9. Gaspra Rotation Sequence

What did we know about Gaspra before Galileo's flyby?

Note: Click on Solar System Exploration: Galileo Legacy Site (NASA-JPL) to get this image at its highest resolution.

This montage of 11 images shows Gaspra growing progressively larger in the field of view of Galileo's camera. Asteroid Gaspra rotates once in 7 hours, 3 minutes and counterclockwise when viewed from above the north pole - these images cover almost one Gaspra "day". Many craters are visible on the surface of Gaspra.
The earliest view (upper left) was taken 5 3/4 hours before closest approach from a range of 164,000 kilometers (102,000 miles).

Galileo's flyby of the asteroid Gaspra marked the first ever spacecraft encounter with an asteroid.
The last view (lower right) was taken at a range of 16,000 kilometers (10,000 miles), 30 minutes before closest approach.

What did we know about Gaspra before Galileo's flyby?

From ground-based observations, quite a bit of information was known about Gaspra before the encounter.
Discovered in 1916 by astronomer Grigori Neujmin at Simeis Observatory in the Ukraine, Gaspra was named for a scientists' resort on the Crimean Peninsula.
Gaspra, an S-type (or stony) asteroid, is believed to be made up of metallic and rocky minerals including iron, nickel, olivine, and pyroxene.
This asteroid is just one of more than 15,000 asteroids comprising the "main belt" - a large doughnut-shaped region midway between Mars and Jupiter.
Gaspra is located about 331 million kilometers (206 million miles) from the Sun, near the inner edge of the main belt.
Asteroids are also known as minor planets; many are much larger than Gaspra, ranging up to more than 1,000 kilometers (600 miles) in diameter.

Investigating asteroids like Gaspra and Ida is important to scientists because asteroids contain important clues to processes in the early solar system.
Asteroids are believed to have formed during the earliest stages of the solar system and thus are primitive bodies that could provide key information about the evolution of the Sun and its planets.
Asteroids were formed when the other planets were formed in the early solar nebula.

In addition, encountering Gaspra helped to calibrate ground-based observations.
Since all previous observations of asteroids have been limited to ground-based viewing, Galileo's encounter provided a unique opportunity to increase our knowledge and update our models about how asteroids form and evolve.
For that matter, since many meteorites are believed to be chunks of asteroids, categorizing the composition of asteroids may allow scientists to coorelate such meteorites with their parent asteroids.

Next slide: Highest-Resolution Image of Gaspra

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Link to: Solar System Exploration: Galileo Legacy Site (NASA - JPL)

Updated: August 21 '96

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