An international team of astronomers has discovered a lonely young planet wandering through space without a parent star to call its own. This “free-floating” planet, called PSO J318.5-22, it formed a “mother” 12 million years ago, making it a baby, as far as planets go. There are probably billions of these lonely planets inhabiting our Milky Way Galaxy, condemned to wander alone in the cold darkness and relative emptiness of space between stars. The discovery of this starless alien world was announced in October 2013, and an article detailing the findings will be published in the Astrophysical journal letters.
With a mass about six times that of Jupiter in our own Solar System, the “free float” they resemble the gas giant planets that orbit young stars. PSOJ318.5-22 was first observed by astronomers using the powerful Pan-STARRS 1 (PS1), on top of Maui’s Haleakala volcano in Hawaii. The strange and lonely world was discovered through its weak heat signature, 80 light-years from our planet; was a fortuitous discovery, because the astronomers who saw it were looking for brown dwarfs. brown dwarfs they are relatively small substellar objects that probably form in the same way as stars, but are too small for their stellar cores to ignite by nuclear fusion.
“We’ve never seen an object floating freely in space like this before. It has all the characteristics of young planets found around other stars, but it’s drifting on its own,” explained team leader Dr Michael Liu, in a statement. October 10, 2013 Institute for Astronomy, University of Hawaii press release. Dr. Liu, from the University of Hawaii at Manoa, added that “I often wondered if such lonely objects existed, and now we know they do.”
Free-floating planets are pariahs: the rejected and cast-out descendants of the billions of star systems in our galaxy. These unfortunate planetary orphans were cruelly cast out to fend for themselves in cold, unforgiving darkness, far from the warmth of their parent stars. Young star systems are turbulent places, where the violent interactions that occur between forming planets and parent stars can ultimately result in the ejection of a doomed baby planet from the system that gave birth to it. Our own Solar System may well have produced far more planets than the eight planets we’re familiar with, and these outcast brethren of our Earth may well be floating free in interstellar space without “a star to guide them.” Astronomers have predicted the actual existence of such orphan worlds for a long time.
Over the last two decades, exoplanets have been found at a dizzying rate, with the number of confirmed worlds now approaching the 1,000 mark! Many alien worlds have been discovered through indirect techniques, such as the wobble or dimming of their parent stars caused by the planet’s influence. However, only a relative handful of exoplanets have been directly imaged, and all of those that have been directly observed are orbiting young, dynamic stars of the tender age of 200 million years or so.
Our Milky Way galaxy may well be teeming with free-floating Jupiter-sized orphan exoplanets; there may be millions upon millions of them, wandering their lonely way around the galactic center, similar to the way our Sun and other stars do. However, these are no stars, they are planets–and they have no star to call their own. Of course, they had a star-father when they were born, but that is no longer the sad case. Dr Frank Drake of the Search for the Institute for Extraterrestrial Intelligence (SETI)in Mountain View, California, put it this way: “We think the planets are in orbits around stars like our Sun. There has been speculation and now apparently evidence for the existence of planets that are not attached to any stars: they’re called orphan planets. The way this happens is that when two bodies pass each other in space, one gains speed and the other loses speed. After enough speed gains and losses, it’s possible for an object to gain escape velocity, and escapes its orbit. Once free, it can continue to travel forever without any orbital restrictions.”
The absence of a dazzling parent star could actually end up being beneficial to observers trying to understand the features of alien worlds beyond our own Solar System. As noted by Dr. Niall Deacon in an October 10, 2013 press release: “Planets found by direct imaging are incredibly difficult to study, as they are right next to their much brighter host stars. PSOJ318.5-22 it’s not orbiting a star so it will be much easier for us to study. It will give us a wonderful view into the inner workings of gas giant planets like Jupiter shortly after their birth.” Dr. Deacon is from the Max Planck Institute for Astronomy in Germany.
A lonely world lost in space
When PSOJ318.5-22 was seen by chance during astronomers’ search for brown dwarfs, stood out in the crowd. Due to its relatively cool temperatures, brown dwarfs they are very faint and show a deep red hue. To avoid these difficulties, Dr. Liu and his team duly examined the data from the ps1 ‘scope. ps1 is scanning the sky every night with a camera sensitive enough to detect faint heat signatures from these very red substellar objects. PSOJ318.5-22 announced his presence as a “weirdo”, because he was even redder than the reddest known brown dwarfs!
“We often describe the search for rare celestial objects as looking for a needle in a haystack. So we decided to search the largest haystack in astronomy, the ps1commented Dr. Eugene Magnier in October 2013 University of Hawaii press release. Dr. Magnier is from Institute of Astronomy at the University of Hawaii at Manoa. He is also a co-author of the study. Dr. Magnier leads the data processing team to ps1, which produces the equivalent of 60,000 iPhone photos every night. The total dataset, as of this writing, is approximately 4,000 terabytes. This is bigger than the sum of the digital version of all the books that have ever been published, all the music albums that have ever been released, and all the movies that have ever been made!
The team followed the ps1 discovery of the lonely alien world with multiple telescopes on top of Mauna Kea on the island of Hawaii. Infrared spectra obtained with NASA Infrared Space Facility and the Gemini North Telescope revealed the true nature of PSOJ318.5-22–could not be a brown dwarf! Based on the signatures detected in its infrared light, it was best identified as a young, low-mass object.
The team then regularly monitored the position of PSO J318.5-22, for a period of two years, with the Canada-France-Hawaii Telescope, and directly measured its distance from our planet. Based on its calculated distance and its motion through space, astronomers concluded that PSO J316.5-22 belongs to a population of young stars called betapictoris moving group that was born approximately 12 million years ago. The homonymous star belonging to this juvenile group, betapictorisit has a young gas giant planet in orbit around it. PSO J318.5-22 is less in mass than betapictoris planet, and probably formed in a different way.
Although “only” about 800 alien worlds have been confirmed (at the time of this writing), some estimates suggest that there are likely tens of billions of exoplanets in the Universe.