The planet that ‘shouldn’t exist’
4 Dec 2013 by hdpqmpdbhq.d hdpqmpdbhq.d
Astronomers have weighed an Earth-sized planet orbiting another star and concluded that it shouldn’t exist.
The results from two independent teams published in Nature confirm Kepler-78b as the first known Earth-sized exoplanet with an Earth-like density. The scorching lava world orbits it star every eight and a half hours at a distance of less than one million miles – one of the tightest known orbits. According to current theories of planet formation, it couldn’t have formed so close to its star, nor could it have moved there – so it shouldn’t exist.
“This planet is a complete mystery. We don’t know how it formed or how it got to where it is today,” said David Latham from the Harvard-Smithsonian Centre for Astrophysics (CfA). “What we do know is it’s not going to last forever.”
“It couldn’t have formed in place because you can’t form a planet inside a star. It couldn’t have formed further out and migrated inward because it would have migrated all the way into the star,” said Dimitar Sasselor, also from CfA. “This planet is an enigma.”
Kepler-78b is a new class of planet which orbits its star in less than 12 hours and is the first to have its mass measured. It’s about 20% larger than Earth, with a diameter of 9,200 miles, and weighs almost twice as much. As a result its density is similar to Earth’s – suggesting an Earth-like composition of iron and rock.
“Achieving this measurement involved measuring the wobble of a star like the Sun that revolves around its common centre of gravity with the planet at a speed equal to human walking pace. This attests to the exquisite precision of the HARPS-North and HIRES instruments on which the European and US teams carried out their independent, cooperative studies.” said Professor Andrew Collier Cameron of the University of St Andrews, who leads the UK contribution to the project.
The planet is, however, a doomed world. Gravitational tides will draw Kepler-78b closer to its star before the star’s gravity rips it apart. Theorists predict the planet will vanish within three billion years. Our solar system could have held a planet like Kepler-78b, although it would have been destroyed long ago, leaving no sign for astronomers today.
An Earth-sized planet with an Earth-like density http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12768.html
