The star HR 8799, about 1.5 times the size of the sun and about 5 times brighter, lies 130 light-years from Earth. Each of the star’s four known planets is larger than any planet in our solar system. The star formed only 30 million years ago and is a variable star (its luminosity changes over a period of about half a day). By studying light reflected from planet HR 8799c, astronomers have found water and carbon monoxide in its atmosphere.
Unlike most exoplanet discoveries, which are inferred from analysis of data, the planets of the HR 8799 system are directly visible from Earth. The planets were discovered in 2008 using the Keck and Gemini telescopes in Hawaii.
Planet HR 8799e, the innermost of the system, is about 9 times the mass of Jupiter. It orbits 14.5 times farther from its star than the Earth is from the sun. HR 8799e takes 45 Earth years to orbit the star.
Planet HR 8799d is about 10 times the mass of Jupiter. It orbits 24 times farther from its star than the Earth is from the sun. HR 8799d takes 100 Earth years to orbit the star.
Planet HR 8799c is also about 10 times the mass of Jupiter. It orbits 38 times farther from its star than the Earth is from the sun. HR 8799c takes 190 Earth years to orbit the star.
The outermost planet, HR 8799b, is about 7 times the mass of Jupiter. It orbits 68 times farther from its star than the Earth is from the sun. HR 8799b takes 460 Earth years to orbit the star.
The HR 8799 system also includes two dust disks. A disk of warm dust orbits within the orbit of HR 8799e. Another belt of cold dust orbits farther from the star than the outermost known planet, HR 8799b.
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