New solar wind samples, salvaged from collecting devices that survived the Genesis spacecraft crash in 2004, may help to resolve how the Sun and Solar System formed. The Genesis spacecraft was the first ever attempt to collect a sample of solar wind, and the first "sample return mission" to return from beyond the orbit of the Moon. It was launched on August 8, 2001, and crash-landed after a design flaw prevented the deployment of its drogue parachute.
NASA's Genesis probe collected particles from the solar wind, a high-energy stream of plasma ejected from the Sun, over a 27-month period from December 2001 to April 2004. The results of the mission are detailed in the journal Science.
Genesis samples are the first extraterrestrial samples returned to
Earth by NASA since the Apollo program, which ended in the early 1970s.
The collectors returned by the Genesis mission contain solar wind atoms which can be analyzed in sophisticated laboratory instruments to measure very precisely the composition of the Sun. Since the Sun contains 99% of the mass in the solar system, knowing its elemental and isotopic composition is a good average measure of the composition of the solar nebula at the time when the planets were forming. Genesis' solar data allow new insights in tracing the chemical evolution of diverse planetary samples, most of which came from a common starting material, the solar nebula.
Astronomers have long debated whether the Sun formed as an isolated star or, as scientists have more recently asserted, as part of a cluster, in a region of high-mass star formation, within a dense molecular cloud.
Astronomers believe that evidence of the early evolution of the Sun
is trapped as isotopic signatures of elements found within the
super-heated surface of the Sun, the solar corona. However, until
star-proof spacecraft are developed, sampling the solar wind is the
closest that scientists can get to understanding how the Sun was born.
Genesis measured the isotopic ratios of neon and argon (both "noble gases") over three solar wind speeds, low speed (less than 475 km/hr), high speed (onset generally 525 km/hr) and during a coronal mass ejection — occasional and spectacular ejaculation of bubbles of plasma. The speed categories are believed to have different physical origins on the Sun and so could reveal the isotopic signature of different physical processes.
The researchers, led by Alex Meshick from Washington University, in St. Louis, U.S., found that the isotopic ratios remained unchanged in the three regimes. This indicates that the solar wind isotopic ratios are probably the same on the Sun; and hints at the isotopic ratios of these noble gases in the early Solar System, before the Sun or planets formed.
Further research is needed before experts can say which theory of formation of the Sun is implicated – but the study is proof of principle that these solar wind samples can be used to probe the star's history.
While not jumping any guns, the researchers noted that the lack of evidence of fractionation between the three speed regimes may help rule out some of the models of solar formation that rely on these elements varying within the Sun. The find will also help experts build a better understanding of how elements change in the extreme physical conditions inside the Sun.
In a commentary on the article in the same issue of Science, astronomer Kurt Marti, from the University of California in San Diego, said that the data provides a new set of references for the interpretation of solar isotopic data.
"Because solar isotopic signatures have been inferred only indirectly from abundance data in meteorites, these new solar reference data are in great demand for proper interpretations of observations in meteorites. They may help to fill some of the gaps in our understanding of how objects in the solar system formed and evolved," he said.
Posted by Casey Kazan.