Lecture 34: Asteroids & Comets

These flashcards cover key vocabulary and concepts related to asteroids, comets, and their significance in the solar system as discussed in the lecture.

Asteroid

Rocky leftovers from the planet formation process.

Ceres

The largest asteroid in the asteroid belt, with a diameter of approximately 1000 kilometers.

Asteroid Belt

A region in space between Mars and Jupiter that contains a large number of asteroids.

Meteoroid

A rock from space that’s still in space.

Meteor

The bright trail left by a meteoroid as it enters Earth’s atmosphere.

Meteorite

A rock from space that has fallen through Earth’s atmosphere.

Comet

Icy counterparts to asteroids, often described as 'dirty snowballs'.

Oort Cloud

A vast region of space where comets are believed to originate, extending to about 50,000 AU.

Kuiper Belt

A disk-shaped region of the solar system beyond Neptune, where many comets and other bodies are found.

Orbital Resonance

When two orbiting bodies exert regular, periodic gravitational influences on each other, often resulting in gaps or clusters in the orbit.

Tails of Comets

The trails formed when comets enter the inner solar system and heat up, causing gas and dust to escape.

Deep Impact Mission

A NASA mission designed to study the nucleus of a comet by impacting it with a projectile.

Iridium Layer

A layer rich in iridium and soot that provides evidence of a meteorite impact associated with the mass extinction event 65 million years ago.

Mass Extinction

A significant decline in biodiversity at a global scale, often due to catastrophic events.

Asteroid Deflection Techniques

Methods proposed to mitigate the threat from potential asteroid impacts, including kinetic impactors and gravity tractors.

Cosmic Collisions

Encounters between celestial bodies that can result in significant impacts, such as comet SL9 impacting Jupiter.

Number of Known Asteroids

There are over 150,000 asteroids cataloged, with probably more than a million having a diameter greater than 1 kilometer.

Total Mass of Asteroids

The combined mass of all asteroids in the solar system is less than that of even a small terrestrial planet.

Physical Characteristics of Asteroids

Asteroids are typically cratered and not spherical in shape.

Asteroid Moons Example

The asteroid Ida has a tiny moon named Dactyl.

Significance of Asteroid Moons

Moons orbiting asteroids provide useful data to calculate the asteroid's density.

Range of Asteroid Densities

Asteroid densities vary widely, ranging from denser than Earth to much less dense.

Hayabusa Mission

A Japanese spacecraft that scooped up small amounts of material from the asteroid Itokawa and successfully returned it to Earth.

OSIRIS-REx Mission

A NASA mission that returned pristine asteroid material from asteroid Bennu to Earth.

Gaps in the Asteroid Belt

Asteroids in orbital resonance with Jupiter experience periodic gravitational nudges that eventually move them out of their orbits, creating gaps in the asteroid belt.

Jupiter's Influence on Asteroid Belt Formation

Jupiter's gravity, through the influence of orbital resonances, stirred up asteroid orbits and prevented them from accreting into a planet.

Comet Formation Location

Comets formed beyond the frost line in the outer solar system.

Comet Tails Occurrence

Most comets do not have tails; tails only form when comets enter the inner solar system and are heated by the Sun.

First to Measure Comets Outside Atmosphere

Tycho Brahe was the first to measure that comets exist outside Earth's atmosphere.

Halley's Comet Prediction

Edmund Halley predicted the reappearance of his namesake comet in 1758 based on Kepler's laws and Newton's gravity, with a period of about 75.3 years.

Coma

The atmosphere that forms around a comet's heated nucleus.

Plasma Tail

A tail of ionized gas escaping from a comet's coma, pushed away from the Sun by the solar wind.

Dust Tail

A tail composed of dust particles escaping from a comet, pushed away from the Sun by photons.

Formation of Meteor Showers

Meteor showers occur when Earth passes through a stream of small particles ejected by a comet that follow its orbit.

Oort Cloud Comet Orbits

Comets in the Oort Cloud follow random orbits that extend to about 50,000 AU.

Kuiper Belt Comet Orbits

Comets in the Kuiper Belt follow orderly orbits within the disk of the solar system, ranging from 30-100 AU.

Origin of Kuiper Belt Comets

Kuiper belt comets formed in the Kuiper belt itself, resulting in a flat plane of orbits aligned with planetary orbits and moving in the same direction.

Origin of Oort Cloud Comets

Oort cloud comets were originally closer to the Sun but were kicked out by gravitational interactions with Jovian planets, resulting in a spherical distribution with orbits in any direction.

Primitive Meteorites

Meteorites whose composition remains unchanged since they first formed 4.6 billion years ago.

Processed Meteorites

Younger meteorites that have undergone geological processes like volcanism or differentiation.

Timing of Dinosaur Extinction

The most recent mass extinction, which ended the reign of the dinosaurs, occurred 65 million years ago.

Evidence for Dinosaur Extinction by Impact

Strong evidence for an impact causing the dinosaur extinction includes the worldwide iridium-rich layer discovered by Luis and Walter Alvarez, dated 65 million years ago, with dinosaur fossils found below this layer.

Consequences of Large Meteorite Impact

A 10-kilometer meteorite impact would eject vast amounts of debris into the atmosphere, reducing sunlight and causing drastic climate change.

Frequency of Extinction-Level Impacts

Impacts large enough to cause mass extinctions occur millions of years apart, while events causing major damage happen every tens to hundreds of years.