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A Triple Asteroid Occultation

Eugenia and one of its moons

Sometimes nature does what huge telescopes can’t manage. Tomorrow night, a careful amateur astronomer may be able to provide information not only about the tiny asteroid 45 Eugenia but also about the two moons that orbit it. At play is an occultation, in which these moons and Eugenia itself helpfully occlude a star for observers in various parts of the southern US and Mexico. Sky & Telescope is reporting the relevant times to be 5:42 to 5:45 UTC on March 9.

Image: Eugenia and its larger moon, Petit-Prince. With a density only 20 percent greater than water, this main belt asteroid is either a loose pile of rubble or an icy object with sparse rocky materials. Petit-Prince orbits it at a radius of 1,190 kilometers. Not shown here is the smaller moon, Petite-Princesse. The animation was assembled from infrared images of the objects. Credit: William Merline (SwRI), Laird Close (ESO), et al., CFHT.

Moons have been discovered in their dozens around asteroids ever since 1994, when the Galileo spacecraft found Dactyl, a satellite of asteroid 243 Ida. But timing observations like these can be helpful in flagging the location of the moons relative to the asteroid they circle, with an accuracy we can’t manage with our best telescopes. David Herald (International Occultation Timing Association) points to the possibilities:

“If this event is well observed, the profiles of the components will be resolved at the 1-km level, relative positions being determined to within a few hundred microarcseconds. So I encourage everyone near the predicted paths to join in the group activity and monitor this event! And remember, the uncertainty in the path location could be a good 100 km or more. So even if you are outside the predicted paths, you should still monitor the event.”

Another opportunity for amateur astronomy, whose practitioners now have a shot at making observations of such tiny objects as the delightfully named Petit-Prince and Petite-Princesse, the known moons of Eugenia (the smaller of these objects is a mere 6 kilometers across). The necessary details are on the IOTA site, which also points to David Breit’s page on the occultation, complete with maps. Even binoculars can track this event, or telescopes with an aperture of at least 2.4 inches and up. CCD cameras, needless to say, would be more than helpful.

Comments on this entry are closed.

  • James M. Essig March 9, 2008, 3:51

    Hi Folks;

    This is good ameture astonomy. It encourages me that the role of ameture astronomers seems to have grown over the past few decades with the discovery of comets, the dscovery of the compostion of some interstellar gas clouds, etc.. It makes me want to run out and buy a telescope. This is a very interesting observational method indeed.



  • philw1776 March 10, 2008, 13:22

    Anyone got links to sites that will be reporting on observations and the data anaylsis?

  • ljk March 20, 2008, 16:01

    UM-Led Team Finds Oldest Known Asteroids

    COLLEGE PARK, Md. — Using visible and infrared data collected from
    telescopes on Hawaii’s Mauna Kea, a team of scientists, led by the
    University of Maryland’s Jessica Sunshine, have identified three
    asteroids that appear to be among our Solar System’s oldest objects.

    Evidence indicates that these ancient asteroids are relatively unchanged
    since they formed some 4.55 billion years ago and are older than the
    oldest meteorites ever found on Earth, say Maryland’s Sunshine and
    colleagues from the City University of New York, the Smithsonian
    Institution, and the University of Hawaii. Their findings are published
    in this week’s edition of Science Express.

    “We have identified asteroids that are not represented in our meteorite
    collection and which date from the earliest periods of the Solar
    System,” said Sunshine, a senior research scientist in the University of
    Maryland’s department of astronomy. “These asteroids are prime
    candidates for future space missions that could collect and return
    samples to Earth providing a more detailed understanding of the Solar
    System’s first few millions of years.”

    In the Beginning

    At the beginning of the Solar System, there was just a disk-shaped cloud
    of hot gas, the solar nebula. When gasses on the edge of the early
    nebula began to cool, the first materials to condense into solid
    particles were rich in the elements calcium and aluminum. As the gasses
    cooled further, other materials also began to condense. Eventually the
    different types of solid particles clumped together to form the common
    building blocks of comets, asteroids, and planets. Astronomers have
    thought that at least some of the Solar System’s oldest asteroids should
    be more enriched in calcium and aluminum, but, until the current study,
    none had been identified.

    Meteorites found on Earth do contain small amounts of these earliest
    condensing materials. As seen in meteorites, these bright white ancient
    materials, the so-called calcium, aluminum-rich inclusions, or CAIs, can
    be as large as a centimeter in diameter. Scientists, in fact, long have
    used the age of CAIs to define the age of the Solar System.

    “The fall of the Allende meteorite in 1969 initiated a revolution in the
    study of the early Solar System,” said Tim McCoy, curator of the
    national meteorite collection at the Smithsonian’s National Museum of
    Natural History. “It was at that time scientists first recognized that
    the remarkable white inclusions — later called calcium, aluminum-rich
    inclusions– which were found in this meteorite, matched many of the
    properties expected of early Solar System condensates.
    “I find it amazing that it took us nearly 40 years to collect spectra of
    these [CAI-rich] objects and that those spectra would now initiate
    another revolution, pointing us to the asteroids that record this
    earliest stage in the history of our Solar System,” said McCoy.

    Sunshine and McCoy, with colleagues Harold Connolly, Jr, City University
    of New York; Bobby Bus, Institute for Astronomy, University of Hawaii,
    Hilo; and Lauren La Croix, Smithsonian Institution, used the SpeX
    instrument at the NASA Infrared Telescope Facility in Hawaii to look at
    the surface of asteroids for evidence of the presence of such early bits
    of high-temperature rock. In particular, they looked for spectral
    “fingerprints” indicative of the presence of CAIs. Because different
    minerals have different reflective properties, the spectrum, or color of
    light reflected from a surface, reveals information about its
    composition enabling telescopic compositional analysis.

    In their paper, Sunshine and colleagues quantitatively compare the
    spectral signatures of asteroid surfaces and CAIs in meteorites from the
    Smithsonian’s National Museum of Natural History collection. “Several
    CAI-rich asteroids have been identified that contain 2-3 times more CAI
    material than any known meteorite,” Sunshine said. “Thus it appears
    ancient asteroids have indeed survived, and we know where they are.”

    This research was supported by NASA and the National Science Foundation

    Making a Deep Impact on Space Exploration

    University of Maryland scientists and engineers are at the forefront of
    many efforts to explore our Solar System and the universe beyond it.
    Maryland astronomers have led or participated in many Solar System
    missions, including: Deep Impact and its current follow-on mission
    EPOXI; the Dawn mission to study dwarf planet Ceres and asteroid Vesta;
    and the NEAR spacecraft that in 2000 became the first to orbit, and then
    land on, an asteroid.

    Scientists of the university’s space physics group have built sensors
    for some 13 spacecraft, including the two Voyager spacecraft, now
    exploring the outer edge of the Solar System; the Cassini mission
    (Saturn); the Ulysses probe to the solar poles; and near-Earth missions
    such as Geotail and the Solar Anomalous and Magnetospheric Particle
    Explorer (SAMPEX).

    The University of Maryland’s Space System Laboratory works to make
    humans more productive while working in space by designing tools and
    suits for astronauts; creating robotic systems capable of assisting
    astronauts in space and studying how the human body works in space. To
    simulate the weightless environment of space, the laboratory uses its
    neutral buoyancy facility, the only such facility located on a college

    # # #
    “Ancient Asteroids Enriched in Refractory Inclusions,” J. M. Sunshine1*,
    H. C. Connolly, Jr.2, 3,4, T. J. McCoy5, S. J. Bus6, and L. M. La
    1Department of Astronomy, University of Maryland, College Park, MD
    2Department of Physical Sciences, Kingsborough Community College of the
    City University of New York, Brooklyn, NY
    3Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ
    85721, USA
    4Department of Earth and Planetary Sciences, American Museum of Natural
    History, New York, NY
    5Department of Mineral Sciences, National Museum of Natural History,
    Smithsonian Institution, Washington, DC
    6Institute for Astronomy, University of Hawaii, Hilo
    7Department of Geological Sciences and Engineering, University of
    Nevada, Reno NV

    Science contact-
    Jessica M. Sunshine