On August 28, 2025, astronomers aimed NASA\u2019s radar system at a region of space where a near-Earth asteroid was expected to appear. Instead, the object failed to show up, leaving researchers puzzled. The unexpected no-show turned what seemed like a routine observation into a surprising case of mistaken identity.<\/p>\n
In a study<\/a> published in Nature Astronomy, a team of scientists reveals the true identity of a near-Earth object with an apparent dual personality. Scientists had been tracking the object for 28 years, assuming it might be an asteroid. Its recent deviation from its predicted path, however, suggested something unexpected is influencing the object\u2019s motion.<\/p>\n Although previous observations of asteroid 1998 SH2 didn\u2019t show obvious comet-like behavior, a more precise measurement of its position in the sky proved that its motion is irregular like that of a comet.<\/p>\n A comet in disguise <\/p>\n Scientists tracked the object\u2019s orbit around the Sun from 1998 to 2016, where it circled our star twice. It wasn\u2019t until 2025 that scientists attempted to carry out additional observations using NASA\u2019s Deep Space Network.<\/p>\n The object, provisionally known as the asteroid 1998 SH2, passed safely within 2 million miles (3 million kilometers) of our planet during its 4.5-year orbit around the Sun. Researchers calculated its position using data from previous orbits and factored in the effects the Sun\u2019s gravity, as well as the planets, would have on its path. They then pointed NASA\u2019s array of giant radio antennas toward that specific point in the sky, but asteroid 1998 SH2 didn\u2019t show up.<\/p>\n \u201cAfter we measured the nongravitational perturbations affecting the motion of 1998 SH2 and recognized they weren\u2019t compatible with the object being an asteroid, we suspected the object could be an active comet,\u201d Davide Farnocchia, a navigation engineer with the Center for Near-Earth Object Studies at NASA\u2019s Jet Propulsion Laboratory and lead author of the study, said in a statement<\/a>.<\/p>\n By scouring previous observations of the near-Earth object, the researchers determined that it may be generating a small thrust by venting gas into space. That small thrust would cause it to deviate from its predicted path.<\/p>\n A closer look <\/p>\n When a comet passes closely to the Sun, the heat from the star turns its ice to gas. Scientists usually identify regular comets by their trademark tail and coma, the gas and dust surrounding a comet\u2019s nucleus. In the case of 1998 SH2, the amount of outpouring gas and dust was in much smaller quantities, so its resulting tail and coma were not detectable in most observations.<\/p>\n The researchers behind the new study set out to get a closer look at 1998 SH2 during its August 2025 close approach. They enlisted the help of astronomers at the 3.6-meter (12-foot) Canada-France-Hawaii Telescope near the summit of Mauna Kea, Hawaii, and the 1.5-meter (5-foot) European Southern Observatory\u2019s Danish Telescope in La Silla, Chile, as well as the European Southern Observatory\u2019s 8.2-meter (27-foot) Very Large Telescope on the Chilean mountain Cerro Paranal.<\/p>\n \u201cThe images we collected from these observatories showed a weak but clear tail, thus confirming that 1998 SH2 is, in fact, a comet,\u201d Olivier Hainaut, an astronomer with the European Southern Observatory and coauthor of the study, said in a statement. \u201cThat\u2019s how science works \u2014 you form a hypothesis, and you set out to test it. This data is exactly what was needed to confirm our hypothesis that 1998 SH2 was a comet.\u201d<\/p>\n As a result, 1998 SH2 will receive an additional comet provisional designation as P\/1998 SH2.<\/p>\n