A mysterious 36-foot-wide object known as 1998 KY26 is accelerating through space, prompting experts to investigate whether the near-Earth asteroid is possibly a lost Soviet spacecraft.
Unexplained Acceleration of 1998 KY26
First identified by the University of Arizona’s Spacewatch project, 1998 KY26 has baffled astronomers since a 2023 study reported non-gravitational accelerations that exceed what can be explained by sunlight or gravity. The object, which rotates once every 5.35 minutes, is currently located approximately 186 million miles from Earth.
“I've not seen any evidence to suggest this is a threat to our planet or anything other than an asteroid,” NASA Administrator Jared Isaacman said.
Discovered to be about one-third smaller than previously thought, the 11-meter asteroid is classified as an Apollo-class asteroid, meaning its orbit crosses Earth’s. Observations have revealed a non-gravitational component to its acceleration, including a component perpendicular to its orbital plane. Because gravity alone cannot fully explain these dynamics, scientists have looked for other potential reasoning.
Under this theory, the sublimation of internal ice would turn to gas and provide a small thrust, altering its trajectory without forming a visible cometary tail. However, a new study published in the journal Icarus by Georgia Institute of Technology aerospace engineers Korbin Hansen and Masatoshi Hirabayashi challenges this explanation.
Using current observations to calculate temperatures throughout the asteroid, the team modeled temperatures across its surface and deep inside using estimates of its shape, size, reflectivity, orbit, and physical properties. Their findings indicate that the asteroid is too warm to retain buried ice.
Even in its coolest regions, the object maintains an orbit-averaged temperature of at least 212 Kelvin, or -78.7°F (minus 61 degrees Celsius). For water ice to survive for long stretches, temperatures need to stay below approximately 145 Kelvin, or minus 128 degrees Celsius.
The researchers calculated that if water ice made up even 1 percent of the mass of 1998 KY26, it would all disappear in just over 2,000 years. If ice itself were the source of the unusual acceleration, its supply would be exhausted in just 62 years—a blink of an eye for an object that has apparently existed for billions of years.
Another possible explanation for the acceleration could be solar radiation pressure and thermal emission forces, as sunlight exerts a tiny force on objects in space.
The Phobos 1 Hypothesis
Harvard Professor Avi Loeb suggests 1998 KY26 could be the remains of Phobos 1, an unmanned Soviet spacecraft that was launched in July 1988 toward Mars but stopped communicating months into its journey after a faulty command caused it to shut down.
According to Loeb’s analysis, the fast spin, exceptional brightness, and dimensions of 1998 KY26 align with artificial spacecraft characteristics, pointing to solar radiation and energy from the sun pushing against its reflective metal outer layers and solar arrays as the cause of its orbital velocity changes.
Using a 3D model of Phobos 1, experts found the object matched several of the 1998 KY26’s brightness changes recorded by telescopes from Earth over the past 25 years.
“Our prediction is that instead of an iceberg, Hayabusa 2's cameras will reveal the label 'Made in the U.S.S.R.,'” Harvard Professor Avi Loeb wrote.
Loeb said, “The similarity of the orbit of 1998 KY26 to the orbit of the lost Phobos 1 spacecraft suggests that the two objects are the same.” While these data points lend considerable support to the concept, the team behind the study emphasized that their simulation does not definitively establish that KY26 is the missing probe, characterizing the hypothesis as highly conceivable yet currently unverified.
Scheduled Rendezvous in 2031
A definitive answer may arrive in July 2031, when the Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft is scheduled to rendezvous with the object. This mission follows the probe’s delivery of a sample capsule containing material from asteroid Ryugu to the Australian outback on December 6, 2020, after which it departed on an extended mission that included a successful flyby of asteroid Torifune in July 2026.
When Hayabusa2 arrives at 1998 KY26, it will examine the approximately 36-foot-wide object using its ONC-W and ONC-T cameras and a Lidar laser altimeter.
Until the spacecraft reaches 1998 KY26, researchers continue to study the small, fast-spinning space rock to clarify the forces acting on it, concluding that it is likely a dehydrated asteroid.
Earlier coverage: Researcher Claims Unidentified Object Passed Near the ISS
