July 18, 2016 – An international team of astronomers, led by the University of Arizona, has discovered more than 100 new extrasolar planets using data from the Kepler Space Telescope on its K2 mission. The planets were confirmed and characterized by a suite of ground-based telescopes.
“The diversity of planets is astounding. We’re finding planets where we don’t see them in our Solar System,” said Evan Sinukoff, a graduate student at the Institute for Astronomy (IfA) at the University of Hawaii. “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 1000 degrees.”
The researchers achieved this extraordinary “roundup” of exoplanets by combining data with follow-up observations by earth-based telescopes including the North Gemini telescope and the W. M. Keck Observatory in Hawaii, the Automated Planet Finder of the University of California Observatories, and the Large Binocular Telescope operated by the University of Arizona. The discoveries are published online in the Astrophysical Journal Supplement Series.
The new planets 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.
One of the most interesting set of planets discovered in this study is a system of four potentially rocky planets, between 20 and 50 percent larger than Earth, orbiting a star less than half the size and with less light output than the Sun. Their orbital periods range from five-and-a-half to 24 days, and two of them may experience radiation levels from their star comparable to those on 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, according to lead author Ian Crossfield.
“Because these smaller stars are so common in the Milky Way, it could be that life occurs much more frequently on planets orbiting cool, red stars rather than planets around stars like our sun,” said Crossfield, a Sagan Fellow at the University of Arizona’s Lunar and Planetary Laboratory.
Both Kepler and its K2 mission discover new planets by measuring the subtle dip in a star’s brightness caused by a planet passing in front of its star. In its initial mission, Kepler surveyed just one patch of sky in the northern hemisphere, measuring the frequency of planets whose size and temperature might be similar to Earth orbiting stars similar to our sun. In the spacecraft’s extended mission in 2013, it lost its ability to precisely stare at its original target area, but a brilliant fix created a second life for the telescope that is proving scientifically fruitful.
After the fix, Kepler started its K2 mission, which has provided an ecliptic field of view with greater opportunities for Earth-based observatories in both the northern and southern hemispheres. Additionally, the K2 mission is entirely community-driven with all targets proposed by the scientific community.
Because it covers more of the sky, the K2 mission is capable of observing a larger fraction of cooler, smaller, red-dwarf type stars, and because such stars are much more common in the Milky Way than sun-like stars, nearby stars will predominantly be red dwarfs.
“K2 casts a wide net for planets,” said Ian Crossfield of the University of Arizona and the lead author of the team’s paper. “The mission has been spectacularly successful at finding planets, particularly planets orbiting stars called red dwarfs that are cooler than the Sun.”
To validate candidate planets identified by K2, the researchers obtained high-resolution images of the planet-hosting stars as well as high-resolution optical spectroscopy data. By dispersing the starlight as through a prism, the spectrographs allowed the researchers to infer the physical properties of a star — such as mass, radius and temperature — from which the properties of any planets orbiting it can be inferred.
With the number of known planets now in the thousands, these hundred new planets are valuable because they orbit relatively nearby and bright stars that are easier to study. The team is already making more detailed measurements of the planets using Keck Observatory, the Hubble Space Telescope, and the Spitzer Space Telescope. These planets are also possible future targets for the Thirty Meter Telescope (TMT) and NASA’s James Webb Space Telescope (JWST).
“This bountiful list of validated exoplanets from the K2 mission highlights the fact that the targeted examination of bright stars and nearby stars along the ecliptic is providing many interesting new planets,” said Steve Howell, project scientist for Kepler and K2 at NASA’s Ames Research Center in Moffett Field, California. “This allows the astronomical community ease of follow-up and characterization, and picks out a few gems for first study by the James Webb Space Telescope, which could perhaps provide information about their atmospheres.”
This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute.
NASA Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA’s Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.