Onboard Autonomous Summarization and Prioritization of CE-ESI MS Data
for the Ocean Worlds Life Surveyor
Abstract
The Ocean Worlds Life Surveyor (OWLS) is a field prototype instrument
suite designed to autonomously search for evidence of water-based life,
developed in preparation for potential future missions to ocean worlds
such as Enceladus and Europa. One instrument included in this suite is a
Capillary Electrophoresis-Electrospray Ionization Mass Spectrometer
(CE-ESI MS), which can detect the presence of organic molecules and
other potential biosignature compounds. Due to the extreme energy costs
involved in communication from these distant worlds, a mission’s
downlink bandwidth is insufficient to return raw data from even a single
recorded dataset. We developed two onboard capabilities to address this
constraint: compression via knowledge summarization, and prioritization
for the most scientifically useful observations. To summarize and
prioritize the data generated by the CE-ESI MS, we developed the
Autonomous CE-ESI Mass-Spectra Examination (ACME) system. ACME performs
content summarization while ensuring that scientifically valuable
signals are retained. First, ACME identifies and characterizes potential
peaks in the mass spectra, each of which may indicate the presence of a
specific compound. Then, ACME uses a decision tree model trained on
expert-labeled data and peak properties such as width and
signal-to-noise ratio to filter only for peaks of likely scientific
interest. Finally, ACME produces a series of Autonomous Science Data
Products (ASDPs): crops of small regions of the raw mass spectra data
around each peak, a summary of the background noise to provide context
and justification for its decisions, estimates of the scientific utility
of the observation, and a brief description of its contents to enable
downlink prioritization based on known science targets of interest as
well as diversity sampling. Typical data sizes of the peak locations,
crops, and background noise summary satisfy the mission downlink
bandwidth constraints with an average compression ratio of 900:1. ACME
was validated on lab- and field-collected data to confirm that
scientists are able to successfully analyze and make valid scientific
conclusions using only ACME’s ASDPs, compared to analyzing the raw data
directly.