The multi-laser set-up of CHILI enables it to analyze samples for compositions of 2-3 elements simultaneously at unprecedented sensitivity and without isobaric interference. Through this novel approach, the precious solar wind (SW) samples from the 2004 NASA Genesis mission can be studied with great efficiency, in order to better understand the solar isotopic and elemental abundances. This data would be able to improve a range of astrophysical models such as solar wind acceleration, planet formation, and solar chemical evolution effects. Specifically, we hope to obtain abundance data that will help inform the ways terrestrial planets and chondritic meteorites differ from the solar composition.
Genesis mission logo.
(Image credit: NASA/JPL)
Diagram of the Genesis flight path from Earth to the first Lagrangian point for solar wind collection.
(Image credit: NASA/JPL)
There is no actual wind in the vacuum of space, rather the term “solar wind”, coined by Prof. Eugene Parker of UChicago's Department of Astronomy and Astrophysics, refers to the stream of ionized particles that emanate from the Sun into the surrounding environment. The outer layers of the Sun’s atmosphere have only changed by around 10% in the past few billion years due to the gravitational settling of heavy elements. Fortunately, this affects all elements in about the same way, and therefore planetary science assumes that the solar atmosphere has preserved the elemental and isotopic composition of the solar nebula.
The solar nebula is considered the source of all planetary materials and objects in the Solar System, and therefore knowing the composition of the solar nebula would inform how so many diverse materials came together to form our local space environment. Due to the minimal compositional changes in outer layers of the Sun, solar wind is widely acknowledged to be demonstrative of solar nebula remnants. Obtaining elemental abundances from the Sun is in itself exciting, but perhaps the stronger driving force for this project is what the analysis of this data can add to our understanding of the evolution of our Solar System.
Schematic of the Genesis spacecraft open for SW collection. The cover array was exposed to all SW regimes while the stacked arrays would rotate out for exposure depending on which SW regime the spacecraft was exposed to.
(Image credit: NASA/JPL)
A detector array with various ultra-high-purity materials for optimized solar wind collection.
(Image credit: NASA/JPL)
Fragments of the detector arrays after the crash. Despite the damage done to the arrays, the Genesis team was able to sort through the mix of fragments and sort which samples contained each SW regime by looking at the different material types and thicknesses.
(Image credit: NASA/JPL)
Genesis was a NASA Discovery mission that put various detector materials on a spacecraft, which was then stationed at the first Lagrangian point to collect implanted solar wind ions. Upon return of the SW samples to Earth, the collector materials were fragmented and exposed to significant terrestrial contamination. This unfortunate contamination has made the analysis of the returned samples much more difficult.
The Genesis collector materials are implanted with SW ions in a distribution of depths, peaking at a depth of ~40 nm but potentially reaching up to a few hundreds of nm (Heber et al., 2014). In principle, standard depth profiling from the front of a sample can performed to measure the amount of SW atoms implanted. However, due to the shallow depth of the implanted SW and the high concentration of contamination, hitting the sample surface from the front with a laser or ion beam could actually lead to some of the contamination being pushed into the collector material that would then mask the SW ions. Therefore, we intend to utilize a technique common in the semiconductor industry called "backside depth profiling" which can circumvent the contamination while still extracting the implanted SW ions.
Periodic table of the elements where the elements within the thick black border are ones that could be ionized with the current optics in CHILI. The grey symbols are elements that have already been analyzed in all regimes of SW from Genesis. The red symbols are elements that have already been studied in the bulk SW samples in Si collector material. The yellow and blue colored elements are ones that have yet to be analyzed and are relevant to the topics of low-FIP fractionation in fast SW and the use of chondrites as a proxy for solar elemental abundances, respectively. Furthermore, all the elements colored yellow and blue are estimated to have >1,000 atoms per 100 square microns of Genesis collector material. This would theoretically provide sufficient ions for abundances with a 2 sigma error of 10%, accounting for CHILI's useful yield of approximately 25%.
(Image credit: Julie Korsmeyer)