Gliese 581g & Gliese 581d Probably do NOT Exist

Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581

Authors:

Robertson et al

Abstract:

The M dwarf Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet—GJ 581 g—is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the Hα line, we measure a stellar rotation period of 130 ± 2 days and a correlation for Hα modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5σ) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g.

Modeling the Atmosphere of Gliese 581g and Other Potentially Tidally Locked SuperEarths

Connecting the dots: A versatile terrestrial planet benchmark for the atmospheres of tidally locked Super-Earths

Authors:

Carone et al

Abstract:

We develop a benchmark for quantifying sustained global dynamics in the atmospheres of tidally locked terrestrial planets using the MITgcm core as the basis of a dry 3D-GCM with simplified thermal forcing. Our forcing employs a Newtonian relaxation scheme based on a simple greenhouse model. Our model is of the same conceptional simplicity than the model of Held& Suarez1994 and is thus versatile and computationally fast. As a case study relevant for Super-Earths, we investigate a Gl581g-like planet with Earth-like atmosphere and irradiation, and present all details on the obtained thermodynamics for representative rotation periods of Prot=10 days and Prot=36.5 days. This provides proof of concept and identifies interesting dynamical features for the rotating regime 3 less than Period of rotation less than 100 days, which was shown by Edson et al. 2011 to be an intermediate regime between equatorial superrotation and divergence.

We confirm that the Prot=10 days case is more dominated by equatorial superrotation dynamics than the Prot=36.5 days case, which shows diminishing influence of standing Rossby-Kelvin waves and increasing influence of divergence at the top of the atmosphere. We argue that this relates to the increase in Rossby deformation radius, in agreement with previous studies using more complex models. However, we also pay attention to other features that are not or only in partial agreement with other studies, like, e.g., the number of circulation cells and strength, the role and extent of thermal inversion layers, and the details of heat transport.