Asteroids



Many missions are currently under way to bring the wonders of the solar system direct to you! You can use this page to catch up on what is going on with our exploration of asteroids.



Asteroids are the rocky leftover debris from the formation of our solar system. The exploration of these worlds has only just begun and the veil of mystery is beginning to lift from these tiny worlds.

The Galileo mission to Jupiter gave us our first close look at an asteroid. Galileo passed by asteroid 951 Gaspra in October of 1991. Gaspra, at left, is thought to be a mix of rock and metal. Like virtually all asteroids, it has an irregular, potato-like shape. It measures some 12 x 7.5 x 7 miles in size.

  • More Galileo Images of Gaspra

    Galileo also made a second asteroid flyby. This time it was in August of 1993 and the target was asteroid 243 Ida. Galileo discovered that Ida has a companion asteroid, which has since been named Dactyl.

    Ida and Dactyl can be seen below right. Ida is about 35 miles long and its satellite, Dactyl is about a mile across. Dactyl is most likely a chunck of of Ida that was blasted off in an ancient collision.

    Ida was thought to be composed of rock and iron, like Gaspra, yet Galileo measured a density that is far too low for that to be the case.

    Like most asteroids, Ida spins fairly fast. Ida rotates once every 4 hours, 39 minutes.

  • More Galileo Images of Ida and Dactyl



    The next close encounter with an asteroid came as the NEAR (Near Earth Asteroid Rendezvous) spacecraft flew past asteroid 253 Mathilde in June of 1997. Mathilde can be seen at the top of this page. Mathilde is about 37 x 29 miles in size - much larger than Gaspra.

    The relative sizes of Mathilde, Gaspra, & Ida are shown below.

    Mathilde is thought to resemble carbonaceous meteorites that have been found on Earth. Checking in at only 1.4 grams per cubic centimeter, Mathilde has the lowest density of any asteroid yet surveyed. This has led to speculation that Mathilde is very porous, possibly somewhat like styrofoam or even just a pile of rubble loosely held together in space.

  • More NEAR Images of Mathilde

    NEAR is now in orbit around the asteroid know as 433 Eros! All of the previous studies of asteroids have been done as a spacecraft made a pass past an asteroid. NEAR is in orbit about Eros giving us a long term look at this world.

    Images and information on Eros will soon be posted here. In the meantime, be sure to visit the NEAR Image of the Day Archive.

    Current Space Missions to comets or asteroids:

  • NEAR - Near Earth Asteroid Rendezvous - is in orbit about the asteroid Eros!
  • Stardust - encounters comet Wild 2 in January, 2004 & returns samples to Earth in 2006.
  • Galileo Mission - is in orbit around Jupiter, but visited some asteroids along the way.
  • Deep Space 1 - now in extended mission. Made a flyby of asteroid 9969 Braille on July 28, 1999. Is expected to make a flyby of comet Borrelly in September, 2001.

    Other Resources:

  • Exploring the Solar System
  • Asteroids from The Nine Planets
  • Fairmount Center for Science and Mathematics Education
  • Lake Afton Public Observatory
  • NASA Jet Propulsion Laboratory
  • Deep Space Network
  • JPL's Space Calendar


    JPL Solar System Ambassadors
    Created 02-19-2000, last updated 08-01-2000