GJ 667C - Habitable candidates in a multi-planet system

Has just gone up on the Exosolar planets encyclopedia

... And gone again ....

Was just short of 6 Earth masses in 7 day orbit

It's still there (or was at least returned). http://www.exoplanet.eu/planet.php?p1=GJ+667C&p2=b

Screw you HD 188753... We have Gliese 667!!

Haha.

While this does seem to be the first confirmed planet orbiting the C-component of a multiple system, it certainly isn't the first planet found in a triple system. 16 Cygni, HD 40979, and HD 65216 are also triple (HD 41004 is if you count HD 41004 Bb as a brown dwarf).

The C component part is really an artifact of the designation systems. If we designate a triple system as (1-2)-3, where stars 1 and 2 form the close binary and 3 is the distant tertiary, the majority of planets in triple systems have been found around component 3, including GJ 667Cb. IIRC the only planet known around one of the stars in the close binary is HD 196885Ab, but this depends on whether the tertiary star BD+10 4351B is actually bound to the system.

The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample

Second planet listed for GJ 667C, a >4 Earth mass planet in a 28.1 day orbit at 0.28 AU. From the paper:

Quote :

This candidate receives about 90% the amount of light received by Earth in our Solar System and we speculate the planet is a habitable candidate (see Delfosse et al., in prep., for a detailed description).

There are also orbital fits for tens of M dwarf-planet systems yet to validate. Impressive! Including the very nearby Luyten's Star.

Data of planet GJ 667C c are wrong period or distance to the star.With this period 28 days planet should be around 0.1-0.12 AU from host star

tommi59 wrote:

Data of planet GJ 667C c are wrong period or distance to the star.With this period 28 days planet should be around 0.1-0.12 AU from host star

Ouch! Good spot, looks like the paper is in error there.

Nevertheless the stellar luminosity of 0.013 times solar given in table 3 fits with the statements about the planet's insolation. Spotted a few other typos lurking around there - the error values given in the period column of table 1 are highly suspect for some of the long-period planets!

A good candidate for habitable planet then

the best we know

Sent an email to one of the authors, got a confirmation that 0.12 AU is indeed the correct figure.

Definitely an interesting system, a multiplanet system in a triple star system. Unfortunately the orbit of GJ 667 AB doesn't look particularly conducive to planet formation (~12 AU semimajor axis, eccentricity 0.58), so probably GJ 667 C is the only one of the three which has planets.

Lazarus wrote:

Sent an email to one of the authors, got a confirmation that 0.12 AU is indeed the correct figure.

Definitely an interesting system, a multiplanet system in a triple star system. Unfortunately the orbit of GJ 633 AB doesn't look particularly conducive to planet formation (~12 AU semimajor axis, eccentricity 0.58), so probably GJ 633 C is the only one of the three which has planets.

667, right?

I think so .In 667ABC system both bigger stars are approaching so close each other that can disable any planet formation.Like i guessed the AU is wrong now is fixed to correct value.Planet 667Cc then is only one super earth no doubts in HZ in this interesting system

Edasich wrote:

667, right?

Yes

I go away for a couple days and all forms of amazing things are announced. Very nice discovery.

EPE has updated the semimajor axis to the 0.1 AU value, however they have the wrong orbital period (21.8 days instead of 28.1)

Using a period of 7.2 d and a semi-major axis of 0.05 AU for the first planet, I'm getting 0.32 M_☉ for the mass of GJ 667 C. For the second planet, a period of 28.1 d and a semi-major axis of 0.12 AU gives me a mass of just 0.29 M_☉. A little off, even if only by 0.03 M_☉, but I'd like to know if I'm missing something here.

Table 3 of the paper gives 0.30 solar masses.
Using this value and the orbital periods of 7.20 days and 28.1 days, I get semimajor axes to 3 significant figures of 0.0489 and 0.121 AU.

In short, the discrepancies you are seeing are due to rounding.

That makes sense, thanks.

Lazarus wrote:

EPE has updated the semimajor axis to the 0.1 AU value, however they have the wrong orbital period (21.8 days instead of 28.1)

It has now been updated.

Space.com: Newfound Alien Planet is Best Candidate Yet to Support Life, Scientists Say.

Update on GJ 667Cc with signs of another planet further out.

Spaceref.com states that there may be multiple additional planet candidates.

Quote :

The researchers found evidence of at least one and possibly two or three additional planets orbiting the star, which is about 22 light-years from Earth

knack.be reports three additional planets. Not sure if that counts the b planet as well.

Der Spiegel reports on the 7.2-day planet, the c planet, a third super-earth, and then a gas giant.

Moderator note:
Because of the accumulating interest in the GJ 667 system, I've split out some posts from the 32 Discoveries from HARPS thread about the discovery of GJ 667 c and merged them into this one to give it some more background information and to consolidate the research developments into one thread. I've also updated the thread title from "GJ 667C b" to reflect our newer understanding of the system.

This one was clearly going to make a news release.

Of all the habitable exoplanet candidates so far, to me this is the most convincing one. As for additional planets, this will certainly be interesting to find out... what planetary system architectures can support habitable planets?

A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone
http://arxiv.org/abs/1202.0446

Quote :

We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported 7.2-day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (Period sim 10 years). The 28-day signal implies a planet candidate with a minimum mass of 4.5 Mearth orbiting well within the canonical definition of the star's liquid water habitable zone, this is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition and interior dynamics. The 75-day signal is less certain, being significantly affected by aliasing interactions among a potential 91-day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal poor compared to the Sun. The presence of a super-Earth in the habitable zone of a metal poor M dwarf in a triple star system, supports the evidence that such worlds should be ubiquitous in the Galaxy.

Ah so this is not a release from the HARPS team, but using publically-available HARPS data.

The paper "The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample" refers to an upcoming publication by Delfosse et al. about this system, will be interesting to see if they draw different conclusions.