A planet’s death spiral: How Kepler-1658b crashes into its star

Updated on 12/21/2022 at 4:07 p.m

• The gas giant Kepler-1658b lies 2,600 light-years from Earth.
• “Hot Jupiter” moves faster and faster and tumbles towards its star in a spiral.
• It is the first time that this phenomenon has been detected “on a planet of a highly developed star”.

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A cosmic catastrophe is looming 2,600 light-years from Earth: The “hot Jupiter” Kepler-1658b is spiraling towards its star and will crash into it in regarding 2.5 million years. This is shown by observations by a research team from the USA and Great Britain.

It is the first time such a death spiral has occurred in a planets of an old, well developed star. The observation also provides an insight into the future of our solar system, according to the scientists in the specialist journal “Astrophysical Journal Letters”.

Phenomenon has never been detected in planets of a well developed star

“We have previously found evidence of planets spiraling toward their stars,” said Shreyas Vissapragada of the Harvard Smithsonian Center for Astrophysics. “But we have never been able to detect this phenomenon on a planet of a highly developed star.”

Such stars have already used up most of their nuclear energy supply and are beginning to expand into a red giant star. Our sun will reach this stage in regarding five billion years.

Also read: Never Observed Before: Dying Star With Possible Livable Planet

However, these stars, the theory goes, should be particularly effective at pulling planets in tight orbits ever closer – until they eventually fall into the star. That should be the case for Kepler-1658b, a Jupiter-sized gaseous planet in an extremely close orbit around its star: its orbital period is just 3.8 days, and its distance from the star is just one-eighth that of Mercury-Sun.

Kepler-1658b is moving faster and closer to the star

To detect any change in this orbit, Vissapragada and his colleagues evaluated observations made by the Kepler and Tess space telescopes and the Palomar Observatory’s Hale telescope from 2009 to 2022. As seen from Earth, Kepler-1658b regularly passes in front of its star, slightly dimming its brightness as it does so.

Measuring these transits provides astronomers with the planet’s orbital period immediately. And an observation over a longer period of time should show whether the orbital period is changing.

However, that sounds easier than it is. Because such changes are very slow. However, with the help of a complex analysis procedure, the team was able to determine a decrease in the orbital period of 131 milliseconds per year. A decrease in the orbital period means: The planet moves faster and faster and approaches the star in a spiral. Vissapragada and his colleagues calculate that it will take regarding 2.5 million years for Kepler-1658b to finally crash into the star.

Expert: “Kepler-1658 is for us a kind of cosmic laboratory”

The cause of the impending cosmic catastrophe are the tidal forces that the star and planet exert on each other at such a small distance. Something similar happens in the earth-moon system: the tides generated by the moon on earth slow down the earth’s rotation – and because of the physical law of conservation of angular momentum, the moon must therefore move further and further away from the earth. If an orbit is very narrow – as in the case of Kepler-1658b – this effect is reversed and thus leads to an inward spiral orbit.

Also read: Fantastic images from Nasa show the dark side of the moon

However, the tidal interaction is complex in detail and also depends, for example, on the internal structure of the celestial bodies. Theoretical models suggest that highly developed stars are particularly effective at accelerating planets into a death spiral.

“We now have, for the first time, an example of a planet spiraling around an evolved star, and we can use it to improve our models for tidal physics,” Vissapragada points out. “So for us, Kepler-1658 is a kind of cosmic laboratory – and with a little luck we can find many more such systems.” (ff/dpa)