discs surrounding newborn stars. When the planet is still forming, i.e. when it is still gathering material, it is called a protoplanet. To date, only two protoplanets had been unambiguously identified as such, PDS 70 b and c, both orbiting the star PDS 70. This number has now been increased to three with the discovery and confirmation of a protoplanet in the disk of gas and dust surrounding HD 169142, a star 374 light years from our solar system.
A protoplanet is an embryonic planet, a large body that is in the process of becoming a planet. It forms from a concentration of gas and dust within a protoplanetary disc, a ring of material that orbits a newly formed star. As this material begins to coalesce, it creates a protoplanet that gradually grows by attracting more of the surrounding material through its increasing gravitational pull.
“We used observations from the SPHERE instrument of the European Southern Observatory’s (ESO) Very Large Telescope (VLT) obtained on the star HD 169142, which was observed several times between 2015 and 2019,” explains Iain Hammond, a researcher at Monash University (Australia) who stayed at ULiège as part of his doctoral thesis. “As we expect planets to be hot when they form, the telescope took infrared images of HD 169142 to look for the thermal signature of their formation. With these data, we were able to confirm the presence of a planet, HD 169142 b, about 37 AU (37 astronomical units, or 37 times the distance from the Earth to the Sun) from its star — slightly further than the orbit of Neptune.”
Back in 2020, a team of researchers led by R. Gratton had previously hypothesized that a compact source seen in their images could trace a protoplanet. Our new study confirms this hypothesis through both a re-analysis of the data used in their study as well as the inclusion of new observations of better quality.
A series of images of the HD 169142 system showing the planet in the formation HD 169142 b moving in its orbit over time. A bright circular arm appears behind the planet, due to the strong interaction between the planet and the disc it is in. The signal from the star, which is 100,000 times brighter than the Earth, was removed by combining the layers of light and image processing (mask in the middle of the image). Images obtained by ESO’s VLT/SPHERE instrument. Credit: ESO/VLT
Various images, obtained by the VLT’s SPHERE instrument between 2015 and 2019, show a coherent source moving over time as the planet is expected to orbit 37 astronomical units from its star. All the data acquired by the SPHERE instrument were analyzed with modern imaging tools developed by the PSILAb group at the University of Liège.
The last information described in our research, which was discovered in 2019, is important for the world to confirm,” says Valentin Christiaens, FRS-FNRS researcher at the PSILAb (STAR Institute / Faculty of Science) of ULiège. “These materials have not been published until now .”
A protoplanetary disk it is a flat, circular disk of dense gas and dust that surrounds a newly formed star. It is formed from the original molecular cloud that collapsed to form the star and contains the remnants of the material that was not in the star. These discs play an important role in planet formation, as they are the places where protoplanets form and grow.
The new images also confirm that the Earth must have formed an annular gap in the disk – as predicted by models. This difference is best seen in the polarized analysis of the disc.
“In the infrared, we can also see a spiral arm in the disc, which is initiated by the planet and then reflected back, suggesting that some protoplanetary discs with spirals may also contain undiscovered planets,” says Hammond.
Polarized light images, as well as infrared spectra measured by the research team, also show that the planet is covered by a large dust cloud that originated from the protoplanetary disk. This dust can be in the form of a circumplanetary disc, a small disc that forms around the earth, which can form the moon. This important finding shows that the detection of planets by direct imaging is possible even in their early stages.
Valentin Christiaens said: “In the last 10 years, there has been a lot of false information about the planets that were created. “Besides the protoplanets of the PDS 70 system, some candidates are still discussed in the scientific community. Protoplanet HD 169142 b seems to have different properties from the protoplanets of the PDS 70 system, which is very interesting. It seems that we caught it at a very young stage of formation. its evolution, since it is still buried inside or surrounded by a lot of dust.”
Considering how few planets have been confirmed to form planets so far, the discovery of this source and its sequencing should help us better understand the structure of planets, especially giant planets like planets.[{” attribute=””>Jupiter, are formed.
Further characterization of the protoplanet and independent confirmation could be obtained through future observations with the James Webb Space Telescope (JWST). The high sensitivity of JWST to infrared light should indeed allow researchers to detect thermal emissions from the hot dust around the planet.
Reference: “Confirmation and Keplerian motion of the gap-carving protoplanet HD 169142 b” by Iain Hammond, Valentin Christiaens, Daniel J Price, Claudia Toci, Christophe Pinte, Sandrine Juillard and Himanshi Garg, 4 April 2023, Monthly Notices of the Royal Astronomical Society: Letters.
DOI: 10.1093/mnrasl/slad027
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