Astronomers discovered GJ 251 c, a rocky planet four times Earth’s mass orbiting in its star’s habitable zone.
Astronomers find GJ 251 c, a rocky super-Earth in its star’s habitable zone
Photo Credit: Guðmundur Stefánssonn/Penn State
An international team including Penn State astronomers has discovered a new ‘super-Earth' exoplanet orbiting the nearby star GJ 251. It has a mass approximately four times that of planet Earth, and it is probably rocky, named GJ 251 c. It rotates within the habitable (Goldilocks) zone of their star – the range over which liquid water might exist. This is one of the most promising possible discoveries so far in the quest to determine alien life.
According to the study, GJ 251 c is roughly four times Earth's mass, putting it in the class known as a super-Earth – a planet larger than Earth but smaller than ice giants like Neptune. Astronomers detected it via the radial-velocity (or “wobble”) method. Tiny Doppler shifts in the star's light occur as a planet tugs on the star. By combining 20 years of observations, the team saw a consistent 54-day wobble in GJ 251's light. Crucial to this discovery was the Habitable Zone Planet Finder (HPF) – a high-precision infrared spectrograph on the Hobby-Eberly Telescope – which split the star's light to reveal the planet's gravitational pull.
Because GJ 251 c lies in the habitable zone, it could have the right conditions for liquid water on its surface. Studying its atmosphere will require more powerful technology. Future 30-meter-class telescopes are expected to directly image nearby rocky planets and probe their atmospheres. Penn State researchers say GJ 251 c is “one of the best candidates” for detecting an atmospheric signature of life in the coming decade. This discovery shows how ever-better instruments and methods (from space transit surveys to precision wobble measurements) are bringing more Earth-like worlds within reach.
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