• 'Iceball' Planet Discovered Through Microlensing

    From baalke@earthlink.net@21:1/5 to All on Fri May 5 23:31:30 2017
    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
    elizabeth.landau@jpl.nasa.gov

    2017-123

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