Astronomers using the Gemini Planet Imager have discovered a young Jupiter-like planet orbiting a nearby star known as 51 Eridani.

The newly-discovered planet, named 51 Eridani b (51 Eri b), is located approximately 97 light-years from Earth in the constellation Eridanus. It is only 20 million years old, a mere infant by astronomy standards.

The planet orbits its host star, also known as c Eridani or HD 29391, at a distance of about 13 AU (astronomical units) – equivalent to being between Saturn and Uranus in our Solar System.

It is roughly twice the mass of Jupiter. Until now, the extrasolar gas giants that have been directly detected have been much larger – 5 to 13 times Jupiter’s mass.

51 Eridani b is the first exoplanet detected by the Gemini Planet Imager (GPI), which was designed to discover and analyze faint, young planets orbiting bright, nearby stars.

“This is exactly the kind of planet we envisioned discovering when we designed GPI,” said Prof James Graham from the University of California, Berkeley, a co-author of the paper published online in the journal Science.

“To detect planets, NASA’s Kepler space telescope sees their shadow. GPI instead sees their glow, which we refer to as direct imaging,” said study lead author Prof Bruce Macintosh of the Stanford University’s Kavli Institute.

“The vast majority of solar systems that have been discovered are very different from our own, with massive planets close to their stars,” added co-author Prof James Larkin from the University of California – Los Angeles.

“Previous search methods couldn’t find systems like our own, with small, rocky worlds close to their star and large, gas giants at large distances like Jupiter and Saturn.”

GPI’s highly advanced spectrometer revealed that 51 Eridani b has the strongest concentration of methane ever detected on a planet outside our Solar System – as well as the presence of water – which indicates that it’s similar to planets in the Solar System.

“Many of the exoplanets astronomers have imaged before have atmospheres that look like very cool stars. This one looks like a planet,” Prof Macintosh said.

The astronomers also reported that 51 Eridani b has a temperature of 800 degrees Fahrenheit (427 degrees Celsius), hot enough to melt lead, but still rather cold compared with other gas giants, which reach temperatures above 1,000 degrees Fahrenheit (528 degrees Celsius).

The discovery is part of the team’s effort to find and characterize new exoplanets called the GPI Exoplanet Survey.

The survey expects to explore over 600 stars that could host planetary systems. The targets were selected because of their youth and relatively close proximity to the Solar System – within about 300 light-years. So far the astronomers have looked at almost 100 stars.

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B. Macintosh et al. Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager. Science, published online August 13, 2015; doi: 10.1126/science.aac5891