Low-mass stars can host giant Jupiter-style planets: Study

A new study challenges the most widely accepted theory of how and where giant planets form. Using observations from NASA's Transiting Exoplanet Survey Satellite (TESS), a team led by UCL and the University of Warwick researchers examined 91,306 low-mass stars and found that stars with less than half the mass of our Sun can host giant Jupiter-style planets.

The researchers identified 15 potential giant planets and 5 of them have so far been confirmed as planets using independent methods. One of these confirmed planets orbits a star that is a fifth of the mass of the Sun - which would not be possible according to planet formation models.

"Low-mass stars are better at forming giant planets than we thought. Our results raise serious questions for planet formation models. In particular, our detection of gas giants orbiting stars as low as 20% of the mass of the Sun poses a conflict with current theory," said lead author Dr Ed Bryant (Mullard Space Science Laboratory at UCL, formerly the University of Warwick), who initiated the work as part of his PhD.

The core accretion theory proposes that gas giants, just like other planets, first form a core of rock, ice and other heavy solids, attracting an outer layer of gas once this core is sufficiently massive. However, low-mass stars have low-mass disks that would not provide enough material to form a gas giant in this way.

The new study contradicts this most widely accepted theory. A possible explanation, according to the researchers, is that gas giants may not form via core accretion but instead through gravitational instability. This occurs when the disk surrounding a star fragments into planet-sized clumps of dust and gas. If this is the case, low-mass stars may have the potential to host enormous gas giants, which could be two or three times the mass of Jupiter.

Nevertheless, this theory is unlikely to hold true because the disks surrounding low-mass stars do not seem to be large enough to undergo fragmentation.

According to the researchers, there is another explanation that suggests astronomers may have underestimated the mass of a star's disk. This means that even small stars could form giant planets through core accretion after all.

"It’s possible we don’t understand the masses of these protoplanetary disks as well as we thought we did. Powerful new instruments such as the James Webb Space Telescope will be able to study the properties of these disks in more detail," explains co-author Dr Dan Bayliss (University of Warwick).

Small stars, giant planets?New data from @NASA's TESS space telescope is changing our understanding about how -- and where -- giant planets form. https://t.co/SruHURCAi7 pic.twitter.com/PzlpGHbbvh

— NASA Exoplanets (@NASAExoplanets) March 22, 2023