≡ Menu

Asteroids: An Outer Belt Anomaly

Have scientists found a new category of asteroid? The evidence for basalt of a hitherto unseen composition on two small objects in the outer asteroid belt points to the possibility. An igneous rock, basalt would indicate that the asteroids were once part of a larger body, one that underwent some form of internal heating. The problem is that basalt is unusual for this part of the asteroid belt, nor is it clear whether the two fragments under study came from the same parent body. Add to that an unusual reflectance spectrum and the picture gets interesting indeed.

The asteroids in question are (7472) Kumakiri and (10537) 1991 RY16, and therein lies a tale. The two were chosen from a group of six candidate asteroids thought to be classified as V-type, a name deriving from Vesta, the second largest of the asteroids. Not long ago it was thought that all basaltic V-type asteroids were simply fragments of Vesta, but in the past few years several V-type objects not belonging to this family have been found in the outer asteroid belt. That alone gets our attention because we’d like to know what happened to the original body.

But the two asteroids now under investigation, and reported at the European Planetary Science Congress in Potsdam, show reflectance spectra that indicate a shallow absorption band around the wavelength of red visible light. No other V-type asteroids have exhibited such spectra, an indication that we may be dealing with a new category of object. Possible sources for the spectral dip include impacts with other asteroids or even comets, or the findings may indicate the presence of olivine. Whatever the case, the asteroids are in for another round of scrutiny.

Rene Duffard (Instituto de Astrofisica de Andalucia), who presented this material in Potsdam, says his team will now look at both objects in the near-infrared to confirm whether or not their surface is basaltic:

“We appear to have detected basalt on the surface of these asteroids, which is very unusual for this part of the asteroid belt. We do not know whether we have discovered two basaltic asteroids with a very particular and previously unseen mineralogical composition or two objects of non basaltic nature that have to be included in a totally new taxonomic class.”

As we wait for NASA’s Dawn mission to provide us with close-up information about Vesta, note the significance of the population of V-type asteroids. Most have orbital elements that suggest their origin as part of Vesta’s crust (the huge impact crater on Vesta’s southern hemisphere may well be the impact site). Few basaltic objects have been detected in the outer asteroid belt, the first being discovered in 2001. If basalt is confirmed on the two asteroids under study here, the question of where they come from opens up a challenging new investigation. And if they turn out not to be basaltic, a new asteroid class could be in the making.

The paper is Duffard and Roig, “Two new basaltic asteroids in the Outer Main Belt,” with preprint available.

Comments on this entry are closed.

  • ljk August 22, 2007, 10:46


    Date: Tue, 21 Aug 2007 12:37:16 GMT (866kb)

    Title: Apollo asteroids (1566) Icarus and 2007 MK6: Icarus
    family members?

    Authors: K. Ohtsuka, H. Arakida, T. Ito, T. Kasuga, J. Watanabe,
    D. Kinoshita, T. Sekiguchi, D. J. Asher, and S. Nakano

    Categories: astro-ph

    Comments: 11 pages, 1 figure, 0 table

    Although it is more complicated to search for near-Earth
    object (NEO) families than main belt asteroid (MBA) families,
    since differential orbital evolution within a NEO family can
    cause current orbital elements to drastically differ from
    each other, we have found that Apollo asteroids (1566)
    Icarus and the newly discovered 2007 MK6 are almost
    certainly related.

    Specifically, their orbital evolutions show a similar profile, time
    shifted by only ~1000 yr, based on our time-lag theory. The
    dynamical relationship between Icarus and 2007 MK6 along
    with a possible dust band, the Taurid-Perseid meteor swarm,
    implies the first detection of an asteroidal NEO family, namely
    the “Icarus asteroid family”.

    http://arxiv.org/abs/0708.2825 , 866kb

  • philw August 23, 2007, 14:06

    Too often we take the asteroids for granite

  • Administrator August 23, 2007, 14:27

    You have to love a guy who thinks like philw!

  • george scaglione August 23, 2007, 15:36

    philw,not lol but ROFLOL and hahahahaha!!!! really cool . thank you very much your friend george

  • andy August 23, 2007, 16:18

    That pun rocks.

  • Administrator August 23, 2007, 18:02

    Ouch! I’m surrounded by these guys…

  • ljk January 8, 2008, 9:13

    An Upper Limit on Gas Production from 3200 Phaethon

    Authors: Paul A. Wiegert, Martin Houde, Ruisheng Peng

    (Submitted on 7 Jan 2008)

    Abstract: Asteroid 3200 Phaethon resembles a comet in some ways, including a highly-eccentric orbit (e=0.89) and a strong associated meteor shower (the Geminids). Yet this object has never been observed to exhibit any cometary activity, i.e., gas production.

    We observed 3200 Phaethon with the Caltech Submillimeter Observatory on two occasions, once while it was near its closest approach to Earth as it neared perihelion, and another while it was further from Earth post-perihelion. Observations of the J=2-1 and J=3-2 rotational transitions of 12CO, typically strong lines in comets and indicative of gas production, yielded no detection. Upper limits on the 12CO production of 1.8e28 molecules/s and 7.6e28 molecules/s for Phaethon were determined on these two occasions.

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0801.0793v1 [astro-ph]

    Submission history

    From: Paul A. Wiegert [view email]

    [v1] Mon, 7 Jan 2008 20:53:13 GMT (36kb)


  • ljk January 17, 2008, 1:32

    The shape distribution of asteroid families — evidence for evolution driven by small impacts

    Authors: Gyula M. Szabo, Laszlo L. Kiss

    (Submitted on 15 Jan 2008)

    Abstract: A statistical analysis of brightness variability of asteroids reveals how their shapes evolve from elongated to rough spheroidal forms, presumably driven by impact-related phenomena. Based on the Sloan Digital Sky Survey Moving Object Catalog, we determined the shape distribution of 11,735 asteroids, with special emphasis on eight prominent asteroid families.

    In young families, asteroids have a wide range of shape elongations, implying fragmentation-formation. In older families we see an increasing number of rough spheroids, in agreement with the predictions of an impact-driven evolution. Old families also contain a group of moderately elongated members, which we suggest correspond to higher-density, more impact-resistant cores of former fragmented asteroids that have undergone slow shape erosion. A few percent of asteroids have very elongated shapes, and can either be young fragments or tidally reshaped bodies.

    Our results confirm that the majority of asteroids are gravitationally bound “rubble piles”.

    Comments: Accepted by Icarus. 22 pages, 1 table, 6 figures, 31 figure panels

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0801.2389v1 [astro-ph]

    Submission history

    From: Gyula Szabo [view email]

    [v1] Tue, 15 Jan 2008 21:48:00 GMT (586kb)


  • ljk January 17, 2008, 1:35

    Physical and orbital properties of the Trojan asteroids

    Authors: M. D. Melita (IAFE, UBA, CONICET Argentina), J. Licandro, (Instituto de Astrofísica de Canarias, Tenerife, Spain.) Jones, D. C. (Astronomy Unit, Queen Mary College, University of London, UK), I. P. Williams (Astronomy Unit, Queen Mary College, University of London, UK)

    (Submitted on 16 Jan 2008)

    Abstract: All the Trojan asteroids orbit about the Sun at roughly the same heliocentric distance as Jupiter. Differences in the observed visible reflection spectra range from neutral to red, with no ultra-red objects found so far. Given that the Trojan asteroids are collisionally evolved, a certain degree of variability is expected. Additionally, cosmic radiation and sublimation are important factors in modifying icy surfaces even at those large heliocentric distances.

    We search for correlations between physical and dynamical properties, we explore relationships between the following four quantities; the normalised visible reflectivity indexes ($S’$), the absolute magnitudes, the observed albedos and the orbital stability of the Trojans.

    We present here visible spectroscopic spectra of 25 Trojans. This new data increase by a factor of about 5 the size of the sample of visible spectra of Jupiter Trojans on unstable orbits. The observations were carried out at the ESO-NTT telescope (3.5m) at La Silla, Chile, the ING-WHT (4.2m) and NOT (2.5m) at Roque de los Muchachos observatory, La Palma, Spain. We have found a correlation between the size distribution and the orbital stability. The absolute-magnitude distribution of the Trojans in stable orbits is found to be bimodal, while the one of the unstable orbits is unimodal, with a slope similar to that of the small stable Trojans. This supports the hypothesis that the unstable objects are mainly byproducts of physical collisions. The values of $S’$ of both the stable and the unstable Trojans are uniformly distributed over a wide range, from $0 %/1000\AA $ to about $15 %/1000\AA$. The values for the stable Trojans tend to be slightly redder than the unstable ones, but no significant statistical difference is found.

    Comments: Accepted in Icarus

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0801.2497v1 [astro-ph]

    Submission history

    From: Mario Melita Dr. [view email]

    [v1] Wed, 16 Jan 2008 14:34:15 GMT (74kb)


  • ljk June 17, 2008, 0:24

    A Spectroscopically Unique Main Belt Asteroid: 10537 (1991 RY16)

    Authors: Nicholas A. Moskovitz (1), Samuel Lawrence (2), Robert Jedicke (1), Mark Willman (1), Nader Haghighipour (1 and 3), Schelte J. Bus (1), Eric Gaidos (3 and 4) ((1) University of Hawaii, Institute for Astronomy, (2) Arizona State University, (3) NASA Astrobiology Institute, (4) University of Hawaii, Department of Geology and Geophysics)

    (Submitted on 13 Jun 2008)

    Abstract: We present visible and near-infrared reflectance spectra and interpreted surface mineralogy for asteroid 10537 (1991 RY16). The spectrum of this object is without precedent amongst the Main Belt asteroids. A unique absorption band centered at 0.63 microns could be attributed to one of several mineralogies.

    Pronounced 1- and 2-micron absorption bands suggest that the composition of 10537 is a mixture of pyroxenes and olivine and that it originated from a parent body that was partially or fully differentiated. The closest available analog is the large Main Belt asteroid 349 Dembowska but 10537 may be an isolated fragment from a completely eroded parent body.

    Comments: 14 pages, 3 figures, to be published in ApJ Letters

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.2185v1 [astro-ph]

    Submission history

    From: Nicholas Moskovitz [view email]

    [v1] Fri, 13 Jun 2008 05:15:14 GMT (263kb)


  • ljk June 20, 2008, 16:52

    Spatial separation effect of asteroids with different albedos

    Authors: A.M. Kazantsev (Kyiv National Taras Shevchenko University, Ukraine)

    (Submitted on 17 Jun 2008)

    Abstract: Numerical calculations of orbit evolutions of 1694 numbered asteroids included in the IRAS catalogue, from 13.11.1996 to 06.03.2006 were carried out. The values da – differences between the catalogue semimajor axes at 06.03.2006 and the calculated ones were computed. The average dependence da on albido p shows decrease of da at increase of p, and it is significant. In other words, semimajor axes of low-albedo asteroids are, on average, increasing as compared with high-albedo ones.

    Speed of such possible spatial separation for very dim and very bright asteroids of from 10 to 50km in order of magnitude is about 1 AU per 100 My.

    To explain this fact it may suppose an existence possibility of a non-gravitational effect. Such supposition is confirmed by distributions p(a) for asteroid families, above all, Flora family. An analysis of errors and residuals in the used asteroid catalogues is evidence of such supposition.

    Comments: Comments: 21 pages, 9 figures, submitted to EM&P

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.2717v1 [astro-ph]

    Submission history

    From: Anatoly Kazantsev [view email]

    [v1] Tue, 17 Jun 2008 08:46:48 GMT (393kb)