Tag Archives: Earth-sized planets

A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates

Want to read the actual paper, “A Sun-like star with three sub-Neptune exoplanets and two Earth-size candidates,” describing the discovery announced yesterday of two Earth-sized planet? You can download it here.

The paper’s closing paragraph sums the discovery up nicely:

A striking feature of the Kepler-20 planetary system is the presence of Earth-size rocky planet candidates interspersed between volatile-rich sub-Neptunes at smaller and larger orbital semi-major axes, as also seen in Kepler candidate multi-planet systems. Assuming that both [Kepler-20e] and [Kepler-20f] are planets, the distribution of the Kepler-20 planets in orbital order is as follows: Kepler-20b (3.7 days, 1.9 Earth radii), [Kepler-20e] (6.1 days, 0.9 Earth radii), Kepler-20c (10.9 days, 3.1 Earth radii), [Kepler-20f] (19.6 days, 1.0 Earth radii), and Kepler-20d (77.6 days, 2.8 Earth radii). Given the radii and irradiation fluxes of the two Earth-size planet candidates, they would not retain gas envelopes. The first, second, and fourth planets have high densities indicative of solid planets, while the other two planets have low densities requiring significant volatile content. The volatile-rich third planet, Kepler-20c dominates the inner part of the Kepler-20 system, by holding much more mass than the other three inner planets put together. In the Solar System, the terrestrial planets, gas-giants, and ice giants are neatly segregated in regions with increasing distance from the sun. Planet formation theories were developed to retrodict these Solar System composition trends. In the Kepler-20 system, the locations of the low-density sub-Neptunes that are rich in water and/or gas, and the Earth-size planet candidates does not exhibit a clean ordering with orbital period, challenging the conventional planet formation paradigm. In situ assembly may form multi-planet systems with close-in hot-Neptunes and super-Earths, provided the initial protoplanetary disk contained massive amounts of solids (∼ 50–100 Earth masses) within 1AU of the star.

First Earth-sized planets found

Big news: The first Earth-sized planets have been found by Kepler.

The two planets, dubbed Kepler-20e and 20f, are the smallest planets found to date. They have diameters of 6,900 miles and 8,200 miles – equivalent to 0.87 times Earth (slightly smaller than Venus) and 1.03 times Earth. These worlds are expected to have rocky compositions, so their masses should be less than 1.7 and 3 times Earth’s.

Both worlds circle Kepler-20: a G-type star slightly cooler than the Sun and located 950 light-years from Earth. (It would take the space shuttle 36 million years to travel to Kepler-20.) Kepler-20e orbits every 6.1 days at a distance of 4.7 million miles. Kepler-20f orbits every 19.6 days at a distance of 10.3 million miles. Due to their tight orbits, they are heated to temperatures of 1,400 degrees Fahrenheit and 800 degrees F.

Once again, this is only the beginning. The announcement of an Earth in the habitable zone is only a matter of months away.