Dense, hot super-Earth is new class of planet

National Geographic : A planet close to Earth’s size and in orbit around a Sun-like star, 55 Cancri e has the density of lead and is the hottest known rocky world. Residing in a five-planet system within the constellation Cancer, 55 Cancri e is 42 light-years away. First discovered in 2004 via ground-based telescopes, the planet’s orbit has now been shown to be 17 hours and 41 minutes long , one-quarter of the original estimate of 2.8 days. This February, Jaymie Matthews of the University of British Columbia and colleagues used Canada’s Microvariability and Oscillations of Stars ( MOST) space telescope to measure the tiny dips in starlight as the planet passed in front of its star. Its 17-hour orbit means that it’s about 20 times closer to its star than Mercury is to Sol. The brightness of the host star meant that MOST was able to determine the planet’s size and mass—60% larger and eight times more massive than Earth. Astronomers’ understanding of the planet is still developing; just this week, a second team independently reported that the planet’s radius may be up to a third larger than the value reported by the MOST team. Both teams agree that whatever its actual radius, 55 Cancri e is a new class of planet.