Astronomers have spotted another “rogue planet” wandering throughout our Milky Way galaxy. Interestingly enough, this exoplanet doesn’t have any parent star attached to it. It was also found out that the traveling planet’s mass is almost similar to the one of Earth and Mars, though it’s 10% heavier. Once confirmed, it would be a huge scientific milestone in observing rogue planets, believed to be in abundance especially outside our galaxy.
Andrzej Udalski, the co-author of a study and investigator of the Optical Gravitational Lensing Experiment (OGLE) project, stated that this recent finding clearly shows that even low-mass free-floating stellar objects can be detected by using ground-based telescopes, although the endeavor is still rather difficult.
Abundant, But Difficult To Find
To date, more than 4,000 exoplanets have already been recorded. Most of them discovered by using the traditional “transit” or “radial velocity” method. The “transit method” involves paying close attention to brightness dips caused when an object crosses the host’s starlight from the viewer’s point of view. While the “radial velocity method” involves looking for the planet’s gravitational pull to spot them.
However, both techniques require a parent/host star. Fortunately, another technique called “gravitational microlensing” was used to observe foreground objects pass in front of stars.
To simplify, “gravitational microlensing” can reveal the target’s mass and other characteristics by carefully watching it pass in front of distant background stars. The closer body will resemble more like a gravitational lens when doing so.
Detecting A Rogue Planet By “Gravitational Microlensing”
Detecting microlensing events are almost one-in-a-million because all factors (lens, light source, and observer), must be perfectly aligned. This is why it would take almost a million years for only one star to be microlensed.
Thankfully, planet hunters don’t have to go this painstaking way. A project led by the University of Warsaw used the data gathered from the OGLE project to observe millions of stars at the same time on clear nights.
Eventually, an OGLE event called OGLE-2016-BLG-1928 was pulled off. It was the shortest microlensing event ever detected (until now), with a duration of just 42 minutes. After the data has been further characterized by the Korea Microlensing Telescope Network, co-author Radoslaw Poleski stated that the event must’ve been caused by a tiny object.
If this planet was orbiting a star, detecting it would’ve been much easier. But because it doesn’t have a host, we can rule out this exoplanet having a star within 8 astronomical units (AU).
One AU is about 150 million km (93 million miles). So, having an 8 AU is roughly the distance between the Sun and Jupiter (or Saturn). You can further read about this new study on arXiv.org.
Rogue Planet Kicked Out From Orbit
Astronomers have discovered only a couple of rogue planets to date. But this small number is believed to be part of a larger population, given the difficulty of detecting these small, exotic worlds.
Astronomers think that most of these rogue planets are born in a normal way, much like our own. But these worlds were eventually kicked out by gravitational forces, especially those that came from their gas-giant neighbors.
A viable theory suggests that most of these rogue worlds have masses between 30 percent to 100 percent that of Earth. So, the OGLE-2016-BLG-1928 is most likely one of them.
Scientists and astronomers could soon start better in handling these new findings. For instance, one of NASA’s Nancy Grace Roman Space Telescope’s main task is to conduct large microlensing surveys. It is expected to find 250 more rogue planets, including 60 more Earth-like ones.
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