By Millarca Valenzuela, MAS´ and AIUC postdoctoral researcher 

Most of you have probably seen a falling star sometime and have made a wish. What you were actually looking were very fine grains of extraterrestrial material (ETM), that most of the time are completely evaporated after passing through our atmosphere. The fall of ETM to Earth, which occur randomly all over the planet, is a common process that brings tens of tons of material every day. Most of them are in the size range of microns and millimeters, and just 1% of all the material can actually be recovered as a meteorite. In contrast to the random fall, meteorites can accumulate in specific areas in the Earth surface where liquid water is scarce, as deserts: cold as the ones in Antarctica, and hot as Sahara, Nullarbor, Oman, Lut or Atacama.

The scientific importance of these extraterrestrial rocks is given by the fact that among them are the oldest solid remnants of the Solar System formation (~4.560 My) and also material that correspond to posterior evolution in planetary entities, that we can easily access here on Earth. Most of them come from asteroids, but a few can also come from the differentiated crusts of the Moon and Mars. Each of them represent a part of the puzzle which scientist from different research areas study in order to better understand how the Earth and the rest of the planets were formed and how and where life started. They represent a clue to understand the first condensed solids, and, together with the material studied in protoplanetary discs by ALMA, can help us to understand the planet building processes and the variety of planetary systems discovered so far. On the other hand, a pressing interest on these falling rocks arises if some of them become a hazard for life on Earth. This happens when its size is larger than, approximately, 25 m, which is big enough to go through the atmosphere without deceleration and impact the surface at supersonic velocities. 

My work with meteorites started more than 10 years ago, participating in annual scientific expeditions to search for meteorites in the Atacama Desert thanks to international partnerships. In those years we proved the Atacama desert has unique conditions to preserve meteorites for longer times than any other hot desert of the world, allowing the concentration of meteorites in old, stable surfaces, with some of them having the incredible meteorite density per area of ~150 met/km2 (compared to the average for hot deserts that is less than 1met/km2!).

How do we find them? We comb the desert! We form rows were each participant walk slowly and coordinately, separated 10 m from one another (Fig.1), scanning the surface just with our eyes. This is a systematical and very effective way of looking for them, which allows us to learn and improve the rate of recovery. After gaining experience we are able to find most of the meteorites, including the small masses (2-10 g). This is very important for a better characterization of the flux.

The first step in the laboratory is to classify them, using petrographic, magnetic, chemical and isotopic techniques, among others. From the ~60 official meteorites reported in Chile in 2005, we have managed to increase the list up to 996 now, thanks to both the expeditions and the collaboration with some professional private collectors. The collection, split between France and Chile, is dominated by ordinary chondrites (OCs, ~90%), but includes also an important number of irons (~7%), and an increasing number of very interesting meteorites as carbonaceous chondrites (the ones that gives clues about the possible origin of life, for its organic components), and others as El Médano 301, part of a new proposed meteorite group of forsteritic chondrites (Fig. 2, Pourkhorsandi et al., submitted to the journal Meteoritics and Planetary Science), that has peculiar mineral compositions, rich in magnesium. The name comes for the abundance of a mineral called forsterite, a type of magnesium olivine. This points to their formation in a nebular region compositionally similar to OCs but in a place closer to the Sun, where less oxygen was available to allow the formation of the more usual mineral compositions.

Photomicrograph of a polished thin section of El Médano 301 forsteritic chondrite (credit Hamed Pourkhorsandi, CEREGE, France).

 

At MAS I’m studying the statistics associated to different meteorite dense collection areas at Atacama, especially at El Médano area; studying specific samples, interesting for Solar System formation (as El Médano 301) in collaboration with colleagues from Chilean and French institutions; leading the project CHACANA, to create the first Chilean network of Allsky cameras to detect fireballs and recover fresh fallen meteorites; working in the consolidation of the first official scientific repository of meteorites in Chile, along with the legal protection as geoheritage objects in the Chilean legislation; forming a first generation of Chilean geoscientists able to incorporate Meteoritics and Planetary Sciences as part of their background, and encouraging the new generation of Chilean astronomers to get involved in Solar System studies. Chile has the raw materials to study these subjects, but needs to arrive at a critical mass of scientists committed to their development to build this exciting new research area.