Alien planet spiralling around star suggests how Earth could end

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Scientists have found an alien planet spiralling to its death around an ageing star, which they say could indicate how Earth will eventually meet its end. The discovery marks the first-ever time that experts have caught a glimpse of an exoplanet (a planet outside our Solar System) whose orbit is decaying around an evolved, or older, host star. While this is millions of lightyears away from the Blue Planet, experts have argued that it could help answer questions how other worlds, including our own planet, could see its fate as solar systems evolve.

According to astronomers, whose observations are recorded in a study published in The Astrophysical Journal Letters,  the distant exoplanet appears to be spiralling closer and closer to its maturing star. Eventually, they believe it could collide with the star, which would completely destroy it.

This, they say, provides fresh insights into the long-drawn-out process of planetary orbital decay by giving the first look at a system at this late stage of evolution. Colliding with stars is thought to be a fate that many planets are destined for. Billions of years from now, as our Sun grows older, this could spell disaster for Earth. 

Lead author of the study Doctor Shreyas Vissapragada, of the Centre for Astrophysics in the US, 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 exoplanet which appears to be heading towards an impending death has been given the name Kepler-1658b. Astronomers spotted it using the Kepler space telescope as part of a mission to find distant planets that was first launched in 2009.

Kepler-1658b is the first exoplanet to have been spotted by the telescopebut, although it did take almost a decade to confirm the its existence. Also dubbed “hot-Jupiter”, the distant world has the same mass and size as the most giant planet in our Solar System, but it is blisteringly hot and has an ultra-close orbit around its host star.

Kepler-1658b is only an eighth of the space between our Sun and its closest orbiting planet, Mercury. But it is not the only planet to have received this nickname (others with similar characteristics have also been coined hot-Jupiter), with many others that are orbiting near host stars expected to meet their fate in similar ways. 

But it is also not so clear cut as so-called orbital decay is hard to measure in exoplanets due to the process slow and gradual nature of the process. According to the authors of the study, Kepler-1658b’s orbital period is declining at a rate of about 131 milliseconds per year, which is considered incredibly slow. But a shorter orbit indicates the hot Jupiter is edging closer toward its host star.

Making this specific observation reportedly took years of keeping a close eye on the planet. They started observing the planet with Kepler, and it later got picked up by the Palomar Observatory’s Hale Telescope in California. The Transiting Exoplanet Survey Telescope (TESS), launched in 2018, has also been keeping tabs on the alien world.

The telescopes have all captured transits – the process where an exoplanet crosses the face of its star, trigging a subtle dimming of the star’s brightness. Over the last 13 years,  the interval between the planets transits has steadily decreased, but only slightly. 

Kepler-1658b’s orbital decay has reportedly been caused by tides – the same process which sees the daily rise and fall in our planet’s oceans. These are created by gravitational interactions between two orbiting bodies.

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In our case, this refers to the interaction between the Earth and our Moon. For Kepler-1658b, it refers to the interaction between the planet itself and its star. The gravities of the bodies alter each other’s shapes, releasing energy as the two bodies respond. 

Dr Vissapragada 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.

“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. I can’t wait to see what all of us end up discovering together.”

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