Advances in cosmochemistry have confirmed the unusual nature of the projectile that excavated Chicxulub, the only known impact crater produced by an asteroid that reached Earth from the outer region of the main belt, beyond Jupiter. Locating its origin helps to better calibrate the dynamic models of these rocky bodies, capable of generating impacts that would definitively mark our destiny.
An asteroid from the outer region of the solar system
These days, a fascinating study published in the journal Scienceled by Mario Fischer-Gödde, has revealed that the asteroid that excavated this enormous crater had a peculiar composition, similar to the carbonaceous chondrites that populate the outer region of the main asteroid belt, a region of our solar system located between the orbits of Jupiter and Mars.
Researchers have closely analyzed isotopic anomalies in various geological outcrops (rocks not covered by other rocks) associated with large impacts. In these locations, it is possible to detect chemical compounds produced by the sedimentation of fine dust produced after asteroid impacts.
The analysis was carried out on several outcrops that are approximately 65 million years old. The date corresponds to the boundary between the Cretaceous and Paleogene (K/Pg boundary, in the jargon), the time when the great extinction of species occurred, including the dinosaurs.
In these stratigraphic environments they have found very high concentrations of the chemical elements of the platinum group, particularly the rare ruthenium.
These chemical anomalies are the result, on the one hand, of the disintegration of the asteroid upon entering at hypervelocity; and on the other, of the process of excavation of the Chicxulub crater, which created an “impact plume”, launching billions of tons of pulverized material into the atmosphere and producing a sudden climate change.
The abundance of ruthenium
The new work exemplifies how advances in cosmochemistry also mark the direction of new discoveries. The discovery has been made possible thanks to the development of a new technique that breaks chemical bonds and allows the elemental abundances in the minerals that form rocks to be unravelled.
In this way, the chemical abundances of ruthenium have been measured in various types of geological samples from the K/Pg boundary generated by the remains of the Chicxulub impactor.
Elemental abundance of ruthenium has remained remarkably stable over billions of years despite the Earth’s geological activity. Thus, the detection of an overabundance, like any anomaly, can be considered a tracer of a cosmic impactor.
The data obtained indicate that the projectile that caused the Chicxulub impact was a carbonaceous asteroid, probably formed beyond the orbit of Jupiter or incorporating primordial materials from the outer region of our planetary system.
The risk of a new asteroid impact
The Chicxulub impact was catastrophic for life on Earth, as demonstrated by a team led by Peter Schulte in 2010. The minimum diameter of the asteroid that caused such an extinction event is estimated to be around 10 km, capable of excavating such a colossal crater and injecting enormous quantities of dust that generated a sudden climate change.
In fact, the Cretaceous/Paleogene (K/Pg) extinction is considered the fifth in a series of mass extinctions that have occurred over the past 540 million years. As a result of indirect effects, it is estimated that the event wiped out about 75% of living species, and its devastating effects were very likely due to the undifferentiated nature of the projectile.
In carbonaceous asteroids we find all the chemical elements of the periodic table, including those that have catalytic properties of compounds harmful to living beings when they reach an oxygen-rich atmosphere like Earth’s.
On the other hand, the results obtained also highlight recent studies of carbonaceous asteroids analysed by the Hayabusa 2 sample return missions of the Japanese space agency (JAXA) and the NASA mission (OSIRIS REx).
There is no longer any doubt that carbonaceous asteroids also impact our planet, although they do so less frequently than silicate-rich asteroids, which are representatives of the so-called ordinary chondrites. It is therefore of great importance to know their composition and the routes they follow, in order to describe the effects they can have on ecosystems depending on their size and chemical composition.