Solar Wind Conditions and Composition During the Genesis Mission as Measured by in situ Spacecraft

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  • Space Sci Rev (2013) 175:125164DOI 10.1007/s11214-013-9960-2

    S P E C I A L C O M M U N I C AT I O N

    Solar Wind Conditions and Composition Duringthe Genesis Mission as Measured by in situ Spacecraft

    Daniel B. Reisenfeld Roger C. Wiens Bruce L. Barraclough John T. Steinberg Marcia Neugebauer Jim Raines Thomas H. Zurbuchen

    Received: 7 August 2012 / Accepted: 19 January 2013 / Published online: 19 February 2013 Springer Science+Business Media Dordrecht 2013

    Abstract We describe the Genesis mission solar-wind sample collection period and thesolar wind conditions at the L1 point during this 2.3-year period. In order to relate the solarwind samples to solar composition, the conditions under which the samples were collectedmust be understood in the context of the long-term solar wind. We find that the state ofthe solar wind was typical of conditions over the past four solar cycles. However, Genesisspent a relatively large fraction of the time in coronal-hole flow as compared to what mighthave been expected for the declining phase of the solar cycle. Data from the Solar WindIon Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE) areused to determine the effectiveness of the Genesis solar-wind regime selection algorithm.The data collected by SWICS confirm that the Genesis algorithm successfully separatedand collected solar wind regimes having distinct solar origins, particularly in the case ofthe coronal hole sample. The SWICS data also demonstrate that the different regimes areelementally fractionated. When compared with Ulysses composition data from the previoussolar cycle, we find a similar degree of fractionation between regimes as well as fractionationrelative to the average photospheric composition.

    The Genesis solar wind samples are under long-term curation at NASA Johnson SpaceCenter so that as sample analysis techniques evolve, pristine solar wind samples will beavailable to the scientific community in the decades to come. This article and a compan-ion paper (Wiens et al. 2013, this issue) provide post-flight information necessary for theanalysis of the Genesis array and foil solar wind samples and the Genesis solar wind ionconcentrator samples, and thus serve to complement the Space Science Review volume, TheGenesis Mission (v. 105, 2003).Keywords Solar wind Solar wind composition Solar wind sample collection Solarcomposition

    Electronic supplementary material The online version of this article(doi:10.1007/s11214-013-9960-2) contains supplementary material, which is available to authorizedusers.

    D.B. Reisenfeld () R.C. Wiens B.L. Barraclough J.T. Steinberg M. Neugebauer J. Raines T.H. ZurbuchenUniversity of Montana, Missoula, MT, USAe-mail: dan.reisenfeld@umontana.edu

  • 126 D.B. Reisenfeld et al.

    Definitions, Abbreviations, and AcronymsB Bulk collectors that were at the top of the stack and in the Canister lid.

    These were exposed continuously during the science collection periodE Collector array directly below the B array. This array was exposed to

    coronal mass ejection flows and questionable flowsH Collector array below the E array. This array was exposed to

    high-speed, or coronal hole flowsL Bottom collector array in the stack. This array was exposed to

    low-speed, or interstream windS Collectors in the SRC lid, primarily to investigate radioactive nuclei

    in the solar windCME Coronal mass ejectionsCH Coronal hole, or fast windIS Insterstream, or slow windS/C SpacecraftSRC Science return capsuleSKM Station keeping maneuvers, which occurred approximately every 2

    monthsLOI L1 orbit insertion, which occurred prior to the beginning of the

    science collection phase of the missionL1 The Lagrangian point between the Earth and the SunUnshaded position Rotational position of the deployable solar-wind collector arrays

    where individual, regime-specific arrays were exposed.Deployed position Rotational position of the deployable solar-wind collector arrays

    where the B array remained during collection, and where theregime-specific arrays were positioned when they were not exposedor acting as a contamination barrier

    1 Introduction

    The Genesis mission was launched in August 2001 to obtain and return a sample of the solarwind for detailed isotopic and elemental analyses (Burnett et al. 2003). The Genesis samplereturn capsule (SRC) returned to Earth on September 8, 2004. Despite a hard landing thatresulted from a failure of the avionics system to deploy the parachute, many samples werereturned in a condition that has permitted analysis. These analyses have been carried out bya number of different techniques used for precise isotopic and elemental abundances. Nearlyall analyses have utilized mass spectrometry in various forms: noble gas mass spectrometry,typically using laser ablation to introduce the sample (e.g., Meshik et al. 2007; Grimberg etal. 2006, 2008; Vogel et al. 2011; Pepin et al. 2012; Heber et al. 2012); secondary ion massspectrometry (SIMS), which uses an ion beam to interrogate the sample (e.g., Marty et al.2011; Huss et al. 2012); a hybrid instrument combining an accelerator, typically used in anaccelerator mass spectrometer, with the main elements of a SIMS instrument (Mao et al.2008; McKeegan et al. 2011); resonance ionization mass spectrometry (RIMS), which useslaser beams to selectively produce excited states and then ionize only the element of interest(e.g., Veryovkin et al. 2004; Crowther and Gilmour 2011); and inductively coupled plasmamass spectrometry (ICP-MS; Humayun et al. 2011). At least one non-mass spectrometrytechnique has been used as well, e.g., grazing-incidence X-ray fluorescence, to determineelemental compositions in solar-wind samples from Genesis (Kitts et al. 2009).

  • Solar Wind Conditions and Composition During the Genesis Mission 127

    A wealth of elemental and isotopic solar wind composition information is present in theGenesis samples. For this reason, the Genesis samples are under long-term curation at theNASA Johnson Space Center, in the same facility that houses the Apollo lunar samples,and we expect analysis of the Genesis samples to continue for many decades to come. Theexpectation of the mission designers is that future advances in sample analysis technologywill lead to even more accurate determination of solar isotopic and elemental abundancesthan what is possible today (Burnett et al. 2003). It is thus important to document in oneplace the collection time periods and the state of the solar wind as measured by in situ in-struments during these collection periods so that current and future sample analysis can beplaced in the proper solar wind context. The solar wind is not by any means an unfraction-ated sample of the Sun, nor is the means by which fractionation occurs fully understood(e.g. von Steiger et al. 2000). Thus, a more comprehensive set of solar wind conditions andcomposition characteristics have been recorded to help elucidate physical processes respon-sible for compositional variations found during the collection period. Ultimately we seek toplace Genesis results into the context of the long-term composition of the solar wind, andthe composition of the Sun and solar nebula.

    The Genesis solar wind samples were collected on a variety of substrates, exposed to thesolar wind either continuously throughout the 27-month collection period or only at timesof certain types of solar wind flow (see Fig. 1). In particular, three collector panels werededicated to specific flow types: flow emanating from coronal holes (CH), from the inter-stream region near closed-loop boundaries (IS), and from coronal mass ejections (CMEs)(Neugebauer 1991). All three types of solar wind are elementally and isotopically fraction-ated in different ways and amounts relative to the solar photosphere. Thus not only do weneed to understand the state of the solar wind averaged over the Genesis sample collectionperiod, but also solar wind conditions within these three regimes. Furthermore, since thedetermination of solar wind regimes was performed autonomously by Genesis (Neugebaueret al. 2003), it is important to confirm the validity of the choices made by comparison tocontemporaneous solar wind parameters not accessible to Genesis during the mission.

    This article and its online appendices serve as a comprehensive repository of solar-windconditions that we deem relevant to the samples. The conditions recorded here include (a) thetimes during which the various samples were collected, (b) solar-wind conditions recordedby the Genesis Ion Monitor (GIM) (Barraclough et al. 2003), and (c) the solar-wind com-position recorded by the Solar-Wind Ion Composition Spectrometer (SWICS) on board theAdvanced Composition Explorer (ACE), which was also orbiting the L1 point during thisperiod (Gloeckler et al. 1998).

    We also explore questions related to the how successfully the Genesis mission met adefining design goalhow to relate Genesis samples to photospheric abundances. In partic-ular:

    How typical was the plasma state of the solar wind during the Genesis sample collec-tion period as compared to the long-term state of the solar wind? Is the Genesis samplerepresentative of the solar wind, or is it somehow atypical?

    How successful was Genesis at collecting solar wind of different origins (interstream,coronal hole, CME) on the different regime arrays. Specifically with regard to the Genesisregime selection algorithm, how good a job did it do at identifying CMEs?We will also rely heavily on the composition measurements of the ACE/SWICS instru-

    ment to tell us about the average elemental fractionation in the Genesis samples within theaccuracy of the ACE measurements:

  • 128 D.B. Reisenfeld et al.

    Fig. 1 The Genesis spacecraft viewed in solar wind collection configuration. Th