For years, scientists have been trying to solve what they call the "Mystery of the Missing Sinks.''
"Humans dump about 9 million tons of carbon daily into the atmosphere, but only half stays there,'' said David Crisp, principal investigator for NASA's Orbiting Carbon Observatory.
"We don't know where the other half is going,'' said Crisp, who's based at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
To solve the mystery, NASA and the Japan Aerospace Exploration Agency are sending up complementary scientific satellites.
The two spaceships will circle the Earth on overlapping paths, more than 400 miles high, analyzing plumes of CO2 rising and falling through the air. (CO2 contains two atoms of oxygen for every atom of carbon.)