Astronomers Reveal 75-Km Three-Headed Asteroid Nysa With 1-Km Moon

Q: What violent cosmic event caused three massive fragments to perfectly fuse together into a single asteroid without shattering completely?

No single violent event has been identified. Astronomers say Nysa’s shape is still best explained by two competing scenarios, both involving ancient impacts, but the evidence does not yet show exactly which one happened. The leading idea is an ancient low-velocity collision that broke a larger body into major fragments, which then slowly reaccumulated and stuck together under their own gravity, forming a “contact trinary.” In that case, the fragments would not have fused in a molten sense; they would have merged gently enough to remain intact while creating the narrow necks seen in the new images. A second possibility is a hit-and-run collision with a larger parent body. That kind of encounter can violently deform or partially disrupt an asteroid, leaving behind an unusually irregular remnant that only looks like three joined pieces. Researchers say this could also explain Nysa’s bizarre outline, though it raises questions about why there is no obvious larger asteroid family nearby. So the short answer is that scientists do not believe three massive fragments “perfectly fused” in one known event. Instead, they suspect an ancient collision history followed by slow gravitational reassembly, or a major hit-and-run impact that reshaped a single body. Future measurements of the newly found moon’s orbit should help determine Nysa’s mass and density, which may show whether it is truly a three-part merger or an extraordinarily deformed single asteroid.

3 articles · Updated · Space.com · Aug 3

New telescope images resolved (44) Nysa as what astronomers say is the first known trilobate asteroid in the solar system, with a tiny moon orbiting it.
75-km-wide Nysa shows two narrow necks that create its three-lobed shape, while the moon—designated S/2026 (44) 1—appears to be about 1 km across.
170 km from the asteroid, that moon was identified in observations from Chile's Very Large Telescope and Arizona's Large Binocular Telescope; Nysa itself was first spotted in 1857.
Researchers said Nysa may be either a contact trinary of three joined components or an unusually irregular single body, offering a rare target for studying material linked to the inner planets' formation.