By Suzanne Metlay
Secure World Foundation
A whistling noise and a thump … and then a discovery that would change their lives, a rock from another world landed in their horse pasture near Berthoud. Megan Clifford and her son Andy found what is now officially recognized as the Berthoud meteorite on Oct. 5, 2004.
The Berthoud meteorite is one of only five “falls” discovered in the state of Colorado. A fall is witnessed during and collected after its descent through Earth’s atmosphere. As is required by international agreement, the other falls were also named for the locations where they were found — Cañon City (1973), Denver (1967), Elbert (1998) and Johnstown (1924). Eighty other official meteorites from Colorado are “finds” — no one saw them drop from the sky but they were analyzed and identified to be extraterrestrial in origin.
The Berthoud meteorite is most likely from the surface of Vesta, one of the largest and most geologically complex asteroids in the region between Mars and Jupiter, known as the Asteroid Belt. Since Ceres was designated a dwarf planet, Vesta is now both the largest and the brightest asteroid in the belt — observers with backyard telescopes can easily see Vesta when conditions are right. Interestingly, the Johnstown meteorite is also thought to be from Vesta. The Berthoud meteorite is classified as a eucrite, which is from the rocky surface of the asteroid; the Johnstown meteorite is a diogenite from just below the asteroid’s surface.
How can we tell where these meteorites come from? Astronomers have been looking at Vesta since 1807 and have long known that this asteroid had a big chunk knocked out of it. Vesta is about 325 miles (525 kilometers) in diameter (roughly the width of the state of Arizona). Along one side, a huge impact crater can be seen showing layers of different kinds of rock such as basalt. The Berthoud and Johnstown meteorites are most likely remnants from a giant collision; the resulting chunks which broke off Vesta orbited around the Sun as small asteroids known as “vestoids”, then were tugged by Jupiter’s gravitational pull out of the Asteroid Belt and thrown toward Earth.
NASA currently has a spacecraft heading toward Vesta. Launched in September 2007, the Dawn mission flew past Mars, where the spacecraft received a gravity assist to fling it faster into the Asteroid Belt in February 2009. Once Dawn arrives at Vesta in September 2011, it will go into orbit around the asteroid and take data that should prove the origin of the Berthoud and Johnstown meteorites. In 2012, Dawn will do something no other space mission has ever done — it will leave Vesta to visit dwarf planet Ceres, arriving in 2015. Unlike originally “hot and dry” Vesta, which clearly had volcanic activity, Ceres is thought to be “wet and cold” with a layer of water ice over its core.
The Berthoud meteorite was analyzed by researchers at the Lunar and Planetary Laboratory at the University of Arizona, the Southwest Meteorite Laboratory and the Planetary and Space Sciences Research Institute at The Open University in the United Kingdom. Their research results were published in the Meteoritical Bulletin, thereby establishing the Berthoud meteorite as an officially classified fall (Meteoritical Bulletin, no. 94, MAPS 43, 1551-1588 (2008)). The main mass of the 960-gram meteorite as well as two additional thin sections reside in a family trust, under leadership of Megan Clifford’s mother, Marilyn Meador.
For more information, contact Suzanne Metlay, Ph.D., 720-352-1844, STMetlay@SWFound.org .