Reasons to Believe

Finding Planets in the Habitable Zone

The inevitable finally happened. Astronomers using the Kepler Telescope detected five Earth-sized planets orbiting in the liquid water habitable zone. Yet, unlike previous bold assertions that such planets will host life, a more circumspect attitude surrounded the announcement.

Kepler regularly monitors roughly 150,000 stars for decreases in light that might signal a planet transited across the face of the star. Using observations taken in 2009, the number of planet candidates seen by Kepler grew to 1,235. (Each of these “candidates” needs follow-up for confirmation, but future observations will likely confirm all but a small fraction as actual planets.) This catalog includes 184 objects Jupiter-sized or larger, 662 Neptune-sized objects, 288 “super-Earths” (roughly 10 times the mass of Earth), and 68 Earth-sized objects. Of all the candidates observed by Kepler, 54 orbit in a region where liquid water could exist. Now it appears that five of those 54 candidates were both Earth-sized and in the liquid water habitable zone!

The first detection of these five planets prompted an editorial in a recent issue of Nature about what constitutes a habitable planet. For example, these five planet candidates orbit smaller M-dwarf stars where any planet in the liquid water habitable zone is tidally locked (the same side of the planet always faces the star). Although the editorial mainly focused on the public’s reaction to too many or too few “habitable planet discoveries,” it also highlights a key distinctive of RTB’s creation model.

Most of the popular discussion regarding habitable planets assumes that finding liquid water on a planet virtually assures the existence of life. According to this “minimalist” model, an Earth-sized planet (or an Earth-sized moon orbiting a gas giant) located in the liquid water habitable zone around its star hosts life. In constrast, RTB’s model argues that life requires far more exacting conditions. Stated briefly, a truly habitable planet will look like Earth, with something similar to the Moon, orbiting a Sun-like star with similar gas giants, and located in a similar location as the Sun in a Milky-Way-like galaxy.

For more information on this planetary discovery, listen to this Science News Flash podcast.

Subjects: Extrasolar Planets

Dr. Jeff Zweerink
