Reasons to Believe

Start and Stops in the Search for Earth-like Planets

Habitability zone

A few weeks ago we reported on the discovery of a new planet circling an M-type dwarf star named Gliese 581 in the constellation Libra. This discovery received a lot of attention in the news because its distance from the parent star fell within the “habitability zone,” where it is possible that liquid water could exist on the planet’s surface and, hence, the planet could support life. As we pointed out in our report, the researchers had to make a number of assumptions to reach this conclusion, but the discovery was exciting nonetheless.

In the meantime, new work has been done on this planetary system. A team of scientists working out of the Potsdam Institute for Climate Impact Research have investigated the system for habitability (see here for a press release, and here for their paper) using planetary formation and climate models that are thought to hold true for these types of systems.

They have concluded that the original planet, Gl 581c, which was suggested as the best candidate for Earth-like conditions is, in fact, likely to have a dense atmosphere with a corresponding high temperature at its surface. So, even though the planet resides at an appropriate distance from its parent star, the thick atmosphere raises the temperature beyond what would be necessary to support life. A similar situation exists in our own solar system with the planet Venus, where its dense atmosphere and consequent high temperature precludes its habitability.

On the other hand, these same researchers investigated another planet (Gl 581d) in the same system that had previously been rejected as habitable because of its greater distance from the parent star. While this planet would normally be too cold on the surface, its denser atmosphere brings that temperature into a region of habitability.

One of the conditions that trouble both of these planets is “tidal lock,” where their distance from the parent star is so close that the action of the stars gravity causes the same side of the planet to always face the star. Consequently, even Gl 581d will have a face that is too hot and an opposite face that is too cold; the only zone where life could possibly exist would be near the transition region between these two faces.

The authors acknowledge that tidal lock—along with many other problems—suggests the search for a home planet for mankind is no easy task. However, the results so far are tantalizing for the scientist looking for planets that can harbor life. As concluded in our earlier report, we expect that further research will, in fact, establish the uniqueness of the Earth and its parent star as a place where advanced life can exist and, therefore, provide further support for the RTB creation model.

For further discussion of habitable planets around M-dwarf stars, see here.

Subjects: Extrasolar Planets

Dr. David Rogstad

Dr. Dave Rogstad received his PhD in physics from Caltech and worked over 30 years for NASA’s Jet Propulsion Laboratory. Though now retired, Dave continues to serve as an RTB board member and participates regularly in several RTB podcasts.