4-Vesta
Parent of HED Meteorites
Vesta is an intriguing asteroid, famous among meteorite hunters, and currently making more history as part of NASA's Dawn program.
Discovered by the German astronomer Heinrich Wilhelm Olbers in 1807, Vesta was named after the Roman goddess of home and hearth. It was also given the number four since it was the fourth asteroid discovered. (See below for current count: How Many Asteroids Are There?)
Here's Vesta compared to the moon and to other early discovered asteroids:
From Wikipedia, the free encyclopedia
The first 10 asteroids profiled against the Earth's Moon. From left to right: 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astraea, 6 Hebe, 7 Iris, 8 Flora, 9 Metis, and 10 Hygiea.
However, besides being the second most massive object in the asteroid belt, and the brightest, Vesta is a Main Belt asteroid.
Side Trip
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt region is also termed the main belt to distinguish it from other concentrations of minor planets within the Solar System, such as the Kuiper belt and scattered disc.
Here's an illustration of the Main Belt.
This is a file from the Wikimedia Commons.
The Main Asteroid Belt (the white donut-shaped cloud), the Hildas (the orange "triangle" just inside the orbit of Jupiter) and the Jovian Trojans (green). The group that leads Jupiter are called the "Greeks" and the trailing group are called the "Trojans" (Murray and Dermott, Solar System Dynamics, pg. 107).
From our studies of Vesta, we have discovered that it is a water-poor, dense asteroid, that has experienced significant heating to melt its interior and separate (differentiate) its internal structure into a basaltic crust, a silicate mantle, and an iron core, like the terrestrial planets.
Here's an illustration of how it was formed:
As shown above, almost forty years ago, scientists determined that the surface of Vesta was composed of a basaltic crust.
However, in the decades since, astronomers have learned that remote sensing is not the only way to study Vesta. Five percent of the found meteoritic samples on Earth, the Howardite Eucrite Diogenite ("HED") meteorites, are thought to be the result of a collision or collisions with Vesta, ejecting pieces of its crust, which eventually find their way to Earth.
Most (but not all) V-type near-Earth asteroids, and some outer main-belt asteroids have been determined to be similar to Vesta and are known as 'vestoids.'
You can find pieces of these in the meteorite collections of your local natural science history museum. (See below: The HEDs)
So, meteorite collections of Vesta's crust, prove the truth of Vesta's evolution.
With the exception of the large impact crater ~460 km in diameter and 13 km deep in the south pole of Vesta, giving us our HED meteorites, Vesta's crust appears to be mostly intact.
Here's a Hubble image, an elevation composite of Vesta, and a model of the asteroid:
From NASA.
Note especially the elevation image, where you can see the huge impact crater and its central peak.
So, what's the value of Vesta, besides its meteoritic history?
It's a miniature planet, which was formed to completion:
- Heated,
- Melted,
- Fractionated, and
- Solidified.
In such an active collisional environment, as what existed in the early solar system formation, a mostly preserved asteroid crust provides a notable marker in the chronology of the evolution of our solar system.
Learning about this evolution is important. It's important enough that we are going there with Dawn....
The HEDs
Adding to our understanding, we have acquired three meteorite samples of this group.
Chaves
Considered a stone, achondrite howardite (AHOW)
From Traz-os-Montes, Portugal
A witnessed fall: May 3, 1925
Howardites are polymict breccias, which means they consist of broken and angular rock fragments, known as clasts, embedded in a matrix of a different material. Howardites come from at or near the surface of Vesta, in other words they are samples of the asteroid's regolith - The layer of loose material, including soil, subsoil, and broken rock, that covers bedrock.
Sioux County
Stone, achondrite eucrite (AEUC)
From Sioux County, Nebraska
A witnessed fall: August 8, 1933
Eucrites are basalts – volcanic rocks of magmatic origin
Bilanga
Stone, achondrite diogenite (ADIO)
From Bilanga, Burkina Faso, Africa
A witnessed fall: October 27, 1999
Diogenites are named for the Greek philosopher Diogenes of Apollonia who, in the fifth century B.C., was the first to suggest that meteorites come from space (a realization forgotten for the next 2,000 years).
Diogenites originate from deep within the crust and consist mostly of magnesium-rich orthopyroxene, with smaller amounts of olivine and plagioclase. The pyroxene is often in the form of sizeable crystals, indicating that it cooled slowly, presumably within magma chambers deep within the crust of Vesta.
How Many Asteroids Are There?
Asteroids in our Solar System may be more numerous than previously thought, according to the first systematic search for these objects performed in the infrared, with ESA's Infrared Space Observatory, ISO.
The ISO Deep Asteroid Search indicates that there are between 1.1 million and 1.9 million 'space rocks' larger than 1 kilometer ( in diameter in the so-called 'main asteroid belt', about twice as many as previously believed.
For more information about this:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29762
Links
A great place to see photos of Main Belt asteroids, as well as other cool stuff:
http://solarsystem.nasa.gov/multimedia/gallery.cfm
A good link that talks about HED meteorites:
http://en.wikipedia.org/wiki/HED_meteorite
An asteroid that has been cratered like Vesta: It's Mathilde:
http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2043
SaharaMet: A cool discussion of HED meteorites from the Sahara Desert:
http://www.saharamet.com/meteorite/gallery/HED/index.html
A scientific article about the complicated geologic history of Vesta:
http://www.psrd.hawaii.edu/June09/Vesta.granite-like.html
A cool flash/video presentation:
http://www.jpl.nasa.gov/multimedia/neo/index.cfm
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