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NASA's Blazing the Trail to Further Understand Comets

Photo of Ray Newburn Ray Newburn, Comet Expert

For the first few decades of the space program a majority of researchers devoted their attention to the planets and their satellites or moons. These planets and satellites were large and obviously fascinating and could be compared easily to our own Earth. Geochemists and astronomers pointed out that these large celestial bodies have greatly evolved over the eons, modified by high temperatures, great pressures, and the forces of chemical reactions and physical erosion. Knowledge of the earliest days of the solar system could only be gained by studying the small bodies within the system such as comets, asteroids, and meteoroids, which were little changed over the past 4 1/2 billion years.

Halley's Comet shown in the Bayeux Tapestry
Halley's Comet shown in the Bayeux Tapestry
Comets have always fascinated mankind because of their unique and strange behavior, appearing unexpectedly, persisting only briefly as a changing object of considerable beauty, and then rapidly disappearing. In medieval times they were often feared as harbingers of catastrophe. Many were afraid that these "serpents" would eat the Earth and destroy mankind. Edmond Halley first showed that comets were a natural part of our solar system by successfully predicted the return of the comet later named after him. Living astronomer, Fred Whipple, in papers published in 1950, first suggested the true nature of comets. The entire cometary phenomenon, with a tail that can stretch over a hundred million miles, originates in the small icy conglomerate of dust and frozen gases, only a kilometer to a few tens of kilometers in diameter, called the nucleus. The visible comet is all a temporary atmosphere of dust and gas escaping from the nucleus and caused by solar heating and radiation.

Image of Comet Hale-Bopp taken by Wally Pacholka
Image of Comet Hale-Bopp taken by Wally Pacholka on April 5, 1997 from the Joshua Tree National Park in California.
Since comet nuclei are so small, it is difficult to study them with Earth-based telescopes. Following the pioneering efforts of the past space missions such as ICE, Giotto, VeGa, and the Suisei spacecraft and their studies of comets Giacobini-Zinner, Halley, and Grigg-Skjellerup, a series of efforts began to study both the operational and cosmological significance of comets. NASA developed a technology spacecraft, Deep Space 1 (DS1) which flew past P/Borrelly in mid-2001 after completing its technology evaluations. The Stardust mission, launched on February 7, 1999, will make the first attempt at serious cosmological study by bringing back a sample of cometary dust (from an encounter with P/Wild 2 on January 2, 2004) to Earth on January 15, 2006. Using the full panoply of instruments available in Earth laboratories, from electron microscopes to particle accelerators, scientist will be able to determine the isotopic and mineralogical composition of comets and the temperature and pressure conditions in the early solar system. On the operational side, the nucleus of P/Wild 2 will be imaged and the amount, size, and atomic composition of the dust, that flows from it, determined by two other instruments. Other small body spacecraft under construction include Contour, Deep Impact, Rosetta, and the recently awarded Discovery mission, DAWN. The next decade should bring great advances in mankind's knowledge of both small bodies and the solar system.

Last Updated: November 26, 2003
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