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Smallest Rogue Planet Wanders the Milky Way Without a Host Star

Astronomers from the United States and Poland have discovered another rogue planet wandering around the Milky Way Galaxy but this one is particularly special as it’s the smallest one ever found.

The majority of known planets orbit a star but scientists think that there are many rogue ones wandering around the galaxy. In fact, some of them believe that there could possibly be more “free-floating” planets than stars in the Milky Way. According to a 2011 study, there could be two rogue planets for each star in our galaxy. Since there are approximately 200 to 400 billion stars in the Milky Way, there could potentially be 400 to 800 billion rogue planets wandering around. That’s absolutely mind-blowing.

(Not the rogue planet mentioned in this article.)

Back in 2011, astronomers discovered ten rogue planets and they were all approximately the same size as Jupiter and did not have a host star within 10 astronomical units from them (for comparison, the distance between Earth and our sun is one astronomical unit). “We can rule out the planet having a star within about eight astronomical units,” the researchers said in regards to the most recently found rogue planet.

This newly discovered exoplanet candidate is much smaller than those previously found as its mass is believed to be in between that of Earth and Mars. “When we first spotted this event, it was clear that it must have been caused by an extremely tiny object,” stated astronomer Radoslaw Poleski from the University of Warsaw, in Poland, and an author of the study.

In order to find this planet, scientists used a method called “gravitational microlensing” which is when the brightened light from distant stars behind the planet become bent and therefore reveals the planet. Przemek Mroz, who is an astronomer from the California Institute of Technology and another author of the study, explained the difficulty of this process, “[The] chances of observing microlensing are extremely slim because three objects — source, lens and observer — must be nearly perfectly aligned.”

(Not the rogue planet mentioned in this article.)

They found the planet by studying data from the Warsaw Telescope at the Las Campanas Observatory in Chile that conducted microlensing surveys of the Galactic Bulge in the central part of our galaxy.

So what causes a planet to become rogue? Scientists believe that these planets are created in the rotating gas and dust discs around young stars and are eventually thrown out of the planetary system after a gravitational disturbance with other bodies send them flying through space.

Their study was published in Astrophysical Journal Letters and can be read in full here.