Habitable Zones & Global Climate: July 2020

At least twice in Earth's history, nearly the entire planet was encased in a sheet of snow and ice. These dramatic "Snowball Earth" events occurred in quick succession, somewhere around 700 million years ago, and evidence suggests that the consecutive global ice ages set the stage for the subsequent explosion of complex, multicellular life on Earth.

Previous studies have shown that sea-ice drift effectively promote the onset of a globally ice-covered snowball climate for paleo Earth and for tidally locked planets around low-mass stars.

The search for exoplanetary life must encompass the complex geological processes reflected in an exoplanet's atmosphere, or we risk reporting false positive and false negative detections.

Habitability has been generally defined as the capability of an environment to support life. Ecologists have been using Habitat Suitability Models (HSMs) for more than four decades to study the habitability of Earth from local to global scales.

Synchronously orbiting, tidally-locked exoplanets with a dayside facing their star and a permanently dark nightside orbiting dim stars are prime candidates for habitability. Simulations of these planets often show the potential to maintain an Earth-like climate with a complete hydrological cycle.

Geological evidence suggests liquid water near the Earth's surface as early as 4.4 gigayears ago when the faint young Sun only radiated about 70 % of its modern power output.

The authors and co-signers of the Terrestrial Planets Comparative Climatology (TPCC) mission concept white paper advocate that planetary science in the next decade would greatly benefit from comparatively studying the fundamental behavior of the atmospheres of Venus and Mars, contemporaneously and with the same instrumentation, to capture atmospheric response to the same solar forcing, and with a minimum of instrument-related variability.

The search for life in the universe is currently focused on Earth-analog planets. However, we should be prepared to find a diversity of terrestrial exoplanets not only in terms of host star but also in terms of surface environment.

Are there hurricanes on exoplanets? Tidally locked terrestrial planets around M dwarfs are the main targets of space missions for finding habitable exoplanets. Whether hurricanes can form on this kind of planet is important for their climate and habitability.