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).
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.
Go to the next chapter or Return
to the table of contents
November 20, 1996
Authors: Dave Dooling, B.L.
Giles
Curator: Linda Porter
NASA Official: Gregory S.
Wilson