Spaceflight Insider

More than 100 exoplanets found by K2

Artist's concept of NASA's Kepler Space Telescope on its K2 mission

This artist’s concept shows NASA’s Kepler Space Telescope on its K2 mission. In July 2016, an international team of astronomers announced they had discovered more than 100 new planets using this telescope. Image Credit: NASA/JPL-Caltech

Astronomers utilizing NASA’s Kepler spacecraft on its K2 mission have announced the discovery of more than 100 new exoplanets orbiting small, red dwarf stars.

K2 is the title of the revised Kepler mission, begun after engineers reconfigured the telescope, which lost its ability to precisely observe a small target area because of malfunctioning reaction wheels.

Both the original and the revamped Kepler missions use the transit method, which involves measuring the dimming of a star’s brightness as a planet passes in front of that star.

In its initial mission, Kepler focused on one narrow region of the northern hemisphere sky to search for Earth-like planets orbiting Sun-like stars.

Earth-like planets are defined as those with sizes, temperatures, and compositions similar to those of our planet.

The telescope’s repair changed its focus, giving it a new ability to observe larger regions in the ecliptic plane in both the northern and southern hemispheres.

With the capability to cover a larger portion of the sky, Kepler scientists decided to target cool, red dwarf stars, which are smaller and less massive than the Sun and also more prevalent in the Milky Way, according to University of Arizona Lunar and Planetary Laboratory Sagan Fellow Ian Crossfield.

“An analogy would be to say that Kepler performed a demographic study while the K2 mission focuses on the bright and nearby stars with different types of planets,” he explained. “The K2 mission allows us to increase the number of small, red stars by a factor of 20, significantly increasing the number of astronomical ‘movie stars’ that make the best systems for further study.”

Of the total 197 planet candidates discovered in the telescope’s latest observation, 104 have been confirmed to be planets.

K2 explained graphic

Engineers developed an innovative way to stabilize and control the spacecraft. This technique of using the Sun as the “third wheel” has Kepler searching for planets again, but also making discoveries on young stars to supernovae. Image Credit: NASA Ames / W Stenzel

Confirmation is done via ground-based telescopes, including the W.M. Keck Observatory and North Gemini telescope in Hawaii, the Automated Planet Finder of the University of California Observatories, and the Large Binocular Telescope operated by the University of Arizona.

Scientists obtain high-resolution images and optical spectroscopy of stars suspected to host planets. By scattering the starlight as through a prism, they can gather spectroscopic data from which they can infer a star’s mass, radius, and temperature. Once they know the star’s properties, they can infer those of orbiting planets.

One notable system found during the latest round of discoveries has four planets orbiting the M dwarf star K2-72, in the constellation Aquarius, 181 light-years away.

All four planets have diameters between 20 and 50 percent that of Earth and could be rocky worlds. The star they orbit is less than half the diameter of the Sun and, therefore, much less bright.

The planets are in close, tight orbits around the star, with orbital periods between five-and-a-half to 24 Earth days. Two of the four are likely subject to irradiation levels from the star comparable to those Earth receives from the Sun.

In spite of the fact that all four planets orbit closer to their star than Mercury does to the Sun, they could potentially be habitable, Crossfield states.

He is the lead author of a paper about the findings published in the Astrophysical Journal Supplement Series online.

Steve Howell, of NASA’s Ames Research Center in California and K2 project manager, said that the abundance of planets recently discovered speaks to the success of targeting bright, nearby stars along the ecliptic.

“These targets allow the astronomical community ease of follow-up and characterization, providing a few gems for the first study by the James Webb Space Telescope, which could perhaps tell us about the planets’ atmospheres.”

The James Webb Space Telescope is scheduled for launch in October 2018.


Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

⚠ Commenting Rules

Post Comment

Your email address will not be published. Required fields are marked *