Astronomers have observed for the first time an exoplanet whose orbit decays around a mature star in a spiral path that appears destined for collision until eventual destruction.
The discovery, published in The Astrophysical Journal Letters, offers new perspectives on the long process of disintegration of planetary orbits, since it is the first time that a system in this advanced phase of evolution has been observed. Stellar death is believed to await many worlds and could spell the final goodbye for Earth billions of years from now, as our Sun ages.
“We have previously detected hints of exoplanets taking inspiration from their stars, but we have never seen such a planet around an evolved star,” said Shreyas Vissapragada, a 51 Pegasi b fellow at the Harvard/Smithsonian Center for Astrophysics and author “Theory predicts that evolved stars are very efficient at extracting energy from the orbits of their planets, and now we can test those theories with observations.”
The exoplanet is named Kepler-1658b. As the name suggests, astronomers discovered the exoplanet with the Kepler space telescope, a pioneering planet-hunting mission that launched in 2009. Interestingly, it was the first new exoplanet candidate Kepler observed but it took nearly a decade to confirm the exoplanet. planet’s existence, at which point the object officially entered Kepler’s catalog as entry number 1658.
Kepler-1658b is a hot Jupiter, a nickname given to exoplanets of similar mass and size to Jupiter, but in blazing ultra-close orbits around their host stars. In the case of Kepler-1658b, that distance is only one eighth of the space between our Sun and Mercury, its closest orbital planet. For hot Jupiters and other planets like Kepler-1658b that are already very close to their stars, orbital decay looks set to culminate in their destruction.
The challenge of measuring orbital decay
Measuring the orbital decay of exoplanets has been a challenge for researchers because the process is very slow and gradual. In the case of Kepler-1658b, according to the new study, its orbital period is decreasing at a minuscule rate of about 131 milliseconds (thousandths of a second) per year, and a shorter orbit indicates that the planet has moved closer to its star. .
Detecting this decline required several years of careful observation. The clock started with Kepler and was later picked up by the Palomar Observatory’s Hale telescope in southern California and eventually the Transiting Exoplanet Survey Telescope, or TESS, which launched in 2018.
All three instruments captured transits, the term for when an exoplanet crosses the face of its star and causes a very slight dimming of the star’s brightness. Over the past 13 years, the interval between Kepler-1658b transits has decreased slightly but steadily.
The fundamental cause of the orbital decay experienced by Kepler-1658b is tides, the same phenomenon responsible for the daily rise and fall of Earth’s oceans. Tides are generated by gravitational interactions between two orbiting bodies, such as between our world and the Moon or Kepler-1658b and its star.
The gravities of the bodies distort the shape of the other, and as the bodies respond to these changes, energy is released. Depending on the distances, sizes, and rotational speeds of the bodies involved, these tidal interactions can result in the bodies pushing each other outward—as in the case of the Earth and the Moon, which slowly spirals outward—or inwards, as in the case of Kepler-1658b towards its star.
There is still a lot that researchers don’t understand about this dynamic, especially in star-planet scenarios. Therefore, a more detailed study of the Kepler-1658 system should prove instructive.
The star has evolved to a point in its stellar life cycle where it has begun to expand, just as our Sun is expected to do, and has entered what astronomers call the subgiant phase.
The internal structure of evolved stars should more easily lead to the dissipation of tidal energy taken from the orbits of hosted planets, compared to unevolved stars like our Sun. This speeds up the process of orbital decay, making it easier to study. on human time scales.
The results help explain an intrinsic oddity of Kepler-1658b, which appears brighter and hotter than expected. According to the team, the tidal interactions that reduce the planet’s orbit may also be generating additional energy within it.
Vissapragada points to a similar situation with Jupiter’s moon Io, the most volcanic body in the Solar System. Jupiter’s gravitational pull on Io melts the bowels of the planet. This molten rock then erupts onto the moon’s famously hellish, pizza-like surface with yellow sulfurous deposits and fresh red lava.
The accumulation of additional observations of Kepler-1658b should shed more light on the interactions of celestial bodies. Vissapragada and her colleagues hope the telescope will continue to scan thousands of nearby stars and discover many more cases of exoplanets spinning down the drains of their host stars.
“Now that we have evidence of the inspiration of a planet around an evolved star, we can start refining our tidal physics models,” Vissapragada says. “The Kepler-1658 system may serve as such a celestial laboratory for years to come.” to come, and hopefully soon there will be many more of these labs.”
Vissapragada, who recently joined the Centro de Astrofísica a few months ago and is now mentored by Centro de Astrofísica astronomer Mercedes López-Morales, hopes that the science of exoplanets will continue to advance dramatically.