Nereid: Neptune’s lone survivor of an ancient moon collision

New James Webb Space Telescope data suggest Neptune’s moon Nereid may be the sole survivor of an ancient collision that destroyed Neptune’s original moon system. Its surface appears highly water-rich and CO2-bearing, unlike many Kuiper Belt objects, challenging a captured-origin scenario. Computer simulations indicate Triton’s arrival over 4 billion years ago would have disrupted the system, but Nereid could have endured on a distant, eccentric orbit, potentially rewriting ideas about how moons around ice giants form.