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.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
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.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
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