The color image was generated by combining three separate images taken through wide-angle camera filters sensitive to light in different wavelengths. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in the single-filter, black-and-white images.
A new view
A NASA mission maps geologic features never before studied on Mercury
The first photos of planet Mercury's hidden side from the NASA spacecraft Messenger were "phenomenal," revealing geologic features scientists had never seen before, says a University of Hawaii planetary researcher.
Scientists were astounded by what they saw in the 1,213 photos taken on Messenger's first flyby of Mercury Jan. 14, said Jeffrey Gillis-Davis, participating scientist on the NASA Messenger science team.
Based on what was found on a previous mission 34 years ago, "we thought Mercury might just be boring," he said.
The Mariner 10 mission mapped about 45 percent of one side of Mercury, and scientists had the impression that the planet was similar to Earth's moon, he said.
"But when we look at this new Messenger data, it's a whole new planet. We are seeing things we've never seen before, such as a spider image. We haven't seen anything like that on any other planets."
"The Spider," as scientists call it, looks like a large crater in the center with troughs radiating out from it.
"We're not quite sure of the timing on that," Gillis-Davis said. "It's almost a chicken-and-egg thing," he said, explaining that the faults, known as grabens, are younger than the crater.
With planetary geology, Gillis-Davis said, scientists try to find similar features on Earth they can study up close. He does not know of anything like the spider pattern on Earth, but said studies of lava lakes that form at times at Kilauea on the Big Island might provide insights as to what is going on with Mercury.
"Where you have magma that starts to cool, actually it will form a cooled sheet of rock, but because there is a lot of action going on below the surface, it can rip the cooled surface."
This image shows Mercury's surface as seen from a low viewing angle off the limb of the planet on the right side of the image. The cratered terrain is on the side of Mercury unseen by spacecraft prior to this Messenger flyby.
There is evidence that Mercury is shrinking as it ages, with faults as long as 750 miles, Gillis-Davis said. "That shows the planet has decreased its radius a lot," he said, explaining as the core of the planet cools and contracts, faults develop from compression.
While Mercury has been compared to the Earth's grayish moon, Messenger's sophisticated cameras reveal it is more colorful with "some evidence or suggestions of volcanism," Gillis-Davis said.
The photos show that, unlike the moon, Mercury has huge cliffs with structures extending hundreds of miles across the surface and impact craters that appear different from lunar craters.
Gillis-Davis said one of his jobs is to study the different geological features and determine whether they were caused by volcanism, crater impact or something else.
"It's a little early to tell, but I think, looking at the Mariner 10 data and this new data, it looks a little more favorable for volcanism," he said.
Mercury has been a mystery to scientists because it is the smallest and densest of the terrestrial planets (others are Venus, Earth and Mars). It is also closest to the sun, which made it difficult to send a spacecraft there until technology advanced, Gillis-Davis said.
He was with the team monitoring Messenger's arrival at Mercury from mission control at Johns Hopkins University Applied Physics Laboratory in Maryland.
"It's a fun job," he said. "We're getting more pieces of the puzzle, and with a greater amount of information we're getting from Messenger, we'll be able to put answers to these long-standing questions (about Mercury) the last 33 years."
Thirty or 40 scientists are working on the data and planning for the next Messenger flyby in October, he said. Another flyby will occur in September 2009, and Messenger will go into orbit around the planet in 2011.
"It will be like Christmas every 12 hours," said the UH planetary researcher.