A Closer Look at Vesta

by Paul Gilster on October 30, 2007

It seems extraordinary to speak of picking up pieces of an asteroid on the surface of the Earth, but the meteorites known as eucrites are confidently identified with Vesta, the brightest asteroid in the sky (and the only one visible with the naked eye). With the Dawn mission on its way to both Ceres and Vesta, we’ll learn much more about the composition of both, but Vesta is coming into its own as a most unusual object that has contributed much to the surrounding system.

Hubble model of Vesta

For the 330-mile wide asteroid sports a huge gouge taken out of its south pole, apparently the result of a collision between protoplanetary objects. The hole, some eight miles deep, once contained a half million cubic miles of asteroid material that was subsequently blasted into interplanetary space, where interaction with Jupiter came into play. Gravitational tugging changes orbits, and some of these objects were put onto trajectories that brought them to Earth.

Image: A 3-D computer model of the asteroid Vesta synthesized from Hubble topographic data. The crater’s 8-mile high central peak can clearly be seen near the pole. The surface texture on the model is artificial, and is not representative of the true brightness variations on the asteroid. Elevation features have not been exaggerated. Credit: Ben Zellner (Georgia Southern University), Peter Thomas (Cornell University) and NASA.

Thus we can study at least part of Vesta — materials from its primordial surface — right here. Says Christopher Russell (UCLA):

“Meteorites are hardy objects indeed. Eucrites are a specific type of meteorite that the science community is confident came from Vesta’s surface. We believe that when Vesta was forming, there was molten rock that flowed onto its surface that cooled rapidly. That rapid cooling created small crystals.”

Indeed, the spectral signature of these meteorites is identical with that of Vesta. The isotopes in eucrites are unlike isotopes found in any other rocks on Earth, the Moon or other meteorites. “Simply put,” adds Russell, “we cannot find another place in the Solar System they could be from.”

This JPL feature offers background. We follow Dawn with interest, but note that finding fragments is the best way to encounter an asteroid on Earth, a reminder that a darker alternative is the kind of impact that leads to planetary catastrophe. Our deepening understanding of asteroids should have us sorting out our options for missions to near-Earth objects in hopes of learning as much about their composition as we’re learning about Vesta, and deducing from that how we go about deflecting them.

{ 8 comments }

ljk October 30, 2007 at 12:04

Origin of volatiles in the Main Belt

Authors: Olivier Mousis, Yann Alibert, Daniel Hestroffer, Ulysse Marboeuf, Christophe Dumas, Benoit Carry, Jonathan Horner, Franck Selsis

(Submitted on 26 Oct 2007)

Abstract: We propose a scenario for the formation of the Main Belt in which asteroids incorporated icy particles formed in the outer Solar Nebula. We calculate the composition of icy planetesimals formed beyond a heliocentric distance of 5 AU in the nebula by assuming that the abundances of all elements, in particular that of oxygen, are solar. As a result, we show that ices formed in the outer Solar Nebula are composed of a mix of clathrate hydrates, hydrates formed above 50 K and pure condensates produced at lower temperatures. We then consider the inward migration of solids initially produced in the outer Solar Nebula and show that a significant fraction may have drifted to the current position of the Main Belt without encountering temperature and pressure conditions high enough to vaporize the ices they contain. We propose that, through the detection and identification of initially buried ices revealed by recent impacts on the surfaces of asteroids, it could be possible to infer the thermodynamic conditions that were present within the Solar Nebula during the accretion of these bodies, and during the inward migration of icy planetesimals. We also investigate the potential influence that the incorporation of ices in asteroids may have on their porosities and densities. In particular, we show how the presence of ices reduces the value of the bulk density of a given body, and consequently modifies its macro-porosity from that which would be expected from a given taxonomic type.

Comments: Accepted for publication in MNRAS

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0710.5179v1 [astro-ph]

Submission history

From: Olivier Mousis [view email]

[v1] Fri, 26 Oct 2007 21:04:05 GMT (514kb)

http://arxiv.org/abs/0710.5179

dad2059 October 30, 2007 at 14:39

We need more missions to the asteroid belt and to Near Earth Objects. In fact, we should investigate NEOs before Moon missions, not just for ways to deflect them, but to get at the resources. It’s easier on fuel supplies working in microgravity instead of a gravity “hole” like the Moon. And we know some of these objects have volitiles. I would surmise that NEO resources would be cheaper to process than Lunar resources, and with less machinery and people.

ljk January 15, 2008 at 1:22

Two new basaltic asteroids in the Outer Main Belt?

Authors: R. Duffard, F. Roig

(Submitted on 2 Apr 2007 (v1), last revised 14 Jan 2008 (this version, v2))

Abstract: The identification of basaltic asteroids in the asteroid Main Belt and the description of their surface mineralogy is necessary to understand the diversity in the collection of basaltic meteorites. Basaltic asteroids can be identified from their visible reflectance spectra and are classified as V-type in the usual taxonomies.

In this work, we report visible spectroscopic observations of two candidate V-type asteroids, (7472) Kumakiri and (10537) 1991 RY16, located in the outer Main Belt (a greater than 2.85 UA). These candidate have been previously identified by Roig and Gil-Hutton (2006, Icarus 183, 411) using the Sloan Digital Sky Survey colors. The spectroscopic observations have been obtained at the Calar Alto Observatory, Spain, during observational runs in November and December 2006. The spectra of these two asteroids show the steep slope shortwards of 0.70 microns and the deep absorption feature longwards of 0.75 microns that are characteristic of V-type asteroids. However, the presence of a shallow but conspicuous absorption band around 0.65 microns opens some questions about the actual mineralogy of these two asteroids. Such band has never been observed before in basaltic asteroids with the intensity we detected it.

We discuss the possibility for this shallow absorption feature to be caused by the presence of chromium on the asteroid surface. Our results indicate that, together with (1459) Magnya, asteroids (7472) Kumakiri and (10537) 1991 RY16 may be the only traces of basaltic material found up to now in the outer Main Belt.

Comments: 13 pages, 3 figures, 2 tables

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0704.0230v2 [astro-ph]

Submission history

From: Rene Duffard [view email]

[v1] Mon, 2 Apr 2007 16:42:38 GMT (334kb,D)

[v2] Mon, 14 Jan 2008 19:06:00 GMT (246kb,D)

http://arxiv.org/abs/0704.0230

ljk January 18, 2008 at 12:50

Asteroid occultations today and tomorrow: toward the GAIA era

Authors: P. Tanga (OCA), M. Delbo (OCA, Inaf-Osservatorio Astronomico Di Torino)

(Submitted on 17 Jan 2008)

Abstract: Context: Observation of star occultations is a powerful tool to determine shapes and sizes of asteroids. This is key information necessary for studying the evolution of the asteroid belt and to calibrate indirect methods of size determination, such as the models used to analyze thermal infrared observations. Up to now, the observation of asteroid occultations is an activity essentially secured by amateur astronomers equipped with small, portable equipments. However, the accuracy of the available ephemeris prevents accurate predictions of the occultation events for objects smaller than ~100 km.

Aims: We investigate current limits in predictability and observability of asteroid occultations, and we study their possible evolution in the future, when high accuracy asteroid orbits and star positions (such as those expected from the mission Gaia of the European Space Agency) will be available.

Methods: We use a simple model for asteroid ephemeris uncertainties and numerical algorithms for estimating the limits imposed by the instruments, assuming realistic CCD performances and asteroid size distribution, to estimate the expected occultation rate under different conditions.

Results: We show that high accuracy ephemerides which will be available in the future will extend toward much smaller asteroids the possibility of observing asteroid occultations, greatly increasing the number of events and objects involved. A complete set of size measurements down to ~10 km main belt asteroids could be obtained in a few years, provided that a small network of ground-based 1m telescopes are devoted to occultation studies.

Subjects: Astrophysics (astro-ph)

Journal reference: Astronomy and Astrophysics 474 (2007) 1015-1022

DOI: 10.1051/0004-6361:20077470

Cite as: arXiv:0801.2684v1 [astro-ph]

Submission history

From: Paolo Tanga [view email] [via CCSD proxy]

[v1] Thu, 17 Jan 2008 14:38:49 GMT (170kb)

http://arxiv.org/abs/0801.2684

ljk January 18, 2008 at 12:51

Formes d’astéroïdes et formation de satellites : rôle de la réaccumulation gravitationnelle

Authors: Jean-François Consigli (OCA), Paolo Tanga (OCA), Carlo Comito (OCA), Daniel Hestroffer (IMCCE), Derek C. Richardson

(Submitted on 17 Jan 2008)

Abstract: Asteroid shapes and satellites: role of gravitational reaccumulation. Following current evidences, it is widely accepted that many asteroids would be “gravitational aggregates”, i.e. bodies lacking internal cohesion. They could mainly be originated during the catastrophic disruption of some parent bodies, through the gravitational reaccumulation of the resulting fragments. The same events produced the dynamical families that we observe.

In this work we address the problem of the origin of shapes of gravitational aggregates, that could contain signatures of their origin. We use a N-body code to simulate the collapse of a cloud of fragments, with a variety of initial velocity distributions and total angular momentum. The fragments are treated as inhelastic spheres, that rapidly accumulate to form rotating aggregates. The resulting shapes and rotational properties are compared with theoretical predictions. The results show that only a precise category of shapes (flattened spheroids) are created via this mechanism. This may provide interesting constraints on the evolution of asteroid shapes, in particular for those with one or more satellites.

Subjects: Astrophysics (astro-ph); Geophysics (physics.geo-ph)

Journal reference: Comptes Rendus Physique 8 (2007) 469-480

Cite as: arXiv:0801.2685v1 [astro-ph]

Submission history

From: Paolo Tanga [view email] [via CCSD proxy]

[v1] Thu, 17 Jan 2008 14:42:12 GMT (131kb)

http://arxiv.org/abs/0801.2685

ljk March 20, 2008 at 9:24

Dawn – mission to asteroids Vesta and Ceres

(Science Show: 15/03/2008)

Vesta and Ceres are the two biggest asteroids in the
asteroid belt. Vesta is barren. Ceres is a mystery. We
have no meteorites from Ceres. One in 20 meteorites
that fall on the Earth are from Vesta. So why is there
nothing from Ceres? Might the meteorites evaporate?
Might they be made of water?

Dawn is a mission launched September 2007 going to
the asteroid belt. Arrival time is 2011. One year at Vesta
will be spent mapping the surface. A spectrometer will
identify minerals. At low altitude, 200km above the surface,
gravity will be measured. Vesta and Ceres are seen as the
building block of planets.

The challenge will be in avoiding asteroids when Dawn is
travelling between the asteroids in the asteroid belt.

Full transcript here:

http://www.abc.net.au/rn/scienceshow/stories/2008/2190092.htm

ljk January 30, 2009 at 0:27

Catalogue of ISO LWS observations of asteroids

Authors: Felix Hormuth (1 and 2), Thomas G. Müller (3) ((1) Centro Astronómico Hispano Alemán, Almería, Spain, (2) Max-Planck-Institut für Astronomie, Heidelberg, Germany, (3) Max-Planck-Institut für extraterrestrische Physik, Garching, Germany)

(Submitted on 28 Jan 2009)

Abstract: (Abridged) The Long Wavelength Spectrometer (LWS) onboard the Infrared Space Observatory (ISO) observed the four large main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (10) Hygiea multiple times.

The photometric and spectroscopic data cover the wavelength range between 43 and 197 um, and are a unique dataset for future investigations and detailed characterisations of these bodies. The standard ISO archive products, produced through the last post-mission LWS pipeline, were still affected by instrument artefacts.

Our goal was to provide the best possible data products to exploit the full scientific potential of these observations. We performed a refined reduction of all measurements, corrected for various instrumental effects, and re-calibrated the data. We outline the data reduction process and give an overview of the available data and the quality of the observations.

We apply a thermophysical model to the flux measurements to derive far-IR based diameter and albedo values of the asteroids. The measured thermal rotational lightcurve of (4) Vesta is compared to model predictions.

The absolute photometric accuracy of the data products was foubd to be better than 10%. The calibrated spectra will serve as source for future mineralogical studies of dwarf planets and dwarf planet candidates.

Comments: 11 pages, 6 figures, accepted for publication in A&A

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:0901.4557v1 [astro-ph.EP]

Submission history

From: Felix Hormuth [view email]

[v1] Wed, 28 Jan 2009 21:21:09 GMT (251kb)

http://arxiv.org/abs/0901.4557

ljk February 23, 2009 at 11:56

Probing the history of Solar System through the cratering records on Vesta and Ceres

Authors: D. Turrini, G. Magni, A. Coradini

(Submitted on 20 Feb 2009)

Abstract: Dawn space mission will provide the first, detailed data of two of the major bodies in the Main Belt, Vesta and Ceres. In the framework of our studies on the origin of Solar System, we modelled the accretion of Jupiter and, through an N-Body code developed on purpose, we evaluated the flux of impactors on Vesta and Ceres keeping track of their formation zones.

We also studied the effects of the possible inward migration of Jupiter on the rate and the characteristics of the impacts. We here describe the different scenarios and their implications for the evolution of Solar System.

Comments: 25 pages, 14 figures

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:0902.3579v1 [astro-ph.EP]

Submission history

From: Diego Turrini [view email]

[v1] Fri, 20 Feb 2009 13:41:16 GMT (318kb)

http://arxiv.org/abs/0902.3579

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