The research team studied the isotopic composition of the rocky planets
Earth and Mars are made up of objects from the inner solar system; Only a small percentage of the “building materials” of these two planets have their origin beyond Jupiter’s orbit. This is the conclusion of a team of researchers led by Westphalian Wilhelms University (WWU) in Münster. Today in the journal “Scientific Advances” they present a very detailed comparison of the original building materials of the Earth, the isotope composition of Mars and the inner and outer solar system. Some of these materials are still found today mostly in unmixed meteorites. The results of the study have long-term effects on our perceptions of the formation process of the planets closest to the Sun, Mercury, Venus, Earth and Mars. This refutes the theory that the four rocky planets grew to their current size by accumulating millimeters of dust from the outer solar system. Thorsten Klein, head of the study, recently became director of the Max Planck Institute for Solar Family Research in Cottingham.
When our solar system was born about 4.6 billion years ago, a disk of dust and gases orbited the still younger Sun. Two theories explain how inner rocky planets formed from this original building material over millions of years. According to the old theory, dust clung together into larger and larger particles, which gradually reached the size of our moon in the inner solar system. Conflicts between these pioneers eventually resulted in Mercury, Venus, Earth and Mars. On the other hand, the most recent theory supports a different growth process: thus, millimeters of dust migrated from the outer solar system toward the sun. Along the way, they discovered planets that were the forerunners of the inner solar system, settled there and gradually aided their current size.
Both theories are based on model calculations and computer simulations that simulate relationships and movements in the early solar system; Both describe the possible path of planetary formation. But which is right? What process really happened? To clarify this question, researchers at the WWU, the Observatoire de la Côte d’Azur (Nice, France), the California Institute of Technology (Pasadena, USA), the Museum of Naturkunde (Berlin) and the Free University of Berlin are currently studying the exact nature of the rocky planets on Earth and Mars. Saw the mixture. “We wanted to find out if the building material for Earth and Mars came from the outer or inner solar system,” said the first author. Christoph Burkard from WWU. Isotopes of rare metals such as titanium, zirconium and molybdenum are found in small traces on the outer, silicate-rich layers of the two planets, providing important clues. Isotopes refer to different types of the same element, differing only in their atomic weight.
Scientists believe that these and other metal isotopes were not evenly distributed in the early solar system. Conversely, their frequency depends on the distance from the sun. Isotope frequencies provide information about where a body’s building material originated in the early solar system.
Researchers use two types of meteorites to indicate the original existence of isotopes in the outer and inner solar systems. These rocks typically find their way to Earth from the asteroid belt between the orbits of Mars and Jupiter. Since the beginning of the solar system they have been considered a largely unchanged object. Carbonaceous chondrites, also known as carbonaceous chondrites, which may contain up to a certain percentage of carbon, appeared on the other side of Jupiter’s orbit and moved to the asteroid belt due to the influence of the growing gas giant, their under-carbon relatives, the children’s real, non-carbonated, inner solar family.
The exact isotope composition of the Earth’s accessible, outer rock layers and both types of meteorites have been researched for some time; So far, there are no comparable detailed studies of the rocks of Mars. In their current study, the researchers studied samples of a total of 17 Martian meteorites that could be assigned to six types of Mars. In addition, scientists are following in the footsteps of three different metal isotopes for the first time.
Samples of Mars meteorites were first pulverized in a complex process and chemically pre-treated. With the help of a multi-collector plasma mass spectrometer at the Institute for Planetary Research at the University of Munster, researchers were able to detect small-scale titanium, zirconium and molybdenum isotopes. In the computer, scientists simulated the ratio of construction materials found today to carbonaceous and non-carbonaceous chondrites, which must be entered in order to reproduce the measured values. They considered two different stages of material input. Because unlike titanium and zirconium, molybdenum mainly concentrates at the metal planet center. The small amounts still found today in the silicate-rich outer layers may have been included only in the last stages of the planet’s development.
The researchers’ results show that the outer rock layers of Earth and Mars have little in common with the carbonaceous chondrites of the outer solar system. Their share in the original construction materials of the two planets is only four percent. “If the predecessors of Earth and Mars had collected dust mainly from the outer solar system, this value would have been almost ten times higher,” says Professor Dr. Thorsten Klein, of WWU, is also the director of the Max Planck Institute for Solar System Research in Cottingham. “We cannot confirm this theory of the formation of inner planets,” he adds.
But the composition of Earth and Mars does not exactly match the meaning of non-carbonaceous chondrites. Sample calculations suggest that other, different types of construction materials must be involved. “This third type of construction material must have appeared inside the solar system. We can infer this from the isotopic composition that should be in our calculations, ”explains Christoph Burkard. Since the rock masses from very close to the Sun never scattered on the asteroid belt, they were almost completely absorbed by the inner planets. They do not occur in meteorites. “It simply came to our notice then that this was a ‘lost building material’,” said Thorsten Klein.
The surprising discovery does not change the results of the study of theories about planetary formation. “Earth and Mars are mainly objects in the inner solar system that go well with the formation of planets from collisions with larger bodies in the inner solar system,” concludes Christoph Burkard.
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