Astronomers have discovered an exoplanet whose orbit is degrading as it orbits an old star.

The unfortunate planet, discovered by the Kepler space telescope, is on a collision course with its expanding star, which will finally destroy it.

Exoplanet Spiraling Towards Its Doom

By providing the first sight of a solar system in its latter phases, the discovery of an exoplanet whose orbit is decaying as it orbits an aging star provides a fresh understanding of the long process of planetary orbital decay.

Many planets, including Earth, are thought to face the fate of being swallowed by a star in around 5 billion years. Scientists estimate that the exoplanet Kepler-1568b has less than 3 million years before it dies.

The first probable exoplanet discovered by the Kepler space telescope, which began in 2009 on a nine-year quest to detect planets circling other stars, was a gas giant orbiting an aged subgiant star 2,600 light years away.

A decade later, researchers determined that Kepler’s first candidate was a genuine exoplanet, naming it Kepler-1658b. Kepler-1658b is essentially a denser Jupiter: envision around six Jupiters’ worth of material packed into a ball about 1.1 times the size of Jupiter.

It is tidally locked to its star, which means that the planet rotates one full turn after completing a circuit around the star, ensuring that the same side of the planet is constantly facing the star. Because the Moon is tidally locked to Earth, we always see the same half of its surface.

And it now appears that the first exoplanet discovered by NASA’s retired planet-hunter is also a doomed world.

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Tidal Forces

The same tidal force that is progressively pushing the Moon away from Earth is pulling Kepler-1658b inward. When a planet revolves around a star (or a moon orbits a planet), the gravity of each item tugs on the mass of the other object, stretching it slightly out of shape.

That is what generates the tides on Earth. And that small tugging also releases energy, which can either accelerate an object’s orbit, propelling it higher — or slow it down, drawing it lower. This method is frequently used by spacecraft to nudge themselves into higher or lower orbits.

Tidal forces can either lift or drag an object, depending on how distant it is from the object it is circling, how big both objects are, and even how fast it rotates. In the case of the Moon, it will eventually be accelerated out of Earth’s orbit.

Unfortunately for Kepler-1658b, physics does not favor the gas giant. The enormous tidal force of a star 1.5 times the mass of our Sun progressively slows the planet’s orbit, causing it to spiral inward in a slow spiral.

And Kepler-1658b doesn’t have much wiggle room. It’s currently orbiting its star at a death-defying one-eighth the distance between Mercury and our Sun, and it’s losing ground (or space) with each pass.

Meanwhile, the same tidal forces that are gradually bringing the gas behemoth to its demise are also scorching it from within.

Here in our Solar System, the same process that keeps the interiors of frozen moons like Europa and Enceladus warm — and powers the volcanic hellscape of Io — may be heating up areas of Kepler-1658b.

This is because the planet’s surface, particularly on the side facing its star, seems brighter than it should if the planet were just reflecting sunlight from the higher layers of its hot, gaseous envelope.

According to Astrophysicist Shreyas Vissapragada of the Harvard-Smithsonian Center for Astrophysics and his colleagues, tidal heating appears to be the most feasible explanation.

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