Käufl, Hans-Ulrich Infrared Instrumentation Department, European Southern Observatory, Garching bei München, Germany.
- Properties of comets
- Nagging questions before Deep Impact
- Additional Readings
The word “comet” is rooted in the ancient Greek word κoμ˙ητης (komētēs), literally, hairy star. Indeed, this wording is a concise synthesis of naked-eye observations, in line with our modern understanding. A comet consists of a small nucleus of volatile material. Close to the Sun, evaporation forms large tails of gas and dust. In the twentieth century comets were finally recognized as the most pristine remnants of the formation of our solar system, about 5 billion (5 × 109) years ago. Comets are heralds of the physical conditions during the formation of our solar system. Starting from the first orbit determination by Edmund Halley, modern comet research suffered from the paradox that many very specific details were known with high precision, while rather fundamental quantities, such as mass or detailed consistency of the nuclei, had to remain the subject of educated guessing. Fly-by spacecraft imagery, starting with the European Space Agency's Giotto passing comet 1P/Halley in 1986 at a distance of 5000 km (3000 mi), is spectacular, but most basic questions can be addressed only by spacecraft directly encountering the nuclei of comets.
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