Three Eccentric Ringlets: Maxwell, Titan, and Huygens
work in progress
Nicole Albers
UVIS Team Meeting
Pasadena, January 2011
Maxwell Ringlet
●
Located in Maxwell Gap in C ring around 87450km
●
Although in C ring it has significant optical depth ranging from 1 to 5
Eccentric ringlet where inner and outer edge are well­described by single streamline with m=1
●
●
Freely­precessing with no known resoncances nearby
Known since Voyager [Esposito et al. (1983) and Porco et al. (1984)]; confined by uniform precession [Goldreich and Tremaine (1979)]
●
Ringlet would diffuse into torus due to its eccentricity gradient between inner and outer edge. Owing to its self­gravity the ringlet maintains shape and has its narrowest point at periapse (all pericenters align) and its widest at apoapse. Inner and outer edge share the same pattern speed. Test used to prove this is typically the width­radius­relation.
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Outer Edge: Crosses
Inner Edge: Diamonds
→ Eccentricity Gradient
Pattern Speeds taken from best fit streamline [and calculated for streamline semimajor axis for comparison] Green: simple­sine fit to the width­vs­clon data
→ Width­radius relation reveals good agreement with the expected linear relation
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Expected variation of optical depth along the ringlet
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Expected variation of optical depth along the ringlet
But peak is offset to “after” the bottleneck of periapse, implications?
Also, the optical depth profile reveals a curious wave “on top” of the expected pattern
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
“Spikes”
“Wave”
Apparent regular k(r) pattern visible in WWZ unlike spiral density or bending waves.
If wave if visible by eye in HSP counts, “spikes” accompany the wave (manifests abrupt changes in optical depth similar to edges or narrow ringlets like the F ring).
“Wave”
Wavenumber k
Wavenumber k
Wavelet­transform of 2 occs
Moreover, k(r)­dependence changes with radial location, corotating longitude, and optical depth. Since all of these are interdependent, who's the hen and who's the egg?
Radial distance across ringlet
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Extracted k(r)­traces from various occs
Is the “wave” self­similar?
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Outer Edge: Crosses
Inner Edge: Diamonds
→ Eccentricity Gradient
Small offset?
Pattern Speeds taken from best fit streamline [and calculated for streamline semimajor axis for comparison] Does the offset explain the small residual scatter from a line?
● What effects does the “wave” pattern produce?
●
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Titan Ringlet
●
Located in Titan Gap in C ring around 77860km
●
Although in C ring it appears opaque in all UVIS occultations Eccentric ringlet where inner and outer edge are well­described by single streamline with m=1
●
●
Known since Voyager [Porco et al. (1984)];
At the time consistent width­radius­
relation suggesting uniform precession, which, contrary to the Maxwell ringlet, is driven by a Titan resonance close­by.
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Outer Edge: Crosses
Inner Edge: Diamonds
→ Eccentricity Gradient
Pattern Speeds taken from best fit streamline [and calculated for streamline semimajor axis for comparison] Green: simple­sine fit to the width­vs­clon data
→ Width­radius relation reveals the linear trend with significant scatter
Note: Error bars are the size of symbols and equal to occultation geometry accuracy of ~1km.
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Both pattern speeds slightly faster than expected for freely­ precessing, consistent with Titan driving the ringlet
● Similar relative residuals from the linear width­radius­ relation as the Maxwell ringlet.
●
Offset again
Same relation to the pattern offset? ●
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Huygens Ringlet
Located in Huygens Gap in the Cassini division around 117820km; right outside of the B ring edge
●
●
Opaque in some UVIS occs and occasionally “some pattern” in WWZ
Eccentric ringlet where inner and outer edge are well­described by single streamline with m=1
●
Known since Voyager [Porco et al. (1984)] with suspected influence of the strong Mimas 2:1 ILR ●
Cassini ISS sees multimode ringlet with additional m=2 and m=6 modes [Spitale et al. (2006, DDA)]
●
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Outer Edge: Crosses
Inner Edge: Diamonds
→ Eccentricity Gradient
Pattern Speeds taken from best fit streamline [and calculated for streamline semimajor axis for comparison] Green: simple­sine fit to the width­vs­clon data
→ No linear trend!
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
Cassini UVIS HSP
Both pattern speeds slightly faster than expected for freely­ precessing, consistent with multiple strong “near­by” resonances driving the ringlet.
●
Significant offset
Again, same relation to the pattern offset? Just more pronounced than in case of Maxwell and Titan? ●
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011
A Few Summarizing, Open Questions
All three ringlets show significant optical depth potentially leading to uniform precession in all three of them. Is the Maxwell ringlet really a textbook example of uniform precession? What is the physical origin of the “wave” pattern?
●
What underlying physical process could be responsible for these apparent similarities between the Maxwell, Titan, and Huygens ringlet when two of them are clearly driven? ●
Titan ringlet suspected to librate with Titan [Porco and Nicholson (1984)]; Huygens most likely influenced by Mimas, but not necessarily with similar complexity as B ring edge; → Do ringlets correlate to resonantly­driven edges, and if exactly how?
●
… to be continued
Nicole Albers
UVIS Team Meeting, Pasadena, January 2011