Generally speaking, the rogue planet used to stay in the star system, but it was expelled because of some kind of gravitational disturbance. These gravitational disturbances include the competition between planets, the interaction between stars in multi-star systems or galaxy clusters, and the close passage of stars.
Theoretical research shows that there may be billions or even trillions of rogue planets in our galaxy. However, since rogue planets are far away from the stars and do not emit light, it is extremely difficult to hide them as ghosts in dark space.
Gravitational microlens method is the best way to find rogue planets. According to Einstein's generalized phase theory, the celestial body bends the surrounding space-time like a lens, distorting and enhancing the background starlight. This is called the gravitational lens effect. The rogue planet has a relatively small mass, but it also produces a weak gravitational lens effect.
Optical Gravitational Lens Experiment (OGLE) and Korean Microlens Telescope Network (KMTN) are two projects that use gravitational microlens method to search for rogue planets. Now, scientists from these two projects claim to have discovered a rogue planet with the same mass as the earth. You know, the known rogue planets is mainly a large wooden planet, and we have only found four earth-like rogue planets before.
The gravitational microlens effect produced by the rogue planet with earth-like mass is extremely weak and lasts for a very short time. The newly discovered rogue planet is named OGLE-2016-BLG-1928, and its gravitational microlens effect lasts only 4 1.5 minutes, which is the shortest gravitational microlens event observed by human beings so far.
In a paper entitled "Quasi-terrestrial rogue planet candidates detected in the shortest gravitational microlens event", the researchers introduced this new discovery. According to the distortion and enhancement of background starlight, the mass of OGLE-2016-BLG-1928 is equivalent to that of the Earth, but its distance from the Earth is uncertain.
It is worth mentioning that because the gravitational microlens effect of OGLE-2016-BLG-1928 lasts too short, the data collected by scientists are very limited-there are only 15 detection data points in this event, which makes this new discovery uncertain.
Even so, this is still a major discovery. The researchers said in the paper that this is one of the best candidates for terrestrial mass planets detected so far.
There is almost no possibility of life on the rogue planet. They will not be the key research objects of scientists, but they are also attractive enough.
In the future, the Nancy Grace Roman Space Telescope planned by NASA will join the search for rogue planets, which is expected to help us detect a large number of rogue planets.