'Young' Jupiter-like exoplanet identified!

Astronomers have discovered a planet very similar to Jupiter but within a young system.

The new planet, called 51 Eridani b, is the first exoplanet discovered by the Gemini Planet Imager (GPI), is a million times fainter than its star and shows the strongest methane signature ever detected on an alien planet, which could serve as a decoder ring for understanding how planets formed around our sun.

GPI was designed specifically for discovering and analysing faint, young planets orbiting bright stars by direct imaging. NASA's Kepler mission indirectly discovered planets by the loss of starlight when a planet blocked a star.

Bruce Macintosh, professor at Stanford University who led the construction of GPI and now leads the survey said that to detect planets, "Kepler sees their shadow; GPI sees their glow."

By targeting young stars, it was possible to catch planets while they were hotter and brighter and they could study how planets evolve over time, said ASU astrophysicist Jennifer Patience.

As far as the cosmic clock is concerned, 51 Eridani (51 Eri) is young - only 20 million years old - and this is exactly what made the direct detection of the planet possible. When planets coalesce, material falling into the planet releases energy and heats it up. Over the next hundred million years they radiate that energy away, mostly as infrared light.

It is also the coldest - 800 degrees Fahrenheit, whereas others are around 1,200 F - and features the strongest atmospheric methane signal on record. Previous Jupiter-like imaged planets 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.

The results are published in the current issue of Science.