The spacecraft Messenger, launched by NASA in August, will travel for six-and-a-half years before it goes into orbit around the planet Mercury for a mission that's to last two days. Two Mercury days, that is—a day on the planet, from sunrise to sunset, being the equivalent of 176 days on Earth. Messenger's instruments will image Mercury's surface—including an entire hemisphere no spacecraft has previously seen—measure the planet's gravity and magnetic field, and collect data on the structure and composition of its crust. Are the outer portions of the planet's gigantic iron core still molten? Of what consequence to Mercury's geologic history were volcanic activity, tectonic faulting and the mighty impacts of objects from space? The evidence needed to answer these questions is more than 50 million miles away, and Messenger has been sent to close the distance.
On the team responsible for the pathbreaking mission is Thomas Watters, a geologist at the Smithsonian's Center for Earth and Planetary Studies (CEPS). Indeed, CEPS scientists regularly assist NASA with its exploration of the heavens. The geologists and geophysicists of CEPS, a research unit within the Smithsonian's National Air and Space Museum (NASM), use images and data from Earth-orbiting satellites and manned and robotic space missions to trace the geologic history of the planets in our solar system. They start from a base of expert knowledge about what they can observe close up (volcanism, flooding, cratering, tectonics and sand movement on Earth), and against that local evidence they read the evidence returned from the heavens.
In January 2004, NASA guided the Rover vehicles Spirit and Opportunity to the surface of Mars, where the two surpassingly capable robots took on the role of flesh-and-blood geologists. They will likely continue in that role for much of 2005, maybe longer. Another CEPS geologist, John Grant, helped plan the Rovers' activities and has contributed to the machines' remote operation. The robots have picked at the planet's surface and touched their instruments to odd boulders, gray bedrock and rounded pebbles that may hold clues to the history of water on Mars. With each mission, we're brought closer to knowing whether water existed on the planet long enough to have sustained some form of life. The inquiry will be advanced yet again in summer 2005, when NASA launches the Mars Reconnaissance Orbiter. On board will be the most capable camera ever lifted into space—as inquisitive as a spy satellite and powerful enough to resolve features less than a yard across on the planet's surface. A radar sounder on the Orbiter will let scientists probe beneath the surface, to depths of more than a half-mile, in search of geologic layering and possible ice deposits. And as the Orbiter scans the planet and peers through its crust, CEPS scientists Bruce Campbell and John Grant will be among the pioneering observers back on Earth.
Great science—achievements that move boundaries, as do the projects in which CEPS researchers participate—is the lifeblood of a great science museum. Of course, collections, whether of objects or of data, are essential too. But at NASM, as throughout the Smithsonian, the collections are presented to the public by scientists, historians and other professionals who can speak of them with authority because of their research experience. CEPS staff, for example, curate two galleries in NASM, one about the Earth, the other about the planets. The exhibitions invite visitors to adjust their minds to the vast stretches of geologic time, and to imagine what it's like to walk other worlds. The effort to be at home on those worlds is, in the end, an effort to be more at home on this one, to better understand, that is, how the Earth came to be—and came to support life. Clues to our history may be lodged on distant planets, just as elements of their history may be etched into ours. And with skills at once visionary and precise, CEPS researchers seek and read the clues.