Washington: A team of astronomers has discovered a Jupiter-like planet within a young system that could serve as a decoder ring for understanding how planets formed around our Sun.

The new planet, called 51 Eridani b, is the first exoplanet discovered by the Gemini Planet Imager, a new instrument operated by an international collaboration headed by Bruce Macintosh, professor of physics at Stanford University.

“To detect planets, NASA’s Kepler sees their shadow. The Gemini Planet Imager instead sees their glow, which we refer to as direct imaging,” said Macintosh, member of the Kavli Institute for Particle Astrophysics and Cosmology.

51 Eridani b is one of the best stars for imaging young planets.

“It is one of the very youngest stars this close to the Sun. 51 Eri was born 20 million years ago, 40 million years after the dinosaurs died out,” added study co-author Eric Nielsen, post-doctoral researcher at Stanford and the SETI Institute.

As far as the cosmic clock is concerned, 20 million years is young, and that is exactly what made the direct detection of the planet possible.

Once the astronomers zeroed in on the star, they blocked its light and spotted light reflecting off 51 Eridani b, orbiting a little farther away from its parent star than Saturn does from the Sun.

The light from the planet is very faint – more than 3 million times fainter than its star – but Gemini can see it clearly.

Observations revealed that it is roughly twice the mass of Jupiter, half or less the mass of the young planets discovered to date.

In addition to being the lowest-mass planet ever imaged, it’s also one of the coldest and features the strongest atmospheric methane signal on record.

Previous Jupiter-like exoplanets have shown only faint traces of methane, far different from the heavy methane atmospheres of the gas giants in our solar system.

All of these characteristics, the researchers say, point to a planet that is very much what models suggest Jupiter was like in its infancy.

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

Of course, it’s not exactly like Jupiter but there are signs it will evolve into a familiar shape.

“In the atmospheres of the cold giant planets of our solar system, carbon is found as methane, unlike most exoplanets, where carbon has mostly been found in the form of carbon monoxide,” explained Mark Marley, astrophysicist at NASA Ames Research Center.

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, he added.

The Gemini imager was designed specifically for discovering and analyzing faint, young planets orbiting bright stars.

While NASA’s Kepler space observatory has discovered thousands of planets, it does so indirectly by detecting a loss of starlight as a planet passes in front of its star. GPI instead searches for light from the planet itself.

Last year, the imager was installed on the eight-metre Gemini South Telescope in Chile, and the team set out to look for planets orbiting young stars, identifying nearly 100 so far.

In addition to expanding the universe of known planets, the imager will provide key clues as to how solar systems form.

“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’,” Macintosh said.

This planet really could have formed the same way Jupiter did – the whole solar system could be a lot like ours, he emphasised.

The results were published in the prestigious journal Science.