Homeless planet CFBDSIR2149, fain blue object at center right, as imaged with the SOFI instrument on the European Southern Observatory's New Technology Telescope. Image Credit: P. Delorme ESO.
Rich in methane and water, this rogue world is 130 light years away and about 70 million years old, an estimate based in part on its coherent motion in the traveling group. Earlier work suggested that stellar gravitational entanglements could eject planets out of their stellar nurseries.
"Although theorists had established the existence of this type of very cold and young planet, one had never been observed until today," said Étienne Artigau, an astrophysicist at the University of Montreal. The five member study effort was led by Philippe Delorme, of the Laboratoire d'Astrophysique de l'Observatoire de Grenoble.
Previous studies of star-forming regions have revealed objects of planetary mass that are about one million years old, Artigau explained in a follow-up e-mail.
"More accurately, we could say that this is the first homeless planet 'out of the stellar nursery.' So in a sense, we knew that these objects existed in our neighborhood, but they become extremely faint in an astronomically short time," said Artigau. "It is very likely that objects similar to CFBDSIR2149 exist even closer to us, but if they are 5 billion years old, they are basically impossible to find with existing technology."
Over the next few hundred million years, CFBDSIR2149 is likely to depart the traveling group, dispersing within the Milky Way.
"Over the past few years, several objects of this type have been identified, but their existence could not be established without scientific confirmation of their age," explained Jonathan Gagné, a doctoral student of physics at the University of Montreal and one of the collaborators. "Astronomers weren't sure whether to categorize them as planets or as Brown dwarfs."
Brown dwarfs, considered failed stars, lack the mass to initiate nuclear reactions in their centers. At 13 Jupiter masses, these objects reach the threshold for ignition.
"Our survey only covered a small fraction of the sky (a region 1,000 times the surface of the full moon), and there are some much more ambitious surveys coming" said Artigau. "I expect a few tens of tens of similar objects to be discovered in the upcoming decade."
Temperatures on the starless world, a calculation based on the depth of absorption by methane and water in the infrared spectrum, are estimated at 400 degrees Celsius, cold considering CFBDSIR2149's planetary mass and youth.
The observations were made with the Canada-France-Hawaii Telescope (CFHT) and the European Southern Observatory's Very Large Telescope (VLT)