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A New Look at Asteroid Distribution

We know that understanding Near-Earth Objects is vital not only for assessing future asteroid surveys and spacecraft missions, but also for tracking potential impactors on Earth. Projects like the Catalina Sky Survey and its now defunct southern hemisphere counterpart, the Siding Spring Survey, are all about asteroid and comet discovery, with a more specific goal of looking for objects posing a potential hazard to our planet. We lost the Siding Spring effort in 2013 due to funding problems, but the Catalina Sky Survey (CSS) is still in robust operation.

The survey draws data from a 1.5 meter telescope on the peak of Mt. Lemmon (Arizona) and a 68 centimeter instrument nearby at Mt. Bigelow. Now we have word that Mikael Granvik (University of Helsinki) and an international team of researchers have drawn on about 100,000 images acquired by the Catalina Sky Survey to study the properties of some 9000 NEOs detected in an eight-year period. The goal is to construct a model for the population of NEOs, giving us better insights into their origins and subsequent trajectories.

Most Near-Earth Objects are thought to originate in the main asteroid belt between the orbits of Mars and Jupiter. An individual asteroid’s orbit can vary over time as heat from the Sun is released from its uneven surface, an effect named after the Russian engineer Ivan Osipovich Yarkovsky, who noted that even this tiny force could have cumulative effects on an asteroid’s orbit. The Estonian astronomer Ernst J. Öpik would subsequently bring the effect to the attention of the larger astronomical community after its initial publication by Yarkovsky.

Asteroid orbits can eventually be affected by the gas giants Jupiter and Saturn, changing their trajectory to push them into the inner system. From this we get our population of NEOs, so classified, according to this University of Hawaii at Manoa news release, when their smallest distance from the Sun during an orbit is less than 1.3 times the average Earth-Sun distance.

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Image: Artist’s impression. An asteroid’s orbit is altered as it passes close to Jupiter, Earth or Venus, such that its new orbit takes it near the Sun. The intense heat from the Sun causes the asteroid’s surface to expand and fracture, and some of the material breaks off. As the surface material disintegrates, it creates dust and pebbles that spread out along the asteroid’s orbit with time. If the orbit of the dust and pebbles ever intersects Earth, it can create a meteor shower. Credit: Karen Teramura, UH IfA.

Most NEOs have been thought to eventually end their lives by plunging into the Sun, but now we learn that they may not make it that far. Using calculations developed by Robert Jedicke (University of Hawaii), the Near-Earth Object population modeling project was able to compute the probabilities that asteroids on different orbits would have been detected by the Catalina Sky Survey. Using CSS data and theoretical orbit distributions of NEOs originating in different parts of the main belt, they developed a more detailed model of the NEO population than any previously available.

The model, however, predicted almost ten times more objects on orbits that approach the Sun within ten Solar diameters than have been observed. Eliminating these asteroids could be accomplished by assuming that a large number of NEOs are destroyed as they move closer to the Sun. The asteroids do not fall into the Sun but are broken up as they approach. Darker asteroids are destroyed further from the Sun than brighter ones, implying a different internal structure and composition. Granvik sees this latter as the most significant result of the research:

“Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes. This is truly remarkable and was completely unexpected when we first started constructing the new NEO model.”

The work also helps to explain meteor streams that should follow in the path of the asteroids or comets from which they are dislodged, and yet most meteor streams have not been matched with known objects. The Granvik study concludes that the parent bodies of these meteor streams were destroyed when they approached too close to the Sun.

The paper is Granvik et al., “Super-catastrophic Disruption of Asteroids at Small Perihelion Distances,” Nature 530 (18 February 2016), 303–306 (abstract).

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Comments on this entry are closed.

  • Larry Kennedy February 17, 2016, 14:41

    I’ve been fascinated with this subject since Gene Schumacher’s work, so many years ago. It’s always surprised me that this work hasn’t caught on faster than it has. I have to confess to be a long time asteroidphile (you saw it here first) whether earthbound, manned or unmanned.

  • Hop David February 17, 2016, 14:52

    So by “destroyed” I guess they mean smeared into a long band?

    • ljk February 18, 2016, 11:59

      Has anyone noticed an increase in the density and brightness of the Zodiacal Light?

  • RobFlores February 17, 2016, 17:28

    What is the astronomical distance from the sun where heating and fracturing begins to erode these near Earth object, for say a stony asteroid?
    There must me some effect between the orbit of Mercury and Venus.

    My thinking is that a ancient NEO that comes close to the SUN , would be a better target for mining. If the heated broken up surface is already porous you don’t need very powerful surface probes or drills for that matter to prospect for more valuable materials deeper in the asteroid. You would just have to give your probe some protection if it is going to remain
    on the surface during closest approach to the Sun.

  • Ricardo Orsini Amarante [ROCA] February 17, 2016, 17:30

    This part on 2nd paragraph “Mikael Granvik (University of Hels 530, 303–306 (18 February 2016)inki)” is truncated.

    • Paul Gilster February 17, 2016, 19:05

      Thank you, Ricardo! Not sure how that happened, but it’s fixed.

  • Alex Tolley February 17, 2016, 18:49

    If the asteroids are not destroyed, but break up into smaller pieces, and that there are so many of these NEOs based on the model, doesn’t that imply that the power law distribution of particles will be different depending on where you measure the distribution? The closer to the sun, the distribution will show a bias towards smaller particles.

    If true, can this be tested by direct observation of particle impact sizes and rates on spacecraft, or possibly by other indirect means?

    • Adam February 17, 2016, 20:07

      Poynting-Robertson drag and YORP will quickly change the distribution for small stuff. Fine dust lasts less than 10,000 years close to the Sun. It either spirals in or is blown out. Unless it impacts a planet – we know a lot about the small stuff from meteorites and meteors.

      Wikipedia’s entry is very useful: Poynting-Robertson Effect

  • ljk February 19, 2016, 10:13

    The latest NASA report on retrieving a small planetoid:

    http://www.astrowatch.net/2016/02/nasa-report-details-expert-team.html

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