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First Mercury orbiter could find ice near the sun

A mosaic of Mercury created from images taken by Mariner 10 during its approach on March 29,  1974
A mosaic of Mercury created from images taken by Mariner 10 during its approach on March 29, 1974  


By Richard Stenger
CNN

(CNN) -- NASA has given official approval to proceed with a mission to Mercury, an orbiting spacecraft that will study the rocky surface, sparse atmosphere and molten interior of the closet planet to the sun.

Known as MESSENGER, the spacecraft is scheduled for launch in 2004 for a yearlong orbit around the planet in 2009, according to NASA, which gave the green light for the $256 million mission on Friday.

Despite its proximity in the inner solar system, Mercury remains a considerable mystery to astronomers. Only one other spacecraft has visited the planet, Mariner 10, which mapped less than half of the mostly metal sphere during three flybys in 1974 and 1975.

Moreover, ground-based and satellite observatories have had little luck studying Mercury, which mostly hides behind the glare of the sun except for brief times around sunrise and sunset. The mighty Hubble Space Telescope avoids looking at the planet to prevent the sun from frying its sensitive camera eye.

 Mercury Fact Box
Diameter: 3032 miles
Length of day: 4222.6 (hours)
Average distance from sun:
36 million miles
Composition: Mostly iron
Average surface temperature:
333 degrees F
Number of moons: 0
Ring system: No
Global magnetic field? Yes

Source: NASA

To escape lethal burns from the sun, which is 11 times brighter on Mercury than Earth, MESSENGER will be equipped with sunscreen made from ceramic, similar to the material that protects the space shuttles.

NASA hopes the Mercury satellite can help answer riddles about the densest planet in the solar system: Why does it consist mostly of iron metal? Why is it the only inner planet besides Earth with a global magnetic field?

And perhaps most puzzling, why does the planet, where daytime temperatures can shoot above 850 degrees at the equator, appear to have ice in polar craters?

"We've had many exciting missions to Mars and Venus that yielded new theories about the processes that shaped the inner planets," said chief mission scientist Sean Solomon.

"And for 25 years now Mercury has clearly stood out as a place where major questions remain to be answered. Mercury is the last piece of the puzzle."







RELATED STORY:
RELATED SITES:
• NASA Home Page
• NASA Solar System Exploration Home Page

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