One of the iron meteorite samples the team analysed. Credit: Aurelia Meister
Even before the Earth and other planets were born, the young sun was encircled by a cloud of gas and dust from beyond our Solar System. Rock shards of various sizes were created from the dust throughout the centuries. Many of these were used as raw materials in the construction of other planets. Others, such as the asteroids in the asteroid belt, never formed a planet and are still in orbit around the sun.
Asteroids that hit Earth as meteorites were studied by researchers from ETH Zurich and the National Center of Competence in Research (NCCR) PlanetS, along with an international team. As a result, they were able to piece together some of their earliest history, which took place during the formation of planets. A paper describing their findings appeared in Nature Astronomy.
Witnesses to the formation of the solar system’s early phases
ETH Zurich researcher Alison Hunt said, “Previous scientific studies demonstrated that asteroids in the solar system have stayed essentially unchanged since their origin, billions of years ago. Hunt describes them as “an archive” because they “preserve the environment of the early solar system.”
Researchers had to meticulously prepare and analyse the extraterrestrial material in order to access this archive. Iron meteorites, which were formerly part of asteroids’ metallic cores, were collected by the crew from 18 different locations. The samples had to be dissolved in order to isolate the elements Palladium, Silver, and Platinum for their detailed study. They used a mass spectrometer to find out how many distinct isotopes of each of these elements were present. atoms of a given element, like Palladium, Silver or Platinum, which all have the same number of protons in their nucleus but differ in the number of neutrons.
The radioactive decay of isotopes heated the metallic asteroid cores during the first few million years of our solar system. As they cooled down, radioactive decay created a specific Silver isotope. In order to figure out when and how quickly the asteroid cores cooled, scientists looked to current Silver isotope ratios in iron meteorites.
Due to strong collisions with other worlds, the asteroids’ outer rocky mantle was broken off and their metal cores exposed to space’s frigid temperatures, according to the findings. While prior investigations based on Silver isotope measurements had indicated a rapid cooling, the time had remained ambiguous.
“We were able to adjust our Silver isotope findings for cosmic irradiation aberrations thanks to new measurements of Platinum isotope abundances. As a result, we were able to accurately date the collisions for the first time “According to what Hunt has to say, Astronomers discovered that all the asteroid cores they studied were exposed within a time span of between 7.8 and 11.7 million years after the solar system was formed.
Team members were able to conclude that the solar system was in an unstable state due to the near simultaneous collisions of the many asteroids. In Hunt’s words, “everything seemed to be smashing together at that time.” Then there was the question of “why,” as she goes on to say.
A journey from the lab to the solar nebula
With the most up-to-date and powerful computer simulations of solar system growth, the team was able to examine a wide range of possible reasons. Together, they might be able to eliminate some of the more speculative possibilities.
According to study co-author and NCCR PlanetS member and Professor of Cosmochemistry at the ETH Zurich, Maria Schönbächler, “the theory that best characterised this energetic early period of the solar system showed that it was principally produced by the dissipation of the so-called solar nebula.” “The remaining gas from the cosmic cloud from which the Sun was born formed this solar nebula. It remained in orbit around the newborn Sun for a few million years until being driven away by solar winds and radiation “According to Schönbächler,
Objects in the sun’s orbit were slowed by the nebula’s air resistance while it was still present. For asteroids to speed and collide like bumper cars that had been put into turbo-mode, experts believe the nebula’s gas drag was no longer present.
“For example, we were able to estimate the probable time at which the solar nebula had dissipated because to advances in laboratory measuring techniques. At the time, planets like Earth were just beginning to form. We may learn more about the origins of other planets in the solar system as a result of this research “Schönbächler draws to a close.
Further information: Alison C. Hunt et al, The dissipation of the solar nebula constrained by impacts and core cooling in planetesimals, Nature Astronomy (2022). DOI: 10.1038/s41550-022-01675-2
Journal information: Nature Astronomy
Source: ETH Zurich