Max Planck Institute for Astronomy/National Astronomical Observatory of Japan
The direct image of GJ 758 B (circled as B) was taken with the Subaru Telescope's HiCIAO instrument in the near infrared. An unconfirmed companion planet or planet-like object, C, can be viewed above B.
updated 12/3/2009 6:01:10 PM ET 2009-12-03T23:01:10

Astronomers say they have taken the first direct image of a planet-like object orbiting a star much like our own sun.

A similar breakthrough was announced last year, when astronomers unveiled direct images of a single-planet and multiple-planet system. However, the host stars of such systems are stellar giants that are much more massive than the sun.

The images of this newly identified object were taken in May and August during early test runs of a new planet-hunting instrument on the Hawaii-based Subaru Telescope.

The object called GJ 758 B orbits a parent star that is comparable in mass and temperature to our own sun, said study team member Michael McElwain of Princeton University. The star lies 300 trillion miles, or about 50 light-years, from Earth.

At least 10 times Jupiter's mass
Scientists aren't sure if the object is a large planet or a brown dwarf, a cosmic misfit also known as a failed star. They estimate its mass to be 10 to 40 times that of Jupiter. Objects above 13 Jupiters (and below the mass needed to ignite nuclear reactions in stars) are considered to be brown dwarfs.

Either way, McElwain says the image is exciting.

"Brown dwarf companions to solar-type stars are extremely rare," he told "It's exciting to find something that is so cool and so low mass with a separation similar to our solar system around a nearby star."

The planet-like object is currently at least 29 times as far from its star as the Earth is from the sun, or about the distance between the sun and Neptune.

'How little we truly know'
The fact that such a large planet-like object might be orbiting at this location defies traditional thinking on how planets form, McElwain said. Astronomers think most large planets form either closer to or farther away from stars, but not in the location where GJ 758 B is now.

"This challenging but beautiful detection of a very low mass companion to a sun-like star reminds us again how little we truly know about the census of gas giant planets and brown dwarfs around nearby stars," said Alan Boss, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was not involved in the research.

"Observations like this will enable theorists to begin to make sense of how this hitherto unseen population of bodies was able to form and evolve."

The instrument attached to the Subaru Telescope, called the High Contrast Coronagraphic Imager with Adaptive Optics, is part of a new generation of instruments specially made to detect faint objects near a bright star by masking its far more intense light.

Possible second companion
The scientists say telescope images have revealed a possible second companion to the star, which they are calling GJ 758 C, though more observations are needed to confirm whether it is actually nearby or just looks that way.

The study team included scientists from Princeton, the University of Hawaii, the University of Toronto, the Max Planck Institute for Astronomy in Heidelberg, Germany, and the National Astronomical Observatory of Japan in Tokyo.

The results were released online Nov. 18 in an electronic version of the Astrophysical Journal Letters.

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