A group of astronomers led by Benjamin Montet of the California Institute of Technology, Pasadena, has discovered a highly irradiated mini-Neptune exoplanet orbiting a low-mass star known as EPIC 201912552. A paper describing the find by Montet and co-authors has been submitted to the Astrophysical Journal and is available on the arXiv.org website.

EPIC 201912552 is an M2.8 dwarf star at a distance of approximately 111 light-years.

The newly-discovered planet, EPIC 201912552b, is a so-called mini-Neptune, about 2.2 times the radius of Earth.

It orbits its host star every 33 days at a distance of approximately 0.15 AU.

According to astronomers from the University of Puerto Rico at Arecibo’s Planetary Habitability Laboratory, EPIC 201912552b has an Earth Similarity Index of 0.73.

Co-author Daniel Foreman-Mackey of the New York University’s Center for Cosmology and Particle Physics found the first evidence of the planet’s existence in publicly available data collected during the Campaign 1 of the extended Kepler-K2 mission in May-August 2014.

The discovery was confirmed with measurements taken by the upgraded SpeX spectrograph on NASA’s Infrared Telescope Facility, and the SuperNova Integral Field Spectrograph on the University of Hawai’i 2.2-m telescope.

The scientists calculated that EPIC 201912552b receives 1.28 times the light intensity of Earth, and its equilibrium temperature is 28 degrees Fahrenheit (271 degrees Kelvin; minus 2 degrees Celsius).

“Although the planet is likely too large to be rocky, its atmosphere is likely to be the focus of many future observations, providing a cool analogue to the highly irradiated planets of a similar size found by Kepler,” Montet and co-authors wrote in the paper.

“Due to the relative brightness of the host star, EPIC 201912552b is likely to become a prime target for atmospheric characterization studies and is ideal as a target for future space-based missions such as the James Webb Space Telescope.”

“This planet is now the closest transiting planet to Earth of the objects of interest listed in the Habitable Exoplanets Catalog‎,” said astronomers from the Planetary Habitability Laboratory.

“This makes the planet a prime target for further observations in search for atmospheric signatures.”

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Benjamin T. Montet et al. 2015. Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 18 Systems, Including a Planet Receiving Earth-like Insolation. ApJ, submitted for publication; arXiv: 1503.07866