GJ 163 - Three planet system with a super-Earth near the HZ

Planetary Habitability Laboratory: A Hot Potential Habitable Exoplanet around Gliese 163

Quote :

A new superterran exoplanet (aka Super-Earth) was found in the stellar habitable zone of the red dwarf star Gliese 163 by the European HARPS team. The planet, Gliese 163c, has a minimum mass of 6.9 Earth masses and takes nearly 26 days to orbit its star. Superterrans are those exoplanets between two and ten Earth masses, which are more likely composed of rock and water. Gliese 163 is a nearby red dwarf star 50 light years away in the Dorado constellation. Another larger planet, Gliese 163b, was also found to orbit the star much closer with a nine days period. An additional third, but unconfirmed planet, might be orbiting the star much farther away.

40% more irradiated around a cooler star, IMHO you don't get to claim a habitable planet with that: the reduced Rayleigh scattering at the longer wavelengths which are the main output of a cooler star results in a lower planetary albedo and contributes to the warming effect.

For a M0 dwarf star at 3700 K, Underwood, Jones and Sleep (2003) give a runaway greenhouse limit at 5% greater insolation than Earth, and a water-loss limit at the same insolation as Earth has, while for the G2 star these limits are at 41% and 10% greater than Earth respectively. Gliese 163 is cooler than this temperature so computing the limits for this star using the quadratic equations would be extrapolation, but it certainly does NOT look like a promising candidate.

Not to mention that at 6.9 M_e, it's almost certainly a mini-Neptune.

I don't yet see the relation between the GJ 163 discovery and the 50 planets announced last year. If no one objects to it, I'll separate this into a new thread when the paper comes out.

I would do that the same sirius with gj 163 c but we need to wait as more data will be available because planets in kepler 11(d,e,f perhaps g) seems to have the lowest density of all within the regime we are most interested

Like gliese 1214 b with density 1.5-1.6 gj 163 c is water world and could be reflective I mean high albedo

Sirius_Alpha wrote:

I'll separate this into a new thread when the paper comes out.

Right... well... still waiting on that paper, and forgot where this was announced on the forum and had to Google search the site to find the reference to GJ 163c. So I'm splitting it out now.

Finally here's the paper. A third planet is found, a Neptune in a 600 day orbit. A fourth and fifth signal await further data to confirm.

The HARPS search for southern extra-solar planets. XXXIV. A planetary system around the nearby M dwarf GJ163, with a super-Earth possibly in the habitable zone
http://arxiv.org/abs/1306.0904

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The meter-per-second precision achieved by today velocimeters enables the search for 1-10 M_Earth planets in the habitable zone of cool stars. This paper reports on the detection of 3 planets orbiting GJ163 (HIP19394), a M3 dwarf monitored by our ESO/HARPS search for planets. We made use of the HARPS spectrograph to collect 150 radial velocities of GJ163 over a period of 8 years. We searched the RV time series for coherent signals and found 5 distinct periodic variabilities. We investigated the stellar activity and casted doubts on the planetary interpretation for 2 signals. Before more data can be acquired we concluded that at least 3 planets are orbiting GJ163. They have orbital periods of P_b=8.632+-0.002, P_c=25.63+-0.03 and P_d=604+-8 days and minimum masses msini = 10.6+-0.6, 6.8+-0.9, and 29+-3 M_Earth, respectively. We hold our interpretations for the 2 additional signals with periods P_(e)=19.4 and P_(f)=108 days. The inner pair presents an orbital period ratio of 2.97, but a dynamical analysis of the system shows that it lays outside the 3:1 mean motion resonance. GJ163c, in particular, is a super-Earth with an equilibrium temperature of T_eq = (302+-10) (1-A)^(1/4) K and may lie in the so called habitable zone for albedo values (A=0.34-0.89) moderately higher than that of Earth (A_Earth=0.2-0.3).

As they note, the five-planet version of the system is unstable, even when the eccentricities of "e" and "f" are set to 0.

Still am not convinced that planet c is a particularly good candidate for habitability.

Like claiming that Venus is habitable...

Does anyone know the size of this star? It is not mentioned in the paper...

Paper mentions Casgrande et al. (2008) as a comparison for the stellar properties.

Here's the data for GJ 163

Angular diameter is given as 0.283 mas, using the parallax of 66.69 mas gives 0.46 solar radii. I'll let you do the calculation of the error. Note this is a computed angular diameter, not a measured one. (See the paper for details.)

Well edasich gj 163 c receives however less energy than venus and being heavier can have much water on the surface I would not rule out possibility planet is habitable.

Lazarus wrote:

0.46 solar radii.

Thanks. I was trying to calculate the transit probability of the two inner planets but i later realized that the probability is low, maybe 3% for planet b and 1% for planet c. Lower than i previously thought.

Up to four planets around the M dwarf GJ 163. Sensitivity of Bayesian planet detection criteria to prior choice
http://arxiv.org/abs/1306.1717

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Exoplanet Doppler surveys are currently the most efficient means to detect low-mass companions to nearby stars. Among these stars, the light M dwarfs provide the highest sensitivity to detect low-mass exoplanet candidates. Evidence is accumulating that a substantial fraction of these low-mass planets are found in high-multiplicity planetary systems. GJ 163 is a nearby inactive M dwarf with abundant public observations obtained using the HARPS spectrograph. We obtain and analyse radial velocities from the HARPS public spectra of GJ 163 and investigate the presence of a planetary companions orbiting it. The number of planet candidates detected might depend on some prior assumptions. Since the impact of prior choice has not been investigated throughly previously, we study the effects of different prior densities on the detectability of planet candidates around GJ 163. We use Bayesian tools, i.e. posterior samplings and model comparisons, when analysing the GJ 163 velocities. We consider models accounting for the possible correlations of subsequent measurements. We also search for activity-related counterparts of the signals we observe and test the dynamical stability of the planetary systems corresponding to our solutions using direct numerical integrations of the orbits. We find that there are at least three planet candidates orbiting GJ 163. The existence of a fourth planet is supported by the data but the evidence in favor of the corresponding model is not yet conclusive. The second innermost planet candidate in the system with an orbital period of 25.6 days and a minimum mass of 8.7 Me is inside the liquid-water habitable zone of the star.

In both papers only periods 8.6 and 25.7 are confirmed others totally way off hmm that is interesting

tommi59 wrote:

In both papers only periods 8.6 and 25.7 are confirmed others totally way off hmm that is interesting

Both papers seem to also find planet d: the error ranges of the two estimates for its period do overlap using the 4-planet solution from the Tuomi and Anglada-Escudé paper - hardly "way off" in this case. (Note however that the Bonfils et al. paper reports 68.3% centred intervals and the Tuomi and Anglada-Escudé paper gives the 99% Bayesian credibility set)