( dpa ) - The US space probe Messenger made its nearest approach Monday to Mercury during its three-year, 3.5-billion- kilometre journey to the rocky planet nearest the sun.
The website for the NASA mission showed a crescent view of Mercury, snapped Sunday as Messenger was 760,000 kilometres from the planet and heading to its close-up survey.
The probe is flying at 200 kilometres above the surface as it passes the planet to collect 1,200 photographs and other data from unknown regions. It's the first time in 33 years, since Mariner 10 flew past in March 1975, that an Earth probe has gotten that near to Mercury.
After the fly-by, Messenger is to have two more encounters with Mercury in October 2008 and September 2009 before special boosters are fired in March 2011 to put it into orbit around Mercury for at least a year.
In Roman mythology, Mercury was the fleet-footed messenger of the gods, and scientists hope to receive clear dispatches with new data about the planet's atmosphere, planetary elements and magnetic fields.
The findings of the current mission could shed light on fundamental scientific questions about Mercury's formation and evolution and "could open new theories and answer old questions in the study of the solar system," Messenger mission officials said.
The first set of fly-by data from Mercury's cratered, rocky surface is to begin transmission about 1700 GMT Tuesday.
The 1.2-ton spacecraft, designed and built by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, has travelled 3.5 billion kilometres since launch.
Mercury's orbit comes within 77.3 million kilometres of Earth's path, but Messenger had to travel a long, looping tour of the inner solar system to get there. The probe had to orbit the sun at least four times and collect two gravity assists from loops around Earth and Venus.
The probe's specially designed ceramic shield was designed to protect it from temperature swings from 426 degrees Celsius to minus 217 degrees.
Among the mysteries NASA hopes to resolve is the nature of deposits languishing in the darkness of permanent shade inside craters at the planet's poles. Scientists say that the material looks like water but could also be sulphur.
The 427-million-dollar mission could expand knowledge about Mercury 's minimal atmosphere and its suspected molten metal core, a feature that distinguishes it from its closest planetary neighbours of Venus, Earth and Mars.
The Mariner 10 probe made three passes of Mercury in the 1970s, giving scientists their first information about the planet's magnetic field.
"Mariner 10 left us with more questions than answers," Orland Figueroa, head of solar system exploration at NASA, said before the 2004 launch of Messenger.