UNWINDING SATURNS TURNS : PROBING THE FAR ULTRAVIOLET PROPERTIES OF - - PowerPoint PPT Presentation

UNWINDING SATURN’S TURNS: PROBING THE FAR ULTRAVIOLET PROPERTIES OF SATURN’S RINGS

Milena Crnogorčević ASTR630 Term Project TERP Conference Dec 10, 2018 Based on the paper by Bradley et al. (2010): Far ultraviolet spectral properties of Saturn’s rings from Cassini UVIS

Upper-left image: NASA / JPL-Caltech / SSI / Ian Regan 1

Motivation

• Saturn’s rings composed mostly of water ice (Cuzzi et al. 1984)
• Decrease in reflectivity shortward of 600 nm à non-icy constituents affecting

the scattering properties of the ring particles

• Water-ice absorption feature at

around 160 nm

• its properties depend on the scattering

distance photons travel through water-ice, as well as the absorption properties

• f the regolith water-ice
• can use spectral information to

characterize mean free path and the symmetry parameters of the rings

Upper-right image: NASA / JPL-Caltech / SSI

Fig 1. (corresponds to Fig. 2 in the paper) Normalized radiance from four different regions summed over four years of observations. Obvious absorption feature present at ~ 160 nm.

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Authors:

C Ring B Ring Cassini division A Ring

• Considered four years of Cassini data

applying certain selection criteria

• Data reduction steps accounted for skewed

field of view and other geometry effects

• Produced I/F spectral plots
• Fit Hapke and Shkuratov model (water-ice

albedo) to the data

• Found limits on L (mean free path length), g

(symmetry parameter across the rings), UV slope, and I/F

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What did I do?

C Ring B Ring Cassini division A Ring

• Considered four years of Cassini data

applying certain selection criteria

• Data reduction steps accounted for skewed

field of view and other geometry effects

• Produced I/F spectral plots
• Fit Hapke and Shkuratov model (water-ice

albedo) to the data

• Found limits on L (mean free path length), g

(symmetry parameter across the rings), UV slope, and I/F

• Using the selection criteria from the

paper, came up with a list of 760

• bservations
• Considered Ring B only (32
• bservations)
• Data reduction steps partially

reproduced

• I/F spectral plot for Ring B partially

reproduced using the limited amount of data

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• Selection criteria:
• Considering the lit side of Saturn’s

rings, phase angles 5 to 30 deg

• Slit width: high and low resolution,

no occulation data

• Considering only the far-UV
• bservations (111.5 – 191.2 nm)
• 760 observations (Ring A (3), Ring

B (32), Ring C (18), and the rest combination of two or more, or not mentioned in the paper)

• Data reduction:
• Background
• Flagging the ”evil” pixels
• Wavelength and flux calibration
• GEOM routines to account for the

skewed field of view and appropriately binning the data

• Lyman-alpha forest accounting
• Calibrating it to the Sun’s flux at

the given time

Fig 2. (analogous to Fig 1) Normalized radiance from Ring B for one of the

• bservations (FUV2005_230_15_15). Similar absorption feature may be seen,

but more data is necessary to conduct any further analysis.

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Paper’s conclusions and its potential extensions

• Conclusions:
• retrieved a measure of the

amount of the water ice that UV photons traverse before leaving the ring from the location of the absorption edge in data

• Mean free path: relatively uniform

from the mid-B ring to the outer A ring, minimum in the inner C ring

• Lack of correlation between L and

UV slope

• Potential future work:
• More data available since 2008
• Consider more spatial coverage

and include more rings

• Consider different radiative

transfer models as applied to the rings

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Thanks! Questions?

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…and today…