Newly-discovered planet is hot, metallic and dense as Mercury (Update)

March 27, 2018 by Luke Walton, University of Warwick
Surface of Mercury. Credit: NASA/JHUAPL/Carnegie Institution of Washington/USGS/Arizona State University

A hot, metallic, Earth-sized planet with a density similar to Mercury—situated 340 light years away—has been detected and characterised by a global team of astronomers, including the University of Warwick.

Named K2-229b, the planet is almost 20% 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).

It finds itself very close to its (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.

Led overall by researchers at Aix-Marseille Université in France, Dr. David Armstrong and colleagues at the University of Warwick's Astronomy and Astrophysics Group independently detected the planet in the first instance, alongside researchers at the Universidade do Porto.

Using the K2 telescope, Dr. Armstrong and colleagues employed the Doppler spectroscopy technique—also known as the 'wobble method' to discover and characterise this faraway planet.

The astronomers knew the planet was there due to dips in the light from its host star as it orbited, periodically blocking starlight.

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 gravitational tug from the planet, which changes depending on the planet's size.

Dr. David Armstrong from the University of Warwick's Astronomy and Astrophysics Group, commented:

"Mercury stands out from the other Solar System terrestrial , 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.

"Interestingly K2-229b is also the innermost planet in a system of at least 3 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."

The dense, metallic nature of K2-229b has numerous potential origins, and 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.

Dr. David Armstrong from the University of Warwick's Astronomy and Astrophysics Group. Credit: University of Warwick

Another possibility is that K2-229b was 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.

Discovering details about far-flung planets across the universe gives us more clues as to how planets in our own solar system formed. As K2-229b is similar to Mercury, knowing more about the former can potentially reveal more about the latter.

Explore further: 'Monster' planet discovery challenges formation theory

More information: An Earth-sized exoplanet with a Mercury-like composition, Nature Astronomy, nature.com/articles/doi:10.1038/s41550-018-0420-5

Related Stories

'Monster' planet discovery challenges formation theory

October 31, 2017

A giant planet, which should not exist according to planet formation theory, has been discovered around a distant star. The new research is presented in a paper recently accepted for publication in the journal Monthly Notices ...

Migrating exoplanets

September 19, 2016

Many known exoplanets orbit close to their host star, within one-tenth of an astronomical unit (one AU is the average distance of the Earth from the Sun). Since their orbital periods are therefore very short and their gravitational ...

Image: Illustration of an Earth-sized 'Tatooine' planet

May 5, 2017

With two suns in its sky, Luke Skywalker's home planet Tatooine in "Star Wars" looks like a parched, sandy desert world. In real life, thanks to observatories such as NASA's Kepler space telescope, we know that two-star systems ...

Recommended for you

Gravitational waves from a merged hyper-massive neutron star

November 14, 2018

For the first time astronomers have detected gravitational waves from a merged, hyper-massive neutron star. The scientists, Maurice van Putten of Sejong University in South Korea, and Massimo della Valle of the Osservatorio ...

The dance of the small galaxies that surround the Milky Way

November 14, 2018

An international team led by researchers from the IAC used data from the ESA satellite Gaia to measure the motion of 39 dwarf galaxies. This data gives information on the dynamics of these galaxies, their histories and their ...

Galaxies like Russian dolls

November 13, 2018

Jairo Méndez Abreu and Adriana de Lorenzo-Cáceres, researchers at the Instituto de Astrofísica de Canarias (IAC), have discovered a peanut-shaped structure in the inner bar of a double-barred galaxy close to the Milky ...

Giant flare detected on a pre-main sequence M star

November 13, 2018

Using the Next Generation Transit Survey (NGTS), astronomers have identified an energetic flare displaying quasi-periodic pulsations on the pre-main sequence M star NGTS J121939.5-355557. The newly detected flare is one of ...

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

CAMason
not rated yet Mar 27, 2018
260 million light years away?
KellyB
not rated yet Mar 27, 2018
That's a typo, the Virgo constellation is about 260 light years away, which I think is what the author intended to say.
mxw
not rated yet Mar 27, 2018
Geez our telescopes are getting better.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.