is a tiny near-Earth asteroid discovered by the University of Arizona's Spacewatch project on 28 May 1998. It measures in diameter and rotates rapidly with a period of 5.35 minutes. It is the target of Japan's Hayabusa2 mission, which will visit the asteroid in July 2031. When the spacecraft arrives, will become the smallest asteroid visited by a spacecraft.
is believed be to most likely a solid chunk of rock, resembling one of the boulders seen on large rubble pile asteroids like Itokawa and Ryugu. Telescope observations have shown it to be an E-type asteroid, whose surface is bright white and rich in enstatite. It shares a similar composition and orbital inclination as 44 Nysa, which suggests that they formed together from a catastrophic collision event. Due to 's small size, its rotation and orbit are gradually accelerated by sunlight-related forces, such as the Yarkovsky and YORP effects. Studies from 2025 have shown no evidence of cometary activity and anomalous acceleration in , which disproves the 2023 speculation that it might be a dark comet.
Observational history Discovery was discovered by Tom Gehrels on the night of 28 May 1998, during routine observations for the University of Arizona's Spacewatch project. The Spacewatch project had the goal of discovering near-Earth asteroids and conducted its observations using a telescope at Kitt Peak, Arizona. In the discovery images, appeared as a small dot moving among background stars with an apparent magnitude of 18.9. During this time, was approaching Earth from an initial distance of 0.03 astronomical units ().
Follow-up observations of began on 31 May 1998, starting with Spacewatch. Several other observatories around the world, including Kleť and Ondřejov Observatory in the Czech Republic, followed suit. With multiple days of observations, the Minor Planet Center (MPC) announced the discovery of on 1 June 1998, one week before the asteroid was set to make its closest approach to Earth.
First characterization
By the time 's discovery was announced, the asteroid was still approaching Earth and brightening in the sky. The asteroid was predicted to brighten up to apparent magnitude 16 and pass within of Earth, providing astronomers the opportunity to study it in detail. From 2 to 8 June, astronomers monitored the brightness of , revealing that it rotates rapidly with a period of several minutes. On 3 June, astronomers made the first measurement of 's color. During 's closest approach between 6 and 8 June, a team of astronomers led by Steven J. Ostro observed the asteroid with the Goldstone Solar System Radar in California, confirming earlier measurements of its rapid rotation and providing the first direct measurement of its size and shape. In July 1999, Ostro's team published their results in the journal Science and in a Jet Propulsion Laboratory press release, proclaiming as the smallest and fastest-rotating asteroid studied in detail at the time.
Hayabusa2 preparation
In 2020, the Japan Aerospace Exploration Agency (JAXA) announced its plan to visit in 2031 with its operational Hayabusa2 space probe. However, at the time the announcement was made, still had a large orbital uncertainty. The asteroid had not been observed since 2002 because it was too dim and far away from Earth. Astronomers had to wait for 's close approach to Earth every three and a half years before they could observe it. By monitoring 's position over several years, its orbital uncertainty can be reduced.
In December 2020, was predicted to pass within of Earth. During that time, the asteroid was predicted to brighten up to apparent magnitude 25, making it very dim and detectable to only the largest optical telescopes. Between 10 and 12 December, European and Japanese teams of astronomers observed with the Very Large Telescope and Subaru Telescope, respectively. The MPC reported the recovery of on 15 December 2020.
In June 2024, made a closer approach to Earth at a distance of . The asteroid was predicted to brighten up to apparent magnitude 20, once again providing astronomers the chance to further refine its orbit and study its properties. During May to June and October to November, a team of astronomers led by Toni Santana-Ros observed using various large optical telescopes around the world. They found that the asteroid was three times smaller and rotating twice as fast as previously thought. They additionally reanalyzed radar data from 1998 and found that it matches their new results. The team published their findings in September 2025, through the journal Nature Communications and in press releases by their affiliated institutions.
will make its next close approach to Earth in 2028, at a minimum distance of . Although the asteroid will be farther away, it may be observable with the James Webb Space Telescope (JWST) in March 2028 or October 2028. The JWST may be able provide a more definitive measurement of 's size and thermal properties before Hayabusa2s arrival in 2031.
Name This asteroid is currently known by its minor planet provisional designation , given by the MPC upon its discovery. The provisional designation encodes the year, half-month, and order of the asteroid's discovery. It has not been given a formal name and a minor planet number, because it has not been observed over enough oppositions. Once the MPC gives a number, the asteroid's discoverer can propose a name for it. According to naming guidelines by the International Astronomical Union's Working Group for Small Bodies Nomenclature, near-Earth asteroids with perihelion distances smaller than should be given mythological names not related to creation or the underworld.
Orbit and classification
orbits the Sun at an average distance (semi-major axis) of 1.23 astronomical units (AU), completing one orbit every 1.36 years. It follows a slightly elliptical and tilted orbit, with an orbital eccentricity of 0.20 and an inclination of with respect to the ecliptic. Throughout its elliptical orbit, 's distance from the Sun ranges from at perihelion to at aphelion. It crosses the orbit of Earth with a minimum orbit intersection distance of , allowing for close approaches to the planet.
Since comes close to Earth, it is classified as a near-Earth asteroid. It is specifically classified as an Apollo asteroid, because it has a wide, Earth-crossing orbit with a semi-major axis above and a perihelion below . It makes close approaches to Earth every three and a half years, although the distances vary from . poses no threat to Earth; if it were on a collision course with the planet, the asteroid would most likely explode in the upper atmosphere and harmlessly drop its fragments to the ground.
The shape and low inclination of 's orbit makes it an accessible target for intercepting with a space probe. For a spacecraft to leave low-Earth orbit and enter a rendezvous trajectory toward , it would require a total velocity change (Δv) of , lower than that needed for a rendezvous with the Moon (). A Hohmann transfer of a spacecraft onto a rendezvous with requires a minimum Δv of . For a direct Earth-to- transfer involving two burn impulses, the required Δv is even smaller at .
Non-gravitational acceleration Due to 's small size and proximity to the Sun, it exhibits noticeable non-gravitational acceleration from sunlight-related forces, such as the Yarkovsky effect. The Yarkovsky effect involves the asteroid absorbing sunlight and asymmetrically re-emitting it as thermal radiation, which causes the asteroid to recoil and deviate from its orbital path. Since is rotating backwards (retrograde) relative to its orbital direction, the Yarkovsky effect gradually shrinks its orbital semi-major axis. , the Yarkovsky effect is believed to be largely responsible for 's observed non-gravitational acceleration. Based on data , the Jet Propulsion Laboratory calculates 's non-gravitational acceleration to be AU/day2, AU/day2, and AU/day2 in the radial (A1), transverse (A2), and normal (A3) directions, respectively. Although experiences a stronger solar radiation pressure than the Yarkovsky effect, the radiation pressure is less efficient at perturbing the asteroid, because it mainly acts in the radial direction.
The Yarkovsky effect was first predicted for in 2000, but it was not detected until 2023. In a 2023 study, a team led by Darryl Seligman noticed that displayed a large normal acceleration, which seemingly could not be explained by the Yarkovsky effect. In that study, Seligman's team proposed that might be a dark comet, whose normal acceleration might be caused by unseen outgassing. The dark comet hypothesis for was disproven in 2025; observations from 2024 showed no evidence of ejected dust from outgassing, and a 2025 reanalysis led by Davide Farnocchia showed that the asteroid's non-gravitational acceleration can be fully explained by the Yarkovsky effect when using the asteroid's updated properties from 2024.
Physical properties
Shape, rotation, and structure
is a tiny asteroid with a diameter of , roughly twice the width of the Hayabusa2 spacecraft (). The asteroid's diameter was determined from radar and optical telescope measurements of its brightness and albedo. Due to its small size, the asteroid's gravity is expected to be extremely weak, with an estimated escape velocity of about . Measurements of 's Yarkovsky acceleration indicate that the asteroid has an area-to-mass ratio of and a bulk density of .
rotates rapidly with a period of 5.35 minutes, with a measurement uncertainty of 6 milliseconds. As it rotates, its brightness fluctuates due to its elongated shape. Observations of 's brightness variations from 1998 to 2024 show that the asteroid has an asymmetric and moderately elongated shape, with slight flattening along its rotation axes. Modeling of the asteroid's shape suggests that it has a large concavity close to its southern hemisphere.
The asteroid's rotational north pole points toward the ecliptic coordinates (λ, β) (36°, −44°), giving it an axial tilt of with respect to the ecliptic. This makes the asteroid's rotation retrograde, meaning it rotates backwards relative to its orbital direction. Calculations predict that the asteroid's rotation is gradually speeding up due to the YORP effect. The YORP effect is estimated to cause an annual fractional change of to 's rotation period, meaning the rotation period decreases by roughly 2 milliseconds per year. The YORP effect has not yet been detected in , and it is not expected to produce a noticeable change to its rotation period by 2030.
Due to 's small size and rapid rotation, centrifugal forces exceed the surface gravity at its equator. For this reason, the asteroid's surface is expected to lack loose boulders, as they would be flung away. For material to stick onto 's surface, it must have a minimum cohesive strength between 4 and 20 pascals. While this makes it possible for to have a rubble pile structure, models suggest that tiny, decameter-sized rubble piles are unlikely to form. is instead more likely to be a solid chunk of rock, resembling one of the boulders seen on the surfaces of larger rubble pile asteroids like Itokawa and Ryugu. Any loose material on 's surface would most likely exist as fine grains covering the asteroid's poles, where centrifugal acceleration is minimal.
Surface composition
Spectroscopic observations from 2024 have shown that is an E-type asteroid, meaning it is a highly reflective asteroid mainly made of enstatite. In visible light, appears white. Its visible spectrum most closely resembles those of EL- and EH-type enstatite chondrite meteorites, although its high geometric albedo of 0.52 aligns more closely with aubrite (enstatite achondrite) meteorites.