Comet Hunter Closes in: Rosetta Can See its Quarry 'Sweat'

The European Space Agency's (ESA) Rosetta spacecraft is closing in on its asteroid "prey" and scientists are beginning to notice some nervous sweating. Rosetta and NASA-made instruments are already detecting water vapor dripping from the comet even 217,480 miles (~350 000 km) away.

Of course, the "sweating" comet in question, 67P/Churyumov-Gerasimenko, cannot actually feel fear as the Rosetta spacecraft continues to make chase. However, even in relatively "cold" space conditions 362 million miles (583 million km) from the Sun, ESA and NASA scientists have determined that the comet is releasing enough water to fill two small glasses of water every second.

"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, the instrument's principal investigator at NASA's Jet Propulsion Laboratory.

"At this rate, the comet 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 significantly," he added in a statement. "With Rosetta, we have an amazing vantage point to observe these changes up close and learn more about exactly why they happen."

This detection was first made by NASA's Microwave Instrument for Rosetta Orbiter (MIRO), which has detected water every day since the initial June 6 discovery, despite the fact that the comet is no longer leaving an extended dust trail called a coma - the standard consequence of a vaporizing stone and ice nucleolus as the comet draws closer to the Sun.

ESA mission operatives explain that while measuring the water vapor production rate can be interesting and important to science, it has a more practical application as well. Once Rosetta draws even closer to the comet, the outflow of gases may affect the craft's trajectory, making predicting out-flow rate a high priority.

"Our comet is coming out of its deep-space slumber and beginning to put on a show for Rosetta's science instruments," Matt Taylor, ESA's Rosetta project scientist, said in a statement. "Rosetta's engineers will also be using MIRO's observations to help them plan for future mission events when we are operating close to the comet's nucleus."

Rosetta was about 44,700 miles (~72,000 km) from 67P/Churyumov-Gerasimenko as of June 30. If all goes well, the craft should be a mere 62 miles (100 km) away from the comet by August 6 - the closest an observational craft has ever been to a comet.