Chapter 1-5: Asteroids, Comets, and Meteorites

Flashcards covering vocabulary, missions, and concepts related to asteroids, comets, meteorites, and the End-Cretaceous impact hypothesis.

Asteroids

Rocky remnants left over from the early formation of our solar system about $4.6\,\text{billion years}$ ago.

Main asteroid belt

The region between Mars and Jupiter where most asteroids are found orbiting the Sun.

Vesta

The largest asteroid, at about $530\,\text{km}$ in diameter, which shows strong evidence of ancient volcanic activity and acts like a differentiated protoplanet.

Ceres

A body $950\,\text{km}$ in diameter reclassified as a dwarf planet in $2006$ after formerly being considered the largest asteroid.

C-type asteroids

Also known as carbonaceous asteroids, these constitute roughly $75\%$ of known asteroids and are characterized by a dark appearance and high carbon content.

S-type asteroids

Also known as stony or silicious asteroids, these form about $17\%$ of known asteroids and are composed mainly of silicate minerals and a metallic nickel-iron mixture.

M-type asteroids

Also known as metallic asteroids, these contain higher concentrations of metal faces like iron and nickel and are primarily located in the middle of the asteroid belt.

Dactyl

A moon discovered in $1993$ orbiting the S-type asteroid Ida; it was the first known moon of an asteroid.

NIRS spacecraft

A NASA probe that performed a high-speed flyby of the C-type asteroid Matilda in $1997$, revealing it to be irregular and heavily cratered.

NIER spacecraft

The first probe to successfully orbit and land on an asteroid, specifically the S-type asteroid Eros, in $2001$.

Apollo asteroids

A group of near-Earth asteroids (NEAs) defined by their Earth-crossing orbits; as of January $2025$, $21,083$ have been discovered.

Potentially hazardous objects

Asteroids designated based on their orbit passing within $0.05\,\text{Astronomical Units}$ of Earth and having a diameter large enough to cause significant regional damage.

Bennu

A carbon-rich near-Earth asteroid that currently poses the greatest risk of impacting Earth, with a $1$ in $2,700$ chance on September $24, 2182$.

OSIRIS-REx

A NASA spacecraft that returned a sample of the asteroid Bennu to Earth in $2023$, which was found to contain the amino acid glycine.

Trojan asteroids

A population of ancient, rocky, icy bodies that share a planet's orbit (specifically Jupiter's) and cluster $60\,\text{degrees}$ ahead and behind at Lagrangian points.

Lagrangian points

Five specific positions in space where the gravitational pull of two large bodies balances the centrifugal force required for a small object to maintain its position.

Comets

Bodies made of water ice, frozen gases, dust, and rock that orbit the Sun in highly elliptical paths.

Nucleus

The solid central part of a comet, often only a few kilometers in diameter, made of ices embedded with dust and rocky material.

Coma

A nebulous envelope around a comet's nucleus that forms a bright ball of light when the comet passes near the Sun.

Dust tail

A white-yellowish, curved comet tail composed of solid particles that points away from the Sun.

Ion tail

A straight, long, bluish comet tail formed by charged gas that points away from the Sun due to solar wind.

Hydrogen envelope

A massive, invisible cloud of hydrogen atoms surrounding a comet's coma and ion tail, created when solar radiation breaks down water vapor.

Halley's Comet

A famous short-period comet that orbits the Sun every $75$ to $77$ years and is the only known comet consistently visible to the naked eye.

Kuiper Belt

The source of short-period comets that take less than $200\,\text{years}$ to orbit the Sun, located at a distance greater than Neptune.

Oort cloud

The source of long-period comets that take hundreds to millions of years to orbit.

Charon

Pluto's largest moon, which has half the diameter of Pluto and is mutually tidally locked with it, forming a double dwarf planet system.

Meteoroids

Small, rocky or metallic bodies in space ranging in size from dust grains to about one meter wide.

Meteors

The glowing streaks seen in the sky when meteoroids enter a planet's atmosphere at high speeds.

Meteorite

A meteor that survives the trip through the atmosphere and hits the ground.

Manukuagin Reservoir

A water body in Central Quebec that fills the sixth largest impact crater in the world, formed approximately $214\,\text{million years}$ ago.

Stony meteorites

The most common type of meteorite ($90\%$ of observed falls), composed primarily of silicate rock-forming minerals with small amounts of nickel-iron metal.

Iron meteorites

Metallic remnants from the cores of early asteroids composed primarily of iron and nickel, often displaying unique crystalline patterns.

Stony-iron meteorites

Rare meteorites (making up only $1$ to $2\%$ of falls) composed of roughly equal parts nickel-iron alloy and silicate minerals.

Mass extinction

A rapid, widespread, and severe reduction in Earth's biodiversity marked by a sharp decrease in species abundance and diversity.

Chicxulub Crater

A peak ring structure buried beneath the Yucatan Peninsula in Mexico, formed approximately $66\,\text{million years}$ ago by an asteroid estimated at $10$ to $15\,\text{kilometers}$ in diameter.

Iridium

A platinum-group metal rare in Earth's crust but abundant in asteroids; its presence in a global clay layer supports the impact hypothesis for the End-Cretaceous extinction.

Tektites

Small, glassy spherules formed as droplets of melted rock that splashed up and cooled after an asteroid impact.

Shocked quartz

A form of quartz with microscopic structural deformations caused by intense shock waves from an asteroid impact.

Tsunamiites

Sedimentary deposits that serve as physical evidence of a tsunami hitting a shoreline or submarine sediments, preserved in the rock record.