Science Background

The Big Idea

Asteroids and comets are messengers from space that have had a significant impact on Earth’s history and are likely to influence the future as well.

The Questions Behind the Exhibit

How did our Solar System form?

What are asteroids & comets like?

What impact have space rocks had on our planet?

Are we at risk?

Our Solar System

KEY QUESTION:

What is gravity?

Gravity Rules

Gravity is the attractive force between objects that have mass. In space, this means that a swarm of small objects eventually collects into a big one under the influence of gravity. This is how moons, rings, planets, and stars form.

Before entering the exhibit, fill in the blanks using the following key words.

galaxy orbit solar system moon star Universe Earth Jupiter planets Sun 100 billion

The Sun is a _________ located at the center of our __________________. Our

home, called __________, is one of 8 planets that orbit around the _________.

Earth has one _________ that orbits around it each month, showing different

phases. Some planets have many moons that ___________ around them.

________________ is the largest planet in the Solar System and has 64 moons!

Our sun is one of about _______________ stars contained in the spiral

_____________ we call the Milky Way. Astronomers are now discovering

Jupiter-sized ____________ that orbit around some of those distant stars. Outer

space is even bigger yet because the Milky Way is only one of an estimated 100

billion (100,000,000,000) galaxies in the ______________!

Exploring the Structure of the Universe

Can You Fill in the Blanks?Click for Answers

star solar systemEarth Sunmoon

orbitJupiter

100 billiongalaxy

planets

Universe Copyright 2000 Cherilynn Morrow – Used with permission

A. Solar System Formation

1. Something (perhaps a supernova) triggers the gravitational collapse of a nearby interstellar cloud.

2. The cloud naturally heats up and spins faster as it collapses. Collisions between particles flatten the cloud into a disk. The Sun and planets start to form in this spinning, flattened disk (proto-planetary disk), with the Sun at the hottest central part.

3. In our Solar System, Earth formed in the inner region of the disk where rocky & metallic material could condense in the greater heat. Ices & hydrocarbons settled in the outer regions where gas giants like Jupiter form.

Crash Course• The largest planet, Jupiter, exerted

a powerful gravitational influence. If Jupiter had formed closer to the Sun, Earth and some of the other inner planets might have been thrown out of the Solar System!

• Jupiter, Saturn, Uranus, and Neptune formed amid a blizzard of icy particles. They swept up much of this frozen material. But much also collected into huge “iceballs.” The powerful gravity of the giant worlds flung most of the iceballs into the outskirts of the Solar System.

• However some were diverted toward Earth, where they crashed and deposited vast amounts of water—maybe enough to fill our oceans. Since life probably started in the oceans, we may owe our existence to these snowballs from afar.

Earth is one of 8 PLANETS in our SOLAR SYSTEM. The planets orbit a central STAR we call the SUN.

Can you name the other planets?

Hit <RETURN> for answers

Mercury

Venus

Earth

Mars

Jupiter Saturn

Uranus

Neptune

Rocky terrestrial planets of the inner Solar System.

Gas & ice giant planets

of the outer Solar System.

Influenced by the gravity of Jupiter & Neptune, icy comets from the outer solar system likely delivered important ingredients for life to the young Earth environment (e.g. water and carbon compounds).

Our Place in the Solar System

How do we explore our Solar System?

Ground-based Telescopes

The most readily available tools for exploring the giant worlds are ground-based telescopes. These include mammoth instruments such as the 110-foot, 500-ton Goldstone Apple Valley Radio

Telescope located in California.

Space TelescopesOne advantage of launching telescopes into space is that they have a view unobstructed by Earth’s atmosphere. Orbiting several hundred kilometers above Earth is the Hubble Space Telescope, which has captured detailed views of the giant planets and their moons.

Space ProbesThe best views of the giant worlds are from up close. Several space probes have made the journey to the realm of giants for “quick-look” flyby missions or for long-duration orbiting missions. Cassini-Huygens is a spacecraft that arrived in orbit around Saturn in 2004.

Asteroid/Comet Locations

Asteroid & Comet Sizes

B. The Story of Asteroids

Lutetia

The Asteroid Belt

Asteroid Facts

• Color: Grey to slightly reddish. Asteroids turn redder and darker as they age.

• Material: Most are similar to ordinary rocks. A small number are nearly pure iron. Still others contain substantial amounts of carbon.

• Surface: Pock-marked. Asteroids are covered with impact craters from collisions with smaller asteroids.

• Temperature: Asteroid temperatures vary a lot depending on how fast they spin and whether you measure the side facing the Sun. Temperatures range from -100ºC to 100ºC.

• Size: Asteroids can be almost any size from tens of meters across to nearly 1/4 the diameter of our moon.

• Hidden Asteroids: We know the most about larger asteroids because we can see them. There are countless asteroids smaller than a kilometer (0.6 miles) that we can’t observe directly.

C. The Story of Comets

What are Comets?• Chunks of Ice and Rock:

“Dirty Snowballs”• The most visible part (tail) is less dense than best lab vacuum.Ion tail: ions created

by sunlight (blue colorCaused by CO2

+). Points away from Sun.

Dust tail: Dust particlesscatter (reflect) sunlight.Direction due to motion.

.Nucleus: Ice withintermixed ‘gravel.’

Cometary Orbital Activity Cycle

Why are Comets Interesting??

• Relatively “pristine” materials from the formation of the solar system.

• Used as proxies to study other parts of the solar system (Kuiper belt, Oort cloud).

• Occasional impacts that also can deliver water to the inner solar system.

A Jupiter Collision: Shoemaker-Levy 9

SL9 broke into pieces during a close encounter with Jupiter in 1992 and collided with Jupiter in July 1994.

Impacts by disrupted objects can make crater chains like this one on Ganymede

The same impact scar transposed onto Earth from Fragment G

CC. Space Rock Impacts & Risk

Moon & Mars: Impact Craters?What about Earth?

Identified impact structures on the Earth

The Inner Solar SystemMain-belt asteroids are shown in green.

Near-Earth asteroids are shown in red.

Trojan asteroids are shown as small blue dots.

Comets are shown as blue open squares.

Positions as of 2 May, 2007.

NEOs: where do they come from?

• Main Belt Asteroids (MBAs) – between Mars and Jupiter

• Kuiper Belt – at or beyond the orbit of Neptune

• Oort Cloud Comets (may also include larger bodies and some asteroids) – long orbits extending out >10,000 AU, 106-yr periods

Tunguska Impact, Siberia,

30 June, 1908; Airburst, no crater

Barringer Crater, Arizona 1.2 km diameter

50,000 years ago

Manicouagan, Canada, 100 km diameter crater214 million years ago

Chicxulub,Mexico, 180 km diameter crater

The impact of a comet or asteroid ~10 km in diameter is now believed to be the cause of the extinction of ~2/3 of the species of life on the Earth, including the dinosaurs, 65 million years ago. Thus, we probably owe our very existence to impacts.

K-T Boundary

CONCLUSION Re-visiting the Big Ideas

We study asteroids and comets because they tell us about the formation of solar systems, our planet, and the conditions necessary for life. Someday we may answer the age-old question of whether there is life beyond Earth.

Asteroids and comets come in a variety of shapes and sizes. They are truly space messengers that have had a significant impact on Earth’s history and are likely to influence our future as well.

http://www.killerasteroids

http://dawn.jpl.nasa.gov