Newly found metallic exoplanet is a lot like Mercury

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Scientists have discovered a hot, metallic, Earth-sized planet with a density similar to Mercury located 339 light years away from Earth.

“…Mercury-like planets are perhaps not as rare as we thought…”

“Mercury stands out from the other solar system terrestrial planets, showing a very high fraction of iron and implying it formed in a different way. We were surprised to see an exoplanet with the same high density, showing that Mercury-like planets are perhaps not as rare as we thought,” says David Armstrong, of the astronomy and astrophysics group at the University of Warwick.

Named K2-229b, the planet is almost 20 percent larger than Earth but has a mass which is over two-and-a-half times greater—and reaches a dayside temperature of over 2000°C (2330 Kelvin).

The new planet is very close to its host star (0.012 AU, around a hundredth of the distance between the Earth and the Sun), which itself is a medium-sized active K dwarf in the Virgo Constellation. K2-229b orbits this star every fourteen hours.

Using the K2 telescope, scientists used the Doppler spectroscopy technique—also known as the “wobble method” to discover and characterize the planet. Astronomers knew the planet was there thanks to dips in the light from its host star as it orbited.

They then calculated the size, position, and mass of K2-229b by measuring the radial velocity of the star, and finding out how much the starlight wobbles during orbit, due to the planet’s gravitational tug, which changes depending on its size.

“Interestingly K2-229b is also the innermost planet in a system of at least three planets, though all three orbit much closer to their star than Mercury. More discoveries like this will help us shed light on the formation of these unusual planets, as well as Mercury itself,” Armstrong says.

Scorching hot Mercury has more ice than we thought

The dense, metallic nature of K2-229b has numerous potential origins. One hypothesis is that its atmosphere might have been eroded by intense stellar wind and flares, as the planet is so close to its star.

Another possibility is that K2-229b formed after a huge impact between two giant astronomical bodies in space billions of years ago—much like the theory that the moon was formed after Earth collided with a body the size of Mars.

Researchers report their findings in Nature Astronomy. Researchers from Aix-Marseille Université in France and the Universidade do Porto in Portugal are coauthors.

Source: University of Warwick