We review the detection and mass-function measurements of free-floating planets (FFPs) or very wide-orbit planets using the microlensing technique. The microlensing surveys have identified several events with extremely short Einstein radius crossing times, t_E<0.5 days, and very small angular Einstein radii of theta_E <10μas. Such events are likely produced by low-mass lenses, potentially...
I will present an analysis of the microlensing event OGLE-2023-BLG-0524, the location of which was serendipitously captured in 1997 with the Hubble Space Telescope (HST). Our team conducted recent follow-up imaging with HST in 2025, thus we achieve a record-breaking baseline length of 28 years between the high-resolution epochs. The very short duration of this microlensing event (tE = 0.346 ±...
Free-floating planet (FFP) candidates detected via microlensing could also be bound planets on wide orbits (>5–10 au). High resolution imaging may break this degeneracy via direct detection of the putative host stars. We are conducting a multi-year Keck AO imaging survey of a large number of microlensing FFP candidates detected over the past two decades. I present preliminary results on phase...
The mass function of free-floating planets (FFPs) could key insights into the planet formation and dynamics. Microlensing provides a powerful technique to probe this population, especially at the low-mass end. We will describe preliminary search results of FFPs using the existing KMTNet survey data (KMTNet Rogue Objects Astrophysical Monitoring, K-ROAM), and the ongoing DECam Rogue Earths And...
NASA’s Nancy Grace Roman Space Telescope — launching in late 2026 — will open up unprecedented discovery space in the infrared universe. Combining Hubble-like sensitivity and resolution with a field of view 100 times larger and a sky-mapping speed 1,000 times faster, Roman will conduct panoramic, high-resolution surveys that will transform our understanding of dark energy, exoplanetary...
The identification and modeling of rogue or wide orbit planets has been a challenging task for gravitational microlensing surveys, in part because of difficulties due to systematic errors and false positive detections. Roman will not have the same systematic errors and false positive signals as ground-based microlensing surveys, but the small number of magnified images and large expected rate...
Launching in less than a year, the Nancy Grace Roman Space Telescope is poised to detect hundreds to thousands of free-floating planets at masses ranging from that of Mars to beyond Jupiter. Reconstructing the mass distribution of these worlds would provide key insight into their origins and dynamical history, and as such, is a prime target for the Roman mission. However, due to the inherent...
JASMINE is an infrared space-based telescope mission being planned in Japan. The telescope is expected to orbit around the Earth and to observe microlensing events in parallax with other space-based telescopes located away from the Earth, such as Roman. As of now, the proposed JASMINE's target regime can support one of the Roman's observation fields close to the Galactic center, and...
One of the key questions about microlensing free-floating planet (FFP) events is whether the lenses are bona fide unbound or bound to a star that is not microlensing because of chance alignment. One avenue to verify boundness is to image the FFP events with high angular resolution in order to directly detect the putative host star. The highest resolution is obtained with interferometry. I will...
