Concept for Remote Chemical Analysis of Enceladus Amino Acid Chirality

Introduction: A concept for an astrobiology science instrument is described here in the context of a future mission to Enceladus [1]. Water jets from the south polar region of this moon form a plume and supply material to the Saturn e-ring [2, 3]. By utilizing remote chemical analysis of free amino acid chirality, the Enceladus Amino Acid Sampler (EAAS) is designed to address the fundamental astrobiology science question, “is there life outside of Earth [4]?” The EAAS instrument concept expands from the capabilities demonstrated by the Ion and Neutral Mass Spectrometer (INMS) instrument on the Cassini spacecraft [5, 6]. The INMS instrument is currently exploring Enceladus’ plume and the atmosphere of Titan with the capability to detect small amino acids, such as glycine and alanine [7]; however, INMS was not designed with the capability to determine the extent of the chirality of alanine. Remote chemical analysis with the EAAS approach employs an aerogel sampler for collecting ice dust while in flight onboard a spacecraft [8], mitigating breakdown of molecules on impact with instruments like the Cometary and Interstellar Dust Analyzer on the Stardust mission [9]. Automation of sample analysis with EAAS is envisioned as a means of expanding the discovery of the identity, inventory and chirality of free amino acids from a potentially habitable subsurface ocean postulated to be present on Enceladus [10, 11, 12]. Remote chemical analysis with an EAAS science instrument is compatible with either an orbiter [1] or sample return spacecraft platform [13]. 5 Science Tiers for Enceladus Exploration with EAAS: A flow chart illustrating the science instrument concept for the operation of EAAS is shown in Figure 1. The foundation of the instrument is a mass spectrometer (MS) that supports 5 science tiers, described as follow: Science Tier 1: Enceladus Encounter. A spacecraft equipped with the EAAS instrument has a rendezvous with the plume or jets of Enceladus. During the encounter the MS operates to collect data in a similar fashion to Cassini’s INMS [5, 6]. Science Tier 2: Aerogel Sampler. Also during the encounter, an aerogel sampler decelerates and entrains ice dust particles [13]. Volatiles liberated upon capture of the ice dust particles by the aerogel are analyzed by the MS. Science Tier 3: Aerogel Analysis of Captured Volatiles. By enclosing the aerogel container after the encounter, heat can be applied, thermally desorbing molecules from the aerogel for analysis with the MS. Additionally, a liquid or carrier gas can be introduced to the aerogel container with controlled heating to transfer a sample to the MS, or to deliver a sample from the aerogel to a lab-on-a-breadboard for further sample processing. Science Tier 4: Amino Acid Inventory Determination. Sample pre-concentration is performed by a labon-a-breadboard subsystem amplifying the amino acid concentration by ~4 orders of magnitude or more. Preconcentrated samples are then delivered to the MS for analysis or are delivered to a lab-on-a-chip subsystem for further processing [14]. Science Tier 5: Amino Acid Chirality Quantification. The EAAS is an astrobiology science instrument capable of measuring amino acid chirality by utilizing lab-on-a-chip technology [15]. The identity of the chiral components of a sample at this stage of the analysis chain will also be verified using the MS.