Interstellar object 3I\/ATLAS continues to fascinate astronomers as it rips through our solar system. And the more we find out about the object \u2014 widely suspected to be an icy comet \u2014 the more questions emerge.<\/p>\n
Latest among those mysteries: the Keck II telescope in Hawaii observed the object when it was just over 2.5 times the distance between the Earth and Sun back in August, and found \u201cevidence for a puzzling anti-tail extension in the direction of the Sun,\u201d as Harvard astronomer Avi Loeb wrote in a blog post<\/a> last week.<\/p>\n In a recent paper<\/a> that has yet to be peer reviewed, a team of astronomers used the Keck data to confirm \u201cpreviously reported cyanide and nickel outgassing,\u201d which are being emitted both in and against the direction of the Sun, which offers \u201cclear evidence for an anti-tail,\u201d according to Loeb.<\/p>\n \u201cMost remarkably, the white light image of 3I\/ATLAS does not show evidence for a familiar cometary tail, as expected for dust which scatters sunlight and is pushed away from the Sun by solar radiation pressure,\u201d he added.<\/p>\n As IFLScience explains<\/a>, the phenomenon could be the result of natural processes. One possibility is that it\u2019s a type of optical illusion<\/a>; because of the Earth\u2019s relative location in space, a comet\u2019s wide tail can fan out from behind it to make it look as if it has a tail growing tail sprouting from either side.<\/p>\n Another possibility is that larger grains of dust are refusing to be pushed away by solar wind on the comet\u2019s Sun-facing side. The comet\u2019s core of sublimating ice could be spinning rapidly and releasing large pieces of debris in both directions along its orbit making it appear to have a Sunward \u201canti-tail\u201d in addition to its regular tail.<\/p>\n Scientists have previously identified<\/a> other comets showing Sun-facing \u201canti-tails\u201d that suggest the \u201cslow ejection of relatively large dust particles predominantly from the sunlit hemisphere.\u201d<\/p>\n \u201cWith a rotating comet nucleus\u2026 ejecta from a spot can come off with heliocentric velocity that puts it either in front of or behind the nucleus,\u201d explained University of California, Los Angeles planetary astronomer Michael Busch in a post on Bluesky<\/a>. \u201cIt does not matter which side it starts from.\u201d<\/p>\n \u201cSmall dust and ejected gas gets pushed out by radiation pressure and solar wind,\u201d he explained in a followup<\/a>. \u201cBut larger pieces of ejecta spread out along the orbit; both in front of and behind the nucleus.\u201d<\/p>\n To Loeb, the anti-tail remains an \u201canomaly that raises two questions,\u201d according to a more recent blog post<\/a>. \u201cWhat is the nature of the anti-tail? Why are comet experts ignoring this anomaly while insisting that 3I\/ATLAS is a familiar comet?\u201d<\/p>\n Fortunately, before 3I\/ATLAS leaves the solar system for good, it will provide us with several more opportunities to examine it. It\u2019s expected to make a close approach Jupiter next month, giving NASA\u2019s Juno spacecraft and the European Space Agency\u2019s Juice spacecraft a chance to get a brief glimpse.<\/p>\n For now, Loeb ranks 3I\/ATLAS as a four out of ten on his \u201cLoeb scale<\/a>\u201d \u2014 which he invented to gauge the likeliness of an interstellar object being extraterrestrial technology \u2014 in a figure that he says means that it has \u201cincreasingly anomalous characteristics.\u201d<\/p>\n