First estimate of the mass of an Earth-like exoplanet

The exoplanet Kepler-78b (a planet located outside our solar system) is one of several that astronomers have identified in recent years. It has of particular to be the first for which the mass and diameter are known. Two international research teams published these results recently in the journal Nature; an FCT-supported researcher from the Astrophysics Center of the University of Porto (CAUP) is part of one of these teams. 

Kepler-78b is in the constellation Cygnus, about 400 light years from Earth. By its density and radius it is the most Earth-like exoplanet, having similar rock and iron compositions. However, it is 40 times closer to its star than Mercury is to the Sun, which causes temperatures to reach 1800 to 3300°C. In fact, it is surprising that the planet exists at all, and current models predict that it will collide with its star in the next 3 billion years. 

The size and orbit of the planet Kepler-78b was initially determined using NASA's Kepler telescope. The two teams that have now published the exoplanet's mass and diameter combined data from the telescope with data from another technique, which measures a planet's gravitational effect on the speed at which its star approaches or moves away from the planet.  

Pedro Figueira, from CAUP, reinforces the importance of these results, "It was not easy to extract from the data the confirmation that the signal found by Kepler was due to a planet. Only after several months of work were we able to identify the planet's signal (...) it is a very clear testimony of the high level of planetary astronomy today, and of the impressive progress made in recent years.