Hyakutake will come within 9 million miles of Earth, a mere one-tenth the distance to the Sun. Astronomers hope to actually focus on the comet's nucleus and measure its size. The only time that has been done before was when European and Soviet spacecraft flew by Halley's Comet in March 1986. Of course, there was no Hubble telescope then. The space telescope's high sensitivity and resolving power make it ideal for observing comets as they approach the inner solar system.
Comets are too small to be seen from large distances.
They populate a huge swarm of comets, called the Oort Cloud, a pool of material left over from the birth of the solar system that extends as far as one light year, or 6 trillion miles, from the Sun. That's one-fourth the distance to the nearest star. Occasionally, nearby stars exerting gravitational forces kick one of these objects out of its distant orbit, and it comes close to the Sun, Feldman said. As it gets closer to the inner solar system the Sun's warmth heats up its frozen core, releasing various gases that brighten the comet. Electrically charged particles from the solar wind react with the cometary gases, forming a large tail that always extends directly away from the Sun.