Impacts in the Solar System

What kinds of objects threaten our planet

Impacts and catastrophes

When do impacts happen

When orbits cross

What could earth collide with

• earth crossing asteroids

• Comets

asteroids

• small, rocky, or metallic objects that orbit the Sun

• leftover rocky planetesimals

• sizes: few km to 1,000km

• millions exits; more than 150,000 cataloged

• mass of all asteroids combined is less than that of the moon

• most of them are in between the orbits of Mars and Jupiter

watch the video on slide 11

yessir

What is the average distance between asteroids in the asteroid belt

1,000,000 miles

Comets

• formed in the cold, outer regions of the solar system, comets are icy counterparts to asteroids

• Most comets don’t have tails, they remain perpetually frozen in the outer solar system

Dirty snowball

Nucleus of a comet

• ice mixed with rock and dust

• The ice itself is made of some hydrogen compound (H2O, CO2, NH3, CH4)

Developing a coma

as comets approach the sun, temps increase, their ices sublimate forming a coma that surrounds the nucleus

Developing a tail

When comets get even closer to the sun, solar wind and light push on the coma, and this thing is formed

Sublimate

To transform from solid to gas

Speed of comet as it approaches sun

Because of gravity, the comet moves faster as it gets closer to the sun

Where do comets spend most of their lives

Far away from the sun

Two tails of a comet

• plasma tail

• Dust tail

Plasma tail

Ionized (atoms that have lost their electrons) gas swept back by solar wind

Dust tail

Dust particles swept back more slowly by radiation

Radiation pressure

Photons capable of colliding and pushing dust away from the sun

A comet’s journey

• most time away from sun

• As it gets closer, nucleus warms and begins to sublimate

• Gas coma forms around nucleus as it gets closer to sun

• Tails form, pushed out by solar wind and radiation

  • Larger particles unaffected by sunlight

  • Dust tail pushed by sunlight

  • Plasma tail swept by solar wind

• Tail points away from sun

• Solar heating diminishes, coma and tail disappear, as it move away from sun

During the majority of comets lives, they

Only have a nucleus

Oort Cloud

• most comets far away from sun

• Region where they live is called this

• Never observed, but can be inferred from the orbits and the frequency of comets we do observe

Which of these events can send a comet from the Oort Cloud into the inner solar system

• Two comets colliding with each other

• two comets passing very close to each other

• a star that passes relatively close to the Oort Cloud, whose gravity slows down a comet in its orbit

Pushing a comet from Oort Cloud into inner solar system

Passing Star’s gravitational attraction pulls on comet, slowing it and changing its orbit

Once a comet from the Oort Cloud is sent into inner solar system…

It will remain in an elliptical orbit for the rest of its life (provided it doesn’t collide with anything)

Meteor

When dust or other debris enters our atmosphere, they burn up producing a brief flash of light, or a bright trail. Meteors are often referred to as shooting stars

Meteorite

A rock from space that falls through the earth’s atmosphere

Meteor showers

An increase in the number of meteors at a particular time of the year

When does earth see a meteor shower

when the earth goes through the orbit of a meteoroid swarm (the leftovers of a comet)

3I/ATLAS Comet

• July 2025 by atlas survey, unusual fast moving comet

• Hyperbolic trajectory — moving too fast to be gravitationally bound to the sun — so must have come from outside solar system

• Only the third confirmed interstellar object observed, first clearly behaving like a typical comet from another star system

• Normal coma and tail, with gas and dust consistent with natural icy body

  • Rare chance to study material formed around another star

Do collisions between objects in the solar system actually happen

Impact craters :0

Impact craters

• 10-15 times the size of meteorites that produced them because large amounts of energy/large velocity

• We know that aren’t volcanoes because volcanic craters are smaller and deeper than impact craters

  • Studying material around crater yields both the thing that crashed and what it crashed on

• Common in solar system and earth

difference between volcanic craters and impact craters

volcanic craters are smaller and deeper than impact craters

Arizona’s Meteor Crater

• formed 50,000 years ago

• 1 km in diameter

• the guy that discovered this was very insistent people study impact craters, and asteroids hitting earth?

Mexico’s chicxulub crater

• area owned by oil company so we couldn’t study it til like 20 years ago

• formed 65 million years ago

• about 180km in diameter

• possibly responsible for global extinction

Comet shoemaker-levy 9 and Jupiter

Tidal forces of Jupiter pushing harder on front of comet rather than back, comet split, so instead of one comet, a ton of tinier pieces crashed into Jupiter

• 20 something really big explosions

• Crashed with energy of atomic bombs

• Forced scientists and government to recognize importance of impacts

What caused comet shoemaker-levy 9 to break into many fragments

Tidal forces

Chelyabinsk meteorite in 2013

a 20 meter meteorite traveling at about 40k mph exploded about 30km above the city of Chelyabinsk in Russia. More than 1000 people were hurt by the blast wave from the explosion. Dozens of cameras captured the event/ This is the largest impact in the last 100 years, and the best documented event