Center for Astrophysics | 2015 Jan 05
[img3="How do you make an Earth-like planet? The "test kitchen" of Earth has given us thisHow do you make an Earth-like planet? The "test kitchen" of Earth has given us a detailed recipe, but it wasn't clear whether other planetary systems would follow the same formula. Now, astronomers have found evidence that the recipe for Earth also applies to terrestrial exoplanets orbiting distant stars. ...
detailed recipe, which also applies to terrestrial exoplanets orbiting distant stars. Image Credit: David A. Aguilar (CfA)"]http://www.cfa.harvard.edu/sites/www.cf ... 1/base.jpg[/img3]
The key to the discovery was the HARPS-North instrument on the 3.6-meter Telescopio Nazionale Galileo in the Canary Islands. (HARPS stands for High-Accuracy Radial velocity Planet Searcher.) It is designed to accurately measure the masses of small, Earth-sized worlds. Those measurements are crucial to determine densities and therefore compositions. ...
Most recently the team targeted Kepler-93b, a planet 1.5 times the size of Earth in a tight, 4.7-day orbit around its star. The mass and composition of this world were uncertain. HARPS-North nailed the mass at 4.02 times Earth, meaning that the planet has a rocky composition.
The researchers then compared all ten known exoplanets with a diameter less than 2.7 times Earth's that had accurately measured masses. They found that the five planets with diameters smaller than 1.6 times Earth showed a tight relationship between mass and size. Moreover, Venus and Earth fit onto the same line, suggesting that all these worlds have similar rock-iron compositions. ...
The team also noted that not all planets less than six times the mass of Earth are rocky. Some low-mass worlds with very low densities are known (such as the planets in the Kepler-11 system). But for typical close-in small planets, the chances are high that they share an Earth-like composition. ...
The Mass of Kepler-93b and The Composition of Terrestrial Planets - Courtney D. Dressing et al
- arXiv.org > astro-ph > arXiv:1412.8687 > 30 Dec 2014