Student solves mystery of icy ‘snowmen’ in solar system’s outer reaches

The objects have largely persisted untouched for billions of years SpaceStudent solves mystery of icy ‘snowmen’ in solar system’s outer reachesThe objects have largely persisted untouched for billions of yearsMark Worgan Monday 02 March 2026 09:34 GMTBookmarkCommentsGo to commentsBookmark popoverRemoved from bookmarksClose popoverRelated: Nasa astronaut shares striking footage of ISS 'cartwheel' around EarthYour support helps us to tell the storyRead moreSupport NowFrom reproductive rights to climate change to Big Tech, The Independent is on the ground when the story is developing. Whether it's investigating the financials of Elon Musk's pro-Trump PAC or producing our latest documentary, 'The A Word', which shines a light on the American women fighting for reproductive rights, we know how important it is to parse out the facts from the messaging.At such a critical moment in US history, we need reporters on the ground. 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We believe quality journalism should be available to everyone, paid for by those who can afford it.Your support makes all the difference.Read moreA student has unravelled a long-standing cosmic enigma concerning some of our solar system’s most peculiar objects: icy ‘snowmen’ that populate its outer reaches.Astronomers have long debated the origins of these 'contact binaries' – objects comprising two connected spheres, reminiscent of a snowman.Now, researchers at Michigan State University claim to have evidence suggesting that a surprisingly simple process could account for these distinctive shapes.These peculiar celestial 'snowmen' are found in the Kuiper Belt, a vast expanse beyond Neptune, which is filled with icy remnants dating back to the solar system's formation. The region lies beyond the turbulent asteroid belt between Mars and Jupiter. These ancient building blocks, known as planetesimals, have largely persisted untouched for billions of years. Roughly one in 10 of these objects are classified as 'contact binaries'. The enduring mystery has been how such delicate structures could have formed without being violently smashed together.open image in galleryContact binaries are made up of two connected spheres, reminiscent of a snowman (Cover Images)Jackson Barnes, a graduate student at the university, has developed the first computer simulation to show how such two-lobed shapes can arise naturally through gravitational collapse. This is the process by which matter contracts under its own gravity, overpowering forces that would otherwise pull it apart. The research has been published in Monthly Notices of the Royal Astronomical Society. Earlier computer models treated colliding objects as fluid-like blobs that quickly merged into single spheres, making it impossible to recreate contact binaries. Using high-performance computing facilities, Mr Barnes’ simulations instead allow objects to retain their strength and settle gently against one another. Other theories have suggested that rare events or exotic conditions might be required to produce these shapes, but researchers say such explanations are unlikely to account for their apparent abundance. open image in galleryAn artist's concept of Kuiper Belt object 2014 MU69, the next flyby target for Nasa's New Horizons mission (Cover Images)“If we think 10 per cent of planetesimal objects are contact binaries, the process that forms them can’t be rare,” said Earth and Environmental Science assistant professor Seth Jacobson, the study’s senior author.“Gravitational collapse fits nicely with what we’ve observed.”Contact binaries were first seen in close detail in January 2019, when Nasa’s New Horizons spacecraft flew past a Kuiper Belt object later nicknamed Ultima Thule. The images prompted scientists to re-examine other distant bodies, revealing that about 10 per cent of planetesimals share the same distinctive shape. In the sparsely populated Kuiper Belt, these objects drift largely undisturbed and are rarely hit by other debris. In the early history of the Milky Way, the galaxy consisted of a disc of gas and dust. Remnants of that era persist in the Kuiper Belt today, including dwarf planets such as Pluto, along with comets and planetesimals. Planetesimals are among the first solid bodies to form as dust and pebble-sized material clumps together under gravity. Much like snowflakes compressed into a snowball, they are loose aggregates pulled from clouds of tiny particles.open image in galleryThe first small 'KBO' ever explored by a spacecraft (Nasa/Johns Hopkins University)Mr Barnes’ simulation shows that as one of these clouds rotates, it can collapse inward and split into two separate bodies that begin orbiting each other. Such binary planetesimals are commonly observed in the Kuiper Belt. Over time, their orbits spiral cl