Asteroids

Asteroids are the ultimate space destination because they contain material resources but have miniscule gravity wells, i.e., the energy needed (change in velocity) to visit and return to Earth is minimal.

Lagrange Points

Each planet defines five Lagrange points with the sun and the moon defines five Lagrange points with the earth. The image below is not in scale, but it illustrates the five earth-sun Lagrange points:

The James Webb Space Telescope (JWST) will be parked at earth-sun L2, one million miles from earth.
L2 is an unstable Lagrange point so JWST will require periodic thrusting to maintain its L2 station.
Lagrange points L4 and L5 are stable, so asteroids tend to collect there.

Trojan and Greek Asteroids

The most massive planet Jupiter has significant collections of asteroids orbiting its stable Lagrange points.

Trojan and Greek asteroids.

Earth-Trojan Asteroids

Visiting an Earth-Trojan asteroid is one of the easiest (requires the least energy) deep space science missions. An Earth-Trojan asteroid was recently discovered (July 2011).

A computer generated orbital plot of the newly discovered Earth-Trojan asteroid.

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Email: Richard dot J dot Wagner at gmail dot com