Astronomers have come a long way since the first confirmed detection of an exoplanet nearly 30 years ago. With a variety of methods now at their disposal, such as the fruitful transit method, over 4,000 planets outside of our solar system have been validated.
To add to this growing list is a super-Earth, called OGLE-2018-BLG-0677Lb, which, like only a handful of other planets, has a size and orbit comparable to that of Earth. If that wasn’t cool enough, the new planet and its host star are situated nearly 25,000 light-years away, making it one of the farthest planets ever detected. In fact, the researchers involved in the planet’s discovery suggest there is a reasonable chance (66.9 percent) this planetary system lies in the Milky Way’s galactic bulge – the densely packed region of stars towards the center of the galaxy.
As you may suspect, an equally magnificent method was needed to detect this distant planet. The technique, called gravitational microlensing, rests on “one in a million” events where one star crosses directly in front of another, as seen from Earth. Light from the more distant star becomes magnified due to the gravitational influence of the closer star, as predicted by Einstein’s theory of general relativity. Add a planet into the mix and this effect will be enhanced for a short time.
“The combined gravity of the planet and its host star caused the light from a more distant background star to be magnified in a particular way,” Dr Antonio Herrera Martin, a postdoctoral fellow at the University of Canterbury and lead author of the recently published paper in The Astronomical Journal, said in a statement. “We used telescopes distributed around the world to measure the light-bending effect.”
Two instruments independently detected this latest super-Earth: the Optical Gravitational Lensing Experiment (OGLE) using a telescope in Chile and the Korea Microlensing Telescope Network (KMTNet) comprised of three identical telescopes in Chile, Australia, and South Africa. Although 3,000 microlensing events are recorded each year by these experiments, the majority are attributed to lensing by single stars with no accompanying planets, the authors explained. To date, only 90 planets have been found using the microlensing technique.
“To have an idea of the rarity of the detection, the time it took to observe the magnification due to the host star was approximately five days, while the planet was detected only during a small five-hour distortion,” Dr Herrera Martin said. “After confirming this was indeed caused by another ‘body’ different from the star, and not an instrumental error, we proceeded to obtain the characteristics of the star-planet system.”
Weighing in at around four times the mass of Earth, the super-Earth or sub-Neptune world has one of the lowest masses of any planet detected using microlensing. Orbiting its host star, which is only about 10 percent the mass of our Sun, at a location comparable to that between Venus and Earth from the Sun, the planet’s “year” consists of approximately 617 days. At least we can be thankful that on Earth 2020 won’t last that long…