How High Does the Fountain spray?
We know from earlier satellites and sounding rockets
that light atoms and ions - including hydrogen, helium, oxygen, and nitrogen
- flow upward into low pressure regions at high altitudes, much as the solar
wind flows away from the sun. We also know that a planetary-scale fountain
of heavy ions rises from the auroral oval around local noon (in effect the
Earth rotates under the spout).
How High Does the Fountain Spray?
It spews an average of 50 tons of plasma per day against the gravitational pull of Earth, the most prolific "leak"of atmosphere from the Earth (don't worry - it's still so small that we are not in danger of running out of air for another few billion years).
The plasma fountain was discovered by using data from MSFC's Retarding Ion Mass Spectrometer on the Dynamics Explorer spacecraft which explored the polar regions to about 4 Earth radii (25,600 km [16,000 miles]) in the 1980s. To explore the source of this fountain - both ions and electrons - NASA on Jan. 25, 1995 launched SCIFER - Sounding of the Cleft Ion Fountain Energization Region - from Andoya, Norway, into the fountain's plasma heating region [shown in the figure]. SCIFER set an altitude record, soaring to 1,450 km (870 mi.). This let scientists assay the fountain at the start so we will know better what might be in the plume at high altitude.
Initial results from the SCIFER mission became the cover story of the July 1, 1996, issue of Geophysical Research Letters (23:14, 1865-1890; seven papers in all).
But this leaves us with the question of what happens to the plasma. Is it trapped in space above the poles? Or does it continue outward, down the magnetic field lines into the magnetotail where it can feed space storms that come back the Earth?
Because the plasmas could be expected to lose energy and to spread out as they moved farther from Earth, measurement of anything above the region explored by Dynamics Explorer would require instruments that could neutralize their own static buildup.
November 20, 1996
Authors: Dave Dooling, B.L. Giles
Curator: Bryan Walls
NASA Official: John M. Horack