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Johns Hopkins Astrophysicist Proposes New Definition For Planets

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Pluto will always be known as the planet that was stripped of its title. An astrophysicist now proposes a new redefinition of planets to exclude large celestial bodies.

Kevin Schlaufman, professor of physics and astronomy at the John Hopkins University, presents a new argument in the scientific debate on planet formations. In his new study, Schlaufman says there must be an upper limit set on the mass of a celestial body for it to be classified as a planet.

He says the limit should be drawn at four to 10 times than the mass of gas giant planet Jupiter, the largest known planet in the solar system.

"While we think we know how planets form in a big picture sense, there's still a lot of detail we need to fill in," says Schlaufman.

"An upper boundary on the masses of planets is one of the most prominent details that was missing."

Giant Planets And Brown Dwarfs

The aim of the study is to help distinguish between giant planets and brown dwarfs.

Brown dwarfs are more massive than giant planets but less so than red dwarfs or the smallest stars.

Like in the controversial case of Pluto. It was known for the longest time as the ninth and most distant planet in the solar system but was relegated to the status of a dwarf planet in 2006 by the International Astronomical Union when a new version of a planetary definition was adopted.

Based on the definition of IAU, "a planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so it assumes a hydrostatic equilibrium (nearly round) shape and, has cleared the neighbourhood around its orbit."

Schlaufman said the advancement in the technology of astronomical observation makes it possible to discover planetary systems and patterns that were not observed before and therefore makes it necessary to narrow the limit of what defines a planet.

How To Know?

The new argument suggests that planets can be identified not just by its size but also through the chemical makeup of its sun.

The astrophysicist observed 146 stellar systems and found that celestial bodies that are 10 times larger than Jupiter were orbiting around metal-rich stars instead of stars that are rich in elements that make rocks. This led him to the conclusion that such celestial bodies are unlikely to form as planets. Brown dwarfs on the other hand, are not so discriminating.

Gas planets form from the bottom-up to build a rocky core beneath massive gaseous clumps. They would be orbit near stars heavy with elements that make rocks, considered as the seed material for planet formations.

Brown dwarfs are formed from the top-down with gas of clouds. Brown dwarfs range from 13 to 90 times the mass of Jupiter or around a tenth of the mass of the sun.

Schlaufman argues that celestial bodies that are 10 times more massive than Jupiter should be classified as brown dwarfs.

The paper "Evidence of an Upper Bound on the Masses of Planets and Its Implications For Giant Planet Formation" is published in the Astrophysical Journal.

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