Chapter 11: Meteors, Asteroids, Comets and Pluto

Goals:

• Survey orbitals and pp, of small bodies in the solar system, meteor, meteors and meteorites
• Asteroids ﻿$-$﻿ minor planets
• Comets
• Pluto
• Dwarf planets ﻿$-$﻿ plutoids
• Meteoroids and Meteors
• Meteoroids are objects orbiting the Sun that are too small to observe.
• Sizes are from about 1 m down to less than 1 mm.
• Speeds are >= 10 km/s and faster, much faster than a bullet.
• When they hit Earth the friction with our atmosphere heats and vaporizes them, creating a meteor ﻿$-$﻿ “shooting star” alerting us to their existence.

Meteorites

• If a meteoroid is large enough to reach the ground without being completely vaporized before it hits the ground.
• Meteorites can be collected and taken into a lab for analysis.

Types of Meteorites

• One type of meteorite is made of silicate compounds ﻿$-$﻿ “stony” meteorites.
• Some, called “chondrites”, contain small grains indicating they have not been heated very strongly before hitting Earth.
• Some are even more “primitive” and contain matter rich in carbon, indicating they have had almost no heating. Some even contain amino acids that are important to life.
• Some stony meteorites have no chondrules, so they are named “achondrites” which indicated that they have been heated strongly enough to melt the chondrules.
• These probably come from larger objects that got hot enough to melt the rock, and were broken apart by a collision.
• Another type of meteorite is made of iron ﻿$-$﻿ “irony” meteorites.
• These probably also came from the broken up large objects.
• The iron in these meteorites has avery distinctive crystalline pattern that forms when the iron cools from molten to solid over millions of years.
• The final type of meteorite is a mixture of irony and stony.
• These probably also came from the broken up large objects, but are from the boundary between stone and iron.
• Studying meteorites shows us what can happen inside larger objects, maybe even inside the Earth and other planets.

Asteroids

• Aster (star) oid (body) ﻿$-$﻿ a rocky body orbiting the Sun that is so small that it looks like a star.
• Another name for these is “minor planets”.
• Discovered by observing that they shift their positions compared to the stars.
• Before photography, they were really hard to find.

Where are Asteroids Located?

• Most asteroids are located in the region between Mars and Jupiter = “asteroid belt”
• A small number of asteroids are located in the orbit of Jupiter, 60 degrees ahead of and 60 degrees behind Jupiter ﻿$-$﻿ Trojan asteroids.
• The Trojan asteroids orbit with Jupiter because of the combined gravity of the Sun and Jupiter.
• The NEOs have probably had a gravitational interactions with Jupiter.
• In the asteroid belt, Jupiter’s gravity creates gaps.

Are Asteroids Important?

• Yes, because:
• They are samples of the material that built the planets.
• They can collide with planets, even Earth.
• Their impact energy is so great that it can cause tremendous damage ﻿$-$﻿ even mass extinction of life on Earth such as happened 65 million years ago.
• Such impacts can/will happen again.

Comets

• Comets are also small bodies orbiting the Sun in very long, thin orbits.
• They are mostly ice with a mixture of frozen gasses and rocky dust.
• When they come into the inner solar system the sunlight causes the ice to turn to gas, freeing the other gasses and dust to produce a gas tail and a dust tail.

Where do Comets “Live”?

• Because comets have very elliptical orbits, they spend most of their time far from the Sun where their ice doesn’t vaporize.
• One location is called the “Kuiper belt”, which is beyond the orbit of Neptune.
• Their other main location is called the “Oort cloud” at the edge of the solar system.

Pluto

• Recall (Ch 10) that Neptune was found because it altered the orbit of Uranus.
• Astronomers thought (incorrectly) that Neptune’s orbit was also being altered and this led to a search that just so happened to discover Pluto in 1930. Pluto was discovered by luck.
• Pluto is so far away (39.48 AU from the Sun) and so faint it couldn’t be studied.

Pluto “Rediscovered”

• In 1978, it was discovered that Pluto has a moon that has been named Charon.
• Charon made it possible to:
• Measure Pluto’s mass ﻿$=$﻿ 0.0021 MEarth.
• Measure Pluto’s radius ﻿$=$﻿ 0.181 REarth.
• Without that moon, we would not know this.

“Plutoids”

• Surveys have discovered other small bodies beyond Neptune that have physical properties and orbits similar to Pluto.
• They all orbit far beyond Neptune.
• They have very elliptical orbits.
• Orbits tilted to the orbits of the major planets.

Dwarf Planets

• Dwarf planets are a new family of objects in the solar system.
• They probably formed closer to the Sun where the solar nebula was denser.