Solar System Exploration: Planet Selector: Asteroids

PLANET SELECTOR

ABOUT ASTEROIDS

Asteroids are rocky, airless worlds that orbit our Sun, but are too small to be called planets. Tens of thousands of these 'minor planets' are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called near-earth objects.
Read More About Asteroids >>

Featured Mission: Dawn
Scheduled for launch in 2007, NASA's Dawn spacecraft will orbit two of the most intriguing asteroids in our solar system - Ceres and Vesta.
Read More About Dawn >>

ASTEROID IDA: VITAL STATISTICS

Average Distance from Sun:	428,000,000 km (266,000,000 miles)
Diameter:	56 x 24 x 21 km (35 x 15 x 13 miles)
Mass:	1,000,000,000,000,000,000 kg (0.000000016 x Earth's)
Length of Day:	4.6 hours
Length of Year:	4.8 Earth years
Known Moons:	1 (Not all asteroids have moons)

SIZE & DISTANCE

Asteroid Ida is about seven times larger than the city of Washington, D.C.

Average Distance from the Sun: 4,820,000 km (2.86 A.U.)

EXTREME SPACE

Queen of the Asteroid Belt
With a diameter of 933 km (580 miles), Ceres is the undisputed ruler of the asteroid belt. The space rock accounts for a quarter of all the mass of all the thousands of known asteroids in or near the main asteroid belt.

Small Change
If you could lump together all the thousands of known asteroids in our solar system, their total mass wouldn't even equal 10 percent of Earth's Moon.

Asteroid Assault
Asteroids have hit every planet in our solar system. Most space rocks that hit Earth burn up or slow down enough not to cause serious damage. Evidence of what happens when they don't can be seen at Barringer Crater in Arizona - a giant hole almost 1.6 km (1 mile) across and 175 meters (570 feet) deep.

Close Call
An asteroid named 1950 DA is considered one of the greatest known threats to crash into Earth. Fortunately, the odds of an impact are fairly slim. The asteroid won't arrive until March 16, 2880 so we have a few hundred years to watch it and make certain it will miss Earth.

Tiny Guardian
Asteroids are often called minor planets. Some even have moons. Back in 1994, NASA's Galileo spacecraft found a tiny moon - about 1.5 km (1 mile) across - orbiting Asteroid Ida. The first known moon of an asteroid was named Dactyl, after the protectors of the young Greek god Zeus.

Touchdown
After NASA's NEAR spacecraft had completed its intensive study of Asteroid Eros, mission controllers decided to try to land the spacecraft. Despite the fact it wasn't designed for landing, NEAR successfully touched down on Eros in 2001 - and went into the record books as the first to land on an asteroid.

TIMELINE

1801 - Italian Giuseppe Piazzi discovers the first asteroid, Ceres. The asteroid is named for the Sicilian goddess of grain.

1898 - German Gustav Witt announces the discovery of Eros, one of the largest near-Earth asteroids.

1960 - Chemical analysis of a meteorite found in Western Australia turns out to be part of the crust of Asteroid Vesta.

1991-1994 - On its way to Jupiter, NASA's Galileo orbiter snaps the first close-up images of an asteroid (Gaspra) and discovers the first moon (Dactyl) of an asteroid (Ida).

2001 - After studying Eros from orbit for more than a year, NASA's NEAR spacecraft makes the first successful landing on the surface of an asteroid.

SLIDE SHOW

Asteroid Eros
Asteroid Eros' Butterscotch Colors
Sunset on Eros
Descending to Eros
Asteroid Ida and its moon, Dactyl
Bone-shaped Asteroid Kleopatra
Asteroid Vesta Elevation Map
Asteroid Gaspra
Asteroid Mathilde
Sizes of Vesta, Eros and Ceres

MOONS

Many asteroids have been captured by a planet's gravity and become moons. Likely included among these are Mars' moon, Phobos and Deimos and most of the distant outer moons of Jupiter, Saturn, Uranus and Neptune. A few asteroids have managed to snare tiny moons of their own. The best known of these asteroid moons is Dactyl, a 0.7 km (1-mile) wide rock orbiting Asteroid Ida. It was the first natural satellite of an asteroid to be found and was discovered when the Galileo spacecraft flew past on its journey to Jupiter.