The headlines had all the usual excitable language you\u2019d expect, while enthusiastic social media posts spoke of possible naked-eye wonders to come. <\/span><\/p>\n Out in the depths of space, though, the icy wanderer had other ideas.<\/span><\/p>\n As it raced towards the Sun, astronomers started to notice ominous changes in its appearance; rather than brightening steadily as it neared perihelion in May this year \u2013 when it would be at the closest point to the Sun in its orbit \u2013 the comet\u2019s glow was faltering.<\/span><\/p>\n Soon, close-up images by astrophotographers showed the head of ATLAS \u2013 ordinarily where a solid, icy nucleus would hide among a shining cloud of gas and dust \u2013 was starting to elongate.<\/span><\/p>\n The comet was falling to pieces. By 20 April, professional astronomers had pointed the orbiting eyes of the Hubble Space Telescope<\/a> to the ensuing chaos, revealing fragments of the comet drifting through the darkness.<\/span><\/p>\n If amateur astronomers in the Northern Hemisphere felt any disappointment at what might <\/span>have been, that was soon tempered by the naked-eye spectacle of Comet NEOWISE<\/a> in the following months; while it graced the northern horizon with its magnificent dust tail, the fizzling away of ATLAS seemed quickly forgotten by most.<\/span><\/p>\n Even in its death, however, ATLAS had a story to tell scientists \u2013 one not just about the fickle nature of comets, but also about the deeper history of our planetary neighbourhood.<\/span><\/p>\n Comets brighten because, as they venture close to the Sun on their long, elliptical orbits, the warmth of our star causes ices to sublimate (change straight from a solid to a gas) from their frosty surfaces.<\/span><\/p>\n As this process unfolds, a cloud of material \u2013 known as a \u2018coma\u2019 \u2013 forms around the nucleus.<\/span><\/p>\n Some comets also develop tails, giving them the striking appearance these icy objects are so well-known for.<\/span><\/p>\n How visible and how bright a comet gets in our night sky depends on several things.<\/span><\/p>\n Such as how big its nucleus is and how close it gets to Earth and the Sun when it sweeps through the inner Solar System, explains Professor Laura Woodney, a planetary scientist and comet expert based at the California State University, San Bernardino<\/a>.<\/span><\/p>\n The age of the surface of the nucleus also plays a role.<\/span><\/p>\n \u201cWe think that the more perihelion passages a comet has around the Sun, the more processed the surface becomes due to sublimation of ice, given that the larger rocky particles either fall back to the surface or are never lifted in \u201cThus short-period comets with their frequent solar passages are less spectacular,\u201d she says.<\/span><\/p>\n For certain comets making their first journey into the inner Solar System \u2013 what astronomers call a \u2018dynamically new\u2019 comet \u2013 the odds can be somewhat against them getting bright too.<\/span><\/p>\n \u201cStatistically speaking, first-time visitors that approach the Sun within 2 AU [Astronomical Units, where 1 AU is the distance between Earth and the Sun] are more likely to fizzle out. But again, outliers are not uncommon. So we don\u2019t really know,\u201d says Dr Ye Quanzhi, an asteroid<\/a> and comet researcher at the University of Maryland<\/a>.\u00a0<\/span><\/span><\/p>\n Anyone who remembers the saga of Comet ISON \u2013 a sungrazing comet that many hoped would become a spectacular sight in late 2013, but actually flopped \u2013 will recall the rollercoaster of emotions that comes with monitoring a dynamically new comet as it approaches perihelion.<\/span><\/p>\n ATLAS, though, was neither a short-period comet nor dynamically new; its crumbling highlights just how hard it is, still, to anticipate the behaviour of these icy travellers.<\/span><\/p>\n Indeed, it\u2019s just one of several comets that astronomers have witnessed breaking up over the years, including Comet 73P\/Schwassmann-Wachmann in 2006 and more recently Comet 332P\/Ikeya-Murakami in 2015.<\/span><\/p>\n \u201c[Disintegration] happens regularly, both to long- and short-period comets and we aren\u2019t good at predicting why yet,\u201d says Woodney.<\/span><\/p>\n \u201cThat\u2019s one of the interesting questions comet scientists are currently working on understanding right now.\u201d<\/span><\/p>\n Might there have been clues from ATLAS\u2019s past, though, that pointed to its fate?\u00a0<\/span><\/span><\/p>\n The comet caught the eye of Ye Quanzhi right from the moment it was found, back in December 2019.<\/span><\/p>\n \u201cThe preliminary orbit closely resembled another comet that appeared almost 180 years ago, C\/1844 Y1,\u201d he says.<\/span><\/p>\n \u201cThe resemblance is a bit too great to be explained by pure coincidence, and it was pretty clear that the orbital period of ATLAS is much, much longer than 170 years.<\/span><\/p>\n \u201cSo this raised the interesting possibility that we are seeing a pair of comets that share a common progenitor and are likely to be the end-product of a prehistoric break-up event.\u201d<\/span><\/p>\n To explore ATLAS further, Ye <\/span>and his colleagues requested time on the Hubble Space Telescope to examine the comet.<\/p>\n \u201cOur motivation back then was primarily to look for fragments produced during ATLAS\u2019s last visit, 6,000 years ago,\u201d he says.<\/p>\n The team\u2019s proposal was sent to Hubble managers in January; but between then and when the orbiting telescope would actually turn its optics toward the comet, in late April, ATLAS underwent its spectacular fragmentation.<\/p>\n \u201cWe secretly hoped, but wouldn\u2019t have really guessed that ATLAS would break apart a bit before our scheduled observation \u2013 that was a really pleasant surprise,\u201d says Ye.<\/p>\n \u201cOur observation happened overnight and I woke up quite early the next day. It felt like opening a gift box when I was downloading the data.\u201d<\/p>\n Another group of researchers had also been allocated observing time as well, and in total three orbits of the space telescope would eventually be dedicated to scrutinising the spectacle occurring out in space.<\/p>\n![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2020\/05\/13_JoseChambo_CometATLAS-c6e7553.jpg?quality=90&resize=620%2C413"\" "\\"\"\"\\"\/")
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Why do comets brighten in the first place?<\/strong><\/h2>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Analysing Comet ATLAS with Hubble<\/strong><\/h2>\n
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