A small, powerful University of Colorado at Boulder instrument will fly on NASA's MESSENGER mission, slated for launch Aug. 2 from Cape Kennedy, Fla., to probe Mercury's searing surface, oddball atmosphere and bizarre magnetic field.
MESSENGER will be only the second mission to visit the tiny planet, said Laboratory for Atmospheric and Space Physics Director Daniel Baker. Baker and Senior Research Associate William McClintock are co-investigators on the MESSENGER mission. McClintock led the development of LASP's $8.7 million Mercury Atmospheric and Surface Composition Spectrometer, or MASCS, designed and built at CU-Boulder and one of seven scientific instruments on the spacecraft.
"Studying Mercury's surface, tenuous atmosphere and magnetic field are a key to understanding the evolution of the inner solar system, including Earth," said Baker. "It is the least explored planet in the inner solar system, so we are anxious to get back."
The only other time Mercury was visited by spacecraft was during 1974 and 1975, when NASA's Mariner 10 spacecraft made three flybys and mapped roughly 45 percent of the planet's rocky surface at the time. "The Mariner 10 mission and subsequent ground-based observations have raised additional questions that the MESSENGER team would like to answer," said Baker.
Some intriguing questions that MASCS will address involve the mineral composition of Mercury's surface, the distribution of gases in its atmosphere and the workings of its comet-tailed sodium gas cloud. Others include whether the 3,000-mile-in-diameter planet has a solid or molten core and whether there have ever been volcanoes on its surface, which reaches daytime temperatures of more than 800 degrees Fahrenheit.
Managed by Johns Hopkins University's Applied Physics Laboratory for NASA, MESSENGER involves about 20 scientists. Sean Solomon of the Carnegie Institution in Washington, D.C., is the chief MESSENGER scientist.
More than three years in development at CU-Boulder, MASCS weighs roughly 7 pounds, said LASP's Mark Lankton, program manager for the instrument. Although it is nearly three times as light as the highly successful UVIS instrument package that LASP scientists used recently to image the rings of Saturn on the Cassini mission, "the MASCS instrument is comparable in power," he said.
According to McClintock, geochemists, geophysicists, geologists and atmospheric scientists involved with MESSENGER will be working closely to link processes between the planet, its magnetic field, atmosphere and solar wind. "One raging controversy is whether Mercury ever had volcanoes," he said.
In addition, ground-based observations since Mariner 10 have determined that Mercury is enveloped in a huge, comet-like sodium cloud. "There has to be a mechanism to replenish this cloud," said McClintock. "But we won't know what it is until after the spacecraft reaches orbit."
Radar studies also show a high reflectivity near Mercury's poles hinting that some permanently shadowed craters may contain some form of water ice. "Determining the nature of those deposits is a primary science goal for MESSENGER," said McClintock.
Baker, a space physicist, is particularly interested in the magnetic field of Mercury and its interaction with the strong solar wind. Scientists have believed the core of this rocky planet should have solidified by now. "We are puzzled over Mercury's relatively strong magnetic field, which should require a liquid or molten core like that on Earth," said Baker.
There also is evidence for small solar "sub-storms" in Mercury's atmosphere, said Baker. "We are interested in how the planet gets energy from the solar wind into the magnetosphere, and would like to see if charged particles are crashing from the atmosphere onto the planet's surface and heating it."
Lankton said the 13-day launch window for MESSENGER beginning Aug. 2 is only 11 seconds per day. In addition, the 1.2-ton spacecraft has to fly past Earth once, Venus twice and Mercury three times to attain Mercury orbit. "From a technical standpoint, it's more difficult to swing by Earth a year from now than to dock with the space station," said Lankton.
The circuitous route of the spacecraft to attain Mercury orbit -- a 4.9 billion mile journey requiring more than seven years and 13 loops around the sun -- forced engineers to miniaturize instruments.
"All of the instruments on MESSENGER had to be extremely light, which stretched our imaginations and creativity," Lankton said. "We have learned a lot, and wound up getting a lot of bang for our buck. I've been involved in a number of missions over my career, and working on MESSENGER is the most fun I have had."
The spacecraft is equipped with a large sunshield and heat-resistant ceramic fabric, since Mercury is about two-thirds of the way nearer to the sun than Earth and is bombarded with 10 times the solar radiation. "MESSENGER essentially will be on a huge rotisserie, with the sun on one side and the hot planet on the other," Baker said.
Unlike many planetary missions, MESSENGER is tailored so that multiple instruments contribute complementary data to answer key science questions, said Baker. "We are pushing the envelope, and Mercury no doubt will surprise us in many ways."
Boulder scientist Clark Chapman of the Southwest Research Institute also is a co-investigator on the MASCS experiment. In addition, Starsys Research of Boulder built the pivot motor for the Mercury Dual Imaging System instrument package on the MESSENGER spacecraft.
Data from MESSENGER will be sent to NASA's Deep Space Network satellites, then to the Applied Physics Laboratory at Johns Hopkins and finally to the LASP facility in CU's Research Park. Baker expects dozens of CU-Boulder undergraduate and graduate students to be involved in data analysis in the coming years.