51 Eridani b is First Exoplanet Discovered with Gemini Planet Imager

Posted on August 14, 2015

Astronomers have discovered a Jupiter-like planet orbiting a star located about 96 light years from Earth. The planet, 51 Eridani b, has the strongest methane signature ever detected on an alien planet. It is also one of the smallest planets to be directly imaged.

51 Eridani b orbits its star a little farther away than Saturn orbits our sun. The light from the planet is very faint but astronomers were able to estimate that it has about twice the mass of Jupiter. It is the faintest and coldest planet ever imaged. The astronomers say the planet is 800 degrees Fahrenheit, which is technically not cold, but is much colder than others directly imaged at around 1,200 degrees Fahrenheit.

The Gemini Planet Imager (GPI) was designed for discovering and analyzing faint, young planets like 51 Eridani b. The GPI is installed on the 26-foot Gemini South Telescope in Chile. Astronomers have examined about 100 stars using the GPI so far.

James Graham, a professor at the University of California, Berkeley and project scientist for GPI, says in the announcement, "This is exactly the kind of planet we envisioned discovering when we designed GPI."

The GMI project is headed by Bruce Macintosh, a Stanford professor of physics and member of the Kavli Institute for Particle Astrophysics and Cosmology. He explains the difference between the GMI and Kepler, which has been used to discover thousands of planets. Macintosh says, "To detect planets, Kepler sees their shadow. The Gemini Planet Imager instead sees their glow, which we refer to as direct imaging."

The image below shows the discovery image of the exoplanet 51 Eridani b taken in the near-infrared light with the Gemini Planet Imager on Dec. 21, 2014. The central star was mostly removed to enable the planet (which is nearly 1 million times fainter) to be detected.

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