New Planet Discovered In Trinary Star System

by Jon Voisey on July 13, 2011

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A planet 6 times the mass of Earth orbits around the star Gliese 667 C, another member of a triple star system. Credit: ESO

Until recently, astronomers were highly skeptical of whether or not planets should be possible in multiple star systems. It was expected that the constantly varying gravitational force would eventually tug the planet out of orbit. But despite doubts, astronomers have found several planets in just such star systems. Recently, astronomers announced another, this time in the trinary star HD 132563.

The detection of the new planet came as part of a larger study on the trinary star system spanning 10 years. The two main stars that comprise the system are both similar to the Sun in mass, although somewhat less prevalent in metals, and orbit each other at a distance of around 400 AU. The main star, HD 132563A is also itself, a binary. This fact was not previously recognized and also reported by the team, led by Silvano Desidera from the Astronomical Observatory in Padova, Italy.

The newly discovered planet orbits the secondary star in the system, HD 132563B. As with the binary component of the main star, the new planet was discovered spectroscopically. The planet is at least 1.3 times the mass of Jupiter, with an average distance from its parent star of 2.6 AU, and an moderately high eccentricity of 0.22.

The team also attempted to image the planet directly using adaptive optics from the Italian Telescopio Nazionale Galileo. While there was a hint in the glare of the star that may have been the planet in question, the team could not rule out that the detection was not an instrumental effect.

With the discovery of this new planet, the total number of discovered planets in multiple star systems lies at eight. while this is rather small numbers from which to draw firm conclusions, it appears that planets can be commonly found orbiting the more remote members of trinary star systems for good periods of time. On the shorter end, the stellar system is anticipated to be 1-3 billion years in aged, based on the amount of stellar activity and amount of lithium present in the star’s atmosphere (which decreases with time). However, fitting of the mass and luminosity onto isochrones suggest the stars may be as much as 5 billion years in age. In either situation, the planetary system is dynamically stable.

Also based on these eight systems, the team also suggests that planets existing around such far removed members of a multiple star system may be as common as planets around wide binaries, or even single stars.


Jon is a science educator currently living in Missouri. He is a high school teacher and does outreach with the St. Louis Astronomical society as well as presenting talks on science and related topics at regional conventions. He graduated from the University of Kansas with his BS in Astronomy in 2008 and has maintained the Angry Astronomer blog since 2006.
For more of his work, you can find his website here.

Anonymous July 13, 2011 at 8:44 PM

Provided that anything could live in such a system, the mind boggles at what it must see in the daytime sky!

Anonymous July 13, 2011 at 11:02 PM

At 400 AU the other 2 stars in that system wouldn’t look much brighter than Sirius does in our sky. Brighter, but they’d still look like point sources of light.

Anonymous July 13, 2011 at 9:42 PM

It would be interesting to know how much AU separtation there is between the primary star and it’s closest companion. I assume the secondary orbits a point between the primary and its binary. It would also be interesting to know what type of star the binary is. At 2.6 AU from the sun-like secondary I assume the planet and it’s probable moons are outside of the habitable zone, but maybe not depending on what luminosity the G type star is. More detail in the story would be appreciated.

William Sparrow July 14, 2011 at 12:39 AM

More information can be obtained by accessing the article(s) at I think Jon was offering us an overview.

Torbjörn Larsson July 15, 2011 at 3:59 PM

Or accessing directly by the proffered link.

William Sparrow July 14, 2011 at 12:39 AM

More information can be obtained by accessing the article(s) at I think Jon was offering us an overview.

Anonymous July 14, 2011 at 12:37 AM

This gives me additional hope for places like Alpha Centauri…

Anonymous July 14, 2011 at 7:17 AM

maby but it will be better if we found a rocky planet around a very close binarie star system. Have they already found a rocky planet around a close binarie star ?

Federico Manzini July 14, 2011 at 12:07 PM

My compliments Silvano!

Anonymous July 14, 2011 at 4:16 PM

that is kinda crazy when you think about it. Wow.

Gustavo Herrera-Marcano July 15, 2011 at 12:00 AM

With the gravitational pull of a triple star, the orbit of this planet may be highly irregular

Torbjörn Larsson July 15, 2011 at 3:57 PM

From the paper:

“Therefore HD 132563B turns out to host a planet with a projected mass msin i = 1.49 MJ at 2.6 AU with a moderately eccentric orbit (e = 0.22).”

IIRC some of these finds have quite low e planets, but that is not a specific memory so someone should check on that.

Alex Hall July 15, 2011 at 9:09 AM

This is just mind-blowing. Imagine being on a planet that’s orbiting a star, that has a binary star in the same system! The views would be incredible!

Torbjörn Larsson July 15, 2011 at 4:02 PM

Actually the very first comment and its reply treated that. It would be easier to deduce stars as suns, but the views would apparently be humdrum.

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