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Astronomers discover doomed exo-planet with an 'extraordinarily eccentric orbit'




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The discovery of a planet with a highly elliptical orbit around an ancient star could help us understand more about how planetary systems form and evolve over time. The new planet, HD76920b, is four times the mass of Jupiter, and can be found some 587 light years away in the southern constellation Volans, the Flying Fish.

At its furthest, it orbits almost twice as far from its star as Earth does from the Sun. So how does this fit into the planet formation narrative, and are planets like it common in the cosmos? A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity. Those tides will be far greater than any we experience on Earth.

That tidal interaction will act over time to circularise the planet’s orbit. The point of closest approach to the star will remain unchanged, but the most distant point will gradually be dragged closer in, driving the orbit towards circularity. All of this suggests that HD76920b cannot have occupied its current orbit since its birth. If that were the case, the orbit would have circularised aeons ago.

One thing we do know is the story is coming to a fiery end. In the next few million years, the star will swell, devouring its final planet. Then, HD76920b will be no more.

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