🪐Intro to Astronomy Unit 14 – Cosmic Samples: Solar System Origins

Key Concepts and Definitions

• Cosmic samples physical materials originating from beyond Earth (meteorites, lunar rocks, interplanetary dust particles)
• Solar system formation process by which the Sun and planets formed from a collapsing molecular cloud ~4.6 billion years ago
  • Involves accretion of dust and gas, planetesimal formation, and planetary differentiation
• Meteorites fragments of asteroids or other planetary bodies that survive passage through Earth's atmosphere
  • Classified as chondrites (contain chondrules) or achondrites (lack chondrules)
• Chondrules small, round grains found in chondrites, among the oldest solid materials in the solar system
• Presolar grains tiny mineral grains that predate the solar system, formed in the outflows of ancient stars
• Isotopic ratios relative abundances of different isotopes of an element, used to determine age and origin of cosmic samples

Solar System Formation Theory

• Solar system formed from the collapse of a molecular cloud, triggered by a nearby supernova or stellar wind
• Collapsing cloud fragments into a protostar surrounded by a protoplanetary disk
  • Protostar becomes the Sun, while planets form from the disk material
• Dust grains in the disk collide and stick together, growing into larger particles and eventually planetesimals
• Planetesimals continue to accrete material, some growing large enough to become planets
  • Terrestrial planets form closer to the Sun from rocky material
  • Gas giants form farther out, accreting large amounts of hydrogen and helium
• Planetary differentiation occurs as heavy elements sink to the core and lighter elements rise to the surface
  • Results in the formation of distinct layers (core, mantle, crust) in terrestrial planets
• Leftover debris from planet formation creates asteroids, comets, and other small solar system bodies

Types of Cosmic Samples

• Meteorites most common type of cosmic sample, divided into several classes based on composition and origin
  • Chondrites (stony meteorites containing chondrules) provide insight into early solar system conditions
  • Achondrites (stony meteorites lacking chondrules) represent material from differentiated planetary bodies
  • Iron meteorites composed primarily of iron and nickel, originate from the cores of asteroids or planets
• Lunar samples rocks and soil collected during Apollo missions or by unmanned Soviet spacecraft
  • Provide information about the Moon's formation, composition, and geologic history
• Interplanetary dust particles (IDPs) tiny grains collected in Earth's stratosphere, believed to originate from comets and asteroids
• Comet samples material collected from the coma or tail of a comet (Stardust mission)
• Asteroid samples material collected directly from the surface of an asteroid (Hayabusa and OSIRIS-REx missions)
• Martian meteorites rare meteorites ejected from Mars by large impacts, provide insight into Martian geology and potential habitability

Collection and Analysis Methods

• Meteorite recovery
  • Found through visual searches in deserts, Antarctica, or after observed falls
  • Collected and cataloged by scientists for study
• Lunar sample collection
  • Astronauts collected samples during Apollo missions using tools like scoops, tongs, and drill cores
  • Unmanned Soviet Luna missions also returned lunar samples
• Stratospheric dust collection
  • High-altitude aircraft with special collectors capture interplanetary dust particles
  • Particles are then analyzed in laboratories
• Sample return missions
  • Spacecraft designed to collect samples from comets, asteroids, or other bodies and return them to Earth
  • Examples: Stardust (comet), Hayabusa (asteroid), OSIRIS-REx (asteroid)
• Laboratory analysis techniques
  • Optical and electron microscopy to study texture and mineralogy
  • Mass spectrometry to measure isotopic ratios and elemental abundances
  • Radiometric dating to determine age of samples
  • Spectroscopy to identify chemical compounds and mineralogy

Major Discoveries from Cosmic Samples

• Age of the solar system determined to be ~4.6 billion years old based on radiometric dating of meteorites
• Evidence for the existence of presolar grains, indicating the incorporation of material from previous generations of stars
• Discovery of amino acids and other organic compounds in meteorites, suggesting the building blocks of life can form in space
• Identification of differentiated meteorites, providing evidence for the existence of planetary cores, mantles, and crusts
• Lunar samples reveal the Moon's geologic history, including ancient volcanic eruptions and impact events
  • Lack of water and organic compounds suggests the Moon has always been dry and lifeless
• Martian meteorites contain evidence of past water on Mars and potential habitable environments
• Comet and asteroid samples provide insight into the composition and structure of these primitive solar system bodies

Implications for Solar System Evolution

• Presolar grains demonstrate the connection between stellar evolution and solar system formation
  • Elements heavier than hydrogen and helium were formed in stars and dispersed through supernova explosions
• Chondrules and calcium-aluminum-rich inclusions (CAIs) in chondrites are among the oldest solar system materials
  • Their presence suggests that the solar system formed rapidly, within a few million years
• Differentiated meteorites indicate that planetary bodies underwent heating, melting, and differentiation early in solar system history
• Variations in isotopic ratios among meteorites and planets suggest the solar nebula was not homogeneous
  • Supports the idea of a dynamic and evolving protoplanetary disk
• Organic compounds in meteorites and comets suggest that the building blocks of life were delivered to Earth by impacts
  • Provides a possible explanation for the origin of life on Earth and the potential for life elsewhere in the solar system

Current Research and Future Missions

• Ongoing analysis of existing cosmic samples using advanced techniques (nanoSIMS, synchrotron radiation) to reveal new insights
• Future sample return missions
  • Hayabusa2 (JAXA) returned samples from asteroid Ryugu in 2020
  • OSIRIS-REx (NASA) will return samples from asteroid Bennu in 2023
• Planned missions to study primitive solar system bodies
  • Lucy (NASA) will study Jupiter's Trojan asteroids
  • Psyche (NASA) will investigate the metallic asteroid 16 Psyche, thought to be a remnant planetary core
• Mars sample return a multi-mission effort to collect and return Martian rocks and soil to Earth for detailed analysis
• Comet Interceptor (ESA) will study a pristine comet or interstellar object, providing insight into the early solar system

Practical Applications and Significance

• Understanding the formation and evolution of the solar system helps predict the existence and location of resources (water, metals, minerals) on other planets and asteroids
  • Important for future space exploration and potential resource utilization
• Studying the delivery of organic compounds and water to Earth by comets and asteroids informs our understanding of the origin of life
  • Has implications for the search for life beyond Earth and the potential habitability of other planets
• Techniques developed for the analysis of cosmic samples have applications in other fields
  • Radiometric dating used in geology and archaeology
  • Mass spectrometry used in chemistry, biology, and environmental science
• Cosmic samples provide a tangible connection to the history and evolution of our solar system
  • Helps engage the public in space science and exploration
  • Inspires future generations of scientists and engineers to pursue careers in planetary science and astrobiology