Introducing 51 Eridani b, the young cousin of our Jupiter (Image Credit: Danielle Futselaar and Franck Marchis, SETI Institute)

Astronomers just announced discovery of a relatively young planet—one that shares characteristics with Jupiter. And that's exciting, because in spite of the fact that it is some 100 light-years away, scientists think this exoplanet may hold the key to understanding how our own solar system formed.

Described in the journal Science, the new planet—dubbed 51 Eridani b—was born just 20 million years ago (where as Earth is 4.5 billion years old). Because of it's relatively young age, it's still quite hot, and it—like other coalescing planetesimals—still emits heat and infrared light,  which aided astronomers in detecting the planet.

Taking the Direct Approach:

Perched atop a ridged in the Chilean Andes foothills, the Gemini Planet Imager (GPI) does things a little differently. Unlike Kepler, which indirectly detects planets, GPI can view the light from exoplanets directly. Faint, young planets near bright stars are precisely what it seeks. In fact, in the right situations, GPI can visualize planets that are ten million times fainter than their star.

Gemini South and the Chilian Andes (Photo Credit: Gemini Observatory)

"To detect planets, Kepler sees their shadow," reported Bruce Macintosh (Kavli Institute for Particle Astrophysics and Cosmology). "The Gemini Planet Imager instead sees their glow, which we refer to as direct imaging."

Astronomers have lofty goals with this approach. Using GPI, they plan to produce a comprehensive survey of giant exoplanets. In particular, astronomers are hunting for planets that lurk the same distances from their stars as our gas-giants do from the Sun. 51 Eridani b was the first to be identified, and it's orbit is only slightly larger than that of Saturn.

"This is exactly the kind of system we envisioned discovering when we designed GPI," said James Graham, a project scientist for GPI.

The Young Exoplanet Offers Clues:

On that end, astronomers believe Eridani b closely mirrors a young Jupiter (only with twice the mass). Like our gas giants, measurements suggest it has a methane atmosphere: In fact, it has the most methane of any known planet. In addition to also being one of the lowest-mass planets ever found, with temperatures reaching 800°F (423°C), it's also one the coldest planets ever directly imaged.

From the GPI, '51 Eri' is the central star, while 51 Eridani b is 'b'. (Image By J. Rameau (UdeM) and C. Marois (NRC Herzberg)

"51 Eri b is the first one that's cold enough and close enough to the star that it could have indeed formed right where it is the 'old-fashioned way," said Macintosh. "This planet really could have formed the same way Jupiter did—the whole solar system could be a lot like ours."

Termed a "cold start" planet, Jupiter is thought to have started with a solid core, before acquiring a huge amount of gas for its atmosphere.

Previous Jupiter-like planets have really looked more like stars. But, because of the presence of methane, this exoplanet looks more like a planet. Mark Marley (NASA's Ames Research Center), agreed. "Since the atmosphere of 51 Eri b is also methane rich, it signifies that this planet is well on its way to becoming a cousin of our own familiar Jupiter."

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