[meteorite-list] STONE: an articifial meteorite experiment

From: Tom aka James Knudson <knudson911_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:57 2004
Message-ID: <002101c3d221$5d270d60$29d043d8_at_malcolm>

Have you all read about this? I could not get the ling to work so I mailed
the article
Thanks, Tom
Peregrineflier <><

 Overview

The Foton-12 mission hosted the ESA experiment STONE, the first artificial
meteorite experiment aiming at studying the modifications suffered by
meteorites during atmospheric entry.

STONE is an investigation about the physical and chemical modifications
occurring in meteorites during atmospheric infall, especially in sedimantary
rocks coming from Mars. Its scientific scope interlinks mineralogy,
planetary science, exobiology and chemistry.

Generally, meteorites differ from ordinary terrestrial rocks by the coloured
fusion crust acquired during the atmospheric entry. However, carbonate-rich
Martian sedimentary rocks may never develop a fusion crust. Indeed, thermal
decrepitation of carbonates during atmospheric infall is likely to produce a
surface texture that is not recognisable as a fusion crust - in which case
such meteorites would be overlooked by the collectors. In addition, the
atmospheric entry may also alter the chemical and isotopic composition of
the samples.

Detailed description of the experiment and its results

by Dr. André Brack, Centre de Biophysique Moleculaire, CNRS, Rue Charles
Sandron, F-45071 Orleans, France, and Prof. Gero Kurat, Naturhistorisches
Museum, Postfach 417, A-1014 Wien, Austria

The study of meteorites
Artificial meteorites offer a unique possibility to identify changes
accompanying atmospheric infall on well-defined material by reference to
original, unexposed samples. They can also be loaded with bacteria and can
therefore be used to evaluate the chances of extraterrestrial microbial
samples to reach safely the surface of the Earth. Real atmospheric entry as
compared to simulation on ground represents the easiest way to study the
physical, chemical and morphological transformations brought to a high speed
object impacting a gradient of nitrogen/oxygen gas mixtures.

Most of the 25 000 meteorites collected so far originate from bodies in the
asteroid belt. There are 18 samples definitely from the Moon. Most lunar
meteorites are regolith samples, as would be expected if rocks are propelled
from planetary surfaces by impact. There are further 14 meteorites, known as
SNC meteorites, lumped together on the basis of a number of common
characteristics which make the samples quite distinct from asteroidal
debris. They are believed to originate from Mars.

None of these SNC meteorites is a surface sample. Because Mars had a warm
and wet past climate, its surface must be covered by both impact generated
regolith and sedimentary rocks deposited by running and/or still water. The
sedimentary rocks should comprise detrital deposits as well as chemical
sediments like evaporites. In addition, groundwater can be expected to
compact loose sediments and regolith by filling the pore space with
evaporitic minerals. Such consolidated sedimentary hard rocks should be
among the Martian meteorites but they are not. It is possible that they did
survive escape acceleration from the Martian surface but did not survive
terrestrial atmospheric entry because of decrepitation of the cementing
mineral which is very likely to be a sulphate.

Description of the STONE experiment
The STONE experiment aims at studying the physical and chemical
modifications in sedimentary rocks during atmospheric infall.

Three terrestrial pieces of rock have been exposed to atmospheric entry at
the outer surface of the Foton 12 capsule:

   1. A basalt to serve as an inflight control to demonstrate that the
impact heat is sufficient to form a dark fusion crust (the entry velocity of
the Foton satellite is lower than that of a meteorite). Basalts are
representative of all planetary surfaces. They are the primitive silicate
liquids formed by partial melting of chondrites, the most primitive matter
of the solar system, i.e., the building blocks of the planets. The sample is
an alkali olivine basalt from Pauliberg, a Tertiary volcano in Burgenland,
Austria.
   2. Dolostone (dolomite), carbonate sedimentary rock, a chemical
sedimentary rock containing also remnants of carbonate fossil shells and
some silicate debris. The rock is very fine-grained, re-crystallised (<50
µm) and dense. It consists of dolomite (Ca-Mg carbonate) and minor amounts
of quartz and feldspar. The rock was collected at the base of the Lagazuoi
Mountain in the bed of Rio Lagazuoi just below Passo di Falzarego, Belluno,
Italy.
   3. An artificial rock simulating the Martian regolith or soil, composed
of 80% basalt crushed into grains of less than 5 mm in size, and 20% gypsum
to cement the grains.

Results of the STONE experiment
The three samples were embedded into the ablative heat shield of Foton-12
which was launched on 9 September and landed on 24 September 1999.

The basalt heat shield holder for unknown reasons failed and the basalt
sample has been lost, probably during the final stage of ablative high-speed
atmospheric entry.

The dolomite rock was burned down to 40% of its original thickness but still
resisted to the atmospheric entry (Figure). Its mineralogy has dramatically
been modified. Dolomite, CaMg(CO3)2, broke down to CaO (solid) + MgO (solid,
periclase) + 2CO2 (gas). CaO reacted partly with H2O from the air to form
Ca(OH)2, the mineral portlandite.

The Martian mock soil was totally burned, as expected, and the small pieces
caused extensive ablation on the lee side holder and heat shield (Figure).
However, small fragments could be collected from underneath the sample
holder.

The two collected entry samples are presently analysed for their chemistry,
mineralogy and isotopic compositions. In each case, changes accompanying
atmospheric infall are made visible by reference to the original, untreated
samples. Preliminary results suggest that some Martian sediments could in
part survive terrestrial atmospheric entry but shall disintegrate in the
terrestrial environment very quickly beyond beyond recognizability if they
are predominantly made of carbonate.
Received on Sat 03 Jan 2004 12:45:21 PM PST