Scientists utilise a phenomenon, known as gravitational microlensing, to find orphaned planets

Rogue planets or orphan planets are difficult to spot. As they wonder vast expanses free from the gravitational influence of a solar system, rogue planets can be elusive, but scientists have utilised gravitational microlensing to track them down.

Our planet luckily belongs to a solar system family and it should remain so for a few billion years. However, some planets aren’t as fortunate and they end up orphaned and become free-floating planetary mass objects. These rogue planets transit the galaxy, orbiting its centre, in virtual darkness. It is thought that supernovae (star explosions) or gravitational collapse could violently eject planets from their solar system, leaving them homeless.

As these planets don’t emit light and they wonder through the galaxy, vast distances from the nearest light source, spotting them is problematic. However, when these celestial bodies pass in front of a star, their mass bends the light coming from that star. Therefore, a phenomenon, known as gravitational microlensing, can be utilised to observe the bending of light that these solar-less planets cause.

A group of Polish scientists, from Warsaw University Observatory, have utilised such a technique to identify the concentration of such planets within our galaxy. The research which has been published in the Nature journal has identified that there are fewer than 25 Jupiter-sized rogue planets, for every 100 main sequence stars, in our galaxy. This new research contradicts previous observations which predicted that there were far more Jupiter-sized rogue planets in our galaxy. However, the new research correlates with predictions about planet formations. Previous results in 2011 concluded that there were twice as many Jupiter-sized orphan planets, in our galaxy, compared to main sequence stars, but these findings did not match with planet formation theories and surveys of young clusters:

“These results, however, do not match predictions of planet-formation theories and surveys of young clusters,” the new study in Nature explains.

In this respect, the recent researcher’s results would reflect the ability that larger planets would have to hang onto their place, within a solar system. Conversely, smaller planets would be more easily dislodged, from their orbits, due to their smaller gravitational pull.

Although the results, for Jupiter-sized planets, are based on gravitational lensing events that last for 1-2 days, it is often more difficult to trace the movements of smaller planets, as their gravitational lensing events only last for a few hours. Results for smaller rogue planets could also be impeded by solar activity such as coronal mass ejections and coronal solar flares. In addition other astrophysical phenomenon could influence results. Although the team of Polish astronomers concluded, based on their results, that smaller Earth-sized rogue planets may appear in more abundance, as they detected some ultrashort timescale events, this would require more research to confirm the predicted prevalence of smaller orphaned planets.