'Iceball' Planet Discovered Through Microlensing

[baa...@earthlink.net]

https://www.jpl.nasa.gov/news/news.php?feature=6827

'Iceball' Planet Discovered Through Microlensing
Jet Propulsion Laboratory
April 26, 2017

Scientists have discovered a new planet with the mass of Earth, orbiting
its star at the same distance that we orbit our sun. The planet is likely
far too cold to be habitable for life as we know it, however, because
its star is so faint. But the discovery adds to scientists' understanding
of the types of planetary systems that exist beyond our own.

"This 'iceball' planet is the lowest-mass planet ever found through microlensing,"
said Yossi Shvartzvald, a NASA postdoctoral fellow based at NASA's Jet
Propulsion Laboratory, Pasadena, California, and lead author of a study
published in the Astrophysical Journal Letters.

Microlensing is a technique that facilitates the discovery of distant
objects by using background stars as flashlights. When a star crosses
precisely in front of a bright star in the background, the gravity of
the foreground star focuses the light of the background star, making it
appear brighter. A planet orbiting the foreground object may cause an
additional blip in the star's brightness. In this case, the blip only
lasted a few hours. This technique has found the most distant known exoplanets
from Earth, and can detect low-mass planets that are substantially farther
from their stars than Earth is from our sun.

The newly discovered planet, called OGLE-2016-BLG-1195Lb, aids scientists
in their quest to figure out the distribution of planets in our galaxy.
An open question is whether there is a difference in the frequency of
planets in the Milky Way's central bulge compared to its disk, the pancake-like
region surrounding the bulge. OGLE-2016-BLG-1195Lb is located in the disk,
as are two planets previously detected through microlensing by NASA's
Spitzer Space Telescope.

"Although we only have a handful of planetary systems with well-determined
distances that are this far outside our solar system, the lack of Spitzer
detections in the bulge suggests that planets may be less common toward
the center of our galaxy than in the disk," said Geoff Bryden, astronomer
at JPL and co-author of the study.

For the new study, researchers were alerted to the initial microlensing
event by the ground-based Optical Gravitational Lensing Experiment (OGLE)
survey, managed by the University of Warsaw in Poland. The planetary signal
was recognized in real time by another ground-based survey, the Microlensing
Observations in Astrophysics (MOA). Study authors used the Korea Microlensing
Telescope Network (KMTNet), operated by the Korea Astronomy and Space
Science Institute, and Spitzer, to track the event from Earth and space.

KMTNet consists of three wide-field telescopes: one in Chile, one in Australia,
and one in South Africa. When scientists from the Spitzer team received
the OGLE alert, they realized the potential for a planetary discovery.
The microlensing event alert was only a couple of hours before Spitzer's
targets for the week were to be finalized, but it made the cut.

With both KMTNet and Spitzer observing the event, scientists had two vantage
points from which to study the objects involved, as though two eyes separated
by a great distance were viewing it. Having data from these two perspectives
allowed them measure the masses of the star and the planet, and the distance
to the planetary system.

"We are able to know details about this planet because of the synergy
between KMTNet and Spitzer," said Andrew Gould, professor emeritus of
astronomy at Ohio State University, Columbus, and study co-author.

Although OGLE-2016-BLG-1195Lb is about the same mass as Earth, and the
same distance from its host star as our planet is from our sun, the similarities
may end there.

OGLE-2016-BLG-1195Lb is nearly 13,000 light-years away and orbits a star
so small, scientists aren't sure if it's a star at all. It could be a
brown dwarf, a star-like object whose core is not hot enough to generate
energy through nuclear fusion. This particular star is only 7.8 percent
the mass of our sun, right on the border between being a star and not.

Alternatively, it could be an ultra-cool dwarf star much like TRAPPIST-1,
which Spitzer and ground-based telescopes recently revealed to host seven
Earth-size planets. Those seven planets all huddle closely around TRAPPIST-1,
even closer than Mercury orbits our sun, and they all have potential for
liquid water. But OGLE-2016-BLG-1195Lb, at the sun-Earth distance from
a very faint star, would be extremely cold -- likely even colder than
Pluto is in our own solar system, such that any surface water would be
frozen. A planet would need to orbit much closer to the tiny, faint star
to receive enough light to maintain liquid water on its surface.

Ground-based telescopes available today are not able to find smaller planets
than this one using the microlensing method. A highly sensitive space
telescope would be needed to spot smaller bodies in microlensing events.
NASA's upcoming Wide Field Infrared Survey Telescope (WFIRST), planned
for launch in the mid-2020s, will have this capability.

"One of the problems with estimating how many planets like this are out
there is that we have reached the lower limit of planet masses that we
can currently detect with microlensing," Shvartzvald said. "WFIRST will
be able to change that."

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission
Directorate, Washington. Science operations are conducted at the Spitzer
Science Center at Caltech in Pasadena, California. Spacecraft operations
are based at Lockheed Martin Space Systems Company, Littleton, Colorado.
Data are archived at the Infrared Science Archive housed at the Infrared
Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.
For more information about Spitzer, visit:

http://spitzer.caltech.edu

http://www.nasa.gov/spitzer

News Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabet...@jpl.nasa.gov

2017-123