A Harvard astrophysicist who proposed that a puzzling object racing through the solar system may be a lost Soviet spacecraft is challenging NASA Administrator Jared Isaacman’s assessment that it is simply an asteroid.
Called 1998 KY26, the object measures about 36 feet across and is generally classified as a near-Earth asteroid. However, its acceleration appears to exceed what gravity alone would produce. Avi Loeb and his colleagues have investigated whether KY26 could instead be Phobos 1, a Soviet probe that lost contact with Earth while en route to Mars in 1988.
Isaacman addressed the object Thursday during an appearance on “Fox & Friends.”
“I’ve not seen any evidence to suggest this is…anything other than an asteroid,” Isaacman said.
Two shape models depict scientists’ estimates for the appearance of near-Earth object 1998 KY26. (Credit: NASA)
Loeb disputed that conclusion in a Friday interview with News Media.
“Well, first of all, it’s not an asteroid because 1998 KY26 appears to have non-gravitational acceleration, meaning it’s being pushed by some force other than gravity, and asteroids are just rocks,” Loeb said.
Researchers have been searching for an explanation for the object’s unexpected additional acceleration.
One possibility is that KY26 is a “dark comet”—a rocky body that behaves like a comet but does not display an obvious coma or tail.
This illustration depicts the Soviet Phobos 1 spacecraft, launched toward Mars in July 1988 before a faulty command caused the probe to shut down and communications to end. (Credit: NASA)
A recent Georgia Tech study questioned whether KY26 could hold enough ice to generate that effect. Other research, meanwhile, has proposed that sunlight pressure and heat released from the object’s surface could explain its movement.
Loeb said his team found that KY26’s path closely tracks the trajectory expected for the failed Soviet mission. The researchers also calculated that sunlight reflecting from Phobos 1 could create a force consistent with the non-gravitational acceleration measured in KY26.
He cited additional observations suggesting that the object is unusually reflective and completes one rotation roughly every five minutes.
A model depicts Phobos 1, the Soviet spacecraft that lost contact with Earth during its 1988 journey to Mars. Harvard astrophysicist Avi Loeb and his colleagues are examining whether mysterious object 1998 KY26 could be the missing probe. (Credit: NASA)
For Loeb, the absence of a visible tail or escaping material is a major weakness in the dark-comet theory.
“It could be a comet shedding some gas backward that is pushing it forward, but in that case we should have seen the gas,” Loeb said. “We should have seen the dust because for comets we see a tail and the dust particles are being pushed away from the sun by the solar radiation.”
“We don’t see a cometary tail. We don’t see any evidence for outgassing around this object. That’s the puzzle,” he added.
Loeb likened the dispute over KY26’s identity to the challenge of classifying an unfamiliar animal.
Avi Loeb speaks at the SALT conference in Manhattan, New York City, on September 14, 2022. (David ‘Dee’ Delgado)
“If you are an expert on zebras and you see an elephant, you would say the elephant is a zebra without stripes,” Loeb said. “But that’s an oxymoron because it’s a completely different animal.”
He argued that scientists should remain open to possibilities beyond the standard asteroid and comet categories when an object’s behavior does not fit either explanation.
“Innovation in science requires some imagination,” Loeb said. “It requires you to allow for the possibility that our knowledge is incomplete.”
News Media contacted NASA for a response to Loeb’s claims and asked whether Isaacman continues to stand by his assessment of KY26.
Jared Isaacman, President Donald Trump’s nominee for NASA administrator, testifies before the Senate Commerce, Science and Transportation Committee during a confirmation hearing at the Russell Senate Office Building on Capitol Hill on April 9, 2025, in Washington. (Kevin Dietsch/Getty Images)
Loeb conceded that his team’s explanation has not been proven. He said the mystery may receive a definitive test in 2031, when the Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft is scheduled to rendezvous with KY26.
He believes that mission could reveal whether scientists have been tracking a remnant of Soviet space history rather than an unusual natural body.
A concept illustration shows an asteroid passing near Earth. (iStock)
“We predict that when they land on it, instead of seeing an iceberg, they will find the label ‘Made in the USSR,’” Loeb said.
Loeb said the Hayabusa2 flyby could ultimately resolve the debate.
When asked whether the Phobos 1 theory would be disproved if the spacecraft reaches KY26 and finds ordinary rock or ice, Loeb answered without hesitation.
“Yes,” he said.