The U.S. space agency, NASA, is preparing to launch a spacecraft to catch pieces of the sun and return them to Earth for study. The mission is called Genesis, because scientists say the ejected solar particles the satellite collects will tell them the composition of the cloud that gave birth to our solar system.
Four and a half billion years ago, the theory goes, a massive swirling molecular cloud collapsed to form our solar system. Now, NASA is seeking samples of that primordial nebula. The chief scientist for the mission Donald Burnett says: "The goal of the Genesis mission is to measure the chemical composition of the solar nebula, the starting composition out of which both the sun and all of the planets formed."
To do this, NASA is sending the 636-kilogram Genesis spacecraft on a 16 month journey to orbit 1.5 million kilometers from Earth. There, Genesis will open like clam and spend a year and a half gathering charged atomic particles streaming from the sun's outer atmosphere, or corona, in the so-called solar wind. "The material from which the planets formed is now stored for us in the outer surface layers of the sun," Mr. Burnett explains. "Solar matter in the corona is escaping from the sun. It is not gravitationally bound. So all you have to do is get little beyond earth and catch the solar wind."
The amount of solar matter Genesis will collect is infinitesimal - just 10 to 20 millionths of a gram of matter, the weight of a few grains of sand. That is miniscule compared to the hundreds of kilograms of moon rocks gathered by U.S. Apollo astronauts in the 1970s, the last time original solar system samples were picked up and returned to Earth. But a geochemist from the Field Museum in Chicago, Meenakshi Wadwa, says the wisps of solar samples will be sufficient to measure the chemistry of the original nebula and test current assumptions about the processes that formed the sun, planets, and other objects.
To do so, however, requires planetary scientists to develop new, more precise analytical procedures than for the moon rocks. "In fact, we are already doing that," Ms. Wadwa says. "We are developing new, ever more sensitive techniques, the precision limits of which are dictated not merely by the instrument hardware but actually by the number of atoms that can be counted in the sample itself."
Scientists have long studied meteorites to infer the ancient nebula's composition because they are thought to be among the first solids that formed. But Ms. Wadwa says that they - like the moon rocks - provide only clues. Another approach measures the wavelengths from the sun's corona because each element gives off a characteristic light. But the geochemist says this way of estimating abundances of elements may be off as much as 20 percent. "So until we actually have a sample of the sun that we can actually analyze in our laboratories with high precision and get some very precise chemical information for it, we cannot be sure of the exact composition of our solar system," Ms. Wadwa says.
Five Apollo moon missions collected solar wind on sheets of aluminum foil for periods up to 45 hours between 1969 and 1972. But the Genesis samples are expected to be more sterile and complete because its ceramic tile collectors are cleaner than the foil and will be bombarded far longer.
The return of the particles will be dramatic. The spacecraft will deorbit in September, 2004. Its solar sampling capsule will crash through the atmosphere and parachute down over the western U.S. state of Utah.
Genesis project manager Chester Sasaki says a helicopter will grab it in mid-air and return it for analysis at NASA's Johnson Space Center in Houston, Texas. "Our engineering mission ends there. Our real mission - the mission of science - starts there," Mr. Sasaki says.