NASA<\/a> on November 20, 2017. <\/p>\nAstronomers recently scrambled to observe an intriguing asteroid that zipped through the solar system on a steep trajectory from interstellar space\u2014the first confirmed object from another star. <\/strong><\/em><\/p>\nNow, new data reveal the interstellar interloper to be a rocky, cigar-shaped object with a somewhat reddish hue. The asteroid, named \u2018Oumuamua by its discoverers, is up to one-quarter mile (400 meters) long and highly-elongated\u2014perhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike asteroids seen in our solar system, it may provide new clues into how other solar systems formed.<\/strong><\/em><\/p>\nThe observations and analyses were funded in part by NASA and appear in the Nov. 20 issue of the journal Nature. They suggest this unusual object had been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our star system.<\/strong><\/em><\/p>\n\u201cFor decades we\u2019ve theorized that such interstellar objects are out there, and now \u2013 for the first time \u2013 we have direct evidence they exist,\u201d said Thomas Zurbuchen, associate administrator for NASA\u2019s Science Mission Directorate in Washington. \u201cThis history-making discovery is opening a new window to study formation of solar systems beyond our own.\u201d <\/strong><\/em><\/p>\nImmediately after its discovery, telescopes around the world, including ESO\u2019s Very Large Telescope in Chile and other observatories around the world were called into action to measure the object\u2019s orbit, brightness and color. Urgency for viewing from ground-based telescopes was vital to get the best data. <\/strong><\/em><\/p>\nCombining the images from the FORS instrument on the ESO telescope using four different filters with those of other large telescopes, a team of astronomers led by Karen Meech of the Institute for Astronomy in Hawaii found that \u2018Oumuamua varies in brightness by a factor of ten as it spins on its axis every 7.3 hours. No known asteroid or comet from our solar system varies so widely in brightness, with such a large ratio between length and width. The most elongated objects we have seen to date are no more than three times longer than they are wide. <\/strong><\/em><\/p>\n\u201cThis unusually big variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,\u201d said Meech. We also found that it had a reddish color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it.\u201d<\/strong><\/em><\/p>\nThese properties suggest that \u2018Oumuamua is dense, comprised of rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over hundreds of millions of years. <\/strong><\/em><\/p>\nA few large ground-based telescopes continue to track the asteroid, though it\u2019s rapidly fading as it recedes from our planet. Two of NASA\u2019s space telescopes (Hubble and Spitzer) are tracking the object the week of Nov. 20. As of Nov. 20, \u2018Oumuamua is travelling about 85,700 miles per hour (38.3 kilometers per second) relative to the Sun. Its location is approximately 124 million miles (200 million kilometers) from Earth — the distance between Mars and Jupiter \u2013 though its outbound path is about 20 degrees above the plane of planets that orbit the Sun. The object passed Mars\u2019s orbit around Nov. 1 and will pass Jupiter\u2019s orbit in May of 2018. It will travel beyond Saturn\u2019s orbit in January 2019; as it leaves our solar system, \u2018Oumuamua will head for the constellation Pegasus.<\/strong><\/em><\/p>\nObservations from large ground-based telescopes will continue until the object becomes too faint to be detected, sometime after mid-December. NASA\u2019s Center for Near-Earth Object Studies (CNEOS) continues to take all available tracking measurements to refine the trajectory of 1I\/2017 U1 as it exits our solar system. <\/strong><\/em><\/p>\nThis remarkable object was discovered Oct. 19 by the University of Hawaii\u2019s Pan-STARRS1 telescope, funded by NASA\u2019s Near-Earth Object Observations(NEOO) Program, which finds and tracks asteroids and comets in Earth\u2019s neighborhood. NASA Planetary Defense Officer Lindley Johnson said, \u201cWe are fortunate that our sky survey telescope was looking in the right place at the right time to capture this historic moment. This serendipitous discovery is bonus science enabled by NASA\u2019s efforts to find, track and characterize near-Earth objects that could potentially pose a threat to our planet.\u201d <\/strong><\/em><\/p>\nPreliminary orbital calculations suggest that the object came from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, it took so long for the interstellar object to make the journey \u2013 even at the speed of about 59,000 miles per hour (26.4 kilometers per second) — that Vega was not near that position when the asteroid was there about 300,000 years ago. <\/strong><\/em><\/p>\nWhile originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it slingshotted past the Sun on Sept. 9 at a blistering speed of 196,000 miles per hour (87.3 kilometers per second). <\/strong><\/em><\/p>\nThe object has since been reclassified as interstellar asteroid 1I\/2017 U1 by the International Astronomical Union (IAU), which is responsible for granting official names to bodies in the solar system and beyond. In addition to the technical name, the Pan-STARRS team dubbed it \u2018Oumuamua (pronounced oh MOO-uh MOO-uh), which is Hawaiian for \u201ca messenger from afar arriving first.\u201d <\/strong><\/em><\/p>\nAstronomers estimate that an interstellar asteroid similar to \u2018Oumuamua passes through the inner solar system about once per year, but they are faint and hard to spot and have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them. <\/strong><\/em><\/p>\n\u201cWhat a fascinating discovery this is!\u201d said Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA\u2019s Jet Propulsion Laboratory, Pasadena, California. \u201cIt\u2019s a strange visitor from a faraway star system, shaped like nothing we\u2019ve ever seen in our own solar system neighborhood.\u201d<\/strong><\/em><\/p>\n
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