Gliese 581g Research Articles

Data Dispute Revives Exoplanet Claim

Last week, the team that discovered Gliese 581g, the first potentially habitable planet outside the solar system, concluded that their own analysis of their critics' data shows that Gliese 581g does indeed exist.

Bayesian re-analysis of the Gliese 581 exoplanet system

A re-analysis of Gliese 581 HARPS and HIRES precision radial velocity data was carried out with a Bayesian multiplanet Kepler periodogram (from one to six planets) based on a fusion Markov chain Monte Carlo algorithm. In all cases, the analysis included an unknown parametrized stellar jitter noise term. For the HARPS data set, the most probable number of planetary signals detected is five with a Bayesian false alarm probability of 0.01. These include the 3.1498 ± 0.0005, 5.3687 ± 0.0002, 12.927+0.006− 0.004 and 66.9 ± 0.2 d periods reported previously plus a 399+14− 16 d period. Their orbital eccentricities are 0.0+0.2− 0.0, 0.00+0.02− 0.00, 0.10+0.06− 0.10, 0.33+0.09− 0.10 and 0.02+0.30− 0.01, respectively. The semimajor-axis and M sin i of the five planets are (0.0285 ± 0.0006 au, 1.9 ± 0.3 M⊕), (0.0406 ± 0.0009 au, 15.7 ± 0.7 M⊕), (0.073 ± 0.002 au, 5.3 ± 0.4 M⊕), (0.218 ± 0.005 au, 6.7 ± 0.8 M⊕) and (0.7 ± 0.2 au, 6.6+2.0− 2.7M⊕), respectively. The analysis of the HIRES data set yielded a reliable detection of only the strongest 5.37 and 12.9 d periods. The analysis of the combined HIRES/HARPS data again only reliably detected the 5.37 and 12.9 d periods. The detection of four planetary signals with the periods of 3.15, 5.37, 12.9 and 66.9 d was only achieved by including an additional unknown but parametrized Gaussian error term added in quadrature to the HIRES quoted errors. The marginal distribution for the σ of this additional error term has a well-defined peak at 1.8 ± 0.4 m s−1. It is possible that this additional error arises from unidentified systematic effects. We did not find clear evidence for a fifth planetary signal in the combined HIRES/HARPS data set. Based on the available data, our analysis does not support the claimed detection of a sixth planet Gliese 581g.

Gliese 581g as a scaled-up version of Earth: atmospheric circulation simulations

We use three-dimensional simulations to study the atmospheric circulation on the first Earth-sized exoplanet discovered in the habitable zone of an M star. We treat Gliese 581g as a scaled-up version of Earth by considering increased values for the exoplanetary radius and surface gravity, while retaining terrestrial values for parameters which are unconstrained by current observations. We examine the long-term, global temperature and wind maps near the surface of the exoplanet --- the climate. The specific locations for habitability on Gliese 581g depend on whether the exoplanet is tidally-locked and how fast radiative cooling occurs on a global scale. Independent of whether the existence of Gliese 581g is confirmed, our study highlights the use of general circulation models to quantify the atmospheric circulation on potentially habitable, Earth-sized exoplanets, which will be the prime targets of exoplanet discovery and characterization campaigns in the next decade.

Habitable Planets: What Are We Learning from Kepler and Ground-Based Searches?

Habitable Planets: What Are We Learning from Kepler and Ground-Based Searches?

Habitability of the Goldilocks planet Gliese 581g: results from geodynamic models

Aims: In 2010, detailed observations have been published that seem to indicate another super-Earth planet in the system of Gliese 581 located in the midst of the stellar climatological habitable zone. The mass of the planet, known as Gl 581g, has been estimated to be between 3.1 and 4.3 Earth masses. In this study, we investigate the habitability of Gl 581g based on a previously used concept that explores its long-term possibility of photosynthetic biomass production, which has already been used to gauge the principal possibility of life regarding the super-Earths Gl 581c and Gl 581d. Methods: A thermal evolution model for super-Earths is used to calculate the sources and sinks of atmospheric carbon dioxide. The habitable zone is determined by the limits of photosynthetic biological productivity on the planetary surface. Models with different ratios of land / ocean coverage are pursued. Results: The maximum time span for habitable conditions is attained for water worlds at a position of about 0.14+/-0.015 AU, which deviates by just a few percent (depending on the adopted stellar luminosity) from the actual position of Gl 581g, an estimate that does however not reflect systematic uncertainties inherent in our model. Therefore, in the framework of our model an almost perfect Goldilock position is realized. The existence of habitability is found to critically depend on the relative planetary continental area, lending a considerable advantage to the possibility of life if Gl 581g's ocean coverage is relatively high. Conclusions: Our results are a further step toward identifying the possibility of life beyond the Solar System, especially concerning super-Earth planets, which appear to be more abundant than previously surmised.

A PALETTE OF CLIMATES FOR GLIESE 581g

We consider a range of possible climates for the habitable-zone planet candidate, Gliese 581g, contingent on a plausible set of hypothetical atmospheres and assuming the planet to be tide locked. The two most habitable states we find are (1) a nearly airless Super-Europa with thin ice at the substellar point and (2) an Eyeball Earth which is mostly frozen but supports a substantial stable pool of open water centered on the substellar point. We discuss the prospects for observational determination of what kind of climate 581g actually supports.

First Goldilocks Exoplanet May Not Exist

At a meeting last week in Turin, Italy, a group of exoplanet hunters announced that its observations show no sign of Gliese 581g, which only a couple of weeks earlier a rival group had announced was the long-sought Earth-like habitable planet.