At 1:30 a.m., fragments of a rare diogenite fell over a radius of 500 meters, 4km NE of a small village in Tunisia. Local Bedouins immediately collected over 12kg of mostly minute fragments which were sent to the Museum National d’Histoire Naturelle in Paris.
Because the larger mass broke up along mineral grain boundaries late in its entry, the unbrecciated orthopyroxene (hypersthene) crystals were not melted and fusion crust is rare, rendering this meteorite difficult to recognize. Tatahouine is light olive-green in color, translucent-to-opaque, and is crisscrossed by small black veinlets up to 2 mm wide. Tatahouine has a cumulate texture with exceptionally large crystals, many reaching 2cm long. Inclusions of silica, troilite, chromite, and minor metal occur throughout.
In 1994, Dr. Alain Carion revisited the strewn field and recovered many more specimens, raising the total recovered wight to ~13.5kg. Other terrestrial weathering effects include increased concentrations of Ba and Sr, and formation of calcite and iron hydroxide.
Asteriod Vesta
Vesta is the second most massive body in the asteroid belt, surpassed only by Ceres, which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta is occasionally visible from Earth with the naked eye. It is the first asteroid to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011, providing new insights into this rocky world.
Celestial Police
In 1596, while determining the elliptical shape of planetary orbits, Johannes Kepler came to believe that a planet should exist in the gap between Mars and Jupiter. Mathematical calculations by Johann Daniel Titius and Johann Elert Bode in 1772 — later known as the Titus-Bode law — seemed to support this prediction. In August 1798, a group known as the Celestial Police formed to search for this missing planet. Among these was German astronomer Heinrich Olbers. Olbers discovered the second known asteroid, Pallas. In a letter to a fellow astronomer, he put forth the first theory of asteroid origin. He wrote, “Could it be that Ceres and Pallas are just a pair of fragments … of a once greater planet which at one time occupied its proper place between Mars and Jupiter?”
Olbers reasoned that the fragments of such a planet would intersect at the point of the explosion, and again in the orbit directly opposite. He observed these two areas nightly, and on March 29, 1807, discovered Vesta, becoming the first person to discover two asteroids. After measuring several nights’ worth of observations, Olbers sent his calculations to mathematician Carl Friedrich Gauss, who remarkably computed the orbit of Pallas in only 10 hours. As such, he was given the honor of naming the new body. He chose the name Vesta, goddess of the hearth, and sister to Ceres.
Physical characteristics of Vesta
Vesta is unique among asteroids in that it has light and dark patches on the surface, much like the moon. Ground-based observations determined that the asteroid has basaltic regions, meaning that lava once flowed across its surface. It has an irregular shape, roughly that of an oblate spheroid (in nontechnical terms, a somewhat smooshed sphere).
- Diameter: 329 miles (530 kilometers)
- Mass: 5.886 X 1020 lbs. (2.67 x 1020 kilograms)
- Temperature: 85 to 255 K (minus 306 to 0 F / minus 188 to minus 18 C)
- Albedo: 0.4322
- Rotation period: 5.342 hours
- Orbital period: 3.63 years
- Eccentricity: .0886
- Aphelion: 2.57 AU
- Perihelion: 2.15 AU
- Closest approach to Earth: 1.14 AU
Surface, composition and formation
When Vesta made a close approach to Earth in 1996, the Hubble Space Telescope mapped its topographic surface and features. This revealed a large crater at the south pole that slices into its interior. The crater averages 460 km in diameter — remember: Vesta itself is only 530 km across. It cuts an average of 13 km into the crust, and most likely formed from an impact in the asteroid’s early life. The material ejected from this collision resulted in a number of smaller — Vestoid — asteroids that orbit near their parent, as well as some of the meteorites that have crashed into Earth.
Unlike most asteroids, the interior of Vesta is differentiated. Like the terrestrial planets, the asteroid has a crust of cooled lava covering a rocky mantle and an iron and nickel core. This lends credence to the argument for naming Vesta as a protoplanet, rather than as an asteroid.
Vesta’s core accreted rapidly within the first 10 million years after the formation of the solar system. The basaltic crust of Vesta also formed quickly, over the course of a few million years. Volcanic eruptions on the surface stemmed from the mantle, lasting anywhere from 8 to 60 hours. The lava flows themselves ranged from a few hundred meters to several kilometers, with a thickness between 5 to 20 meters. The lava itself cooled rapidly, only to be buried again by more lava until the crust was complete.
In 1960, a fireball streaking through the sky over Millbillillie, Australia, announced the arrival of a piece of Vesta on Earth. Composed almost entirely of pyroxene, a mineral found in lava flows, the meteorite bears the same spectral signals as Vesta.
NASA’s Dawn spacecraft, which visited the asteroid in 2012, discovered that the rocky body had a surprising amount of hydrogen on its surface. It also found bright, reflective regions that may have been left over from its birth.
"Our analysis finds this bright material originates from Vesta and has undergone little change since the formation of Vesta over 4 billion years ago," said Jian-Yang Li, a Dawn participating scientist at the University of Maryland, College Park, in a statement.
Vestal visitors to Earth
In fact, Vesta’s unique composition means that it is responsible for an entire group of meteorites. The HED meteorites — made up of howardites, eucrites and diogenites — tell the story of Vesta’s early life. The eucrites form from hardened lava, while the diogenites come from beneath the surface. Howardites are a combination of the two, formed when a large impact mixed the two sections together.
If the orbit of Vesta lies beyond Mars, how did pieces of it manage to arrive on Earth? The fragments of Vesta pass Jupiter once every three orbits around the sun, allowing the gravity of the largest planet to affect them. Such tugging could have shifted the fragments enough to cause their eventual impact with Earth.
As a result, Vesta is one of three bodies from which scientists have samples. The other two are the moon and Mars.
Tatooine to Tatahouine: Sci-fi meets reality
We first meet young Luke Skywalker, hero of the Star Wars movies, on the desert planet Tatooine on the fringe of the Galactic Republic. Luke worked on his Uncle Owen’s “moisture farm” but like any future Jedi knight, he knew he was destined for greater things. At the end of the first scene, Skywalker gazes skyward toward that planet’s two suns, pulled toward a fate he could only guess.
As far as planets go, Tatooine will always be one of my favorites. The exotic dual sunsets, wild expanses of desert and cool architecture of the future left a wonderful impression when I first saw Star Wars back in 1977.
American film producer George Lucas filmed scenes for his fictional planet at various locations across the real deserts of Tunisia. As for the name Tatooine, it was adapted from the Tunisian city Tatahouine, an oasis town in southern part of that country.
In the film, it’s pronounced “tatoo-een” but the locals call it “tat-ween”. Although Lucas didn’t film any scenes in the city, the landscape there and across the deserts of Tunisia were the inspiration for Luke’s homeland.
Tatooine/Tatahouine boasts yet another outer space connection. 81 years ago to the day on June 27, 1931 at 1:30 a.m. local time, a fireball exploded above the Tunisian desert 2.5 miles northeast of Tatahouine. Soon after the fall, local Bedouins collected hundreds of small meteorite fragments that peppered a hillside.
What they plucked from the dust was a rare, green-colored meteorite found deep within an asteroid’s crust called a diogenite. Many years later, scientists identified the Tatahouine meteorite’s true home – the asteroid Vesta – by analyzing light reflected from the meteorite and the asteroid. They were a close match.
More recently, the Dawn space probe, which has been keeping an orbital eye on Vesta for months, confirmed that Tatahouine and other diogenite meteorites originated on this little world. A likely scenario for Tatahouine’s delivery to Earth involved a massive impact on the asteroid. Chunks of crustal material were sent flying into space where they drifted for some 38 million years before finding their way to our planet on a tepid June morning in 1931.
Evidence for the power of the impact can be seen in the web of black shock veins of melted rock created instantaneously upon impact. The large orthopyroxene crystals give Tatahouine a unique green color found in few meteorites.
Since the meteorite shattered into thousands of small pieces, tourists to the area can still find fragments to this day. Tatahouine fragments look “naked” or without the typical black fusion crust coating many other meteorites. It blew to bits at a very low altitude, too late and moving too slowly for air friction to melt the exterior of each small piece.
In 2011 NASA announced it had found the first planet in orbit about a double sun like the fictional Tatooine. Named Kepler 16b, the Saturn-mass planet orbits orange and red stars with a period 229 days. With temperatures ranging from 100 to 150 below F, this gas giant Tatooine sadly couldn’t host Jabba the Hut and the delightful cantina pictured in Star Wars.
