The majority of exo-planets discovered are called “Super Jupiters.” They’re the most discovered because their great size contributes to the slight tug, or wobble, of the star they orbit–much like an Olympic athlete when competing in the hammer throw. And in this orbit, they’ll annually pass in front of their star, dimming the starlight output from our relative view, alerting us to its presence–like a bug flying in front of a lightbulb. Unlike most “Super-Jupiters,” which have the characteristics of very cool stars, 51 Eridani b is much more like a gas giant planet. It orbits its star about 13 times the diameter of Earth’s orbit around the Sun. The 51 Eridani system lies about 100 light years away.
Discovered in December 2014 using the newly installed Gemini Planet Imager (GPI) on the Gemini South telescope in Chile, 51 Eridani b may soon be confirmed as the smallest directly-imaged exoplanet to date. Bruce Macintosh (Stanford University) and a team of over 80 collaborators report in the journal Science of a planet, likely having only twice the mass of Jupiter, and the strongest spectral signature of methane every detected in the atmosphere of an exoplanet. The planet, a companion to the star 51 Eridani, is also the lowest-mass self-luminous planet ever directly imaged.
Macintosh and his team estimate that 51 Eridani b is twice as massive as Jupiter, and 2.5 times farther from its star. Unlike our familiar gas giant, however, which is about 4.5 billion years old and a chilly -145 degrees Celsius at its cloud tops, 51 Eridani b is much younger and hotter—no older than 25 million years, with methane-laced clouds heated to nearly 400 degrees C.
51 Eridani b is glowing in the infrared like a planet-sized light bulb, which is how the GPI team managed to glimpse it from nearly 100 light-years away.