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An Earth-size planet is careening untethered through the galaxy,



 
 
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Old October 31st 20, 02:51 PM posted to alt.astronomy
a425couple
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Default An Earth-size planet is careening untethered through the galaxy,

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https://www.livescience.com/earth-si...ue-planet.html

An Earth-size planet is careening untethered through the galaxy,
scientists find
By Brandon Specktor - Senior Writer a day ago

Nobody has ever seen one here — until now.

A rogue planet bends the light of the star behind it, relative to Earth.
(Image: © Jan Skowron / Astronomical Observatory, University of Warsaw)

Earth orbits the sun like a ship sailing in circles around its anchor.
But what if someone — or something — cut that ship loose? Unbound from
any star or solar system, what would become of a tiny 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 in the Milky Way, but so far only a handful of candidates have
turned up among the 4,000-or-so worlds discovered beyond our solar
system. Most of these potential rogue planets appear to be enormous,
measuring anywhere from two to 40 times the mass of Jupiter (one Jupiter
is equivalent to about 300 Earths). But now, astronomers believe they've
detected a rogue world like no other: a tiny, free-floating planet,
roughly the mass of Earth, gallivanting through the gut of the Milky Way.

This discovery, reported today (Oct. 29) in the Astrophysical Journal
Letters, may mark the smallest rogue planet ever detected, and it could
help prove a long-standing cosmic theory. According to the study
authors, this little world could be the first real evidence that
free-floating, Earth-sized planets may be some of the most common
objects in the galaxy.

Related: 9 Strange Excuses for Why We Haven't Met Aliens Yet

"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 very common in the Milky Way. They may
be as common as stars."

CLOSE
Einstein's magnifying glass
Most exoplanets in our galaxy are visible only because of their host
stars. In a literal sense, stars provide the light that allows
astronomers to directly observe alien worlds. When a planet is 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
radial velocity method) or by the flickering that occurs when a planet
passes in front of the star's Earth-facing side (the transit method).

Rogue planets, by definition, have no star to light their way — or to
light a telescope's way to them. Instead, detecting rogue planets
involves a facet of Einstein's theory of general relativity known as
gravitational lensing. Through this phenomenon, a planet (or even more
massive object) acts as a cosmic magnifying glass that temporarily bends
the light of objects behind it from Earth's perspective.


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

An artist's impression of a gravitational microlensing event by a
free-floating, or rogue, planet. In microlensing, gravity from an object
causes the light from a background source to bend, an astronomical
phenomenon that shows up as distortions in images taken from Earth.

An artist's impression of a gravitational microlensing event by a
free-floating, or rogue, planet. In microlensing, gravity from an object
causes the light from a background source to bend, an astronomical
phenomenon that shows up as distortions in images taken from Earth.
(Image credit: Jan Skowron / Astronomical Observatory, University of Warsaw)
The smaller that light-bending object is, the briefer the star's
perceived brightening will be. While a planet several times the mass of
Jupiter might create a brightening effect that lasts a few days, a
measly planet the mass of Earth will brighten the source star for only a
few hours, or less, the researchers said. This exceptionally rare
occurrence is called "microlensing."

"Chances of observing microlensing are extremely slim," Mroz added in
the statement. "If we observed only one source star, we would have to
wait almost a million years to see the source being microlensed."

Fortunately, Mroz and his colleagues weren't observing just one star for
their study — they were watching hundreds of millions of 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 at least 17 exoplanets since 1992, the team stared into the center of
the Milky Way, looking 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 in the
densest part of the galaxy, brightened for just 42 minutes. Calculations
showed that the offending object was not bound to any star within 8
astronomical units (AU, or eight times the average distance from Earth
to the sun), suggesting it was almost certainly a tiny planet on the
run, ejected from its home solar system after a brush with a much more
massive object.

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

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"Theories of planet formation have predicted that the majority of
free-floating planets should be of Earth mass or smaller, but this is
the first 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 tiny
piece of rock floating in 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 in the mid-2020s), will be much 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 some of the most common denizens of the galaxy, it shouldn't
be long before many more of them turn up.
 




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