4 Vesta

below, and its rim rises 4-12 km above the surrounding terrain, with total surface relief of about 25 km. A central peak rises deep are also present. A dark albedo feature about across has been named "Olbers" in honour of Vesta's discoverer, but it does not appear in elevation maps as a fresh crater would, and its nature is presently unknown, perhaps an old basaltic surface.B. J. Zellner et al "Hubble Space Telescope Images of Asteroid Vesta in 1994", Icarus, Vol. 128, p. 83 (1997).] It serves as a reference point with the 0° longitude prime meridian defined to pass through its center.

The eastern and western hemispheres show markedly different terrains. From preliminary spectral analyses of the Hubble Space Telescope images, the eastern hemisphere appears to be some kind of high albedo, heavily cratered "highland" terrain with aged regolith, and craters probing into deeper plutonic layers of the crust. On the other hand, large regions of the western hemisphere are taken up by dark geologic units thought to be surface basalts, perhaps analogous to the lunar maria.

Fragments

Some small solar system objects are believed to be fragments of Vesta caused by collisions. The Vestoid asteroids and HED meteorites are examples. The V-type asteroid 1929 Kollaa has been determined to have a composition akin to cumulate eucrite meteorites, indicating its origin deep within Vesta's crust.M. S. Kelley et al "Quantified mineralogical evidence for a common origin of 1929 Kollaa with 4 Vesta and the HED meteorites", Icarus, Vol. 165, p. 215 (2003).]

Because a number of meteorites are believed to be Vestian fragments, Vesta is currently one of only five identified Solar system bodies for which we have physical samples, the others being Mars, the Moon, comet Wild 2, and Earth itself.

Exploration

The first space mission to Vesta will be NASA's "Dawn" probe--launched on September 27, 2007--which will orbit the asteroid for nine months from August 2011 until May 2012. Dawn will then proceed to its other target, Ceres and will probably continue to explore the asteroid belt on an extended mission using remaining fuel. The spacecraft is the first that can enter and leave orbit around more than one body, thanks to its weight-efficient ion driven engines.

NASA attempted to cancel Dawn in 2006, citing budget pressures and technical issues, but scientists appealed and won an additional $100 million to continue the program. Total mission costs will now be about $450 million.

Visibility

Its size and unusually bright surface make Vesta the brightest asteroid, and it is occasionally visible to the naked eye from dark (non-light polluted) skies. In May and June 2007, Vesta reached a peak .]

Less favourable oppositions during late autumn in the Northern Hemisphere still have Vesta at a magnitude of around +7.0. Even when in conjunction with the Sun, Vesta will have a magnitude around +8.5; thus from a pollution-free sky it can be observed with binoculars even at elongations much smaller than near opposition. [ [http://homepage.mac.com/andjames/PageVesta000.htm VESTA] ]

See also

* 3103 Eger
* 4055 Magellan
* 3908 Nyx
* 3551 Verenia
* V-type asteroid
* HED meteorites
* Diogenite
* Eucrite
* Howardite
* Asteroids in fiction
* List of Solar System bodies formerly considered planets

Notes and references

Footnotes

General references

* – Horizons can be used to obtain a current ephemeris
* K. Keil, "Geological History of Asteroid 4 Vesta: The Smallest Terrestrial Planet" in Asteroids III, William Bottke, Alberto Cellino, Paolo Paolicchi, and Richard P. Binzel, (Editors), Univ. of Arizona Press (2002), ISBN 0-8165-2281-2

External links

* NASA video clips of [http://hubblesite.org/newscenter/archive/releases/solar-system/asteroid/2007/27/video/ Vesta rotating in color]
* Views of the Solar System: [http://www.solarviews.com/eng/vesta.htm Vesta]
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/40/ HubbleSite] : Hubble Maps the Asteroid Vesta
* [http://www.britannica.com/eb/article-9075181/Vesta Encyclopaedia Britannica, Vesta - full article]
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/1997/27/ HubbleSite] : Hubble Reveals Huge Crater on the Surface of the Asteroid Vesta
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/20/video/a HubbleSite] : short movie composed from Hubble Space Telescope images from November 1994.
* Adaptive optics views of Vesta from [http://www2.keck.hawaii.edu/ao/vesta-ao.html Keck Observatory]
* [http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/20/image/c Differentiated interior] of Vesta
* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=4;orb=1 Orbital simulation] from JPL (Java)
* [http://www.spacetelescope.org/images/archive/freesearch/4+vesta/viewall/1 4 Vesta images at ESA/Hubble]
* [http://planetary.org/blog/article/00001013/ Hubble views of Vesta on the Planetary Society Weblog] "(includes animation)"
* cite web
last=Farinella | first=Paolo | year=2005
url=http://meteoritemag.uark.edu/612.htm
title=Houston: Focus on Vesta and the HEDs
publisher=Arkansas Center for Space & Planetary Sciences
accessdate=2007-10-25