Primordial comet fragment discovered inside meteorite gives clues to the origin of the Solar System

An international team including researchers from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Space Sciences (ICE, CSIC) has discovered a pristine comet fragment inside a meteorite. This finding demonstrates that the class of meteorites known as carbonaceous chondrites contains clues to the composition of more fragile objects that formed in regions distant from the Sun, more than 4,560 million years ago. The results are published in the journal Nature Astronomy.
 
After a three-year study of the carbonaceous chondrite LaPaz 02342, from NASA's Antarctic collection, researchers have come to the conclusion that the comet fragment, of about one hundred microns, is composed of an unusual mixture of organic materials, amorphous and crystalline silicates, sodium sulphates, sulphides, and presolar grains; the latter synthesised in stars that enriched the original materials of our Solar System. Among other instruments, a secondary ion mass spectrometer (nano-SIMS) of the Carnegie Institution for Science (USA) has been used for its analysis, which allows studying at a nanometric scale the composition of the meteorite at an isotopic and elemental level.
 
"This fragment, technically known as xenolith, has unusual characteristics that we think were produced from the incorporation of primitive materials embedded in ice", says IEEC–CSIC researcher Josep Maria Trigo-Rodríguez, who works at ICE and co-leads the study. "Many objects in the Solar System have a very different composition than the meteorites available in terrestrial collections. Carbonaceous chondrites, such as LaPaz 02342, constitute a fossil legacy of the creation of the planetesimals in their interior and are capable of preserving unique samples of other objects much richer in organic and volatile matter, known as comets", explains Trigo-Rodríguez.
 
As the researcher points out: "The asteroid progenitor of this carbonaceous chondrite underwent aqueous alteration[1], but fortunately, it was neither extensive nor homogeneous. This led to the preservation of the unique properties of this cometary dust speck, among which the richness in tiny mineral grains formed in stars of the same environment in which the Sun was born.”
 
The most primitive meteorites
Carbonaceous chondrites come from transitional bodies, a category falling between asteroids and comets. Given their sizes typically smaller than a few hundred kilometres, such bodies never melted or suffered internal chemical differentiation as occurred to the planets. The materials that make up these objects are usually fragile and do not usually survive the transit of tens of millions of years that transport them from their parent bodies to the Earth orbit. In case they do, they fragment and volatilise when entering into the atmosphere at hypersonic velocities. Precisely because of this reason, ultracarbonaceous materials such as those discovered are extremely rare and have only been identified as micrometeorites.
 
The search for primordial materials among the most primitive meteorites can be carried out at ICE, given that it is the only international repository of NASA’s Antarctic meteorites in Spain. The samples studied by the IEEC–CSIC scientific team come from NASA's Johnson Space Center. Hence, researchers have access to unique specimens, being able to select those that have not undergone thermal metamorphism[2] or extreme aqueous alteration.
 
This discovery is part of the National Astronomy and Astrophysics Plan project (AYA-2015-67175-P) for the study of primitive materials preserved in meteorites led by Josep M. Trigo-Rodríguez. Carles E. Moyano-Cambero and Safoura Tanbakouei, from IEEC at ICE (CSIC), have also participated. The international cooperation has been led by Larry Nittler from the Carnegie Institution for Science, in collaboration with his colleagues Conel Alexander and Jemma Davidson, as well as Rhonda Stroud and Bradley De Gregorio of the U.S. Naval Research Laboratory.

Figure 1. Section of the carbonaceous chondrite LaPaz 02342 and extension of the cometary clast. Credit: IEEC-CSIC/Carnegie Institution.

Notes

[1] The change in the composition of a rock, as a response to interactions with water-bearing ices, liquids, and vapors by chemical weathering.
[2] A type of metamorphism resulting in a chemical reconstitution controlled by a temperature increase.

Links

– IEEC
– ICE
– CSIC
 
More information
 
This research is presented in a paper entitled “A cometary building block in a primitive asteroidal meteorite”, by Nittler L.R. et al., to appear in the journal Nature Astronomy on 15 April 2019.
 
The Institute of Space Studies of Catalonia (IEEC  — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of over 20 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.
 
IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the University of Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Autonomous University of Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Polytechnic University of Catalonia (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. IEEC is integrated in the CERCA network (Centres de Recerca de Catalunya).
 

Contacts
 
IEEC Public Information Office
Barcelona, Spain
Rosa Rodríguez Gasén
E-mail: comunicacio@ieec.cat
 
Scientist at IEEC-ICE/CSIC
Barcelona, Spain
Josep Maria Trigo Rodríguez
Institute of Space Science (CSIC)
E-mail: trigo@ice.csic.es