|
The results of a study of the planetary system around the star 55 Cancri A, 40 light years from Earth, carried out by Rebekah Dawson (astronomy PhD student at Harvard) and Daniel Fabrycky (Hubble Fellow at UCSC) will soon be published in The Astrophysical Journal.
This system includes 5 planets discovered between 1997 and 2008, and the new research has focused on the properties of one of these, 55 Cancri e, a 'super-Earth' with a diameter of 21,000 km, 60% greater than our own planet.
Re-analysing all the available data on this system, Dawson and Fabrycky found that the orbital period was much less than previously thought. This was actually confirmed by Josh Winn (Massachusetts Institute of Technology) and Matt Holman (Harvard-Smithsonian Center for Astrophysics) that used the Canadian space telescope 'MOST' (Microvariability & Oscillations of STars) to measure a cyclical drop in the star's observed brightness. This was found to have a period of 17 hours and 41 minutes, in perfect agreement with the estimate of Dawson e Fabrycky.
From the measured drop in brightness of 55 Cancri A (1/50th of a percent) the researchers have calculated the diameter of 55 Cancri e, and from the Doppler shift of spectral lines from the star have also calculated the planet's mass, which turns out to be 8 times more massive than Earth. A simple calculation leads to value for the density, which is twice that of our planet, almost as dense as lead; a real record!
The presence of an atmosphere on 55 Cancri e has been excluded, given the proximity to its host star (about 2.4 million km) would lead to a surface temperature of around 2700°C. Any volatile material has certainly been stripped away by the stellar wind.
|
