Advertisement

A New Dawn

Since 17 July 2011, NASA's spacecraft Dawn has been orbiting the asteroid Vesta—the second most massive and the third largest asteroid in the solar system (see the cover). Russell et al. (p. 684) use Dawn's observations to confirm that Vesta is a small differentiated planetary body with an inner core, and represents a surviving proto-planet from the earliest epoch of solar system formation; Vesta is also confirmed as the source of the howardite-eucrite-diogenite (HED) meteorites. Jaumann et al. (p. 687) report on the asteroid's overall geometry and topography, based on global surface mapping. Vesta's surface is dominated by numerous impact craters and large troughs around the equatorial region. Marchi et al. (p. 690) report on Vesta's complex cratering history and constrain the age of some of its major regions based on crater counts. Schenk et al. (p. 694) describe two giant impact basins located at the asteroid's south pole. Both basins are young and excavated enough amounts of material to form the Vestoids—a group of asteroids with a composition similar to that of Vesta—and HED meteorites. De Sanctis et al. (p. 697) present the mineralogical characterization of Vesta, based on data obtained by Dawn's visual and infrared spectrometer, revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle. The global color variations detailed by Reddy et al. (p. 700) are unlike those of any other asteroid observed so far and are also indicative of a preserved, differentiated proto-planet.

Abstract

The Dawn spacecraft targeted 4 Vesta, believed to be a remnant intact protoplanet from the earliest epoch of solar system formation, based on analyses of howardite-eucrite-diogenite (HED) meteorites that indicate a differentiated parent body. Dawn observations reveal a giant basin at Vesta’s south pole, whose excavation was sufficient to produce Vesta-family asteroids (Vestoids) and HED meteorites. The spatially resolved mineralogy of the surface reflects the composition of the HED meteorites, confirming the formation of Vesta’s crust by melting of a chondritic parent body. Vesta’s mass, volume, and gravitational field are consistent with a core having an average radius of 107 to 113 kilometers, indicating sufficient internal melting to segregate iron. Dawn's results confirm predictions that Vesta differentiated and support its identification as the parent body of the HEDs.

Get full access to this article

View all available purchase options and get full access to this article.

Supplementary Material

Summary

Supplementary Text
Figs. S1 and S2

Resources

File (684.mp3)
File (russell.sm.pdf)

References and Notes

1
H. Y. McSween, G. R. Huss, Cosmochemistry (Cambridge Univ. Press, Cambridge, 2010).
2
Urey H. C., The cosmic abundances of potassium, uranium, and thorium and the heat balances of the Earth, the Moon, and Mars. Proc. Natl. Acad. Sci. U.S.A. 41, 127 (1955).
3
Coradini A., et al., Space Sci. Rev. 164, 25 (2011).
4
Russell C. T., Raymond C. A., Space Sci. Rev. 163, 1 (2011).
5
McCord T. B., Adams J. B., Johnson T. V., Asteroid vesta: Spectral reflectivity and compositional implications. Science 168, 1445 (1970).
6
Schenk P., et al., Science 336, 694 (2012).
7
Binzel R. P., Xu S., Chips off of Asteroid 4 Vesta: Evidence for the parent body of basaltic achondrite meteorites. Science 260, 186 (1993).
8
Marzari F., et al., Astron. Astrophys. 316, 248 (1996).
9
Marchi S., et al., Science 336, 690 (2012).
10
De Sanctis M. C., et al., Science 336, 697 (2012).
11
Vesta’s volume was estimated using three methods: (1) a stereophotoclinometrically derived (SPC) shape model that filled in the unmeasured northern latitudes with spherical harmonics fit to the measured region; (2) the SPC shape model that used the Thomas shape model (11) to fill in the northern cap; and (3) the stereophotogrammetrically derived shape model filled in the north with the SPC harmonics. The differences were 0.28% between models 1 and 2 and 0.059% between 1 and 3, indicating that the unmeasured northern cap is unlikely to cause a large uncertainty in the volume estimate. Model 2 is used throughout this report.
12
Konopliv A., et al., The Dawn gravity investigation at Vesta and Ceres. Space Sci. Rev. 163, 461 (2011).
13
Konopliv A., et al., Mars high resolution gravity fields from MRO, Mars seasonal gravity, and other dynamical parameters. Icarus 211, 401 (2011).
14
See supplementary materials on Science Online.
15
Thomas P., et al., Vesta: Spin pole, size, and shape from HST images. Icarus 128, 88 (1997).
16
Ruzicka A., Snyder G. A., Taylor L. A., Vesta as the howardite, eucrite and diogenite parent body: Implications for the size of a core and for large-scale differentiation. Meteorit. Planet. Sci. 32, 825 (1997).
17
The error in bulk density was estimated by assuming uncertainties in the axial dimensions of a best-fit ellipsoid of 100 m equatorial and 500 m polar, and forward-calculating the density variation. The quoted value is three times that estimate.
18
J ¯ 2 is the gravitational moment associated with the normalized spherical harmonic coefficient of the Legendre polynomial p ¯ 2 c ¯ 20 and is related to the gravitational flattening (31).
19
Vesta’s shape and the values of J ¯ 2 , C22, and S22 (C22, 0.0043590 ± 0.0000003; S22, 0.000254 ± 0.000005) indicate that Vesta is not currently in hydrostatic equilibrium, but its rotation dominates the second harmonic of its gravity field. Vesta may have been closer to hydrostatic equilibrium at the time of core formation, in which case its core may have frozen in an oblate shape. The dependence of the derived bulk silicate density on the core’s shape demonstrates that its influence is weak.
20
V. F. Buchwald, Handbook of Iron Meteorites (Univ. of California Press, Berkeley, CA, 1975).
21
Righter K., Drake M. J., A magma ocean on Vesta: Core formation and petrogenesis of eucrites and diogenites. Meteorit. Planet. Sci. 32, 929 (1997).
22
N. L. Chabot, H. Haack, in Meteorites and the Early Solar System, D. S. Lauretta, H. Y. McSween, Eds. (Univ. of Arizona Press, Tucson, AZ, (2006), pp. 747–771.
23
McSween H. Y., et al., Space Sci. Rev. 163, 141 (2010) and references therein.
24
Zuber M. T., et al., Space Sci. Rev. 163, 77 (2011) and references therein.
25
Beck A. W., McSween H. Y., Diogenites as polymict breccias composed of orthopyroxenite and harzburgite. Meteorit. Planet. Sci. 45, 850 (2010).
26
Dreibus G., Wanke H., Z. Naturforsch. C 35a, 204 (1980).
27
Britt D., et al., Lunar Planet. Sci. Conf. 41, 1869 (2010).
28
Weiss B. P., et al., Magnetism on the angrite parent body and the early differentiation of planetesimals. Science 322, 713 (2008).
29
Jaumann R., et al., Science 336, 687 (2012).
30
Reddy V., et al., Science 336, 700 (2012).
31
W. Kaula, Theory of Satellite Geodesy: Applications of Satellites to Geodesy (Dover, Mineola, NY, 2000).
32
R. Greeley, G. Batson, Planetary Mapping (Cambridge Univ. Press, Cambridge, 1990).

(0)eLetters

eLetters is a forum for ongoing peer review. eLetters are not edited, proofread, or indexed, but they are screened. eLetters should provide substantive and scholarly commentary on the article. Embedded figures cannot be submitted, and we discourage the use of figures within eLetters in general. If a figure is essential, please include a link to the figure within the text of the eLetter. Please read our Terms of Service before submitting an eLetter.

Log In to Submit a Response

No eLetters have been published for this article yet.

Information & Authors

Information

Published In

Science
Volume 336 | Issue 6082
11 May 2012

Submission history

Received: 19 January 2012
Accepted: 22 March 2012
Published in print: 11 May 2012

Permissions

Request permissions for this article.

Acknowledgments

We thank the Dawn team for the development, cruise, orbital insertion, and operations of the Dawn spacecraft at Vesta. C.T.R. is supported by the Discovery Program through contract NNM05AA86C to the University of California, Los Angeles. A portion of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Dawn data are archived with the NASA Planetary Data System.

Authors

Affiliations

C. T. Russell* [email protected]
Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095–1567, USA.
C. A. Raymond
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
A. Coradini
Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome, Italy.
H. Y. McSween
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996–1410, USA.
M. T. Zuber
Massachussetts Institute of Technology, Cambridge, MA 02139–4307, USA.
A. Nathues
Max-Planck-Institut fur Sonnensystemforschung, Katlenburg-Lindau, Germany.
M. C. De Sanctis
Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica, Rome, Italy.
R. Jaumann
Institute of Planetary Research, DLR, Berlin, Germany.
A. S. Konopliv
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
F. Preusker
Institute of Planetary Research, DLR, Berlin, Germany.
S. W. Asmar
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
R. S. Park
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
R. Gaskell
Planetary Science Institute, Tucson, AZ 85719, USA.
H. U. Keller
Max-Planck-Institut fur Sonnensystemforschung, Katlenburg-Lindau, Germany.
S. Mottola
Institute of Planetary Research, DLR, Berlin, Germany.
T. Roatsch
Institute of Planetary Research, DLR, Berlin, Germany.
J. E. C. Scully
Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095–1567, USA.
D. E. Smith
Massachussetts Institute of Technology, Cambridge, MA 02139–4307, USA.
P. Tricarico
Planetary Science Institute, Tucson, AZ 85719, USA.
M. J. Toplis
Institut de Recherche en Astrophysique et Planetologie, Université de Toulouse, France.
U. R. Christensen
Max-Planck-Institut fur Sonnensystemforschung, Katlenburg-Lindau, Germany.
W. C. Feldman
Planetary Science Institute, Tucson, AZ 85719, USA.
D. J. Lawrence
Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
T. J. McCoy
Smithsonian Institution, Washington, DC 20560, USA.
T. H. Prettyman
Planetary Science Institute, Tucson, AZ 85719, USA.
R. C. Reedy
Planetary Science Institute, Tucson, AZ 85719, USA.
M. E. Sykes
Planetary Science Institute, Tucson, AZ 85719, USA.
T. N. Titus
U.S. Geological Survey, Flagstaff, AZ 86001, USA.

Notes

*
To whom correspondence should be addressed. E-mail: [email protected]

Metrics & Citations

Metrics

Article Usage

Altmetrics

Citations

Cite as

Export citation

Select the format you want to export the citation of this publication.

Cited by

  1. Gaia search for early-formed andesitic asteroidal crusts , Astronomy & Astrophysics, 671, (A40), (2023).https://doi.org/10.1051/0004-6361/202245311
    Crossref
  2. Anatomy of rocky planets formed by rapid pebble accretion, Astronomy & Astrophysics, 671, (A74), (2023).https://doi.org/10.1051/0004-6361/202142141
    Crossref
  3. Secondary Cratering From Rheasilvia as the Possible Origin of Vesta's Equatorial Troughs, Journal of Geophysical Research: Planets, 128, 3, (2023).https://doi.org/10.1029/2022JE007473
    Crossref
  4. Calcium Isotope Evolution During Differentiation of Vesta and Calcium Isotopic Heterogeneities in the Inner Solar System, Geophysical Research Letters, 50, 4, (2023).https://doi.org/10.1029/2022GL102179
    Crossref
  5. Lead-lead (Pb-Pb) dating of eucrites and mesosiderites: Implications for the formation and evolution of Vesta, Geochimica et Cosmochimica Acta, 348, (369-380), (2023).https://doi.org/10.1016/j.gca.2023.03.026
    Crossref
  6. Could near-Earth watery asteroid Ceres be a likely ocean world and habitable?, Water Worlds in the Solar System, (523-544), (2023).https://doi.org/10.1016/B978-0-323-95717-5.00015-3
    Crossref
  7. Petrogenesis of HED clan meteorites: Constraints from crystal size distribution, Journal of Earth System Science, 132, 1, (2023).https://doi.org/10.1007/s12040-023-02051-y
    Crossref
  8. Physical Characterization of 2015 JD 1 : A Possibly Inhomogeneous Near-Earth Asteroid , The Planetary Science Journal, 3, 8, (189), (2022).https://doi.org/10.3847/PSJ/ac7e4f
    Crossref
  9. Serpentinization in the Thermal Evolution of Icy Kuiper Belt Objects in the Early Solar System, The Planetary Science Journal, 3, 3, (54), (2022).https://doi.org/10.3847/PSJ/ac5175
    Crossref
  10. Asteroids and Their Mathematical Methods, Mathematics, 10, 16, (2897), (2022).https://doi.org/10.3390/math10162897
    Crossref
  11. See more
Loading...

View Options

Check Access

Log in to view the full text

AAAS ID LOGIN

AAAS login provides access to Science for AAAS Members, and access to other journals in the Science family to users who have purchased individual subscriptions.

Log in via OpenAthens.
Log in via Shibboleth.

More options

Register for free to read this article

As a service to the community, this article is available for free. Login or register for free to read this article.

Purchase this issue in print

Buy a single issue of Science for just $15 USD.

View options

PDF format

Download this article as a PDF file

Download PDF

Full Text

FULL TEXT

Media

Figures

Multimedia

Tables

Share

Share

Share article link

Share on social media