The X-shaped comet-like object may have been created by a collision of two asteroids, possibly siblings of the rogue rock blamed for killing the dinosaurs millions of years ago, scientists said.
Nasa described the debris pattern and trailing streamers of dust as "mysterious" but said the images caught on its Hubble Space Telescope suggest a head-on collision between two asteroids.
The object, known as P/2010 A2, was circling about 90 million miles from Earth in the main asteroid belt between Mars and Jupiter when it was spotted last week.
A Nasa spokesman said: "Astronomers have long thought the asteroid belt is being ground down through collisions, but such a smash-up has never been seen before."
Asteroid collisions are energetic, with an average impact speed of more than 11,000 miles per hour, or five times faster than a rifle bullet, the Nasa website said.
David Jewitt, of the University of California in Los Angeles, said: "This is quite different from the smooth dust envelopes of normal comets.
"The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies."
Mr Jewitt added: "If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight."
The orbit of P/2010 A2 is consistent with membership in the Flora asteroid family, produced by "collisional shattering" more than 100 million years ago, Nasa said.
The Press Association has contributed to the report.