Meet the free-ﬂoating planets that like to ﬂy solo.
Up until the late-20th century the only planets we knew of were those found in our own Solar System. Now, thanks to missions such as NASA’s Kepler spacecraft, we know of hundreds more that exist in other planetary systems across the cosmos. But in the last decade, we’ve started to ﬁnd some planets drifting freely through space, and estimates suggest that there could be millions more in our Milky Way alone. First theorized in 1998, several rogue planets have been found since 2012. The predominant theory as to how these planets come to be ‘going solo’ surmises that these bodies were knocked out of a planetary system by some major event – perhaps a passing star or a nearby unbalanced young system.
Another emerging theory, however, suggests that some rogue planets could be born without a parent star in clouds of dust and gas. These planets would then form in a similar way to stars, except they would be too small to ignite fusion at their cores, so end up remaining as planets rather than developing into stars. Studies indicate free-ﬂoating planets may be able to retain some heat, although they are most likely to be cold and barren worlds.
Detecting rogue planets is a tricky business. Our usual methods of ﬁnding exo-planets, by noticing their effect on their parent star, are impossible here. Instead, scientists either try to directly image them or notice the gravitational microlensing effect a rogue planet has as it passes in front of a background star.
One of the closest rogue planets to our Solar System, and the ﬁrst to ever be conﬁrmed in 2012, was CFBDSIR2149-0403. Found about 100 light years from us, its proximity has allowed it to be studied in detail. Observed by the European Southern Observatory’s Very Large Telescope (VLT) in Chile and the Canada-France-Hawaii Telescope (CFHT) on Hawaii, astronomers have deduced it is between 50 and 120 million years old. It is thought to have a surface temperature of 400 degrees Celsius (750 degrees Fahrenheit) and a mass four to seven times that of Jupiter. Interestingly some observations have also detected water and methane in its atmosphere.