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  • richardmitnick 7:42 am on February 23, 2017 Permalink | Reply
    Tags: Accidental find, , , Trojan Asteroids,   

    From New Scientist: “Far-off asteroid caught cohabiting with Uranus around the sun” 


    New Scientist

    16 February 2017
    Ken Croswell

    Now with added Trojans. NASA/Erich Karkoschka (Univ. Arizona)

    A rare Trojan asteroid of Uranus has been found, following the same orbit as the planet. Its existence implies there could be many more of these companion asteroids, and that they are more common than we thought.

    A Trojan asteroid orbits the sun 60 degrees ahead of or behind a planet. Jupiter and Neptune have numerous Trojans, many of which have been in place for billions of years. These primordial rocks hold information about the solar system’s birth, and NASA has just announced plans to visit several of them in the 2020s and 2030s.

    But Saturn and Uranus live in a rougher neighbourhood: the giant planets on either side of them yank Trojans away through their gravitational pull. So Saturn has no known Trojan, and Uranus had only one.

    In July, though, astronomers reported a new asteroid, named 2014 YX49, that shares Uranus’s orbital period of 84 years. Now computer simulations of the solar system by brothers Carlos and Raul de la Fuente Marcos at the Complutense University of Madrid, Spain, indicate the asteroid is a Uranus Trojan. The simulations show that the asteroid has maintained its position ahead of Uranus for thousands of years.

    “It is bigger, probably twice as big as the first one,” says Carlos. The new asteroid is brighter than the first, but its exact size depends on how much light its surface reflects. If it reflects half the sunlight striking it, it’s 40 kilometres across; if it reflects 5 per cent, its diameter is 120 kilometres.

    Accidental find

    The new asteroid was found by accident, which Carlos says implies there should be more waiting to be discovered. He thinks its Trojans could number in the hundreds.

    Unlike the Trojans of Jupiter and Neptune, the simulations suggest that the two known Uranus Trojans are transient rather than permanent. Carlos suspects Uranus lacks primordial Trojans because the other giant planets kicked them away.

    The simulations indicate that the new asteroid was once a centaur, an object that skirts between the orbits of the giant planets. About 60,000 years ago, buffeted by their gravitational tugs, it was caught ahead of Uranus in its orbit around the sun and became a Trojan; it is likely to remain so for another 80,000 years, before eventually becoming a centaur again.

    Although Carlos thinks Uranus has no permanent Trojans, David Jewitt at the University of California at Los Angeles is willing to wait and see. “In the end the answer will come — as always — from observations,” he says. “People will either find permanent Uranus Trojans or not.”

    And Saturn? “The neighbourhood of Saturn is even more chaotic than that of Uranus,” Carlos says, due to Jupiter’s proximity. Still, he thinks Trojans of Saturn could exist.

    Journal references: Monthly Notices of the Royal Astronomical Society and ArXiv, arxiv.org/abs/1701.05541

    See the full article here .

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  • richardmitnick 10:08 am on September 29, 2016 Permalink | Reply
    Tags: , rans-Neptunian Objects (TNOs), Trojan Asteroids, ,   

    From UH Institute for Astronomy via Universe Today: “Five New Neptunian Trojans Discovered” 

    U Hawaii

    University of Hawaii

    U Hawaii 2.2 meter telescope, Mauna Kea, Hawaii, USA
    U Hawaii 2.2 meter telescope, Mauna Kea, Hawaii, USA

    IFA at Manua Kea


    Universe Today

    23 Sept 2016
    Matt Williams

    The Solar System is filled with what are known as Trojan Asteroids – objects that share the orbit of a planet or larger moon. Whereas the best-known Trojans orbit with Jupiter (over 6000), there are also well-known Trojans orbiting within Saturn’s systems of moons, around Earth, Mars, Uranus, and even Neptune.

    Until recently, Neptune was thought to have 12 Trojans. But thanks to a new study by an international team of astronomers – led by Hsing-Wen Lin of the National Central University in Taiwan – five new Neptune Trojans (NTs) have been identified. In addition, the new discoveries raise some interesting questions about where Neptune’s Trojans may come from.

    For the sake of their study – titled The Pan-STARRS 1 Discoveries of Five New Neptune Trojans– the team relied on data obtained by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). This wide-field imaging facility – which was founded by the University of Hawaii’s Institute for Astronomy – has spent the last decade searching the Solar System for asteroids, comets, and Centaurs.

    The PS1 telescope at dawn, with the mountain of Mauna Kea visible in the distance. Credit: pan-starrs.ifa.hawaii.edu

    The team used data obtained by the PS-1 survey, which ran from 2010 to 2014 and utilized the first Pan-STARR telescope on Mount Haleakala, Hawaii. From this, they observed seven Trojan asteroids around Neptune, five of which were previously undiscovered. Four of the TNs were observed orbiting within Neptune’s L4 point, and one within its L5 point.

    The newly detected objects have sizes ranging from 100 to 200 kilometers in diameter, and in the case of the L4 Trojans, the team concluded from the stability of their orbits that they were likely primordial in origin. Meanwhile, the lone L5 Trojan was more unstable than the other four, which led them to hypothesize that it was a recent addition.

    As Professor Lin explained to Universe Today via email:

    “The 2 of the 4 currently known L5 Neptune Trojans, included the one L5 we found in this work, are dynamically unstable and should be temporary captured into Trojan cloud. On the other hand, the known L4 Neptune Trojans are all stable. Does that mean the L5 has higher faction of temporary captured Trojans? It could be, but we need more evidence.”

    Animation showing the path of six of Neptune’s L4 trojans in a rotating frame with a period equal to Neptune’s orbital period.. Credit: Tony Dunn/Wikipedia Commons

    From this, said Lin, they derived two possible explanations:

    “The L4 “Trojan Cloud” is wide in orbital inclination space. If it is not as wide as we thought before, the two observational results are statistically possible to generate from the same intrinsic inclination distribution. The previous study suggested >11 degrees width of inclination, and most likely is ~20 degrees. Our study suggested that it should be 7 to 27 degrees, and the most likely is ~ 10 degrees.”

    “[Or], the previous surveys were used larger aperture telescopes and detected fainter NT than we found in PS1. If the fainter (smaller) NTs have wider inclination distribution than the larger ones, which means the smaller NTs are dynamically “hotter” than the larger NTs, the disagreement can be explained.”

    According to Lin, this difference is significant because the inclination distribution of NTs is related to their formation mechanism and environment. Those that have low orbital inclinations could have formed at Neptune’s Lagrange Points and eventually grew large enough to become Trojans asteroids.

    Illustration of the Sun-Earth Lagrange Points. Credit: NASA

    On the other hand, wide inclinations would serve as an indication that the Trojans were captured into the Lagrange Points, most likely during Neptune’s planetary migration when it was still young. And as for those that have wide inclinations, the degree to which they are inclined could indicate how and where they would have been captured.

    “If the width is ~ 10 degrees,” he said, “the Trojans can be captured from a thin (dynamically cold) planetesimal disk. On the other hand, if the Trojan cloud is very wide (~ 20 degrees), they have to be captured from a thick (dynamically hot) disk. Therefore, the inclination distribution give us an idea of how early Solar system looks like.”

    In the meantime, Li and his research team hope to use the Pan-STARR facility to observe more NTs and hundreds of other Centaurs, Trans-Neptunian Objects (TNOs) and other distant Solar System objects. In time, they hope that further analysis of other Trojans will shed light on whether there truly are two families of Neptune Trojans.

    This was all made possible thanks to the PS1 survey. Unlike most of the deep surveys, which are only ale to observe small areas of the sky, the PS1 is able to monitor the whole visible sky in the Northern Hemisphere, and with considerable depth. Because of this, it is expected to help astronomers spot objects that could teach us a great deal about the history of the early Solar System.

    See the full article here .

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