A team of researchers has discovered a rare, extremely hot planet with a highly eccentric orbit. TOI-1355 b circles its star, which is also significantly hotter than our Sun, in just two Earth days. At the same time, its orbit is changing in an unusual way.
Hot Jupiter TOI-1355 b Around a Hot Star
Project researcher Noriharu Watanabe and Professor Norio Narita of the University of Tokyo’s Graduate School of Arts and Sciences, together with their international team, study exoplanets and are particularly interested in those that differ from anything found in our Solar System. And, as phys.org reports, they recently found something truly important.
They recently discovered the planet TOI-1355 b, a so-called hot Jupiter, meaning that it is similar to the largest gas giant in our system but orbits very close to its star. In this case, the star is also much hotter than the Sun — 8,400°C (15,100°F) compared with 5,500°C (9,900°F) at the surface of our star. The most interesting feature, however, turned out to be the elliptical orbit of this new world.
When astronomers studied changes in the brightness of TOI-1355 using earlier data, they found that the secondary eclipse — the phenomenon in which the planet passes behind the star — occurred earlier than predicted for a circular orbit. This was unusual for hot Jupiters orbiting hot stars, which is why scientists began studying this gas giant in detail.
Clues to the Cause of the Orbit’s Changing Eccentricity
NASA’s Transiting Exoplanet Survey Satellite (TESS) recently detected periodic dimming of the star TOI-1355, and Narita’s team determined that it was caused by a planetary transit. They measured the planet’s mass and orbital eccentricity — the degree to which the orbit deviates from a circle — based on changes in the brightness of the star and planet observed by TESS.
The discovery of a hot Jupiter with a highly eccentric orbit is important because it supports the theory that similar worlds around large stars may have a dramatic history involving dynamical migration, possibly caused by gravitational interactions between planets that alter one another’s orbits. Such interactions are thought to produce high eccentricity, which gradually becomes more circular over time.
“It is thought that the planetary orbit initially became highly elliptical due to gravitational interactions with other celestial bodies, such as other giant planets, and later gradually shrank due to the tidal effects of its host star,” Watanabe said.
Limited Time to Study the Planet
The biggest challenge so far has been measuring the planet’s mass from the brightness variations in the TESS data. Scientists had to derive more complex model equations because of its elliptical orbit.
This unusual orbit may provide a rare opportunity to study this class of planets and how such planets move and evolve. However, because the planet’s orbit is changing, it will no longer be possible to observe it after approximately 2033.
The research team is preparing another paper examining how much the planet’s orbit is tilted relative to the star’s rotation. They also plan to submit a proposal for observations using NASA’s James Webb Space Telescope.
