An international research team, including Korea, has discovered a new "rogue planet," a planet drifting alone through space.
The Korea AeroSpace Administration said on the 2nd that a research team involving the Korea Astronomy and Space Science Institute (KASI) discovered a Saturn-mass rogue planet by jointly using data from the Korea Microlensing Telescope Network (KMTNet) and the European Space Agency (ESA)'s Gaia space telescope. The findings were published on the 1st (local time) in the international journal Science.
The newly discovered planet is named KMT-2024-BLG-0792. Its mass is estimated at about 0.7 times that of Saturn, and it is located about 10,000 light-years from Earth (a light-year is the distance light travels in one year, about 9.46 trillion kilometers). In particular, this planet is the first rogue planet whose distance was measured accurately by using both ground-based and space telescopes simultaneously.
A rogue planet is, literally, a planet that does not orbit a particular star and drifts alone in space. Such an object may be a planet that originally orbited a star but was ejected by gravitational interactions, or it may have formed alone from the outset. As a result, it provides key clues to how planetary systems form and how they change over time.
The problem is that rogue planets emit little to no light on their own, making direct observation extremely difficult. For now, microlensing is regarded as the key method for finding rogue planets. Gravitational microlensing is a phenomenon in which the gravity of an unseen foreground object slightly bends the light of a background star, making that star appear briefly brighter from Earth. By analyzing the shape and duration of the brightening, researchers can infer information such as the mass and distance of the lensing object.
The team captured the microlensing signal of this rogue planet with KMTNet observations. KMTNet operates three telescopes installed on separate continents in Chile, Australia, and South Africa. This allowed continuous observation of microlensing events that pass quickly, from a few hours to about a day.
The decisive factor was Gaia's observations of the same region. When the microlensing occurred, Gaia had observed the same patch of sky six times over 16 hours, and combining those data with KMTNet's allowed a more accurate calculation of the planet's distance and mass.
This study confirmed for the first time that planets can indeed be found in the so-called "Einstein desert," where rogue planets had been rarely detected. In microlensing observations, researchers use the "Einstein radius" as a yardstick for how much an object's gravity bends starlight. The range where this value is about 9–25 microarcseconds (μas) has been difficult to observe and has been called a "desert."
Kang Kyung-in, director of space science exploration at the Korea AeroSpace Administration, said, "Korea is leading the discovery of exoplanets by observing microlensing with KMTNet built by KASI," and added, "We will continue to pursue new discoveries through simultaneous observations with ground-based telescopes and international space telescopes."
References
Science (2026), DOI: https://doi.org/10.1126/science.adv9266