NASA has made a pretty exciting discovery again! Making use of the data from the Spitzer Space Telescope, the team led by Ian Bond of Massey University found the Earth-size world at a distance from its parent star similar to that of Earth.
They call it OGLE-2016-BLG-1195Lb and things are pretty chilly there. It’s the smallest planet to ever be detected through gravitational microlensing, a quirk of physics that briefly makes distant objects appear brighter when a massive object passes between it and Earth.
This plant orbits a tiny M-dwarf star and it is far too frigid to ever harbor life as we know it. The temperatures are believed to be around -400 degrees F (-240 degree C). This officially makes this plant as cold as Pluto.
Finding a separation between a planet and a star like this is also difficult. Most exoplanet searches, especially those relying on transits, rely on short period planets — those that orbit their planet in days, weeks, or months instead of years. To confirm a planet via transit, you need to witness multiple transits, so a Jupiter-distance planet would take 24 years to discover at the minimum as Jupiter has a 12-year period. Indeed, even a Mars-distance object might have only swept by the initial Kepler field twice in the first mission’s history. Around 12 percent of all discovered exoplanets have a period longer than Earth (roughly 425 planets out of 3,405 confirmed.)
Another challenge that was faced is the fact that OGLE-2016-BLG-1195Lb is really, really, really far away. It’s more or less 23,400 light-years away from Earth. This is one of the reasons why the discovery of this planet is pretty exciting! On record, this is one of the farthest planets to be ever found. It was found through the magic of gravitational lensing.
Every object in the universe sort of “presses down” on the fabric of space-time. The more massive an object, the more it makes an impression in space. This effect can be visually observed when a massive object passes in front of something else. For instance, a large star close to Earth passing in front of a small star far from Earth can reveal the distortions caused by the closer object. But this event also magnifies the more distant object from our point of view, bringing forth details we normally wouldn’t be able to see.
While some microlensing events can lead to the direct imaging of planets, this discovery still relied on a transit dimming of the parent star to observe it.
So far, there are 56 planet-like objects that have been discovered by gravitational microlensing. Most of them done by the Optical Gravitational Lensing Experiment (OGLE) program that also found -1195Lb. The previous least-massive object known, OGLE-2005-169L b, is around the mass of Neptune. -1195Lb is estimated to be about five Earth masses, making it likely a super-Earth.
Follow-up studies may be difficult — microlensing events happen by chance. For now, we’ll just have to patiently wait to see if another star comes between us and the planet to discover anything new.