The warmth of a sun has long been thought to be a key ingredient to life . But astronomers say 'rogue ' , sun-less planets that wander the stars could still harbour extra-terrestrials . While it sounds like science fiction , these planets may offer scientists a new avenue in their search for alien life . The warmth of a sun has long been thought to be a key ingredient to life . But astronomers say 'rogue ' , sun-less planets that wander the stars could still harbour extra-terrestrials . This is according to Sean Raymond , an astrophysicist with the Laboratoire d'Astrophysique de Bordeaux in France , who has taken a look at how life can form on rogue planets . Writing in Aeon , he says : 'To have any chance of life – at least life like our own – a free-floating Earth would need liquid water . ' A planet needs to keep warm for liquid water to form , and without the sun , this heat would have to come from its interior . ' A layer of ice on a planet 's surface can act as a strong insulator , locking in a planet 's heat , ' claims Raymond . Globulettes - regions of dust and gas that can form planets - could make rogue more common than first thought . Rogue planets are of particular interest to astronomers because they represent objects that have likely failed to form into a star . PSO J318.5-22 was detected 80 light years away from Earth and it is estimated to have a mass six times that of Jupiter . Several years ago , an international team of astronomers discovered a large planet floating freely through space with no star to orbit . Planets traditionally travel in a uniform , singular direction , around a star . However , the free-floating planet , named PSO J318.5-22 , was found without a host . Its movement is n't structured , and scientists do not understand how it formed and they are baffled by what - if anything - controls it . PSO J318.5-22 was detected 80 light years away from Earth and it is estimated to have a mass six times that of Jupiter . Astronomers believe it formed 12 million years ago , and is considered a newborn in planetary terms - Earth is thought to be around 4.5 billion years old . Dr Michael Liu of the Institute for Astronomy at the University of Hawaii identified the rogue planet from its 'faint and unique heat signature ' . We have never before seen an object free-floating in space that that looks like this . 'It has all the characteristics of young planets found around other stars , but it is drifting out there all alone , ' explained Liu . 'If the ice layer is thick enough , then a planet can maintain an ocean of liquid water beneath the ice . ' He calculates that the ice layer needs to be at least 10 km ( 6 miles ) thick to prevent it from freezing for billions of years . Raymonds comments echo a similar conclusion reached by scientists in Chicago several years ago . They calculated that life can cling on to a planet for billions of years without a star to provide a direct source of warmth . Research by astrophysicists Dorian Abbot and Eric Switzer from the city 's university discovered that heat would come from the breakdown of radioactive elements inside the planet 's core . The scientists named their discovery a 'Steppenwolf ' planet because they claimed any life found there would 'exist like a lone wolf wandering the galactic steppe ' . However the pair refused to speculate on what life forms would be discovered , but agreed that they would me microscopic in size . As well as internal heat , Raymond says another way a planet can keep warm is using a thick atmosphere . ' A free-floating Earth with a thick hydrogen atmosphere could keep its surface temperature above the freezing point of water , ' writes Raymond . 'The planet could have lakes and oceans ( and possibly life ) on its surface . ' Rogue planets are hard to find because , without orbiting a star , they reflect very little light . But 50 have now been found in the past 15 years , leading some to suggest they may be abundant in the universe . Rogue planets are of particular interest to astronomers because they represent objects that have likely failed to form into a star . Brown dwarfs , for example , are substellar objects that are not massive enough to sustain fusion , but are still more than 13 times the mass of Jupiter . The exact boundary between a giant planet and a low-mass brown dwarf is still being debated , but finding more rogue planets could shed light on this mystery . And this could indicate that there are more rogue planets than we know of in the cosmos .
Comments were made by Sean Raymond , an astrophysicist in France . He says internal heat of rogue planets could allow liquid water to form . Writing in Aeon , he also says a thick atmosphere may help life develop . Astronomers have found 50 of these rogue planets in the past 15 years .