Astronomers have discovered a ‘super-Earth’ exoplanet in the habitable zone of LHS 1140, a small, cool star in the constellation of Cetus, approximately 39 light-years away from Earth. The discovery is being published in the April 20, 2017 issue of the journal Nature.
The super-Earth exoplanet LHS 1140b is located in the liquid water habitable zone surrounding its parent star, LHS 1140. Image credit: M. Weiss, CfA.
“This is the most exciting exoplanet I’ve seen in the past decade,” said Dr. Jason Dittmann, an astronomer at the Harvard-Smithsonian Center for Astrophysics and lead author of the Nature paper.
The newfound world, named LHS 1140b, is about 1.43 times larger than the Earth. It has a diameter of 11,322 miles (18,221 km), compared to the Earth’s diameter of 7,918 miles (12,742 km).
The planet is about 6.6 times as massive as the Earth and is probably made of rock with a dense iron core.
“A simple structural mode consisting of a dense iron core surrounded by a magnesium silicate mantle can explain the observed mass and diameter,” Dr. Dittmann and his colleagues explained.
“We conclude that LHS 1140b is a rocky planet without a substantial gas envelope.”
The planet’s parent star, LHS 1140, is a red dwarf about one-fifth the size of the Sun.
Also known as GJ 3053 and 2MASS J00445930-1516166, the star is approximately 5 billion years old, whereas the Sun is 4.6 billion years old.
LHS 1140b takes 24.7 days to orbit it, and the orbit is seen almost edge-on from Earth.
The planet is about 10 times closer to the star than the Earth is to the Sun, right in the middle of the LHS 1140’s habitable zone. It receives about half as much sunlight from the star as the Earth.
“For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere,” the astronomers said.
“When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them.”
“In this case, LHS 1140b’s large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.”
“The present conditions of the red dwarf are particularly favorable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars,” added co-author Dr. Nicola Astudillo-Defru, an astronomer at Geneva Observatory in Switzerland.
The team found LHS 1140b using the MEarth-South Observatory, an array of eight identical 16-inch-aperture telescopes that monitor small stars (less than 33% the size of the Sun) located within 100 light-years of the Sun.
ESO’s HARPS instrument then made follow-up observations which confirmed the presence of the planet.
“The LHS 1140 system might prove to be an even more important target for the future characterization of planets in the habitable zone than Proxima b or TRAPPIST-1,” concluded co-authors Dr. Xavier Delfosse and Dr. Xavier Bonfils, both at the CNRS and IPAG in Grenoble, France.
“This has been a remarkable year for exoplanet discoveries.”
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J.A. Dittmann et al. A temperate rocky super-Earth transiting a nearby cool star. Nature, published online April 20, 2017; doi: 10.1038/nature22055
