Lecture Notes: Earth's Formation and Asteroid Bennu

Introduction

• Four-and-a-half billion years ago: Earth's formation
• Focus on asteroid Bennu, a survivor from that era
• NASA's involvement in exploring Bennu's history

The Milky Way and the Solar System

• The Milky Way: Home to billions of stars and worlds, including Earth
• Questions on the formation of the Sun, Earth, and planets
• Advances in understanding the solar system's evolution
• Deep questions remain, leading astronomers to study asteroid Bennu

Asteroid Bennu: A Time Capsule

• Bennu: A small asteroid, early building blocks of the solar system
• Originated in a stellar nursery (cloud of hydrogen, helium, dust)
• Nearby supernova explosion triggered the collapse of this cloud
• Formation of a protostar and a rotating disc of dust and gas

Formation of Chondrules and Asteroids

• Chondrules: Flash-heated droplets of molten rock, building blocks of the solar system
• Gravity and turbulence clump chondrules into asteroids, mountains, planets
• Asteroids: Rubble piles of rock, metal, ice, and organics

Bennu's Parent Body and the Early Solar System

• Formation of a protoplanet (Bennu's parent body)
• Ignition of the protostar, forming the Sun
• Jupiter's formation and its gravitational impact on the asteroid belt
• Heavy bombardment period: Delivery of organics and water to inner planets

Survival of Bennu's Parent Body

• Bennu's parent body survives the heavy bombardment period
• The solar system stabilizes and assumes its current structure
• Quiet period for billions of years

Bennu's Journey

• A billion years ago: Collision shatters the protoplanet, forming Bennu
• Bennu's migration towards the Sun due to solar heating (Yarkovsky effect)
• Interaction with Saturn's gravity alters Bennu's trajectory
• Close encounters with Earth and Venus stretch and reform Bennu

NASA's Osiris Rex Mission

• NASA's mission to explore Bennu and retrieve a sample
• Bennu's near-Earth orbit brings its secrets within reach
• Goal: Learn more about the solar system's history, formation, evolution, and our place in it