In the distant past, people were both awed and alarmed by comets, perceiving them as long-haired stars that appeared in the sky unannounced and unpredictably. Chinese astronomers kept extensive records for centuries, including illustrations of characteristic types of comet tails, times of cometary appearances and disappearances, and celestial positions. These historic annals are a valuable resource for later astronomers.
We now know that comets are leftovers from the dawn of our solar system around 4.6 billion years ago and may yield important clues about the formation of our solar system. They might have brought water and organic compounds, the building blocks of life, to the early Earth and other parts of the solar system. As comets consist mostly of ice coated with dark organic material, they have been referred to as "dirty snowballs." Carey Lisse, a planetary astronomer at Johns Hopkins University’s Applied Physics Laboratory, highlights what we know about comets and their impact on the solar system and what we hope to find out.
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The Grand Tour of the Solar System series treks to the Sun and the four inner terrestrial planets before traveling outward to the asteroid belt, four Jovian planets, and beyond. At each session, a professional astronomer explores a solar system body, presenting the latest research.
Following the talk and a question-and-answer period, Peter Plavchan, a professor of physics and astronomy at George Mason University, brings that night’s sky right into participants’ living rooms via remote control of the university observatory, weather permitting.
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