Researchers recently discovered a space object about 500 light-years away, but are unsure whether to call it a strange planet or a failed star.
The object, which orbits a young star, is challenging common definitions of the word "planet," a University of Toronto news release reported.
"We have very detailed measurements of this object spanning seven years, even a spectrum revealing its gravity, temperature, and molecular composition. Still, we can't yet determine whether it is a planet or a failed star - what we call a 'brown dwarf'. Depending on what measurement you consider, the answer could be either," Thayne Currie, a McLean Postdoctoral Fellow in the Department of Astronomy and Astrophysics at the University of Toronto and lead author of the report, said in the news release.
The object, dubbed ROXs 42Bb, is about nine times the mass of Jupiter; which is not massive enough for most researchers to classify it as a brown dwarf.
"At first I was very skeptical. In most cases, objects imaged around young stars like ROXs 42B turn out to be unrelated background stars. After convincing ourselves that the companion really was orbiting ROXs 42B, we were then worried that the companion was just a normal (much more massive) brown dwarf. But our spectrum of this object really seems consistent only with a young, planetary-mass object," Currie told Headlines and Global News in an e-mail.
The object also orbits at about 30 times farther away from its parent star than Jupiter does from our own Sun.
"This situation is a little bit different than deciding if Pluto is a planet. For Pluto, it is whether an object of such low mass amongst a group of similar objects is a planet," Currie said in the news release. "Here, it is whether an object so massive yet so far from its host star is a planet. If so, how did it form?"
Gas giants, such Jupiter and Saturn, are believed to form through a process called core accretion; meaning the spawn from a solid core before it accretes a "gaseous envelope." Core accretion is believed to be most successful closer to the object's host star, but ROXs 42Bb orbits at a relatively great distance.
Disk instability (when "a fragment of a disk gas surrounding a young star directly collapses under its own gravity into a planet") is another planet-formation theory that is believed to work better farther away from a star.
Objects that are about 10 times the mass of Jupiter and are located within 15 times the distance between Jupiter and the Sun are believed to be planets; while those that orbit more than 50 times further out than Jupiter's separation from the Sun and are more massive are generally thought to be something other than planets. ROXs 42Bb sits in a sort of "limbo" between these two classifications, and it's not the only object to do so.
"While I think that ROXs 42Bb is the best case of an uncertain object (maybe a planet, maybe a brown dwarf), there are a few others whose formation is hard to understand. For example, the recently announced companion called HD 106906 b is planet mass but almost assuredly not a planet, but is unusually light for a failed star," Currie told HNGN.
The researchers hope to learn more about the mysterious object in the future.
I think the next step is to better constrain the companion's temperature, gravity and other atmospheric properties (like clouds). We were very conservative in our analysis. With new data we will understand ROXs 42Bb's physical properties in better detail and thus better understand how it compares to the atmospheres of other planets and low-mass brown dwarfs," Currie told HNGN.
