Imaging the planet-sized companion of a nearby star

Oct 15, 2010
A processed infrared image of the star GJ 758 and its planet/brown-dwarf companion (circled). The image was taken by the Clio instrument on the MMT Observatory. Credit: MMTO and T. Currie, et al.

(PhysOrg.com) -- Of the nearly 500 extra-solar planets that have been confirmed to date, only about a dozen have actually been seen in images. Because planets are so much fainter than their host stars, special techniques are needed to obtain such images, and even these work only when circumstances are optimum, for example, when the stellar system is viewed face-on and the planet is far enough away from the star.

Nearly all planetary detections use more common methods that monitor stellar wobble or stellar brightness variations (due to transiting or lensing). Besides being visually dramatic, direct imaging has the advantage of readily determining a planet's distance from the star, and sampling its light directly. If the planet is a giant (as large or larger than Jupiter), then it may have an internal heat source as well as a reflecting atmosphere, in which case it can stand out more distinctly from its stellar host at . Astronomers trying to improve the statistics of imaged planets are on the lookout for nearby stellar systems which might permit discovery or the direct detection of an extrasolar planet.

The MMT Observatory has a relatively new , called Clio, that can take advantage of the superb angular resolution possible there. Daniel Fabrycky and Ruth Murray-Clay, along with four colleagues, used Clio to image the nearby star GJ 758 (located only about 50 light-years away from earth) and its previously detected companion. Their infrared images not only showed the planet, but allowed them to measure its flux well enough to estimate its temperature and mass, the latter depending on its age and on models of planet evolution.

The scientists report that the object orbiting GJ 758 has an atmospheric temperature of about 290 degrees Centigrade or about 560 kelvin. If the planet is as young as about one billion years, it has a mass of between 10 and 20 Jupiter-masses; if it is as old as 8.7 billion years, then its mass is more likely twice as large. In either case the mass result is a particularly important conclusion for three reasons. First, the companion might not be a "planet" at all. It appears large enough to be a small star, a so-called "brown dwarf" - not big enough to burn hydrogen (as occurs in a star's nuclear furnace), but able to burn deuterium (deuterium, a hydrogen-like atom with one neutron in its nucleus along with one proton, fuses into helium at lower temperatures than does hydrogen). If the companion is a brown-dwarf, then it would be an exception to the postulated "brown-dwarf desert" theory in which stellar companions can be or other but (for unknown reasons) not easily brown dwarfs.

The other two important conclusions are equally provocative. In the context of this , its large size seems to exclude (or at least make less likely) those theories of planet/companion formation in which mass is steadily accreted by the growing planet, the alternative being that it grows as the result of sticking collisions between smaller bodies. Moreover, if the companion really is a small star, then GJ 758 is actually a binary star and not a planetary system - and one of the smallest known binaries at that.

Explore further: Quest for extraterrestrial life not over, experts say

Related Stories

The star, the dwarf and the planet

Oct 19, 2006

Astronomers have detected a new faint companion to the star HD 3651, already known to host a planet. This companion, a brown dwarf, is the faintest known companion of an exoplanet host star imaged directly ...

Team using Subaru Telescope makes major discovery

Dec 03, 2009

An international team of scientists that includes an astronomer from Princeton University has made the first direct observation of a planet-like object orbiting a star similar to the sun.

Six new planets discovered

Jun 14, 2010

(PhysOrg.com) -- An international team, including Oxford University scientists, has discovered six diverse new planets, from 'shrunken-Saturns' to 'bloated hot Jupiters', as well a rare brown dwarf with 60 ...

A sub-stellar Jonah: Brown dwarf survives being swallowed

Aug 02, 2006

Using ESO's Very Large Telescope, astronomers have discovered a rather unusual system, in which two planet-size stars, of different colours, orbit each other. One is a rather hot white dwarf, weighing a little bit less than ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Adam
not rated yet Oct 16, 2010
Excellent news, but the musings on planet vs brown dwarf is kind of pointless. The distinction depends on the favoured theory of planet formation - core accretion vs gravitational instability - both of which have merits. If giant planets form just like brown dwarfs and stars via gravitational instability then there is no reasonable distinction. A "brown dwarf" burns deuterium for ~50 million years and after that it is slowly contracting as its heat trickles away, much like a cooling gas giant. A Main Sequence star however undergoes significant structural changes due to the proton-burning process and is quite distinctive. Brown-dwarfs are more like planets and less like stars, but it's an argument that serves little purpose anyway. Just try not to muddy the waters so much.
genastropsychicallst
1 / 5 (2) Oct 16, 2010
... (pre)image (pro)pion (re)Ceres (dis)core (pri)geddon ...

More news stories

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...