‘Iceball’ planet discovered through microlensing
Scientists have discovered the lowest-massed exoplanet ever detected using gravitational microlensing. The “iceball” exoplanet, OGLE-2016-BLG-1195Lb, is located in the constellation Scorpius some 13,000 light-years from Earth.
Similar to Earth in both mass and distance from its host star, the similarities to Earth seem to end there. Unlike Earth’s temperate location within the habitable zone of the Sun, this exoplanet is believed to be a frozen ball of ice due to the dimness and coolness of its star, which scientists aren’t entirely sure is even technically a star.
The body in question, OGLE-2016-BLG-1195, has a measured mass of just 7.8 percent that of the Sun and is on the cusp of what is thought to be large enough to be able to ignite internal fusion within its core, which classifies a body as a star. It will take further study and close observation to determine whether this object is in actuality an ultra cool red dwarf star or if it is simply a star-like brown dwarf.
The exoplanet was initially discovered by the Optical Gravitational Lensing Experiment (OGLE) survey managed by the University of Warsaw in Poland. OGLE contacted Korea Astronomy and Space Science Institute which began tracking the event with the Korea Microlensing Telescope Network (KMTNet), which consists of three wide-field telescopes located in Australia, Chile, and South Africa.
KMTNet, along with the Spitzer Space Telescope, managed by NASA’s Jet Propulsion Lab in Pasadena, California, for NASA’s Science Mission Directorate in Washington, D.C., observed and tracked the event from these ground positions on Earth as well as Spitzer’s location in space.
This combined perspective allowed scientists to calculate parallax using angular distance to determine the size and distances within the system, in addition to the microlensing which allowed both the central bulge as well as the disk of the system to be viewed. These observations made it possible for scientists to uncover the orbit and mass of the exoplanet as well as the mass of the suspected star.
Spitzer, which is an infrared instrument designed to look for tiny differences in heat in the cold of space, was unable to detect any additional smaller mass heat signatures within the central bulge of OGLE-2016-BLG-1195 beyond that of the star. This suggests that OGLE-2016-BLG-1195Lb, which is located further out in the disk of the system, is likely the central most planet within the system in addition to two other exoplanets previously detected further out in the planetary disk via microlensing by NASA’s Spitzer Space Telescope.
Microlensing is a technique which allows distant objects to be seen by using background stars as virtual flashlights. When one star crosses exactly in front of another bright star behind it, the gravity of the star in the foreground focuses the light of the star in the background making it appear brighter. If there is a planet orbiting the star in the foreground, this may cause an additional increase in the star’s brightness. In the case of OGLE-2016-BLG-1195Lb, the increase only lasted for a few hours.
Whether a brown or red dwarf, the discovery of its exoplanet helps add to the greater understanding of how stellar and planetary systems form and evolve, and their frequency and distribution within our galaxy. Astronomer Geoff Bryden with JPL, who is co-author of the study, stated that “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.”
Gravitational microlensing, which is the same technique used to discover the TRAPPIST-1 system with seven Earth-sized planets orbiting an ultra-cool M-class red dwarf star earlier this year, has allowed scientists to locate the most distant exoplanets from Earth, as well as those in extended orbits from their host stars, something that other techniques such as the transit method used by the Kepler space telescope to discover a confirmed 2,482 exoplanets, makes difficult.
Unlike the TRAPPIST-1 exoplanets that all orbit within the diameter of Mercury’s orbit, and despite this exoplanet’s similarities to Earth in mass and orbital distance, scientists believe it to be colder even than Pluto and highly unlikely to be able to maintain any liquid water on its surface.
Due to the limitations of current observational technology, smaller mass exoplanets are unlikely to be discovered using gravitational microlensing at this point.
“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,” said Yossi Shvartzvald, a NASA postdoctoral fellow based at JPL, and lead author of a study published in the Astrophysical Journal Letters. “WFIRST will be able to change that.”
NASA’s upcoming Wide Field Infrared Survey Telescope (WFIRST), which is expected to be launched in the mid-2020s, should have the capability to detect low-mass planetary objects that are significantly more distant from their stars than the Earth is from the Sun.
JPL manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate in Washington, D.C. 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.
A native of the Greater Los Angeles area, Ocean McIntyre's writing is focused primarily on science (STEM and STEAM) education and public outreach. McIntyre is a NASA/JPL Solar System Ambassador as well as holding memberships with The Planetary Society, Los Angeles Astronomical Society, and is a founding member of SafePlaceForSpace.org. McIntyre is currently studying astrophysics and planetary science with additional interests in astrobiology, cosmology and directed energy propulsion technology. With SpaceFlight Insider seeking to expand the amount of science articles it produces, McIntyre was a welcomed addition to our growing team.