News and commentary about the Great Frontiers

ISS007-E-10807 (21 July 2003) --- This view of Earth's horizon as the sunsets over the Pacific Ocean was taken by an Expedition 7 crewmember onboard the International Space Station (ISS). Anvil tops of thunderclouds are also visible. Credit: Earth Science and Remote Sensing Unit, NASA Johnson Space Center

Image Credit: ISS007-E-10807 (21 July 2003) – Earth Science and Remote Sensing Unit, NASA Johnson Space Center

From Giotto to Stardust – 20 Years of Comet Exploration



The modern robotic investigation of comets began with a spacecraft from the European Space Agency (ESA) named Giotto. Giotto captured in 1986 the first close-up images of a cometary nucleus and a wealth of other data. ESA is marking the 20th anniversary of Giotto’s successful flyby of Comet Halley on the eve of a NASA press conference regarding science results from the Stardust mission. Twenty years after Giotto, our knowledge about comets, those cold remnants of our solar system’s formation, is undergoing a revolution.

By 1986, six spacecraft were ready for an unprecedented scientific investigation of Comet Halley as it returned to the inner solar system. Due to budget cuts, NASA’s ambitious plans to study Comet Halley were reduced to long distance observations using the International Sun-Earth Explorer 3 (ISEE-3) spacecraft (renamed Interplanetary Comet Explorer (ICE)) already in operations. Meanwhile, after flying by Venus, the Russian Space Research Institute (IKI) spacecrafts VEGA-1 and VEGA-2 were directed toward Comet Halley. Japan’s Institute of Space and Aeronautical Science, which in 2003 became part of Japan Aerospace Exploration Agency (JAXA), used their existing SAKIGAKE (MS-T5) spacecraft for long distance observations and launched SUISEI (PLANET-A), a spacecraft specifically built to study Comet Halley. ESA’s Giotto spacecraft rounded out “Halley Armada.”

Named after the painter of “Adoration of the Magi” which includes a representation of a comet widely believed to be based on Comet Halley, Giotti flew closer to the comet than any of the other spacecraft. The dramatic images and other data returned revealed that Halley was not a round and icy “snow ball” as expected but instead an irregular and dark “dirt ball.” Jets of ice and gas volatiles erupted from the sun-heated surface of the nucleus, creating the bright and extensive coma and tail visible from the Earth.

This first close-up look at a comet revolutionized our understanding of the objects. Since then, several other robotic missions have provided even more highly detailed images and data. Tomorrow, scientists will hold a press conference to report the first science results from their analysis of the first pristine cometary material returned to Earth for extensive analysis. What we learn from the Stardust mission will no doubt radically advance our knowledge.

In twenty years, from the first close-up images of a comet to the first cometary material returned for study, we have learned more about the formation of our solar system and perhaps even the history of life on Earth than in all the thousands of years of comet observation that preceded the Space Age. From Giotto to Stardust in the blink of an eye.

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