How Common is Earth?

This year alone, there have been over 1200 exoplanets detected, with new planets being identified every week. The majority are of a type unfamiliar to our Solar System. Some are large, gas giant planets that orbit in periods of only days or weeks – so called Hot Jupiters. Others are terrestrial planets multiple times the size of Earth known as Super-Earths. With so many distinct planet types, what were the preconditions for life to develop around the Sun? Likewise, is the story of Earth a common one, or is it wholly unique?

Earth - A Second Generation Planet

Our early Solar System was home to dramatic planetary movements that created the possibility of life on Earth. Under this new theory, known as the Grand Tack, a Super-Earth could have formed via the constant accretion of small rocks in the early Solar System. Jupiter then formed in the periphery of the system. Through interactions with the Solar disk, the gas giant moved inwards, to about the position of Jupiter. The planetary migration of such a large planet threw the early Solar System into imbalance. Rocks that would be used to create large terrestrial planets, were ground down as they begin colliding at ever increasing rates. Our hypothetical Super-Earth would have been completely destroyed as chaos rocked the early system.

As Saturn began to form, a gravitational interaction known as a mean motion resonance developed with Jupiter. Under orbits in a low-integer ratio, the jovian giants tugged on each other periodically, dragging them further and further from the Sun. By this point, Jupiter and Saturn existed in the outer region of the Solar System, while the inner region was left with a smaller amount of rocks and volatile elements. Terrestrial planet formation would begin again – but with a twist. With less mass avaliable, planets developed to be small rocky worlds. Most importantly, these ‘second generation’ worlds harbored much thinner atmospheres than any predecessors would have, allowing for the hospitable conditions on Earth.

What are the chances that such conditions developed in other Solar Systems? We may not yet be able to detect Earth-like planets consistently, but with new instruments, like the European Extremely Large Telescope and the James Webb Space Telescope, researchers will be able to more precisely characterize exoplanetary systems.

Click here to view the full SpaceRip show.