1. Sodium glow reveals Mercurys comet-like tail
Mercurys gravity is too weak to hold a permanent atmosphere. Thus, when atoms are evaporated from the surface by solar photons or other energetic processes, some of these atoms are accelerated to escape velocity by solar radiation pressure. The neutral components of this escaped gas form a comet-like tail that points away from the Sun. Baumgardner et al. study this tail by observing the bright yellow-orange light emitted by the sodium atoms in the tail. The authors find that the tail, previously detected out to 15 times the radius of Mercury, actually extends more than 100 times that distance, or 2.5 million kilometers (1.6 million miles) away from the planet. Further analysis shows that the time of flight for the sodium atoms in the tail, from the time they are sputtered from the surface to when they reach the tails maximum observed extent, is approximately 15 hours. The authors note that although sodium atoms compose only a small fraction of the atoms sputtered from the surface, the bright emission from the sodium can serve as a tracer for other constituents invisible to ground-based observers.
Title: Imaging the sources and full extent of the sodium tail of the planet Mercury
Authors: Jeffrey Baumgardner, Jody Wilson, and Michael Mendillo: Center for Space Physics, Boston University, Boston, Massachusetts, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL032337, 2008; http://dx.doi.org/10.1029/2007GL032337
2. Satellite tracks summer Arctic ice motion
For more than 15 years, daily sea ice drifts in winter (October through May) have been monitored with satellite passive microwave sensors, including the 89-GHz channel of the Earth Observing Systems Advanced Microwave Scanning Radiometer (AMSR-E) on the Aqua satellite. Noting that reliable estimates of summer
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American Geophysical Union