Positive Charge for Rosetta

Illustration of Rosetta sitting on comet surface. The banner image, taken by ESA’s Rosetta comet-chaser spacecraft, shows the Earth-Moon system from a distance of 70 million kilometers (42 million miles).
Credit: ESA

The Ion and Electron Spectrometer (IES), one of three NASA instruments aboard the European Space Agency (ESA) Rosetta comet orbiter, successfully underwent an intensive commissioning exercise that qualified it for operation during the next decade.

"IES will perform very high-resolution measurements of the solar wind and the comet’s ionized gas environment with exceptionally low mass (1.1 kg) as compared to previous instruments of its type," says IES Principal Investigator Dr. Jim Burch, vice president of the Space Science and Engineering Division at Southwest Research Institute. "We eagerly anticipate that IES and the other Rosetta instruments will contribute to great strides in our understanding of comets and the origin of the solar system."

The spectrometer is flying aboard Rosetta with another SwRI-developed instrument, the Alice ultraviolet imaging spectrometer, which successfully passed its checkout in April 2004. A lander and 14 other instruments complete the suite of science investigations flying aboard the first mission ever to orbit a comet. The target for Rosetta is Comet 67P/Churyumov-Gerasimenko, which was discovered by two Soviet astronomers in 1969.

The approximately 4 kilometer cometary nucleus to be landed upon by the Rosetta and its harpooning landing hooks
Credit: Hubble

Despite its small size, laboratory tests showed the spectrometer achieves sensitivity comparable to instruments weighing five times more. IES is designed to measure the solar wind, detect ions that are sputtered off the comet’s nucleus, measure photoelectrons emitted from the surface and determine how ions are funneled into the comet’s ion tail.

Funded by NASA for flight aboard Rosetta, IES will help determine how comets respond to bombardment by the solar wind. The orbiter will rendezvous with the comet near the orbit of Jupiter, where the comet will be like a frozen snowball with no atmosphere or tail. Rosetta will then continuously orbit the comet for three years as it moves closer to the Sun and develops an atmosphere (the coma), along with a dust tail and an ion tail. During the mission an excursion down the ion tail will take place, and the lander will be dropped off on the surface.

The Rosetta spacecraft launched in February 2004, and the mission is expected to end in 2015. Prior to reaching the comet, Rosetta will make close flybys of the Earth (twice), Mars and two asteroids, with IES contributing to the associated science investigations.

After its lander reaches Comet 67P/Churyumov-Gerasimenko, the main spacecraft will follow the comet for many months as it heads towards the Sun. In 10 years time, it will have travelled distances of over one thousand million kilometers (600 million miles) from Earth, and about 800 million kilometers (480 million miles) from the Sun, to meet it cometary destination.

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This artist’s impression shows the Rosetta Lander anchored to the comet’s surface with instruments, legs and solar panels. Credit: ESA 2001. Illustration by Medialab

Past missions that have flown by a comet have been: NASA’s ICE mission in 1985, the two Russian Vega spacecraft and the two Japanese spacecraft Suisei and Sakigake that were part of the armada that visited Comet Halley in 1986; NASA’s Deep Space 1 flew by Comet Borelly in 2001 and NASA’s Stardust, which flew by Comet Wild 2 earlier in January and has captured samples of the comet’s coma to be returned in 2006. On Valentine’s Day, 2001, the Near-Shoemaker spacecraft successfully landed on the asteroid, Eros. Its remarkable journey–to soft-land on a peanut shaped asteroid about 176 million kilometers (109 million miles) from Earth, prompted Andrew Cheng, NEAR Project Scientist, to note: "On Monday, 12 February 2001, the NEAR spacecraft touched down on asteroid Eros, after transmitting 69 close-up images of the surface during its final descent. Watching that event was the most exciting experience of my life."



Related Web Pages

Harpooning a Comet
Comet Cruise Glimpses Earth
Extraterrestrial Capture
Reading Rosetta
Coma for Halley’s Comet