All seven scientific instruments worked flawlessly when NASA's MESSENGER spacecraft made its first flyby of Mercury after a journey of more than 2.2 billion miles and three and a half years. The event that took place on January 14, 2008 produced a stream of surprises that amazed and delighted the science team. The 1,213 mages conclusively show that the planet is a lot less like the moon than many previously thought, with features unique to this innermost world. The puzzling magnetosphere appears to be very different from what Mariner 10 discovered and first sampled almost 34 years ago.
"This flyby allowed us to see a part of the planet never before viewed by spacecraft, and our little craft has returned a gold mine of exciting data," stated Sean Solomon, principal investigator and the director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. "From the perspectives of spacecraft performance and maneuver accuracy, this encounter was near-perfect, and we are delighted that all of the science data are now on the ground....."
MESSENGER has shown that Mercury is even more different from the Moon than was originally thought. The tiny spacecraft discovered a unique feature that the scientists dubbed "The Spider." This type of formation has never been seen on Mercury before, and nothing like it has been observed on the Moon. It is in the middle of the Caloris basin and consists of over a hundred narrow, flat-floored troughs (called graben) radiating from a complex central region. "
Unlike the Moon, Mercury also has huge cliffs or scarps, structures snaking up to hundreds of miles across the planet's face, tracing patterns of fault activity from early in Mercury's -- and the solar system's -- history. The high density and small size of Mercury combine to provide a surface gravity about 38 percent that of Earth and almost exactly the same as that of Mars, which is some 40 percent larger than Mercury in diameter (2.7 times Mercury's volume). Because gravity is stronger on Mercury than on the Moon, impact craters appear very different from lunar craters; material ejected during impact on Mercury falls closer to the rim and many more secondary crater chains are present.
"We have seen new craters along the terminator on the side of the planet viewed by Mariner 10 where the illumination of the MESSENGER images revealed very subtle features. Technological advances that have been incorporated in MESSENGER are effectively revealing an entirely new planet from what we saw over 30 years ago," said Science Team co-investigator Robert Strom, professor emeritus at the University of Arizona and the only member of both the MESSENGER and Mariner 10 science teams.
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