Dead Comets Ice gone - dust remains Remnant spreads out in elliptical donut shape - a meteoroid swarm If Earth gets in the way, meteor shower

Meteor Showers

Asteroids

Asteroids – How We Know What We Know A few moons are probably captured asteroids A handful of asteroids were passed en route to elsewhere Gaspra (’91), Ida & Dactyl (’93), Braille (’99), Annefrank (’02), Steins (’08) and Lutetia (’10) A small number of dedicated asteroid missions NEAR flew past Mathilde (’97) and orbited Eros (’00 –’01) Hayabusa visited Itokawa (’05), returned dust particles Dawn orbited Vesta (’11–’12) and Ceres (’15–’16) Hayabusa 2 is at Ryugu (’14–’19) and will return sample to Earth (’20) First sample taken on Feb. 22 OSIRIS-REx sample return mission at Bennu (’16 – ’23) Meteorites are small fallen asteroids!

Dedicated Asteroid Missions NEAR Dawn Hayabusa

Asteroids – General Characteristics From microscopic up to nearly 1000 km Largest would be considered medium moons Shape Largest (Ceres) and perhaps a few others are spheres Most are irregular Orbits Most lie between Mars and Jupiter A few make it in near Earth Composition: Rock, metal, or rock mixed with metal Some of the largest may have some water

The Asteroid Belt Q. 57: Composition of Asteroids vs. Comets Region between Mars and Jupiter where most asteroids lie Q. 57: Composition of Asteroids vs. Comets

Asteroids We’ve Seen Close Up

Vesta, Third Largest Asteroid

Ceres The largest asteroid 952 km in diameter Dawn went in orbit around it Bright spots – salt deposits Indicates briny ices just below

Ceres Composition

Meteors and Meteorites A meteor is the flash of light that occurs when a natural object falls to Earth from space A meteorite is the object we find on the Earth afterwards

Meteorite Classification Primitive Contain metal bits mixed in Some also contain carbon-rich materials! Non-primitive Stony Pure stone, no metal bits Iron Pure metal, mostly iron Stony-Iron Inhomogeneous mix of stony and iron meteorites

Meteorite Classification Stony Primitive Stony - Iron Iron

Primitive Meteorites Primitive with Carbon Primitive no Carbon The carbon-compound bearing meteorites have never been heated They come from the formation of the solar system We can find age of solar system from these Solar system is 4.56 billion years old Q. 58: Age of Solar System

Why Is There an Asteroid Belt? Normal planetary coalescence: Planetismals in near circular orbits Collisions are gentle Easy for little pieces to stick together

Collisions in the Asteroid Belt Jupiter disturbs orbits Planetismals collide at high velocities Pieces get smashed apart as often as they stick together. Jupiter

How We Got Different Meteorites Planetismal: Primitive w/ carbon Now smash the protoplanet! Stony - Iron Collided Planetismal: Primitive no carbon Stony Differentiated Protoplanet Iron

Large Meteor Craters on Earth

The Iridium Layer Thin layer in Earth contains high fraction of iridium Common in meteorites Dates from demise of dinosaurs

Chicxulub Impact Site 65 Myr old Precursor about 10 km in diameter

Extrasolar Planets Found = 3999, Systems Found = 2987 What’s an Extrasolar Planet? An extrasolar planet is a planet that goes around another star A star is something that is hot enough to fuse hydrogen More on this later A brown dwarf is too small to be a star, and too large to be a planet A planet is something that is large enough, but not too large Lower limit – irrelevant, we can’t see them that small Upper limit – about 13 times Jupiter’s mass Extrasolar Planets Found = 3999, Systems Found = 2987

Detection Methods Methods for finding them Direct Imaging Gravitational Microlensing Astrometry Pulsar Timing Other Timing Radial Velocity Transit Method Dynamical Methods

Direct Imaging Score = 122 Disadvantages Almost impossible to see planet next to bright star Must be done from space Advantages Can estimate size of planet Can study spectrum of planet Score = 122

Gravitational Microlensing The Technique Einstein – Light is bent by gravity Any object passing in front of a distant star can cause it to look brighter Foreground Star Distant Star Planet By measuring brightening carefully, can tell if there is just a star or star plus planet

Gravitational Microlensing Disadvantages Requires lucky alignment Tells little about the planet Cannot be repeated Advantages Can monitor many stars cheaply Sensitive to small masses Score = 89

Dynamical Methods Astrometry Pulsar Timing Other Timing Radial Velocity How they work Planet orbits star Star also goes in a small circle Easier to detect motion of star than of planet

Astrometry Score = 6 How it works Star moves left and right as viewed by us Disadvantages Insensitive Massive planets Large Orbits Patience Advantages Can see planets with large orbits Score = 6

Gaia Mission Q. 59: Astrometry from Space European spacecraft repeatedly measuring millions of stellar positions Will allow accurate parallax (distance) to countless stars Should discover thousands of planets Final data releases in 2020 and 2021 Q. 59: Astrometry from Space