2000年6月7日 · What Are Comets? * Comets are small, fragile, irregularly shaped bodies composed of a mixture of grains and frozen gases. They have highly elliptical orbits that repeatedly bring them very close to the Sun and then swing them deeply into space, often beyond the orbit of Pluto. * Comet structures are diverse and very dynamic, but they all develop a surrounding cloud of diffuse material, called ...

Asteroids and comets – and the meteors that sometimes come from them – are leftovers from the formation of our solar system 4.6 billion years ago.

Halley is often called the most famous comet because it marked the first time astronomers understood comets could be repeat visitors to our night skies. Astronomers have now linked the comet's appearances to observations dating back more than 2,000 years. Halley was last seen in Earth's skies in 1986 and was met in space by an international fleet of …

The planetary system we call home is located in an outer spiral arm of the Milky Way galaxy. Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids. Beyond our own solar system, there ...

Stardust: A Mission With Many Scientific Surprises The primary goal of the Stardust mission was to collect samples of a comet and return them to Earth for laboratory analysis. Comets are ancient bodies of frozen ice and dust that formed beyond the orbit of the most distant planet. They were expected to contain materials that the solar system formed from, …

Over a lifetime, most people are fortunate enough to see at least a few bright comets grace the night sky. The bright ones, along with their more numerous faint siblings, are mysterious travelers from the frigid and most distant parts of the solar system. When a comet approaches the sun, its surface warms and it dramatically becomes brighter. To an observer on Earth, a …

2000年6月7日 · Why Study Comets? Don Yeomans Jet Propulsion Lab April 1998 Life on Earth began at the end of a period called the late heavy bombardment, some 3.8 billion years ago. Before this time, the influx of interplanetary debris that formed the Earth was so strong that the proto-Earth was far too hot for life to have formed. Under this heavy bombardment of asteroids and comets, the early Earth's oceans ...

2000年6月7日 · Comets & The Question Of Life From astronomical observations and previous space missions, comet dust grains are known to contain various minerals and some organic compounds, but we do not currently know the detailed chemical makeup of these minerals and compounds. The question has been asked whether comets might contain some sort of alien life form, and if so, could there be an associated ...

NASA’s real-time science encyclopedia of deep space exploration. Our scientists and far-ranging robots explore the wild frontiers of our solar system.

Discovery Comet 2P/Encke was first discovered by Pierre F. A. Mechain on Jan. 17, 1786. Other astronomers located this comet in subsequent passages, but these sightings were not defined as the same comet until Johann Franz Encke calculated its orbit. Overview Comet 2P/Encke is a small comet. Its nucleus measures approximately 2.98 miles (4.8 kilometers) in diameter, which is about a third of ...