New exoplanet discovery builds better understanding of planet formation

An international team of scientists have discovered an unusual Jupiter-sized planet orbiting a low-mass star called TOI-4860, located in the Corvus constellation.

The newly discovered gas giant, named TOI-4860 b, is an unusual planet for two reasons: stars of such low mass are not expected to host planets like Jupiter, and the planet appears to be particularly enriched by heavy elements.

The study, led by University of Birmingham astronomers, is published today (Friday 4th August) in a letter published within the Monthly Notices of the Royal Astronomical Society.

The planet was initially identified using NASA's Transiting Exoplanet Survey Satellite as a drop of brightness while transiting in front of its host star, but that data alone was insufficient to confirm that it was a planet.

The team used the SPECULOOS South Observatory, located in the Atacama Desert in Chile, to measure the planetary signal in several wavelengths and validated the planetary nature. The astronomers also observed the planet just before and after it disappeared behind its host star, noticing that there was no change in light, meaning the planet was not emitting any. Finally, the team collaborated with a Japanese group using the Subaru Telescope in Hawai'i. Together they measured the mass of the planet to fully confirm it.

Following this star and confirming its planet was the initiative of a group of PhD students within the SPECULOOS project.

George Dransfield, one of those PhD students, who recently submitted her thesis at the University of Birmingham, explains: "Under the canonical planet formation model, the less mass a star has, the less massive is the disc of material around that star.

"Since planets are created from that disc, high-mass planets like Jupiter, were widely expected not to form. However, we were curious about this and wanted to check planetary candidates to see if it was possible. TOI-4860 is our first confirmation and also the lowest mass star hosting such a high mass planet."

Amaury Triaud, Professor of Exoplanetology at the University of Birmingham, who led the study said: "I am ever thankful to the bright PhD students of our team for proposing to observe systems like TOI-4860. Their work has really paid off since planets like TOI-4860 are vital to deepening our understanding of planet formation.

"A hint of what might have happened is hidden in the planetary properties, which appear particularly enriched in heavy elements. We have detected something similar in the host star too, so it is likely that an abundance of heavy elements catalysed the planet formation process."

The new gas giant takes about 1.52 days to complete a full orbit around its host star, but because its host is a cold low mass star, the planet itself can be referred to as a 'Warm Jupiter'. This is a subclass of planet that holds particular interest for astronomers looking to build on their initial observations and learn more about how these kinds of planets are formed.

Mathilde Timmermans, another student of the SPECULOOS project, working at the University of Liege in Belgium concludes: "Thanks to its very short orbital period, and to the properties of its host star, the discovery of TOI-4860 b provides a brilliant opportunity to study the atmospheric properties of a warm Jupiter and learn more about how gas giants are formed."

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New planetary formation findings

Rochester Institute of Technology's Joel Kastner, a professor in the Chester F. Carlson Center for Imaging Science and School of Physics and Astronomy, and a team of researchers with the European Southern Observatory (ESO) have discovered new evidence of how planets as massive as Jupiter can form, using images from the ESO's Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA).

The combination of VLT and ALMA imaging have yielded detections of dusty clumps close to the young star V960 Mon that could collapse to create giant planets. The work is based on an infrared image obtained with the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument on ESO's VLT and a radio-wavelength image with ALMA that together reveal, in fascinating detail, the material around the star.

This young star attracted astronomers' attention when it suddenly increased its brightness more than 20 times in 2014. SPHERE observations taken shortly after the onset of this brightness "outburst" revealed that the material orbiting V960 Mon is assembling together in a series of intricate spiral arms extending over distances bigger than the entire solar system.

Kastner worked on the SPHERE imaging project with former RIT student David Principe '14 Ph.D. (astrophysical sciences and technology), who is now at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology.

"The two of us put SPHERE observing proposals together to look at these outbursting objects," said Kastner. "We were hoping to see structure around them that is lit up by the outbursts, but we really weren't sure what kind of structure we might see. We thought we might be able to see the dusty material around the star that is feeding the star and maybe forming planets, and this was a great case where both appear to have been detected."

Astronomers believe that giant planets form either by "core accretion,"' when dust grains slowly coagulate to form a massive core that sweeps up gas, or by "gravitational instability," when large fragments of the material around a star quickly contract and collapse. While researchers have previously found evidence for the first of these scenarios, support for the latter has been scant. The images from VLT now show a real observation of gravitational instability happening at planetary scales.

"It's a confirmation that one of the basic ideas of how planets form works," said Kastner. "It's a pretty good demonstration of what has been shown in very detailed simulations of discs around young stars to determine if they are making planets."

The research team presented its findings in the July 25 issue of The Astrophysical Journal Letters. Authors span across the globe while the VLT and ALMA are located in Chile's Atacama Desert.

The ESO enables scientists worldwide to discover the secrets of the universe for the benefit of all. Established as an intergovernmental organization in 1962, today ESO is supported by 16 member states (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland, and the United Kingdom), along with the host state of Chile and with Australia as a strategic partner.

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Planetary heist: Astronomers show massive stars can steal Jupiter-sized planets

Jupiter-sized planets can be stolen or captured by massive stars in the densely populated stellar nurseries where most stars are born, a new study has found.

Researchers from the University of Sheffield have proposed a novel explanation for the recently discovered B-star Exoplanet Abundance STudy (BEAST) planets. These are Jupiter-like planets at large distances (hundreds of times the distance between the Earth and the Sun) from massive stars.

Until now their formation has been something of a mystery, as massive stars emit large amounts of ultraviolet radiation that stops planets from growing to the size of Jupiter -- the largest planet in our solar system.

Dr Emma Daffern-Powell, Co-author of the study, from the University of Sheffield's Department of Physicsand Astronomy added:"Our previous research has shown that in stellar nurseries stars can steal planets from other stars, or capture what we call 'free-floating' planets. We know that massive stars have more influence in these nurseries than Sun-like stars, and we found that these massive stars can capture or steal planets -- which we call 'BEASTies'.

"Essentially, this is a planetary heist. We used computer simulations to show that the theft or capture of these BEASTies occurs on average once in the first 10 million years of the evolution of a star-forming region."

Dr Richard Parker, Lecturer in Astrophysics in the University of Sheffield's Department of Physics and Astronomy explains: "The BEAST planets are a new addition to the myriad of exoplanetary systems, which display incredible diversity, from planetary systems around Sun-like stars that are very different to our Solar System, to planets orbiting evolved or dead stars

"The BEAST collaboration has discovered at least two super-Jovian planets orbiting massive stars. Whilst planets can form around massive stars, it is hard to envisage gas giant planets like Jupiter and Saturn being able to form in such hostile environments, where radiation from the stars can evaporate the planets before they fully form.

"However, our simulations show that these planets can be captured or stolen, on orbits very similar to those observed for the BEASTies. Our results lend further credence to the idea that planets on more distant orbits (more than 100 times the distance from Earth to Sun) may not be orbiting their parent star."

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