Astronomers Confirm a Rogue Earth-Sized Planet Careening Through Our Galaxy

 Earth orbits the sun sort of a ship sailing in a circle around its anchor. But what if someone - or something - cut that ship loose?

Unbound from any star or system, what would become of a little world flying helplessly and heedlessly through interstellar space? What happens when a planet goes rogue?

Scientists suspect that billions of free-floating or "rogue" planets may exist within the Milky Way, but to this point, only some of the candidates have turned up among the 4,000-or-so worlds discovered beyond our scheme.

Most of those potential rogue planets appear to be enormous, measuring anywhere from two to 40 times the mass of Jupiter (one Jupiter is such as about 300 Earths). But now, astronomers believe they've detected a rogue world like no other: a small, free-floating planet, roughly the mass of Earth, gallivanting through the gut of the extragalactic nebula.

This discovery, reported on October 29 within the Astrophysical Journal Letters, may mark the littlest rogue planet ever detected, and it could help prove a long-standing cosmic theory.

According to the study authors, this small world may well be the primary real evidence that free-floating, Earth-sized planets could also be a number of the foremost common objects within the galaxy.

"The odds of detecting such a low-mass object are extremely low," lead study author Przemek Mroz, a postdoctoral scholar at the California Institute of Technology, told Live Science in an email.

"Either we were very lucky, or such objects are quite common within the galaxy. they'll be as common as stars."

Einstein's hand glass

Most exoplanets in our galaxy are visible only due to their host stars. in a very literal sense, stars provide the sunshine that enables astronomers to directly observe alien worlds.

When a planet is simply too small or too distant to be seen directly, scientists can still detect it from the slight gravitational pull it exerts on its host star (called the velocity method) or by the flickering that happens when a planet passes ahead of the star's Earth-facing side (the transit method).

Rogue planets, by definition, don't have any star to light their way - or to light a telescope's thanks to them. Instead, detecting rogue planets involves a facet of Einstein's theory of relativity referred to as gravitational lensing.

Through this phenomenon, a planet (or even more massive object) acts as a cosmic hand glass that temporarily bends the sunshine of objects behind it from Earth's perspective.

"If a large object passes between an Earth-based observer and an overseas source star, its gravity may deflect and focus light from the source," Mroz explained in an exceeding statement. "The observer will measure a brief brightening of the source star."

The smaller that light-bending object is, the briefer the star's perceived brightening is going to be. While a planet several times the mass of Jupiter might create a brightening effect that lasts some days, a measly planet the mass of Earth will brighten the source star for under some hours or less, the researchers said. This exceptionally rare occurrence is termed "microlensing."

"Chances of observing microlensing are extremely slim," Mroz added within the statement. "If we observed just one source star, we might wait almost 1,000,000 years to work out the source being microlensed."

Fortunately, Mroz and his colleagues weren't observing only 1 star for his or her study - they were watching many several them. Using observations from the Optical Gravitational Lensing Experiment (OGLE), a star survey based at the University of Warsaw in Poland that has turned up a minimum of 17 exoplanets since 1992, the team stared into the middle of the extragalactic nebula, searching for any signs of microlensing.

In June 2016, they witnessed the shortest microlensing event ever seen. The star in question, located roughly 27,000 light-years away within the densest part of the galaxy, brightened for just 42 minutes.

Calculations showed that the offending object wasn't sure to any star within 8 astronomical units (AU, or eight times the typical distance from Earth to the Sun), suggesting it had been almost certainly a little planet on the run, ejected from its home system after a brush with a far more massive object.

Depending on how far-flung the earth is from the source star (it's impossible to inform with current technology), the rogue world is probably going between one-half and one Earth mass. In either case, this roaming world would be the lowest-mass rogue planet ever detected. consistent with Mroz, that's a "huge milestone" for the science of planet formation.

"Theories of planet formation have predicted that the bulk of free-floating planets should be of Earth-mass or smaller, but this can be the primary time that we could find such a low-mass planet," Mroz said.

"It's really amazing that Einstein's theory allows us to detect a small piece of rock floating within the galaxy."

Many more tiny pieces of rock may soon follow, study co-author Radek Poleski of the University of Warsaw told Live Science.

Future planet-hunting telescopes, like NASA's Nancy Grace Roman Space Telescope (slated to launch within the mid-2020s), are rather more sensitive to the galaxy's teensiest microlensing events than the nearly 30-year-old OGLE experiment is, Poleski said. If orphan planets of roughly Earth's mass are indeed a number of the foremost common denizens of the galaxy, it should not be long before more of the surface.