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CosmosUp | July 15, 2020

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Astronomers have Caught a Star Eating a Planet

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Astronomers have Caught a Star Eating a Planet

Astronomers have found that some sun-like stars have the ability to consume Earth-like planets. During their developmental stages, these sun-like stars swallow large amounts of rocky material, from which small, rocky planets such as Earth, Venus and Mars are formed.

Since long, astronomers have been detecting extrasolar planets in huge numbers. Since planets are proportionally richer in elements heavier than helium as compared to stars, absorbtion increases the metallicity of the stars and according to some theories, high metallicity stars are likely to have planets.

Stars are mostly made up of hydrogen and helium (98%), meaning other elements only make up about 2% of the star. These elements (all of which are heavier than hydrogen and helium) are referred to as metals and when it comes to iron abundance, you will sometimes see the term “metallicity” referred to, concerning the ratio of iron to hydrogen.

To expand on previous studies concerning metallicity and how planets form, Mack (a graduate student in astronomy at Vanderbilt University) examined sun-like stars to see the abundance of 15 elements, especially those such as aluminum, silicon, calcium and iron — considered to be the foundation of rocky planets such as the Earth.

  Mack chose stars, HD 20781 and 20782, unique in wide binary pair and both have planets in orbits. Both stars are of G-class like that of the sun. HD 20781 has two planets, the mass of which is similar to that of Neptune. One has a similar orbit like that of Mercury and the other much close than it. On the other hand, HD 20782 has a planet that is almost twice the Jupiter’s mass.

“Imagine that the star originally formed rocky planets like Earth. Furthermore, imagine that it also formed gas giant planets like Jupiter. The rocky planets form in the region close to the star where it is hot and the gas giants form in the outer part of the planetary system where it is cold. However, once the gas giants are fully formed, they begin to migrate inward and, as they do, their gravity begins to pull and tug on the inner rocky planets. With the right amount of pulling and tugging, a gas giant can easily force a rocky planet to plunge into the star. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect,” noted Mack.

“When we find stars with similar chemical signatures, we will be able to conclude that their planetary systems must be very different from our own, and that they most likely lack inner rocky planets,” added Mack. “And when we find stars that lack these signatures, then they are good candidates for hosting planetary systems similar to our own.”

The study was published earlier this month in the Astrophysical Journal.



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