Starship Asterisk*

Artist Rendering of the Genesis Spacecraft During Collection Phase [i](Credit: NASA/JPL-Caltech)[/i]

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Concentrator Target Being Disassembled at JSC Prior to Long-Term Nitrogen Storage Post-Return [i](Credit: NASA/JPL-Caltech/JSC)[/i]

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Researchers analyzing samples returned by NASA's 2004 Genesis mission have discovered that our sun and its inner planets may have formed differently than previously thought.

Data revealed differences between the sun and planets in oxygen and nitrogen, which are two of the most abundant elements in our solar system. Although the difference is slight, the implications could help determine how our solar system evolved.

"We found that Earth, the moon, as well as Martian and other meteorites which are samples of asteroids, have a lower concentration of the O-16 than does the sun," said Kevin McKeegan, a Genesis co-investigator from UCLA, and the lead author of one of two Science papers published this week. "The implication is that we did not form out of the same solar nebula materials that created the sun -- just how and why remains to be discovered."

The air on Earth contains three different kinds of oxygen atoms which are differentiated by the number of neutrons they contain. Nearly 100 percent of oxygen atoms in the solar system are composed of O-16, but there are also tiny amounts of more exotic oxygen isotopes called O-17 and O-18. Researchers studying the oxygen of Genesis samples found that the percentage of O-16 in the sun is slightly higher than on Earth or on other terrestrial planets. The other isotopes' percentages were slightly lower.

Another paper detailed differences between the sun and planets in the element nitrogen. Like oxygen, nitrogen has one isotope, N-14, that makes up nearly 100 percent of the atoms in the solar system, but there is also a tiny amount of N-15. Researchers studying the same samples saw that when compared to Earth's atmosphere, nitrogen in the sun and Jupiter has slightly more N-14, but 40 percent less N-15. Both the sun and Jupiter appear to have the same nitrogen composition. As is the case for oxygen, Earth and the rest of the inner solar system are very different in nitrogen.

"These findings show that all solar system objects including the terrestrial planets, meteorites and comets are anomalous compared to the initial composition of the nebula from which the solar system formed," said Bernard Marty, a Genesis co-investigator from Centre de Recherches Pétrographiques et Géochimiques and the lead author of the other new Science paper. "Understanding the cause of such a heterogeneity will impact our view on the formation of the solar system."

Data were obtained from analysis of samples Genesis collected from the solar wind, or material ejected from the outer portion of the sun. This material can be thought of as a fossil of our nebula because the preponderance of scientific evidence suggests that the outer layer of our sun has not changed measurably for billions of years.

"The sun houses more than 99 percent of the material currently in our solar system, so it's a good idea to get to know it better," said Genesis Principal Investigator Don Burnett of the California Institute of Technology, Pasadena, Calif. "While it was more challenging than expected, we have answered some important questions, and like all successful missions, generated plenty more."

Genesis launched in August 2000. The spacecraft traveled to Earth's L1 Lagrange Point about 1 million miles from Earth, where it remained for 886 days between 2001 and 2004, passively collecting solar-wind samples.

On Sept. 8, 2004, the spacecraft released a sample return capsule, which entered Earth's atmosphere. Although the capsule made a hard landing as a result of a failed parachute in the Utah Test and Training Range in Dugway, Utah, it marked NASA's first sample return since the final Apollo lunar mission in 1972, and the first material collected beyond the moon. NASA's Johnson Space Center in Houston curates the samples and supports analysis and sample allocation.

Genesis mission yields solar isotopic composition despite hard landing

[size=85][i]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.[/i][/size]

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Two papers in this week’s issue of 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 percent for nitrogen and up to 7 percent 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.

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.

• Science 332(6037) 1509 (24 June 2011) DOI: 10.1126/science.1206965

• Science 332(6037) 1528 (24 June 2011) DOI: 10.1126/science.1204636

• Science 332(6037) 1533 (24 June 2011) DOI: 10.1126/science.1204656