The Solar Wind Concentrator is a special instrument built by a team at Los Alamos National Laboratory to enhance the flow of solar wind onto a small target to make possible oxygen and nitrogen measurements. Shown here, the target section of the concentrator, which produced essential samples of nitrogen and oxygen. Photo: Los Alamos National Laboratory |
Two
papers in Science report the
first oxygen and nitrogen isotopic measurements of the sun, demonstrating that
they are very different from the same elements on Earth. These results were the
top two priorities of NASA’s Genesis
mission, which was the first spacecraft to return from beyond the Moon,
crashing in the Utah
desert in 2004 after its parachute failed to deploy during re-entry.
Most
of the Genesis payload
consisted of fragile solar-wind collectors, which had been exposed to the solar
particles over a period of two years. Nearly all of these collectors were
decimated during the crash. But the capsule also contained a special instrument
built by a team at Los Alamos National Laboratory to enhance the flow of solar
wind onto a small target to make possible oxygen and nitrogen measurements. The
targets of this Solar Wind Concentrator survived the crash and eventually yielded
today’s solar secrets.
“Genesis is the biggest comeback mission
since Apollo 13,” said Roger Wiens, a Los Alamos National Laboratory
physicist and Genesis flight
payload lead. “Everyone who saw the crash thought it was a terrible
disaster, but instead the project has been fully successful, and the results
are absolutely fascinating.”
The
results provide new clues to how the solar system was formed. Oxygen and
nitrogen samples collected from various meteorites, as well as nitrogen sampled
in lunar soil and in the Jupiter atmosphere by the Galileo probe, vary
significantly from that on Earth by cosmochemical standards: 38% for nitrogen
and up to 7% for oxygen. With the first solar wind samples in hand, showing the
early sun’s composition, scientists can begin the game of determining where
Earth’s different O and N came from.
“For
nitrogen, Jupiter and the sun look the same,” said Wiens. “It tells
us that the original gaseous component of the inner and outer solar system was
homogeneous for nitrogen, at least. So where did Earth gets its heavier
nitrogen from? Maybe it came here in the material comets are made of. Perhaps
it was bonded with organic materials.”
For
oxygen, the evidence points toward a different astrophysical mechanism called photochemical
self-shielding, which the
authors believe modified the composition of space dust before it coalesced to
form the planets, including Earth. According to the article, the Sun shows an
enrichment of pure 16O relative to Earth instead of differences in 16O, 17O,
and 18O that are proportional to their atomic weight or some other mixture that
doesn’t show exclusive enrichment of a single isotope. This unique arrangement
strongly favors the self-shielding theory, in which solar UV radiation was
responsible for uniformly enhancing the two rarer isotopes, 17O and 18O, in the
terrestrial planets.
The Science papers are titled “A
15N-poor isotopic composition for the solar system as shown by Genesis solar
wind samples” and “The oxygen isotopic composition of the Sun
inferred from captured solar wind.” Wiens is among several collaborating
authors on both papers, which together are cover stories for this issue. Other
LANL coauthors, Beth Nordholt and Ron Moses, along with former LANL scientist
Dan Reisenfeld, were all part of the team to develop and fly the Solar Wind
Concentrator that provided the samples for the studies reported in Science.
And
now that some of the particles flowing past Earth from the sun are in hand,
“It’s going to make a mission to a comet all the more interesting,”
Wiens said.
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