Solar wind ions salvaged from NASA鈥檚 crashed Genesis space capsule could yet help trace the primordial composition of the solar system, fulfilling the mission鈥檚 main goal, the mission鈥檚 first scientific results suggest.
But the task will not be easy 鈥� more than half of the samples appear too damaged to be useful and the remaining ones are chemically contaminated from the crash.
The Genesis capsule smashed into the ground in Utah on 8 September 2004 because of a design flaw that prevented its parachutes from activating. It had spent 27 months in space collecting charged particles blown from the Sun鈥檚 outermost layer. That layer is thought to reflect the composition of the gas-and-dust cloud, known as the solar nebula, from which the solar system formed, about 4.6 billion years ago.
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杏吧原创s had hoped this primordial composition would provide a baseline to understand how different planets and meteorites later evolved such a wide range of isotopes of key elements such as oxygen and nitrogen.
But the capsule鈥檚 crash landing threw that possibility into question after dirt from Utah鈥檚 salt flats entered the ruptured science canister and most of the delicate wafers on the mission鈥檚 five collector arrays shattered.
From the ashes
However, mission members picked up the pieces, literally, and sought novel ways to study the particles. Now, preliminary studies offer fresh hope for the mission鈥檚 science goals. They were reported on Tuesday at the Lunar and Planetary Science Conference in Houston, Texas, US.
鈥淭he most important result is that we have results,鈥� says Don Burnett, the mission鈥檚 principal investigator at Caltech in Pasadena, US. 鈥淭hese are our first steps in coming back from the ashes.鈥�
The mission鈥檚 most important target was oxygen, which exists on different planets and meteorites in bafflingly different ratios of its three most common isotopes. Because the solar wind is 99% ions of hydrogen and helium, mission planners designed an instrument to repel these light elements and trap heavier ions such as oxygen at concentrations at least 20 times greater than normally found in the solar wind.
Scary finding
This instrument used a curved, electrically charged mirror to focus the heavy ions onto a target made of several ultra-pure materials. But because different isotopes of the same element react differently in an electric field, they segregate in different concentrations at different places on the target. So to get an accurate measurement of all the isotopes, this separation effect needed to be calibrated.
Researchers used neon from the solar wind, a noble gas that is rare on Earth, to try to understand exactly how this separation worked. At first, the neon observations did not line up at all with predictions made before the samples were returned. 鈥淲e were quite scared,鈥� says planetary scientist Rainer Wieler of the Swiss Federal Institute of Technology in Zurich.
But then other team members developed a new theoretical model that included data such as the spacecraft鈥檚 measurement of the speed of the solar wind. Now, the new model agrees with the observed neon distribution with an uncertainty of a few percent. 鈥淲e鈥檇 like it to be better,鈥� says team member Ian Franchi of Open University in the UK. 鈥淏ut it鈥檚 an important step.鈥�
The calibration with neon is encouraging for the mission鈥檚 main target, says Wieler: 鈥淚t suggests it should be possible to detect the oxygen composition in the solar wind.鈥�
Three winds
Researchers were also anxious to know how well the samples collected by Genesis actually traced the composition of the early solar system. For this, they needed to understand how accurately the solar wind represents the composition of the Sun鈥檚 outermost layer and whether that layer, in turn, has truly remained unchanged since the solar system formed from a dusty nebula.
This is a complicated question, since there are actually three different types of solar wind. Each moves at a different speed and may accelerate different elements 鈥� and possibly different isotopes 鈥� by different amounts, complicating the interpretation of the Sun鈥檚 true composition.
Genesis used sensors to gauge the speed of the solar wind and then deployed specific collectors to gather up particles from each of the three types. The new studies show that regardless of the type of solar wind measured, the ratio of neon isotopes collected did not vary. This hints that the samples do indeed trace the composition of its outer layer and that 鈥渨hat we measure in the Sun can apply to the solar nebula鈥�, says Burnett.
Brown stain
The new research is especially heartening for the team because more than half of the collectors smashed into pieces too tiny to study, and what pieces remained were covered by what researchers call a 鈥渂rown stain鈥�.
This stain was caused during the crash when the spacecraft released molecules of gas, which then fused into long polymers on the collectors鈥� surfaces when exposed to ultraviolet light from the Sun.
The brown stain contains carbon and oxygen, contaminating the pristine samples. But researchers have devised a number of ways to remove the stain 鈥� such as using ozone to react with the polymers. Removing the contamination is complicated and time-consuming, says Franchi: 鈥淏ut I don鈥檛 think anybody鈥檚 saying we can鈥檛 do this.鈥�
鈥淚n principle, we might be able to do everything we started out to do,鈥� agrees Burnett.
