Astronomers photograph an exoplanet

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51 Eridani b

Cool image time! Astronomers have used the Gemini Telescope on Mauna Kea to take the clearest image yet of a Jupiter-sized gas giant orbiting another star 96 light years away.

Once the astronomers zeroed in on the star, they blocked its light and spotted 51 Eri 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 one million times fainter than its star – but GPI can see it clearly. Observations revealed that it is roughly twice the mass of Jupiter. Other directly imaged planets are five times the mass of Jupiter or more. In addition to being the lowest-mass planet ever imaged, it’s also the coldest — about 800 degrees Fahrenheit — 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.

The exoplanet is the bright spot near the bottom of the image.



  • D.K. Williams

    How can this planet be 800 degrees F so far away from its Sun?

  • Gas giants the size of Jupiter or larger can be quite warm because of internal heat produced by radioactivity and the compression of mass by gravity. Jupiter for example radiates more energy out than it receives from the Sun. And like the Earth its core is hot, estimated to be around 20,000 Kelvin.

  • mpthompson

    Can anyone explain how the mass of the planet is estimated? I didn’t see an explanation in the article. Is it inferred from the planet’s apparent brightness? Or, are there effects on the parent star that can be measured. Since the planet must have an orbit that is roughly 50 to 100 years in length, such effects must be very, very subtle.

    Also, can the orbital plane be inferred yet, or will that take many years of observation of its orbital motion?

    Finally, no other similar planets look to be visible. For instance, could a Saturn or Neptune class planet be detected with this method?

    So many questions from such a photo. It’s a joy to be experiencing the golden age of planetary discovery…

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