Science & Technology

Death by star: Scientists spot alien planet spiralling to ruin

Kepler-1658b’s orbit is getting closer to its ageing star; likely to crash in 2.5 million years

By Rohini Krishnamurthy
Published: Tuesday 20 December 2022
An artist's concept of the Kepler-1658 system. Photo: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias
An artist's concept of the Kepler-1658 system. Photo: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias An artist's concept of the Kepler-1658 system. Photo: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias

Scientists have spotted a planet plunging to its doom for the first time. Kepler-1658b, which is some 1,050 light years away from Earth, is spiralling closer to an ageing star and is on the verge of death, according to a study published in The Astrophysical Journal Letters

The dying alien planet was first discovered in 2019. Over the last decade, Kepler-1658b’s orbital period around its star has reduced by about 131 milliseconds (thousandths of a second) per year. 

At this rate, it will likely crash into its host star in 2.5 million years, lead author Shreyas Vissapragada from the Center for Astrophysics, Smithsonian Astrophysical Observatory and Harvard College Observatory told Down To Earth.

Read more: Cosmic cliffs, galaxy group: 1st series of photos by James Webb Space Telescope

This “death by star” fate could also befall Earth, too. But scientists predict that it is billions of years away.

Kepler-1658b is a gas giant exoplanet or a ‘Hot Jupiter’. These planets are more than twice the diameter of Earth and possess enough gravity to hold onto hydrogen, the most abundant element in the universe, according to the United States’ National Aeronautics and Space Administration (NASA).

The exoplanet, according to NASA, takes 3.8 days to complete one orbit and is only 0.0544 Astronomical Unit (roughly the distance from Earth to the Sun) away from its star.

Vissapragada and his colleagues observed Kepler-1658b, thanks to the now-retired Kepler space telescope, Palomar Observatory’s Hale Telescope in Southern California and the Transiting Exoplanet Survey Telescope (TESS). 

These instruments recorded transits — dimming of a star’s brightness when an exoplanet passes between it and a telescope — for over 13 years.

Vissapragada said his team was looking at the orbital properties of planets orbiting evolved or ageing stars. Kepler-1658 b’s star is an evolved system as it is beginning to run out of its fuel, hydrogen and is going through major structural changes, he added. 

When a star exhausts its hydrogen reserves, it collapses and expands in size, becoming a red giant — a dying star, according to NASA.

The three telescopes showed that the time Kepler-1658b took to complete one orbit has steadily declined over the years.

The star is heading towards its demise, thanks to tidal forces. They are generated by gravitational interactions between two orbiting bodies, such as between Earth and the Moon or Kepler-1658b and its star, according to the researchers.

Based on the rotation rates or orbits, tidal interactions can result in bodies pushing each other away (for example, between Earth and the Moon) or towards each other (like Kepler-1658b and its star), the researchers noted.

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Further, Kepler-1658b was much hotter than expected, with dayside temperature of 3450 Kelvin (3176.85 degrees Celsius), according to the study.

The tidal interactions could be heating the planet. “We postulated that some of the energy from the decaying orbit could be lost inside the planet,” Vissapragada explained.

In the future, when the exoplanet clashes with its star, the latter may witness a temporary increase in chemical elements that are more abundant in the alien world.

The researchers plan to hunt for more such evolved systems. “If they are common, we can learn a lot about the last stages of many planets’ lives,” the expert added. 

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