Newly found planets are 'roasted remains'By Jonathan Amos Science correspondent, BBC News
Planets impression (S.Charpinet) An artist's impression of the two planets circling close to their parent - a former red giant star
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Just a day after announcing the discovery of the first Earth-size planets ever detected outside our Solar System, scientists have confirmed the existence of two even smaller worlds.
There is something very unusual about these objects, however.
It appears they are the roasted remains of planets that spent a period of time inside the outer layers of their star.
Scientists tell Nature magazine that these worlds are therefore likely to have been much bigger in the past.
Once again, these worlds were identified using data from Nasa's Kepler telescope, which was put in orbit in 2009 with the specific goal of hunting down small planets.
This latest haul was detected around a star known as KIC 05807616. They have diameters that are just 76% and 87% of that of Earth.
What is interesting about this star is that it is a former red giant, a so-called "hot B subdwarf".
Red giant refers to a late phase in a star's life when it has begun to exhaust its hydrogen fuel.
Deep spiral
A star in this phase will expand, its outer layers will cool and it will glow a more reddish colour. Our own Sun will go through this phase in a few billion years' time.
But the consequence is that any planets that happen to be orbiting relatively close to the star will likely be engulfed in its expanding envelope of gas.
This will happen to the Earth and it appears to have been the case with the newly detected planets named KOI 55.01 and KOI 55.02, which whip around their host star in just a matter of hours.
Kepler artist impression (STSCI) The Kepler telescope was put in orbit in 2009
Their presence so close to KIC 05807616 is a tell-tale for what must have happened to them.
Going into the expanding outer layers of a star would have severely eroded the worlds, ripping away any gaseous or liquid material.
What the team sees in its data are probably just the remnant cores of what were once giant gas planets not unlike our own Jupiter.
"The details of all this are of course uncertain and would require dedicated modelling but we expect that, due to friction and tidal dissipation, the engulfed planets must have spiralled in even deeper inside the star," said lead researcher Stephane Charpinet, Toulouse University, France.
