Life in the Solar System?

Life in the Universe, Chapter 19

The number of detected Terrestrial planets is currently 359 (4/1/2017). The size of the habitable zone as a function of the central star. The habitable zones of low mass stars fall near the stars. For our Solar System, Mars may or may not fall within the habitable zone.

In our Solar System, for Life As We Know It (LAWKI) to form requires a planet with conditions such that liquid water (oceans) may form on its surface. For the Solar System this defines the Habitable Zone which stretches from around 0.85 Astronomical Units to (optimistically) 2 Astronomical Units. The notion of liquid oceans is key to the size of the Habitable Zone. Without liquid oceans, it is expected that our atmosphere would have experienced a Runaway Greenhouse Effect (as did Venus) driving our surface temperature up to many hundreds of degrees Farenheit (on Venus, the surface temperature is 800 to 900 F) or that we could not have maintained a thick atmosphere and we would be an airless planet (so, why is Mars at a distance of 1.5 Astronomical Units from the Sun have an atmosphere which is only 1 % the mass of the atmosphere of the Earth?).

Artist's rendition of the two Saturn-sized planets in orbit about their star, named Kepler-9. The planets were named Kepler-b and Kepler-9c.

Important work for discovering Earth-like planets is being performed by the NASA satellite Kepler. Kepler announced the discovery of two transiting planets in one planetary system. The two planets are around the mass of Saturn (~1/3 that of Jupiter) with tight orbits, periods 19 days and 38 days. The orbit of Saturn is ~9.6 Astronomical Units and Saturn's orbital period is around 29.5 years. Interestingly, there is evidence for a third planet with Earth-like properties, 1.5 times the mass of the Earth but in an orbit which is only 1.6 days long. The planet is not in the Habitable Zone, however, it orbits way too close to its parent star.

Planets on Which Life Develops:

DNA

Plagiomnium