Planet spotted spiraling to its doom gives insight into how our world will end

By Stephen Beech via SWNS

An alien planet spotted spiraling to its doom around an aging star may indicate how the world will eventually end.

Scientists say that the condemned planet could help answer questions about the fate of other worlds - including Earth - as their solar systems evolve.

It is the first time that astronomers have spotted an exoplanet whose orbit is decaying around an evolved, or older, host star.

They say that the stricken world appears destined to spiral closer and closer to its maturing star until collision and ultimate obliteration.

The discovery offers new insights into the long-winded process of planetary orbital decay by providing the first look at a system at such a late stage of evolution.

Death-by-star is a fate believed to await many worlds and could be the Earth's ultimate ending billions of years from now as our Sun grows older, astronomers say.

Study lead author Doctor Shreyas Vissapragada, of the Center for Astrophysics, said: "We've previously detected evidence for exoplanets inspiraling toward their stars, but we have never before seen such a planet around an evolved star.

"Theory predicts that evolved stars are very effective at sapping energy from their planets' orbits, and now we can test those theories with observations."

The ill-fated exoplanet is named Kepler-1658b. Astronomers discovered the exoplanet with the Kepler space telescope, a pioneering planet-hunting mission that launched in 2009.

It was the very first new exoplanet candidate Kepler ever observed, but it took nearly a decade to confirm the planet's existence. At that time, the object entered Kepler's catalog officially as the 1,658th entry.

Kepler-1658b is a so-called "hot Jupiter" - the nickname given to exoplanets on par with Jupiter's mass and size but in scorchingly ultra-close orbits about their host stars.

For Kepler-1658b, that distance is merely an eighth of the space between our Sun and its tightest orbiting planet, Mercury.

For hot Jupiters and other planets such as Kepler-1658b that are already very close to their stars, orbital decay looks certain to culminate in destruction.

Measuring the orbital decay of exoplanets has challenged researchers because the process is very slow and gradual.

In the case of Kepler-1658b, according to the new study published in The Astrophysical Journal Letters, its orbital period is decreasing at the miniscule rate of about 131 milliseconds per year - with a shorter orbit indicating the planet has moved closer to its star.

Detecting this decline required many years of careful observation. The watch started with Kepler and then was picked up by the Palomar Observatory’s Hale Telescope in Southern California and finally 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’s transits has slightly but steadily decreased.

Scientists say that the root cause of the orbital decay experienced by Kepler-1658b is tides - the same phenomenon responsible for the daily rise and fall in 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 bodies’ gravities distort each other’s shapes, and as the bodies respond to these changes, energy is released.

Depending on the distances between, sizes, and rotation rates of the bodies involved, the tidal interactions can result in bodies pushing each other away - such as in the case of the Earth and the slowly outward-spiraling Moon — or inward, as with Kepler-1658b toward its star.

Dr. Vissapragada explained that Kepler-1658b's star has evolved to the point in its stellar life cycle where it has started to expand, just as our sun is expected to, and has entered into what astronomers call a subgiant phase.

He said: "The internal structure of evolved stars should more readily lead to dissipation of tidal energy taken from hosted planets’ orbits compared to unevolved stars like our Sun.

"This accelerates the orbital decay process, making it easier to study on human timescales.

"The results further help in explaining an intrinsic oddity about Kepler-1658b, which appears brighter and hotter than expected.

"The tidal interactions shrinking the planet’s orbit may also be cranking out extra energy within the planet itself."

Dr. Vissapragada points to a similar situation with Jupiter’s moon Io, the most volcanic body in the Solar System.

He says the gravitational push-and-pull from Jupiter on Io melts the planet’s innards. This molten rock then erupts out onto the moon’s famously infernal, pizza-like surface of yellow sulfurous deposits and fresh red lava.

Dr. Vissapragada said: "Now that we have evidence of inspiraling of a planet around an evolved star, we can really start to refine our models of tidal physics.

"The Kepler-1658 system can serve as a celestial laboratory in this way for years to come, and with any luck, there will soon be many more of these labs."

He added: "I can't wait to see what all of us end up discovering together."