Since their first discovery in 1995, hot Jupiter exoplanets (hot Jupiters, for short) quickly challenged our understanding of exoplanet formation and evolution, including exoplanetary system architecture. This is because, as their name implies, they orbit at extremely close distances to their host stars, ranging from a few days to a few hours. Some of their orbits are even oval-shaped, called eccentric in the scientific community, meaning their orbit is oval-shaped. But could such an orbit cause a hot Jupiter to completely vanish from view, preventing astronomers from studying it?
Now, an international team of researchers might have shed new light on the fate of hot Jupiters, as they present new findings announcing the discovery of a hot Jupiter whose eccentric orbit tilt could change in less than a decade, preventing astronomers from observing it. This study was recently published in the Publications of the Astronomical Society of Japan and could help astronomers better understand the evolution of hot Jupiters with eccentric orbits and whether this orbital tilt change is common across other exoplanets.
For the study, the researchers examined transit data from the hot Jupiter, TOI-1355 b, which is located about 805 light-years from Earth, has a mass and radius of about 5.84 and 1.42 Jupiters, respectively, and orbits its star in about 2.17 days. A transit occurs when an exoplanet passes in front of its host star, resulting in small decreases in starlight, with this method often being used to measure an exoplanet’s mass and radius. As noted, TOI-1355 b’s orbit is eccentric compared to Earth at 0.22 with Earth’s eccentricity being 0.0167. Eccentricity measured from 0 to 1, with 0 being a perfect circle and 1 being a parabola. Researchers hypothesize that hot Jupiters with eccentric orbits indicate their orbits could have changed from circular to eccentric over time due to gravitational interactions with other objects in their system.
After analyzing data from NASA’s Transiting Exoplanet Survey Satellite (TESS) spacecraft and the ground-based Okayama Observatory of Kyoto University, the researchers determined that TOI-1355 b’s orbit is slowly tilting. As a result, the researchers estimate that the current orbital tilt trajectory will cause TOI-1355 b to become unobservable from Earth in 2033. This means when it transits its star, it will transit it in a different location preventing Earth-based telescopes from seeing it. Essentially, astronomers have less than seven years to gain as much scientific knowledge about TOI-1355 b before its transits disappear, possibly for good.
“Planet surveys around stars as hot or cooler than the sun are flourishing, and thousands of planets have been discovered around such stars,” said Dr. Noriharu Watanabe, who is a project researcher at the University of Tokyo and lead author of the study. “But planet surveys around hotter stars are still not advanced. In this project, we hunted for planets around hot stars to examine the diversity of exoplanets more broadly. When we investigated the change in brightness of TOI-1355 from prior data, we found that the secondary eclipse, a phenomenon in which a planet passes behind a star, occurred faster than the timing assumed for a circular orbit. This was unusual for hot Jupiters around hot stars, and this is why we began to research this planet in detail.”
While there is an almost negligible chance of finding life on hot Jupiters, their existence has nonetheless challenged our understanding of planetary formation and evolution. This includes a leading hypothesis that hot Jupiters initially started off orbiting much farther out only to migrate inwards in a process called planetary migration. Astronomers hypothesize that Jupiter began to migrate inward only a few million years after our solar system formed but was pulled into its current orbit from a gravitational tug from Saturn, which formed exterior to Jupiter’s orbit.
As the researches discuss, a hot Jupiter’s eccentric orbit could indicate it has undergone a tumultuous history. Thus, studying TOI-1335 b, even if only for a few more years, could help researchers gain insights into this orbital evolution and potentially use it for other hot Jupiters.
What new insights into TOI-1355 b and other vanishing hot Jupiters will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
