Abstract
Abstract From 2004 to 2017, the Cassini spacecraft orbited Saturn, completing 127 close flybys of its largest moon, Titan. Cassini’s Composite Infrared Spectrometer (CIRS), one of 12 instruments carried on board, profiled Titan in the thermal infrared (7–1000 μm) throughout the entire 13 yr mission. CIRS observed on both targeted encounters (flybys) and more distant opportunities, collecting 8.4 million spectra from 837 individual Titan observations over 3633 hr. Observations of multiple types were made throughout the mission, building up a vast mosaic picture of Titan’s atmospheric state across spatial and temporal domains. This paper provides a guide to these observations, describing each type and chronicling its occurrences and global-seasonal coverage. The purpose is to provide a resource for future users of the CIRS data set, as well as those seeking to put existing CIRS publications into the overall context of the mission, and to facilitate future intercomparison of CIRS results with those of other Cassini instruments and ground-based observations.
Highlights
Titan is the largest moon of Saturn—5150 km in diameter— and the only moon in the solar system to possess a substantial atmosphere
This required that position-step sizes, slewing rates, and other spacecraft-pointing maneuvers were customized according to distance from Titan, and by detector type, both of which combined to determine the projected size of the footprint in kilometers, according to the formula s = rΔθ, where s is the footprint size, r is the distance, and Δθ is the angular size of the detector (Figure 6)
One striking conclusion is that the original nine types of observations (Table 1), planned long before orbit insertion, remained in use throughout the entire 17 yr mission with only minor modifications, a strong testament to the thoughtful forward planning that was put into constructing the standard observation templates
Summary
Titan is the largest moon of Saturn—5150 km in diameter— and the only moon in the solar system to possess a substantial atmosphere. CIRS continued to operate at full capacity during the entire 13 yr mission and was allocated the most Titan observation time as the “prime” instrument of any Cassini instrument, by virtue of its ability to observe both Titan’s day and night sides, and to conduct high-value science over the entire range of spacecraft distances. The objective is to provide a complete and comprehensive description of the CIRS observations of Titan—the science goals, observation implementation, and spatial and temporal coverage This is anticipated to be of value to multiple groups: members of other Cassini instrument teams in their ongoing data analysis efforts, future users of CIRS data accessible through the Planetary Data System (PDS; McMahon 1996; see Appendix A), ground-based observers analyzing complementary data sets such as the ALMA archive (Stoehr et al 2014), and perhaps science planners of future Titan instruments and missions.
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