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February 19, 2026<\/p>\n
3 min read<\/p>\n
Add Us On Google<\/span>Add SciAm<\/span><\/span><\/p>\n Our solar system is surrounded by weird peanut-shaped objects. Astronomers think they know why<\/p>\n A study published today helps explain how \u201cplanetesimals\u201d\u2014the building blocks of planets\u2014came to be<\/p>\n By Joseph Howlett edited by Lee Billings<\/span><\/p>\n The planetesimal Arrokoth, as pictured by the New Horizons flyby in 2019 (with color enhanced). About one in 10 planetesimals in the Kuiper Belt share Arrokoth\u2019s peanut-like shape.<\/p>\n NASA\/Johns Hopkins University Applied Physics Laboratory\/Southwest Research Institute\/Roman Tkachenko<\/p>\n Out in the Kuiper Belt, the massive doughnut of debris beyond Neptune, about one in 10 kilometer-scale objects have surprised scientists with their unexpected shape. Rather than resembling a ball, each of these remnants from the solar system\u2019s early history is composed of two different-sized lobes, like a peanut or a lazily assembled snowman.<\/p>\n Astronomers got their clearest view yet of the phenomenon when NASA\u2019s New Horizons mission flew by the two-lobed Kuiper Belt object Arrokoth in 2019. But they\u2019ve steadily found additional examples of these strangely shaped \u201cplanetesimals\u201d\u2014the technical term for the icy, rocky building blocks that assembled into our solar system\u2019s planets billions of years ago. Solving the mystery of these snowmanlike objects, researchers hope, could unlock a deeper understanding of how exactly Earth and other worlds first came to be.<\/p>\n Now one team has an explanation, helping place another piece in the ongoing puzzle of planet formation.<\/p>\n If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n \u201cWhen we first saw the results of our simulations, we were very excited,\u201d says Jackson Barnes, a graduate student at Michigan State University. Barnes is lead author of the new paper, which was published today in the Monthly Notices of the Royal Astronomical Society. \u201cIt was even more exciting to see that it was not unique, and we had in fact created many of these bilobed objects with different lobe shapes and sizes.\u201d<\/p>\n \u201cIt is marvelous work,\u201d says William McKinnon, a planetary scientist at Washington University in St. Louis who was not involved with the new work. \u201cWhat the authors have done is demonstrate that the most direct pathway is indeed quite physically plausible.\u201d<\/p>\n Previous studies assumed that these peanuts\u2014called \u201ccontact binaries\u201d\u2014were originally two separate spheres that were locked in a spiraling dance until a glancing impact fused them at the hip. But this cosmic mating ritual would have been too slow to have already ended for every contact binary we see. The new study instead depicts them forming in unison.<\/p>\n \u201cFormation of contact binaries from two separate bodies does not work too well,\u201d says David Nesvorn\u00fd, an astronomer at the Southwest Research Institute in Boulder, Colo., who was not involved in the study. \u201cSo we suspected that contact binaries formed during gravitational collapse, but this is the first work that simulates their formation in detail.\u201d<\/p>\n Some 4.6 billion years ago, a giant cloud of gas and dust collapsed under its own gravity to ignite our sun. The leftovers coalesced into a dusty disk swirling around the infant star. Then, astronomers believe, denser swarms of pebbles within that disk also collapsed much like the original cloud, forming kilometer-scale planetesimals.<\/p>\n Think of the Kuiper Belt as an outer reach of this protoplanetary disk that was frozen in time at that moment. Out there, the planetesimals are too sparse and move too slowly to find one another often, and therefore most have never agglomerated into planets.<\/p>\n So why were so many of them peanut-shaped? Either the pebble clouds sometimes collapsed into two separate, co-orbiting bodies that spiraled closer together over time or this binary formed at once, with the rapid spinning and stickiness of the icy pebbles somehow producing the strange shape. To astronomers, the former couldn\u2019t explain the shape\u2019s ubiquity, but the latter was difficult to mathematically model.<\/p>\n The new study rectifies this with high-powered computing, breaking a virtual dust cloud into tiny chunks and simulating how they all interact during a gravitational collapse. About 4 percent of the simulations result in contact binaries. That\u2019s less than the observed prevalence in the Kuiper Belt, suggesting the model is far from perfect, but it\u2019s the first time any simulation has produced these primordial peanuts directly from a single cloud\u2019s collapse.<\/p>\n \u201cThe results look very promising,\u201d Nesvorn\u00fd says, though he points out that Arrokoth\u2019s narrow neck has been hard to reproduce in the simulated binaries, many of which look more bulbous at the center. He also notes that the simulations are left spinning faster than Arrokoth, the best-studied Kuiper-Belt planetesimal we\u2019ve got.<\/p>\n Precisely because Arrokoth constitutes the archetypal, best-yet view of these objects, it has been the dominant target for theorists, says Audrey Thirouin, a planetary scientist at Lowell Observatory in Flagstaff, Ariz., who was uninvolved with the team\u2019s study. But this singular focus comes at the cost of failing to account for the broader spectrum of known contact binaries. \u201cSo I like the fact that this paper is trying to present a more generic work about the formation of these systems,\u201d she says.<\/p>\n \u201cThis was something that had been hypothesized ever since the flyby of Arrokoth in 2019,\u201d Barnes says. It\u2019s encouraging, he adds, that just by breaking up the cloud and throwing more computation at the problem, \u201cwe\u2019re rewarded with a variety of shapes including contact binary shapes just like Arrokoth.\u201d<\/p>\n If you enjoyed this article, I\u2019d like to ask for your support. Scientific American<\/span> has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.<\/p>\n I\u2019ve been a Scientific American<\/span> subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm <\/span>always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.<\/p>\n If you subscribe to Scientific American<\/span>, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.<\/p>\n In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.<\/p>\n There has never been a more important time for us to stand up and show why science matters. I hope you\u2019ll support us in that mission.<\/p>\n","protected":false},"excerpt":{"rendered":" February 19, 2026 3 min read Add Us On GoogleAdd SciAm Our solar system is surrounded by weird peanut-shaped objects. Astronomers think they know why A study published today helps explain how \u201cplanetesimals\u201d\u2014the building blocks of planets\u2014came to be By Joseph Howlett edited by Lee Billings The planetesimal Arrokoth, as pictured by the New Horizons<\/p>\n","protected":false},"author":1,"featured_media":44794,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[58],"tags":[4341,10135,23166,14933,22531,23184,2174],"class_list":{"0":"post-44793","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-astronomers","9":"tag-belt","10":"tag-kuiper","11":"tag-objects","12":"tag-packed","13":"tag-peanutshaped","14":"tag-weird"},"_links":{"self":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/44793","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=44793"}],"version-history":[{"count":0,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/posts\/44793\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=\/wp\/v2\/media\/44794"}],"wp:attachment":[{"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=44793"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=44793"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/naijaglobalnews.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=44793"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}On supporting science journalism<\/h2>\n
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