A team of astronomers has reported a huge haul of new exoplanets discovered and confirmed using data from the first year of the Kepler/K2 mission. Among the 104 confirmed planets (57 in multi-planet systems) is the first planetary system comprising four low-mass, potentially terrestrial planets.
An artist’s rendition of the K2-72 planetary system. Image credit: NASA / JPL.
The newly-confirmed exoplanets range in size from smaller than Earth to larger than Jupiter.
All of the planets orbit close to their host stars, and many of the stars show evidence for multiple planets.
The discoveries will be published online in the Astrophysical Journal Supplement Series (arXiv.org preprint).
“The diversity of planets is astounding. We’re finding planets where we don’t see them in our Solar System,” said co-author Evan Sinukoff, from the University of Hawaiʻi at Mānoa.
“For example, we discovered many planets about twice the size of the Earth orbiting so close to their host stars that they are hotter than 1,000 degrees Celsius.”
One of the most interesting sets of planets discovered by the team is a system of four potentially rocky planets orbiting a star less than half the size of (and much fainter than) the Sun.
These four planets are orbiting K2-72 (also known as EPIC 206209135), an M-type dwarf star located approximately 181 light-years away in the constellation Aquarius.
The planets – named K2-72b, c, d, and e — are between 20% and 50% larger than Earth by diameter.
They have orbital periods of 5.58, 7.76, 15.19, and 24.16 days, respectively, and two of them — K2-72d and e — may experience irradiation levels from their star comparable to those on Earth.
According to the astronomers, K2-72d is likely about 10% warmer than Earth and K2-72e would be about 6% colder than Earth.
“Despite their tight orbits — closer than Mercury’s orbit around the Sun — the possibility that life could arise on a planet around such a star cannot be ruled out,” said lead author Dr. Ian Crossfield, from the University of Arizona’s Lunar and Planetary Laboratory.
The team also discovered and confirmed four new two-planet systems: K2-80, K2-83, K2-84, and K2-90 (also known as EPIC 210403955, 210508766, 210577548, and 210968143, respectively).
The brightest confirmed planetary system, K2-65 (EPIC 206144956), hosts a planet just 60% larger than Earth.
Also of interest is K2-89 (EPIC 210838726), which contains a highly irradiated, roughly Earth-sized planet on a one-day orbit around an M dwarf.
To validate candidate exoplanets identified by the Kepler Space Telescope, the astronomers obtained high-resolution images of the planet-hosting stars from Keck Observatory’s near infrared camera (NIRC2), the Gemini and Large Binocular Telescope as well as high-resolution optical spectroscopy using Keck Observatory’s high resolution spectrograph (HIRES) instrument and the AUtomated Planet Finder (APF).
By dispersing the starlight, the spectrographs allowed the team to measure the physical properties of a star — such as mass, radius and temperature — and infer the properties of any planets orbiting it.
“Our analysis shows that by the end of the K2 mission, we expect to double or triple the number of relatively small planets orbiting nearby, bright stars,” Dr. Crossfield said.
“And because these planets orbit brighter stars, we’ll be able to more easily study everything possible about them, whether it’s measuring their masses with Doppler spectroscopy — already underway at Keck Observatory and APF — or measuring their atmospheric makeup with NASA’s James Webb Space Telescope in just a few years.”
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Ian J. M. Crossfield et al. 2016. 197 Candidates and 104 Validated Planets in K2’s First Five Fields. ApJS, accepted for publication; arXiv: 1607.05263
