Astronomers say that there may be billions of planetary nomads without home star systems floating around in the void of space.
Scientists—and even science fiction writers—have long speculated that there may be orphaned planets who have, for one reason or another, left their home stars. While there are theories on the existence of these planets, actual evidence of them is scarce. These planets are difficult to observe directly as they float in dark space. One might pass in front of a star, thus causing an observable “blip”. However, these occurrences are very rare.
When a rogue planet passes in front of a star, the planet's gravitational field acts as a magnifier for the star's light. This is called a microlensing event. When this happens, scientists can determine not just the planet's existence, but its mass as well. Larger planets the size of Jupiter amplify a star's light for one to several days, while smaller planets do so for only a few hours.
It sounds simple, but it's only deceptively so. It actually takes complicated calculations and assumptions to come to these basic conclusions. However complicated they are, though, they are doable. Astronomers are now at their telescopes, keeping watch on hundreds of millions of stars 24/7 to look for signs of rogue planets.
Poland’s Optical Gravitational Lensing Experiment's team (OGLE) has six years of observation under its belt. It has observed 50 million stars and analyzed over 2,600 microlensing events. According to the team's estimates, there is possibly one Jupiter-sized rogue planet for every four stars in the Milky Way.
Thus, the findings show that there aren't really as many Jupiter-sized planets without star systems as scientists previously thought. The Microlensing Observations in Astrophysics (MOA) had published a paper claiming that Jupiter-sized rogue planets are twice as common as stars. Many other scientists had been skeptical of these claims. Researchers at OGLE once backed MOA's claims, until their own data proved the previous data to be inaccurate. However, it's possible that smaller rogue planets traverse the universe, unencumbered. OGLE had identified extremely short microlensing events, which had lasted less than half a day. It's thus possible that objects one to ten times the mass of the Earth are free-floating around space.
Exactly how many of these objects exist and how big they might be are still the subject of debate. Different observatory teams, like MOA and OGLE, have their own findings. However, the evidence itself for these findings is circumstantial, especially for smaller planets closer to the mass of Earth.
The question, of course, is why it's so important to find evidence of these rogue planets, however big or small they may be? For one thing, more evidence means more information. More information, meanwhile, will allow scientists to learn more about how planets form. There's still a wealth of knowledge on the formation of planets lying under the surface, and it's worth finding out. Knowing more about rogue planets that don't have home star systems can reveal more about our own planet and the others in this solar system.
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