From: Roger Greenway, ENN
Published July 3, 2014 06:32 AM

What are comets?

Scientists have speculated for centuries about comets. Why do the become visible on an irregular interval? Why does the tail always point away from our sun? What are comets made of? Are they balls of ice, or more like an asteroid?

Now NASA may finally get some concrete answers with a current mission that will land on a comet later this year!


Comet 67P/Churyumov-Gerasimenko is releasing the Earthly equivalent of two glasses of water into space every second. The observations were made by the Microwave Instrument for Rosetta Orbiter (MIRO), aboard the European Space Agency's Rosetta spacecraft on June 6, 2014. The detection of water vapor has implications not only for cometary science, but also for mission planning, as the Rosetta team prepares the spacecraft to become the first ever to orbit a comet (planned for August), and the first to deploy a lander to its surface (planned for November 11).

"We always knew we would see water vapor outgassing from the comet, but we were surprised at how early we detected it," said Sam Gulkis, principal investigator of the MIRO instrument at NASA's Jet Propulsion Laboratory in Pasadena, California. "At this production rate, comet 67P/Churyumov-Gerasimenko would fill an Olympic-size swimming pool in about 100 days. But, as the comet gets closer to the sun, the gas production rate will increase. With Rosetta, we have an amazing vantage point to observe these changes up close and learn more about exactly why they happen."

MIRO first detected water vapor from the comet when the Rosetta spacecraft was about 217,000 miles (350,000 kilometers) away from it. At the time, comet 67P/Churyumov-Gerasimenko was 363 million miles (583 million kilometers) from the sun. After the initial June 6 discovery, water vapor was also detected every time the MIRO instrument was pointed toward the comet. Observations are continuing to monitor variability in the production rate, and to determine the global gas production rate, as a function of its distance from the sun. The gas production rate that MIRO determined provides scientists a measure of the evolution of the comet as it moves both toward, and then away, from the sun. The gas production rate is also important to the Rosetta navigation team controlling the spacecraft, as this flowing gas can alter the trajectory of spacecraft.

"Our comet is coming out of its deep-space slumber and beginning to put on a show for Rosetta's science instruments," said Matt Taylor, Rosetta's project scientist from the European Space Agency's Science and Technology Centre in Noordwijk, The Netherlands. "The mission's engineers will be using this MIRO data to help them plan for future mission events when we are operating in close proximity to the comet's nucleus."

Rosetta is currently about halfway between Mars and Jupiter, 261 million miles (420 million kilometers) from Earth and 354 million miles (569 million kilometers) from the sun. Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in-situ observations, the Rosetta mission should be a key to unlocking the history and evolution of our solar system, as well as answering questions regarding the origin of Earth's water and perhaps even life. Rosetta will be the first mission in history to rendezvous with a comet, escort it as it orbits the sun, and deploy a lander to its surface.

Artist's impression of the Rosetta orbiter at comet 67P/Churyumov-Gerasimenko. The image is not to scale. The Rosetta spacecraft measures 105 feet (32 meters) across including the solar arrays, while the comet nucleus is thought to be about 2.5 miles (4 kilometers) wide. Credit ESA/ATG Medialab

Read more at NASA.

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