A telescopic instrument in Chile specifically designed to locate distant gas-shrouded planets like Jupiter has discovered and photographed its first such find, astronomers say.

The exoplanet 51 Eridani b, discovered by the Gemini Planet Imager instrument, looks like a young Jupiter and sits in a solar system so much like ours, it may reveal insights into how our cosmic home system formed, they say.

The exoplanet has the greatest methane signature ever seen on a planet outside our solar system, which may yield further clues about how it formed, the researchers report in the journal Science.

It orbits in a young planetary system just 20 million years old as compared with our own solar system, which has existed for around 4.5 billion years.

That means 51 Eridani b could be an example of what Jupiter looked like during the earliest days of our system and is exactly what astronomers hoped the Gemini Planet Imager would reveal, researchers say.

"This is exactly the kind of planet we envisioned discovering when we designed GPI," says James Graham, an astronomy professor at the University of California, Berkeley and a GPI project scientist. "We wanted to find planets when they're young so we can figure out the formation process."

The exoplanet is around twice Jupiter's mass, the scientists estimate, orbiting in its solar system at about the same distance as Saturn orbits our sun.

In addition to methane, spectrographic analysis of the planet shows water, both also thought to exist deep in the atmosphere of Jupiter.

"Judging by its low luminosity, low temperature and strong methane signature, this is the most Jupiter-like exoplanet ever directly imaged," Graham says.

If it formed in the same way Jupiter did, then the rest of its home solar system could be very much like ours, says GPI project leader Bruce Macintosh, a physics professor at Stanford University.

"51 Eri b is the first [detected exoplanet] that's cold enough and close enough to the star that it could have indeed formed right where it is the 'old-fashioned way,' " he says.

There's more, the researchers say; the distant solar system contains a pair of dust belts similar to ones in our solar system that are the left-over remnants of planet formation.

Such an "architectural similarity" to our system suggests it may look something like what our home system was like in its infancy, they explain, and help us toward a beginning understanding of planetary formation.

"Our knowledge today of how planets form reminds me of our knowledge 50-60 years ago of how stars form," Graham says.