Gemini Planet Imager discovers Jupiter-like exoplanet

Astronomers have discovered a Jupiter-like planet within a young system that could help scientists understand how planets formed around our sun.

The new planet, called 51 Eridani b, is the first exoplanet discovered by the Gemini Planet Imager, an adaptive optics instrument installed on the Gemini South Telescope in Chile.

The results are published in the current issue of Science.

One of the best ways to learn how our solar system evolved is to look to younger star systems in the early stages of development. Eridani b is a million times fainter than its star and shows the strongest methane signature ever detected on an alien planet, which should yield additional clues as to how the planet formed.

The Gemini Planet Imager (GPI) was designed specifically for imaging extrasolar planets orbiting nearby stars. In 2011, the GPI began an 890-hour survey campaign from 2014 to 2016 to search and characterise exoplanets around 600 stars.

The adaptive optics (AO) subsystem is the heart of GPI, and allows planets to be imaged directly. It is responsible for making fast visible-light measurements of the wavefront external to GPI and correcting that wavefront using its deformable mirrors.

The adaptive optics sharpen the image of a star, and then block out the starlight. Any remaining incoming light is then analysed, the brightest spots indicating a possible planet.

Compared to other planets, 51 Eridani (51 Eri) is relatively young – only 20 million years old – which is what allowed the planet to be detected. ‘By targeting young stars, we can catch planets while they are hotter and brighter and can study how planets evolve over time,’ said Jennifer Patience, an Arizona State University astrophysicist and part of the GPI Exoplanet Survey Team.

51 Eri b was seen to be orbiting a little farther away from its parent star than Saturn does from the sun. Observations revealed that it is roughly twice the mass of Jupiter.

In addition to being the lowest-mass planet ever imaged, it’s also the coldest, 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, point to a planet that is very much what models suggest Jupiter was like in its infancy, the researchers said.

GPI will also provide key clues as to how solar systems form. Astronomers believe that the gas giants in our solar system formed by building up a large core over a few million years and then pulling in a huge amount of hydrogen and other gases to form an atmosphere.

However, the Jupiter-like exoplanets that have so far been discovered are much hotter than models predicted, hinting that they could have formed much faster as material collapses quickly to make a very hot planet. Therefore, the core-buildup process could explain how rocky planets like the Earth were formed; whereas a fast and hot collapse might only make giant gaseous planets.

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Eyes on the sky: Greg Blackman discovers that building larger ground-based telescopes is pointless without adaptive optics

Further information

The Gemini Planet Imager Exoplanet Survey

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