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 don'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 Science News 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 don't orbit a star they reflect little light and are hard to find .