Assessing the Potential Visibility of Comets like C/2025 R2 (SWAN) by NEO Surveyor

We investigate the potential detectability of the newly discovered and close-approaching long-period comet C/2025 R2 (SWAN) by NEO Surveyor using the NEO Surveyor Survey Simulator ( nss ). The comet, with a minimum orbital intersection distance with Earth of 0.047 au, was discovered just one month before its closest-approach to Earth and a few days after its perihelion. We simulate “bare nuclei” test objects without cometary activity and find that NEO Surveyor, if the mission were currently operating, may have discovered C/2025 R2 90–150 days before perihelion for a nucleus with diameter d ≥ 0.6 km. This range would represent a multi-month improvement over the real-life timeline. These results highlight NEO Surveyor’s capabilities to provide early-warning for close-approaching comets, complement ground-based surveys, and enable long-term monitoring of cometary activity, all of which are crucial for planetary defense and solar system science.