One of the first, 2003 RM, exhibited non-gravitational acceleration that could not be explained even after accounting for solar radiation pressure and the Yarkovsky effect \u2014 the tiny thrust caused by heat re-emission. A year later, the interstellar visitor \u2018Oumuamua<\/a> showed a similar unexplained boost as it exited the solar system, reinforcing the idea that a whole category of comet-like bodies might be hiding in plain sight.<\/p>\n By 2024, scientists had catalogued 14 such objects. Research suggests they may be more than curiosities: if some contain hidden water ice, they could be key to understanding how Earth\u2019s oceans formed. They might also represent an overlooked impact hazard, capable of altering their orbits suddenly enough to surprise planetary defense teams.<\/p>\n Two Families, One Mystery<\/p>\n Studies led by planetary scientist Darryl Seligman revealed that dark comets<\/a> seem to fall into two distinct groups. Outer dark comets, or \u201couties,\u201d are larger, more reflective bodies \u2014 some hundreds of meters across \u2014 with comet-like orbits originating near Jupiter.<\/p>\n The smaller inner dark comets, or \u201cinnies,\u201d are less than 50 meters wide, with circular orbits confined to the inner solar system. These are harder to explain: despite constant exposure to the Sun\u2019s heat, they still show signs of acceleration that could indicate trapped subsurface ice. <\/p>\n Their tiny size makes them vulnerable to destruction, either by spinning apart or vaporizing completely \u2014 yet they persist. The possibility remains that innies are the late-stage remnants of outies, or perhaps main-belt comets that have nearly exhausted their water supply.<\/p>\n Hayabusa2\u2019s Unexpected Mission<\/p>\n The Japanese space agency JAXA<\/a> launched Hayabusa2 in 2014 to retrieve samples from the asteroid Ryugu<\/a>, a mission it completed with stunning success in 2020. With fuel to spare, the spacecraft was reassigned to explore smaller objects for planetary defense research. Its final destination \u2014 chosen before dark comets were recognized \u2014 turned out to be 1998 KY26<\/a>, an inner dark comet spinning once every ten minutes and measuring only about 30 meters across.<\/p>\n \u201cIt\u2019s really exciting,\u201d says mission manager Yuichi Tsuda, who notes the coincidence was pure luck. When Hayabusa2 arrives, it will first observe the object from several kilometers away, searching for any signs of sublimation. If comet-like outgassing is the cause of its odd acceleration, the spacecraft should detect it. Later, the probe could descend closer, possibly even firing a projectile to create a crater and reveal the object\u2019s interior composition.<\/p>\n A Race To Uncover Answers<\/p>\n The Hayabusa2 encounter will be part of a broader scientific push to understand these elusive bodies. Ground-based facilities like the Lowell Discovery Telescope<\/a> will continue monitoring known dark comets, while the upcoming Vera C. Rubin Observatory<\/a> promises to find many more once it begins operations.<\/p>\n The stakes are high. Dark comets could rewrite our understanding of the solar system\u2019s formation. They might also reshape planetary defense strategies, ensuring that Earth can anticipate objects whose movements defy conventional prediction. As \u00a0Aster Taylor of \u00a0the University of Michigan puts it, \u201cIf we can\u2019t detect these objects correctly, we will not be able to know if they\u2019re going to hit us.\u201d<\/p>\n If Hayabusa2\u2019s 2031 rendezvous confirms the icy nature of 1998 KY26, the term \u201cdark comet\u201d may no longer refer to a mystery \u2014 but to a well-defined class of objects that has been hiding, quite literally, in the dark.<\/p>\n","protected":false},"excerpt":{"rendered":"A Japanese spacecraft is on a remarkable journey toward one of the most puzzling celestial objects in our…\n","protected":false},"author":2,"featured_media":72269,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[48],"tags":[79,193],"class_list":["post-72268","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-science","tag-space"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/72268","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=72268"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/72268\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/72269"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=72268"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=72268"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=72268"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Esa](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2025\/08\/ESA-Rosetta-NAVCAM-800x800.webp.webp\"\/)
Credit: ESA\/ Rosetta\/ NAVCAM<\/p>\n