Meteorites That Helped Form Earth May Have Formed In The Outer Solar System

Our solar system is believed to have formed from a cloud of gas and dust, the so-called solar nebula, which began gravitationally condensing around 4.6 billion years ago. As this cloud contracted, it began to spin and form into a spinning disk around the highest gravity mass at its center, which would become our Sun. Our solar system inherited all of its chemical composition from an earlier star or stars that exploded as supernovae. Our Sun picked up a general sample of this material as it formed, but the residual material in the disk began to migrate due to its propensity to freeze at a given temperature. As the Sun became dense enough to initiate nuclear fusion reactions and become a star, it picked up a general sample of this material during its formation, but the remnants in the disk formed solid material to form planetary bodies based on its propensity to freeze at any given time. Temperature. When the Sun irradiated the surrounding disk, it created a heat gradient in the early solar system. For this reason, the inner planets, Mercury, Venus, Earth, and Mars, are mostly made of rock (mainly composed of heavier elements, such as iron, magnesium, and silicon), while the outer planets are made of rock. largely composed of lighter elements, in particular hydrogen, helium. , carbon, nitrogen and oxygen.

Earth is thought to have formed partly from carbonaceous meteorites, which are thought to have originated from asteroids in the outer main belt. Telescopic observations of outer main-belt asteroids reveal a common reflectance feature of 3.1 μm that suggests that their outer layers host either water ices or ammonia clays, or both, which are stable only at very low temperatures. Interestingly, although several lines of evidence suggest that carbonaceous meteorites are derived from such asteroids, meteorites recovered from Earth generally lack this feature. The asteroid belt thus raises many questions for astronomers and planetary scientists.

A new study by researchers at the Tokyo Institute of Technology’s Earth-Life Science Institute (ELSI) suggests that these asteroid materials may have formed very far away in the early solar system and then been transported into the inner solar system by chaotic mixing processes. In this study, a combination of asteroid observations using the Japanese AKARI space telescope and theoretical modeling of chemical reactions in asteroids suggests that surface minerals present on outer main belt asteroids, in especially ammonia (NH3)-bearing clays, formed from raw materials containing NH3 and co2 ice that are only stable at very low temperatures and in water-rich conditions. Based on these findings, this new study proposes that outer main belt asteroids formed in distant orbits and differentiated to form different minerals in water-rich mantle and rock-dominated cores.

To understand the source of the discrepancies in the measured spectra of carbonaceous meteorites and asteroids, using computer simulations, the team modeled the chemical evolution of several plausible primitive mixtures designed to simulate primitive asteroid materials. They then used these computer models to produce simulated reflectance spectra to compare with those obtained by telescope.

Their models indicated that to match the asteroid spectra, the starting material had to contain a significant amount of water and ammonia, a relatively low abundance of CO2, and react to temperatures below 70℃, suggesting that the asteroids formed far beyond their current locations in the early solar system. In contrast, the absence of the 3.1 mm feature in meteorites can be attributed to a possibly deeper reaction inside the asteroids where temperatures reached higher values. Thus, recovered meteorites can sample deeper parts of asteroids.

If true, this study suggests that the formation of the Earth and its unique properties resulted from particular aspects of the formation of the solar system. There will be several opportunities to test this model, for example, this study provides predictions on what analysis of samples returned by Hayabusa 2 will find. This distant origin of asteroids, if correct, predicts that there will be ammonia salts and minerals in samples returned by Hayabusa 2. Further verification of this model will be provided by analyzes of materials returned by the mission. NASA’s OSIRIS-Rex.

This study also investigated whether the physical and chemical conditions of outer main belt asteroids should be able to form the observed minerals. The proposed cold and distant origin of asteroids suggests that there should be a significant similarity between asteroids and comets and raises questions about how each of these body types formed.

This study suggests that the materials that formed the Earth may have formed very far away in the early solar system, then were introduced during the solar system’s particularly turbulent early days. Recent observations of protoplanetary disks by the Atacama Large Millimeter/submillimeter Array (ALMA) have found numerous ring structures, which are thought to be direct observations of planetesimal formation. As lead author Hiroyuki Kurokawa summarizes the work, “Whether the formation of our solar system is a typical outcome remains to be determined, but many measurements suggest that we may soon be able to put our cosmic history into context.”

Reference

H. Kurokawa1*, T. Shibuya2Y.Sekine1BL Ehlmann3.4F.Usui5.6S.Kikuchi2and Mr. Yoda1.7Distant Formation and Differentiation of Outer Main Belt Asteroids and Carbonaceous Chondrite Parent Bodies, AGU Advances, DOI: 10.1029/2021AV000568

  1. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan
  2. Super-cutting-edge Grand and Advanced Research Program (SUGAR), Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
  3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  5. Institute of Space and Astronautical Sciences, Japan Aerospace Exploration Agency, Sagamihara, Japan
  6. Center for Planetary Science, Graduate School of Science, Kobe University, Kobe, Japan
  7. Department of Earth and Planetary Sciences, University of Tokyo, Tokyo, Japan

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Tokyo Institute of Technology (Tokyo Tech) is at the forefront of research and higher education as the leading science and technology university in Japan. Tokyo Tech researchers excel in fields ranging from materials science to biology, computer science and physics. Founded in 1881, Tokyo Tech enrolls more than 10,000 undergraduate and graduate students each year, who become scientific leaders and some of the most sought-after engineers in the industry. Embodying the Japanese philosophy of “monotsukuri”, meaning “technical ingenuity and innovation”, the Tokyo Tech community strives to contribute to society through high-impact research.

The Earth-Life Science Institute (ELSI) is one of Japan’s ambitious international research centers, whose goal is to achieve progress in broadly interdisciplinary fields of science by inviting the world’s greatest minds to come to Japan. and to collaborate on the most ambitious scientific projects. problems. ELSI’s main goal is to address the origin and co-evolution of Earth and life.

The World Premier International Research Center Initiative (WPI) was launched in 2007 by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) to help build globally visible research centers in Japan. These institutes promote high research standards and exceptional research environments that attract frontline researchers from around the world. These centers are highly autonomous, allowing them to revolutionize conventional ways of operating and administering research in Japan.

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