Scientists Discovered an Entire Group of Free-Floating Planets a Lot Like Earth

Not every Earth-like planet gets to have a nice, warm sun.

A team of scientists just found a mysterious group of "free-floating" planets that might not have any host stars whatsoever, and some of them might have masses not very different than Earth's, according to a recent stud published in the Monthly Notices of the Royal Astronomical Society.

And with the forthcoming space-based Roman Telescope from NASA, we're about to find a lot more.

Twenty-seven 'free-floating' planets found via microlensing

Data gathered in 2016 during the K2 mission phase of NASA's Kepler Space Telescope was analyzed in the study by Iain McDonald of the University of Manchester in the U.K., which is now located at the Open University. Throughout the two-month Kepler mission, the telescope monitored a crowded population of millions of stars close to the center of our Milky Way every 30 minutes, to identify gravitational microlensing events, which point to the presence of planets beyond our solar system.

The team identified 27 short-duration candidate signals via microlensing whose timescales spanned from an hour to 10 days. Many of these were seen before in data obtained at the same time from ground-based telescopes, but the four shortest events strongly suggest the existence of planets with masses close to Earth's in scope. But something was missing: the conventional presence of a host star. In other words, these planets are floating free in the abyssal depths of outer space without the gravitationally centering force of a star.

Planets wandering outside of any solar system, or rogue planets, might have initially formed in orbit of a host star before being flung out via the gravitational pull of other, heavier planets within the system. The method of detection, called microlensing, was predicted by Albert Einstein 85 years ago, as an implication of his General Theory of Relativity. And the theory holds that light from a background star may be temporarily magnified via the presence of other stars in a viewer's relative foreground. When this happens, the viewer will see a short flash in the brightness of the background star that could last from hours to days, and roughly one of every million stars in the galaxy is affected by microlensing at any random time. But just a few are predicted to involve planets.

NASA's Roman Telescope will likely find more earth-sized rogue planets

Kepler wasn't designed to detect planets via microlensing, nor was it launched to peer into the maddeningly dense star fields of the inner Galaxy. So to make it work this way, scientists had to improvise new data reduction techniques to scan for signals hidden in the dataset. "These signals are extremely difficult to find," said McDonald, in a Phys.org report. "Our observations pointed an elderly, ailing telescope with blurred vision at one [of] the most densely crowded parts of the sky, where there are already thousands of bright stars that vary in brightness, and thousands of asteroids that skim across our field."

"From that cacophony, we try to extract tiny, characteristic brightenings caused by planets, and we only have one chance to see a signal before it's gone," added McDonald in the report. "It's about as easy as looking for the single blink of a firefly in the middle of a motorway, using only a handheld phone." That might sound daunting, but a forthcoming space-based array from NASA called the Nancy Grace Roman Space Telescope, in addition to the ESA's Euclid mission, are specifically designed to seek out microlensing signals, and offer scientists more evidence of Earth-sized, free-floating planets.