(1) A comet is discovered and as it comes closer to earth, it becomes apparent it may strike our planet.

(2) Warming from the sun causes frozen organic compounds on a comet 's surface to sublime, or vaporize.

(3) The spacecraft's point of view now captures the shadowed side of the comet 's nucleus.

(4) A bright comet is a spectacular astronomical event.

(5) He saw a comet passing far, far away in the distance from where he made his steps.

(6) The Hawaii researchers observed the comet on July 17 and July 18 and discovered many more fragments.

(7) The spacecraft will orbit the comet 's nucleus.

(8) Sometimes, the stresses are strong enough to break off chunks of the comet 's nucleus.

(9) A bright comet had appeared on 14 November 1680.

(10) Rather, they are produced by bits of dusty debris shed by orbiting comets and asteroids.

(11) Dozens of comets are discovered each year as well, many by automated telescopes and spacecraft.

(12) He observed the comets of 1665, and made other astronomical observations, publishing his descriptions of these events.

(13) By studying meteor showers, scientists can learn more about cometary debris, but it is going a step further with its Rosetta comet-chasing mission which will examine a comet at close range.

(14) Some explanations for extinctions and evolution include strikes by asteroids or comets .

(15) As orbiting comets pass near the sun, intense heat strips them of a layer of dust and ice.

(16) There are vast numbers of comets in the solar system, more than there are asteroids, but most lie out of sight beyond Pluto.

(17) Several bright comets streaked across the sky and then disappeared in an instant.

(18) Bombardment by asteroids and comets is an extraterrestrial process that may release huge quantities of water.

(19) She discovered eight comets , a record by a female astronomer until 1987.

(20) At a distance of one light-week, our solar system is lost in the Sun's glare; even farther out is a collection of cometary objects called the Oort Cloud, depicted as a sphere one light year across.