Synthesis Of Complex Organic Molecules From Simple Precursors In The Stardust SRC Heat Shield During Atmospheric Reentry
- Paper number
IAC-07-A1.5.-A1.7.03
- Author
Ms. Maegan Spencer, Stanford University, United States
- Coauthor
Prof. Richard Zare, Stanford University, United States
- Year
2007
- Abstract
Heat shield material used on the Stardust Sample Return Capsule (SRC) is unique in its simplicity and reentry parameters, making it a rather ideal test bed for natural meteor events. As a phenolic impregnated carbon ablator (PICA), this material contains amorphous carbon and aromatic hydrocarbons. PICA was chosen for Stardust owing to its outstanding ability to protect and insulate the sample payload. In dissipating the heat of reentry, it undergoes chemical reactions causing the emission of gases and development of a fine-grain residual char. This layer of char can be several mm thick, suggesting a depth dependence on the extent of PICA alteration. The SRC reentered Earth’s atmosphere in January 2006 at approximately 12.6 km/s, a speed comparable to that of natural meteors, making it the first spacecraft to reenter at meteor-relevant speeds. Heat shield ablation products interact with atmospheric molecules in the reentry shockwave just as molecules might during a natural meteor event. Characterization of products generated during the SRC reentry reveals information relevant to natural meteor events, enabling the direct analysis of reentry-induced organic synthesis in a meteor-like object.
Two-step laser mass spectrometry (µL 2MS), a surface analysis technique, was used in this study to perform depth-resolved characterization of polycyclic aromatic hydrocarbons (PAHs) in two different heat shield samples. The selectivity and high sensitivity in the femtomole to attomole regime for PAHs makes µL 2MS well suited for this analysis. Core samples from the post-reentry Stardust heat shield and an analogous heat shield model material were obtained and sectioned into ∼ 1mm thick slices depth-wise. Stardust analog heat shield material was exposed to simulated reentry conditions in the laboratory (NASA ARC) using an arc jet. Portions of each core slice were analyzed using µL 2MS with no further sample preparation. A complex distribution of PAHs, including high-mass functionalized PAHs, was detected in both samples. Identity and abundance of this PAH envelope varies nonlinearly with depth in core samples, eventually approaching the “pristine” heat shield composition. We conclude that complex organic synthesis can readily occur during meteor events using precursors in the reentering body.
This study gives insight into the chemical processes that might occur when an extraterrestrial body enters planetary atmospheres. These processes are not well understood and may have significant impact on the interpretation of cometary organic molecules delivered to early Earth and other planets, an important topic considering the international endeavor to detect the possible existence of extraterrestrial life.
- Abstract document
- Manuscript document
IAC-07-A1.5.-A1.7.03.pdf (🔒 authorized access only).
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