Scientists have claimed that free-floating planets could form from dust clouds deep out in interstellar space – a finding that challenges the belief that planets are only created near stars.
Boffins from Japan's Osaka University had previously revealed the existence of hundreds of millions of orphan planets, but the latest research – compiled by a group of Swedish and Finnish researchers – offers a clearer indication of how they might form.
It was thought that the planets were flung out of solar systems before embarking upon their lonely interstellar journey. But the latest research suggests they could form "on their own", far from the gravity and warmth of a star.
A team of astronomers from Sweden and Finland focused their lenses on the Rosette Nebula, a cloud of gas and dust 4,600 light years from Earth in the constellation Monoceros (the Unicorn). They examined radio waves from molecules of carbon monoxide to gather information on the mass and structure of these clouds.
They observed a number of small, round clouds floating about that had all the "right characteristics" to turn into planets.
”The Rosette Nebula is home to more than a hundred of these tiny clouds – we call them globulettes,” said Gösta Gahm, astronomer at Stockholm University.
“They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of planetary mass, less than 13 times Jupiter’s mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment."
The team suggested the small, dark clouds are being thrown out of the Rosette Nebula and will form into planets deep out in space. Millions upon millions of similar nebula have formed throughout the long life of the Milky Way, which means that a staggering number of these globulettes would have formed. Some of them may even have turned into failed stars known as brown dwarfs, which are somewhere between the size of a planet and a star.
“If these tiny, round clouds form planets and brown dwarfs, they must be shot out like bullets into the depths of the Milky Way”, Gahm added.
“There are so many of them that they could be a significant source of the free-floating planets that have been discovered in recent years”, he says.
The team found that the globulettes are very heavy and compact, some with very dense cores.
”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars," explained Minja Mäkelä, astronomer at the University of Helsinki. "They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre."
It is thought that the Milky Way contains 200 billion free floating planets. So far, about 900 planets have been observed circling other stars.
The study is summarised in a paper called "Mass and motion of globulettes in the Rosette Nebula and is published in the July issue of the journal Astronomy & Astrophysics. ®