Nearby Brown Dwarf System May Harbor Closest Exoplanet to Earth

by Shannon Hall on January 16, 2014

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WISE J104915.57-531906 as seen in NASA’s All-WISE survey (centered) and resolved to show its binary nature by the Gemini Observatory (inset). (Credit: NASA/JPL/Gemini Observatory/AURA/NSF). Read more: http://www.universetoday.com/100682/wise-nabs-the-closest-brown-dwarfs-yet-discovered/#ixzz2qW1lletG

WISE J104915.57-531906 as seen in NASA’s All-WISE survey. It was later resolved by the Gemini Observatory to show its binary nature. The possible exoplanet has not yet been directly imaged. Credit: NASA/JPL/Gemini Observatory/AURA/NSF

In 2012 astronomers announced the discovery of an Earth-like planet circling our nearest neighbor, Alpha Centauri B, a mere 4.3 light-years away. But with such a discovery comes heated debate. A second group of astronomers was unable to confirm the exoplanet’s presence, keeping the argument unresolved to date.

But not to worry. One need only look 2.3 light-years further to see tantalizing — although yet unconfirmed — evidence of an exoplanet circling a pair of brown dwarfs: objects that aren’t massive enough to kick-off nuclear fusion in their cores. There just may be an exoplanet in the third closest system to our Sun.

Astronomers only discovered the system last year when the brown dwarfs were spotted in data from NASA’s Wide-field Infrared Explorer (WISE). Check out a past Universe Today article on the discovery here. They escaped detection for so long because they are located in the galactic plane, an area densely populated by stars, which are far brighter than the brown dwarfs.

Henri Boffin at the European Southern Observatory led a team of astronomers on a mission to learn more about these newly found dim neighbors.  The group used ESO’s Very Large Telescope (VLT) at Paranal in Chile to perform astrometry, a technique used to measure the position of the objects precisely. This crucial data would allow them to make a better estimate of the distance to the objects as well as their orbital period.

Boffin’s team was first able to constrain their masses, finding that one brown dwarf weighs in at 30 times the mass of Jupiter and the other weighs in at 50 times the mass of Jupiter. These light-weight objects orbit each other slowly, taking about 20 years.

But their orbits didn’t map out perfectly — there were slight disturbances, suggesting that something was tugging on these two brown dwarfs. The likely culprit? An exoplanet — at three times the weight of Jupiter — orbiting one or even both of the objects.

“The fact that we potentially found a planetary-mass companion around such a very nearby and binary system was a surprise,” Boffin told Universe Today.

The next step will be to monitor the system closely in order to verify the existence of a planetary-mass companion. With a full year’s worth of data it will be relatively straightforward to remove the signal caused by the exoplanet.

So far only eight exoplanets have been discovered around brown dwarfs. If confirmed, this planet will be the first to be discovered using astrometry.

“Once the companion is confirmed, this will be an ideal target to image using the upcoming SPHERE instrument on the VLT,” Boffin said. This instrument will allow astronomers to directly image planets close to their host star — a difficult technique worth the challenge as it reveals a wealth of information about the planet.

Once confirmed, this planet will stand as the closest exoplanet to the Sun, until the debate regarding Alpha Centauri Bb is resolved.

The paper has been accepted for publication as an Astronomy & Astrophysics Letter and is available for download here. For more information on Alpha Centauri Bb please read a paper available here and published in the Astrophysical Journal.

About 

Shannon Hall is an aspiring science journalist and is an editorial intern at Sky & Telescope magazine. She holds two bachelor's degrees from Whitman College in astrophysics and philosophy, and recently received her master's degree in astrophysics from the University of Wyoming.

Guest January 16, 2014 at 12:47 PM

Thanks. Nice article. However Luhman A&B is at 6.6 light-year from us, and not 2.3 lyr as you mentioned in the article. see the abstract of Luhman (2013) http://adsabs.harvard.edu/abs/2013ApJ…767L…1L

Dan Balkwill January 16, 2014 at 1:05 PM

It says 2.3 light years FURTHER AWAY than Alpha Centauri B, not 2.3 ly from here.

Jesse Federico January 16, 2014 at 1:15 PM

She was inferring 6.6 to begin with. She said we only need to look 2.3 light years further than 4.3. Which is 6.6 like you said. She wasn’t saying it was literally 2.3 light years away from earth.

Franck Marchis January 16, 2014 at 12:49 PM

Cool article. Please ignore my previously posted comments. I read this before having my coffee :-)

InTheory January 16, 2014 at 8:18 PM

Packing my bags! :-)

Jesse Federico January 17, 2014 at 10:34 PM

To go live on a gas giant?

InTheory January 17, 2014 at 10:52 PM

No, just for a neighborly visit. Think of it as leaf peeping on a grand scale.

I wonder how easy it is to spot a Sol type solar system, as most, if not all exo-systems are not exactly “Sol standard”. Are we just spotting the “freaks” because they’re easier to spot or are there Sol type candidates being studied or is the technology not there yet?

Jesse Federico January 17, 2014 at 11:15 PM

Well binary (or more) systems are easy to spot because they are two or more stars orbiting each other and emit heaps of light, but a brown dwarf system would be hard to spot because we can see barely any of their light from here, they don’t emit much. A sol system (Yellow dwarf) would be easier to spot than a brown dwarf system. The reason there hasn’t been any new discoveries of Sol like systems within 10 light years of us is because they are easy (easier?) to see and most probably have all been detected already. If there’s tech to spot brown dwarfs and red dwarfs then we can definitely spot yellow dwarfs (sol type). I believe -and correct me if I am wrong- that most exoplanets have been found around orange and yellow main sequence stars.

InTheory January 18, 2014 at 7:45 PM

Actually what I was wondering was what if our system was observed from 10-20 ly away, what would we detect? Would the rocky inner planets produce perturbations large enough or dim the primary’s light enough to be detected? Would the gas giants be detectable since they’re not insanely close to the primary and zipping around in orbits that take days instead of years?

Are we at the point where we could detect an earth-like planet orbiting 1 AU from a Sol-like star?

tecton47 January 17, 2014 at 1:05 PM

Perhaps one day soon, our space-based telescope technology will have advanced enough to start imaging exoplanets directly. Imagine that first, clear image of a planetary sphere with hints of its surface detail, or at least seeing the cloud tops. What an incredible day that will be!

marcosanthonytoledo January 17, 2014 at 1:23 PM

Could the third object be a brown dwarf it self since it’s bigger than Jupiter.

Jesse Federico January 17, 2014 at 10:32 PM

A triple star system perhaps, unless the tug isn’t strong enough to be a another brown dwarf and they have already ruled that out?

Jesse Federico January 18, 2014 at 8:25 PM

I’m not exactly sure but I do know that Kepler-78b which is almost the same size and density of earth was discovered around a slightly smaller star than the sun around 400 light years away although it rotates it’s parent star very quickly (Which means it’s very close) and is a very hot planet. I’m almost sure that 1 AU is probably too far for detection of earth sized planets at the moment (Although it’s not impossible), a lot of the detected exoplanets are very hot and close to their parent star but don’t worry, technology gets better and better every year, I’m sure we’ll be able to find them soon enough.

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