Planets wandering through space , unattached to any star or solar system , may be much more common that previously thought , according to an expert . The 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 . Ashley Yeager for Science News has explained that solo planets ( artist 's impression shown ) could be common . This is thanks to more regions of dust and gas than we thought . Planets become 'rogue ' when they are ejected or form on their own and about 50 have been found in the last 15 years . The potential for these free-floating planets to be common was discussed in an article by Ashley Yeager for Science News . Rogue planets , or interstellar planets , are planetary objects that were either formed by themselves or were ejected from a system . A brown dwarf is commonly regarded as the ‘ missing link ’ between stars and planets . They are too large to be classed as true planets , but too small to have ignited nuclear fusion at their cores and be classed as stars . When a celestial body first forms , its size will determine what sort of object it becomes . As a star forms from a cloud of gas , its core becomes so large that hydrogen fuses into helium . Conversely , a planet forms into a smaller sphere that is not large enough to have nuclear fusion at its core . Brown dwarfs fall somewhere in between . They are the size between a gas giant like Jupiter and a small star . Their mass , meanwhile , can be anything from 15 to 75 times the mass of Jupiter . This is not enough to sustain fusion but , owing to their size , this has led astronomers to coin brown dwarfs ‘ failed stars ’ . As they do n't emit much light it ’ s thought there may be many rogue brown dwarfs drifting through the galaxy waiting to be discovered . How abundant they are in the universe , though , has been the cause of some debate . But Ms Yeager explained so-called globulettes - regions of dust and gas that can form planets - could make them more common than thought . The number of possible planets in one such region is not known , and this depends on what the boundary between cloud density and planet formation is . ‘ Globulettes are very numerous , ’ Dr Thomas Haworth from the University of Cambridge told Science News . ‘ Even if only a small fraction can be made to collapse , they could make a significant contribution to the population of free-floating planets. ’ 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 . Yeager explained that so-called globulettes - regions of dust and gas that can form planets - could make them more common than first thought . However , the number of possible planets that can be found in one such region is not known . Shown is a star-forming region known as Thackeray 's Globules .
Ashley Yeager for the University of Cambridge explained solo planets could be common . This is thanks to more regions of dust and gas than we thought . Planets become 'rogue ' when they are ejected or form on their own . About 50 have been found in the last 15 years . But as they do n't orbit a star they reflect little light and are hard to find .