quinta-feira, 24 de março de 2011

Tunisia, in search of ancient meteorites

Imagine picking up a piece of the asteroid Vesta from a rocky desert hillside, the first person ever to touch that meteorite in history. That’s exactly what all of the members of Astronomy magazine’s Tunisian tour group got to do around noontime on Wednesday, March 23. We were guests of Aljane Habib, director of the Museum of the Memory of Earth, the geological museum in Tataouine, Tunisia. He escorted us about 4 kilometers northwest of the town to a hillside containing mostly Jurassic limestone that is centered on the meteorite’s strewn field, the area where pieces of the stones landed. What an electric thrill for all 22 of our travelers, accompanied by tour operator Melita Thorpe, planetary scientist Chris McKay, and me, to find numerous small pieces of the fabled meteorite.

The meteorite fell June 27, 1931, and resulted from an airburst above ground that produced fractured stones without a significant fusion crust. Tataouine fragments fell over a strewn field of about a square kilometer, and about 13.5 kilograms of the meteorite have been recovered to date. It is an achondrite, a rare type called a diogenite, which ties it to the asteroid 4 Vesta as the parent body. This is a real rarity: The origins of most meteorites are not known. Tataouine has a strange, olive-green color that comes from the fact that it contains large orthopyroxene crystals, silicate minerals that contain some iron, which colors them green. They also have black inclusions of chromite — iron chromium oxide. Overall, the stones appear agate-like, and are sometimes almost translucent; this made spotting them on the ground of the Sahara possible because the hill containing the strewn field must have had 10 million rocks on it. We all spotted small green pieces of the meteorite, some as large as a centimeter and a half or more, but most very small. Nonetheless, it was a thrill to pick up meteoritic pieces for the first time.

Before going to the strewn field, we visited Ksar Ouled Soltane, an ancient Berber fortified hilltop granary. This amazing ancient site is now something of a tourist attraction, and its incredible state of preservation astonishes visitors who see it. The site was also used in at least one Star Wars film as a movie backdrop, and the region inspired the fictional planetary setting Tattooine from the Star Wars series.

To cap off the day, I spoke to the group about the explosive advances in understanding the universe that we’ve witnessed over the past 10 to 15 years, ranging from understanding black holes to exoplanet discoveries, to the formation of the Moon, to dark energy, to the Milky Way’s structure, and many more topics. We called it a day with a nice, relaxing dinner, all of us astonished to have explored a meteorite field for the first time in our lives.

News Source: CS Astronomy

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