Researchers from Los Alamos National Laboratory and other institutions today reported in Science magazine the first measurements of one way that happens. Their measurements and analysis of data from the POLAR satellite provide insight into one of the many byways through which water and other materials leave and enter Earth's atmosphere, and should improve models of how the atmospheres of Earth and other planets evolve.
Using a unique instrument to reduce electrical interference from the satellite, the team took the first accurate high-altitude measurements of the so-called polar wind - charged gas or plasma escaping from Earth and its ionosphere through the poles, like the charged gases from the sun's corona that make up the solar wind. Plasmas from Earth and the sun are trapped and flow along Earth's magnetic field lines, or magnetosphere, and make up such spectacular electrical phenomena as auroras.
The research team proved that the polar wind is one mechanism by which the atomic constituents of water vapor and other atmospheric gases are dragged outward from the ionosphere and spiral along the planet's magnetic field lines. Sunlight breaks the water into ionized hydrogen and oxygen gases in the upper atmosphere.
"We know that planetary atmospheres evolve, and we have models of that evolution, but this is the first time we've observed this particular evolutionary mechanism at high altitudes," said Los Alamos physicist Beth Nordholt. "This gives us a look at the cutting edge of atmospheric evolution and the dynamic way material flows from Earth into space, contributing significantly to Earth's space weather."
Their measurements of the hydrogen and oxygen plasmas along the POLAR satellite's orbit - ranging from 7,000 to 35,000 miles above the poles - imply that roughly 1,000 gallons of water leaves Earth's atmosphere every day.
Lead author of "High Altitude Observations of the Polar Wind" is Tom Moore of NASA Marshall Space Flight Center in Huntsville, Ala., who now works at NASA Goddard Space Flight Center, Greenbelt, Md. Co-authors are Nordholt, Michelle Thomsen and David McComas of Los Alamos; Mike Chandler, Paul Craven and Barbara Giles, also of Marshall Space Flight Center; Craig Pollock, Jim Burch, Dave Young and Hunter Waite of the Southwest Research Institute in San Antonio, Texas; Jean-Jeacques Berthelier of the Centre d'Etudes Terrestraire et Planetaire in St. Maur-des-Fosses, near Paris, France; Weldon Williamson and R. Robson of the Hughes Research Laboratories in Malibu, Calif.; and Forrest Mozer of the University of California, Berkeley.
The flow of charged gases from Earth is extremely diffuse and hard to detect. To complicate matters, previous space instruments couldn't get accurate readings due to electrical interference from the spacecraft that carried them. That's why the team designed two instruments for the POLAR satellite: the Plasma Source Instrument and the Thermal Ion Dynamics Experiment.
When photons from the sun strike spacecraft, they drive off electrons and give the entire craft a slight positive charge, which keeps positively charged gases from reaching the craft and its measuring instruments. The Plasma Source Instrument spews out low-energy ions of xenon gas that flood the outside of the POLAR spacecraft, effectively neutralizing it and allowing the TIDE instrument to detect the energies and masses of ions flowing into it.
The TIDE instrument has seven large apertures that give it high sensitivity in identifying and measuring charged hydrogen, helium, oxygen and other heavier ions from the ionosphere, along with helium from the solar wind.
"The contribution of ionospheric gases to the polar wind has been predicted for a long time, but since they hadn't been measured before, there was no way to incorporate them accurately into atmospheric evolution models," Nordholt explained.
Data collected by the team indicate that hydrogen plasmas are flowing faster than predicted by theory, and that oxygen plasmas are hotter and more plentiful than predicted. Additional research will be needed to understand why, but Nordholt said the success of the two instruments will help greatly in the design of future research missions.
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and Washington Group International for the Department of Energy's National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.