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Sun and planets formed from different ingredients
Posted: 28 June 2011

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Samples recovered from NASA's ill-fated Genesis mission suggest that the Solar System's inner planets may have formed from different solar nebula materials than those that created the Sun.

Artist impression of Genesis in its collecting configuration. Image: JPL/NASA.

Genesis flew to the Sun in 2001, collecting fragile solar wind particles for over two years before returning them to Earth in 2004, with the goal of learning about the building blocks that went into planet construction 4.6 billion years ago. Sadly, the parachute descent system failed on the sample return capsule and the mission crash landed in a desert in Utah, destroying nearly all of its precious cargo. But the mission was far from a failure; samples cocooned inside one instrument – the Solar Wind Concentrator, built by a team at Los Alamos National Laboratory – were recoverable, providing the first direct oxygen and nitrogen isotopic measurements of the Sun, and thus the first measurements of the "fossils" of the original solar nebula.

Oxygen and nitrogen are two of the most abundant elements in the Solar System and have already been measured in meteorite samples from the Moon and Mars that have fallen to Earth, in the lunar soil by Apollo astronauts and in Jupiter’s atmosphere by the Galileo spacecraft. They all show variations in composition to the Earth, begging the question, where did Earth’s oxygen and nitrogen come from? This is where the Genesis results are shedding some light.

Essential samples of nitrogen and oxygen were preserved in the target section of Genesis’ Solar Wind Concentrator. Image: LANL.

Nitrogen has one isotope, N-14, that makes up nearly 100 percent of the nitrogen atoms in the Solar System, but there is also a small contribution of N-15. The Genesis results showed that the Sun and Jupiter have the same nitrogen composition, but that they have slightly more N-14 and around 40 percent less N-15 than the Earth. Genesis scientists speculate that Earth might have received its heavier nitrogen from comets that smashed into the Earth during the Solar System's youth. A sample return mission to a comet would help answer that question.

Similar to nitrogen, nearly 100 percent of oxygen atoms are O-16, but there are also small amounts of isotopes O-17 and O-18. “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,” says Kevin McKeegan, a Genesis co-investigator from UCLA. The other isotopes’ percentages were slightly lower in the Sun than the Earth. “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.”

Roger Wiens, the Genesis flight payload lead likens the mission to Apollo 13. “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 analysis of the Genesis samples are discussed in two papers featured in the journal Science this week.