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  • richardmitnick 12:38 pm on April 8, 2018 Permalink | Reply
    Tags: , , , , How ‘Oumuamua Got Shredded, , The interstellar asteroid 'Oumuamua   

    From Nautilus: “How ‘Oumuamua Got Shredded” 

    Nautilus

    Nautilus

    Apr 01, 2018
    Sean Raymond

    1
    ‘Oumuamua may be a piece of a torn-apart comet, gravitationally launched into interstellar space, that roamed the galaxy before dropping on our doorstep.ESO / M. Kornmesser / Wikicommons.

    Our solar system’s first houseguest—at least, the first one we have seen in our midst—is a strange one. Scientists have taken to calling it ‘Oumuamua (pronounced “Oh-MOO-ah-MOO-ah”), after it was seen, last October, as a faint streak against a backdrop of stars, by the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) telescope, in Hawaii.

    Pannstars telescope, U Hawaii, located at Haleakala Observatory, Hawaii, USA, Altitude 3,052 m (10,013 ft)

    In Hawaiian, ‘Oumuamua means “a messenger from afar arriving first.”

    How do we know it’s “from afar”? ‘Oumuamua is fast. Minus the sun’s gravitational tug, it’s clocking 16 miles per second. A massive planet like Jupiter can gravitationally kick an object hard enough to reach that speed, but get this: ‘Oumuamua entered the solar system from above the plane of the planets! There is nothing in the solar system (including Planet Nine if it exists) that can explain its speed. That is why scientists are confident that it came from beyond.

    2
    ‘Oumuamua’s trajectory through the solar system. It was only found after its closest passage to Earth.Brooks Bays / SOEST Publication Services / UH Institute for Astronomy.

    ‘Oumuamua also looks like nothing we’ve seen before. Its brightness in the sky oscillates by about a factor of 10 every seven hours or so, and models show that this may be due to the spinning of a cigar-shaped body (as in Fig. 2). A pair of potato-shaped bodies with different reflectivities could also account for the oscillation. The brightness pattern does not perfectly repeat, indicating that ‘Oumuamua is spinning chaotically—“tumbling” might be the right way to put it.

    3
    A simulation of ‘Oumuamua’s rotation (left) and the variations in observed brightness that this produces.nagualdesign / Wikicommons.

    Another peculiar thing: ‘Oumuamua looks like a water-rich object, but it has no surface water. Measurements of its colors at different wavelengths show an object similar to volatile-rich bodies in the solar system—think comets and water-rich asteroids. But ‘Oumuamua passed closer than Mercury’s orbit, and showed no signs of activity: No gases escaping to form a coma, no jets, no tails. So, even though it looks like a comet, it does not behave like a comet, at least not like the flamboyant, bright comets that we know and love.

    So what is it? The simplest explanation is that ‘Oumuamua is a planetary leftover called a planetesimal, born in a planet-forming disk around another star but got left out of the finished product. Instead it was kicked out into interstellar space by a giant planet similar to Neptune, or maybe Jupiter. ‘Oumuamua wandered for millions to billions of years, then happened to pass close to the sun.

    That can explain how ‘Oumuamua came to roam outside of a planetary system—but it falls short: It doesn’t explain ‘Oumuamua’s weird shape and spin, nor why it looks like a comet with no surface water.

    This is where computer simulations come in. Almost a decade ago, I ran thousands of simulations of how giant planets interact with disks of planetesimals. My goal was to study how planets behave, but what I’ve found is that these same simulations can be used to understand ‘Oumuamua’s origins. Before they are kicked out into interstellar space, some planetesimals pass super close to a giant planet, so close that they should be shredded to pieces, due to gravity: The pull on the planet-facing side of the planetesimal is much larger than on the opposite side. The strong stretching force might play a role in explaining ‘Oumuamua’s unusual shape and tumbling spin, although it has not been carefully modeled yet. This is still speculation.

    This sort of shredding event isn’t just based on calculations, though. We have actually seen it in action. In 1992, comet Shoemaker-Levy 9 passed too close to Jupiter and was torn into a string of fragments. They fell back onto Jupiter in 1994 (some on my 17th birthday).

    4
    Fragments of comet Shoemaker-Levy 9 observed with the Hubble Space telescope in 1994.NASA / ESA / H. Weaver and E. Smith (STScI).

    My simulations find that about 1 percent of planetesimals are torn apart by coming too close to a giant planet, like comet Shoemaker–Levy 9. Instead of bashing into the planet, most of the pieces are eventually thrown out of their planetary systems. If ‘Oumuamua is a planetesimal fragment, it must have gotten shredded very violently.

    This still doesn’t explain ‘Oumuamua’s comet-like appearance. In this way, ‘Oumuamua is like another class of objects in the solar system called the Damocloids: They have comet-like orbits and surfaces but don’t give off any gases when they are heated. We think they are extinct comets that, after a certain number of trips too close to the sun, burned off all of their surface ices. Over the past few decades, researchers have figured out how quickly extinction must happen.

    Back to my simulations. Remember: about 1 percent of planetesimals should have been torn apart before being kicked out into interstellar space. And guess what? About two-thirds of them passed close to their stars a bunch of times before getting kicked out—enough times that they should have become extinct.

    So, ‘Oumuamua may be a piece of a torn-apart comet, as my colleagues and I argue in two recent papers (here [The Astrophysical Journal] and here [MNRAS]): After the disruption, ‘Oumuamua passed close enough to its star enough times to lose its surface volatiles, becoming extinct. Then it was gravitationally launched into interstellar space and roamed the galaxy before dropping on our doorstep.

    5
    ‘Oumuamua’s origin story?Sean Raymond / planetplanet.net.

    We could test this by cracking ‘Oumuamua open. Is there ice buried deep, too deep for the sun to vaporize it? It’s zooming away so fast that tracking it down—the goal of Project Lyra—is no small feat. If that fails we can bank on the Large Synoptic Survey Telescope, which is coming online around 2021, to help us find objects similar to what ‘Oumuamua seems to be. Our story predicts that extinct comets should outnumber “normal” ones about two-to-one, and almost all of these objects should be fragments of larger bodies, meaning they might bear some trace of their violent pasts, either in terms of their shapes and spins or something else.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    If we end up finding a lot of extinct comet fragments, we can be confident ‘Oumuamua is one, too.

    Sean Raymond is an astronomer studying the formation and evolution of planetary systems. He also blogs at htp://www.planetplanet.net.

    See the full article here .

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  • richardmitnick 4:43 pm on November 20, 2017 Permalink | Reply
    Tags: , , , , ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before, , , , The interstellar asteroid 'Oumuamua   

    From ESO: “ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before” 

    ESO 50 Large

    European Southern Observatory

    20 November 2017
    Olivier Hainaut
    ESO
    Garching, Germany
    Tel: +49 89 3200 6752
    Email: ohainaut@eso.org

    Karen Meech
    Institute for Astronomy
    Honolulu, Hawai`i, USA
    Cell: +1-720-231-7048
    Email: meech@IfA.Hawaii.Edu

    Richard Hook
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1
    For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.

    2
    This very deep combined image shows the interstellar asteroid ‘Oumuamua at the centre of the picture. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving asteroid. This image was created by combining multiple images from ESO’s Very Large Telescope as well as the Gemini South Telescope. The object is marked with a blue circle and appears to be a point source, with no surrounding dust. Credit: ESO/K. Meech et al.


    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    3
    This diagram shows the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Unlike all other asteroids and comets observed before, this body is not bound by gravity to the Sun. It has come from interstellar space and will return there after its brief encounter with our star system. Its hyperbolic orbit is highly inclined and it does not appear to have come close to any other Solar System body on its way in. Credit: ESO/K. Meech et al.

    4
    This plot shows how the interstellar asteroid ‘Oumuamua varied in brightness during three days in October 2017. The large range of brightness — about a factor of ten (2.5 magnitudes) — is due to the very elongated shape of this unique object, which rotates every 7.3 hours. The different coloured dots represent measurements through different filters, covering the visible and near-infrared part of the spectrum. The dotted line shows the light curve expected if ‘Oumuamua were an ellipsoid with a 1:10 aspect ratio, the deviations from this line are probably due to irregularities in the object’s shape or surface albedo. Credit: ESO/K. Meech et al.


    For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was travelling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The video is available in 4K UHD. Credit: ESO


    This animation shows the path of the interstellar asteroid 1I/2017 (‘Oumuamua) through the Solar System. Observations with ESO’s Very Large Telescope and others have shown that this unique object is dark, reddish in colour and highly elongated. Credit:ESO, M. Kornmesser, L.Calcada. Music: Azul Cobalto

    On 19 October 2017, the Pan-STARRS 1 telescope in Hawai`i picked up a faint point of light moving across the sky.

    Pann-STARS telescope, U Hawaii, Mauna Kea, Hawaii, USA, 4,207 m (13,802 ft) above sea level

    It initially looked like a typical fast-moving small asteroid, but additional observations over the next couple of days allowed its orbit to be computed fairly accurately. The orbit calculations revealed beyond any doubt that this body did not originate from inside the Solar System, like all other asteroids or comets ever observed, but instead had come from interstellar space. Although originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it passed closest to the Sun in September 2017. The object was reclassified as an interstellar asteroid and named 1I/2017 U1 (‘Oumuamua) [1].

    “We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “’Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”

    ESO’s Very Large Telescope was immediately called into action to measure the object’s orbit, brightness and colour more accurately than smaller telescopes could achieve. Speed was vital as ‘Oumuamua was rapidly fading as it headed away from the Sun and past the Earth’s orbit, on its way out of the Solar System. There were more surprises to come.

    Combining the images from the FORS instrument on the VLT using four different filters with those of other large telescopes, the team of astronomers led by Karen Meech (Institute for Astronomy, Hawai`i, USA) found that ‘Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.

    ESO/FORS1

    Karen Meech explains the significance: “This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”

    These properties suggest that ‘Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years. It is estimated to be at least 400 metres long.

    Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago. ‘Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.

    Astronomers estimate that an interstellar asteroid similar to ‘Oumuamua passes through the inner Solar System about once per year, but they are faint and hard to spot so 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.

    “We are continuing to observe this unique object,” concludes Olivier Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”

    Notes

    [1] The Pan-STARRS team’s proposal to name the interstellar objet was accepted by the International Astronomical Union, which is responsible for granting official names to bodies in the Solar System and beyond. The name is Hawaiian and more details are given here. The IAU also created a new class of objects for interstellar asteroids, with this object being the first to receive this designation. The correct forms for referring to this object are now: 1I, 1I/2017 U1, 1I/’Oumuamua and 1I/2017 U1 (‘Oumuamua). Note that the character before the O is an okina. So, the name should sound like H O u mu a mu a. Before the introduction of the new scheme, the object was referred to as A/2017 U1.

    More information

    This research was presented in a paper entitled A brief visit from a red and extremely elongated interstellar asteroid, by K. Meech et al., to appear in the journal Nature on 20 November 2017.

    The team is composed of Karen J. Meech (Institute for Astronomy, Honolulu, Hawai`i, USA [IfA]) Robert Weryk (IfA), Marco Micheli (ESA SSA-NEO Coordination Centre, Frascati, Italy; INAF–Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy), Jan T. Kleyna (IfA) Olivier Hainaut (ESO, Garching, Germany), Robert Jedicke (IfA) Richard J. Wainscoat (IfA) Kenneth C. Chambers (IfA) Jacqueline V. Keane (IfA), Andreea Petric (IfA), Larry Denneau (IfA), Eugene Magnier (IfA), Mark E. Huber (IfA), Heather Flewelling (IfA), Chris Waters (IfA), Eva Schunova-Lilly (IfA) and Serge Chastel (IfA).

    See the full article here .

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