1Proximal +/- 1 hr Priorities June 5, 2014

RPWS Team Science Priorities (+/- 1 hr)

W. Kurth and D. A. Gurnett

For the RPWS Team

Cassini PSG Telecon

5 June 2014

Also shown at Joint Juno/Cassini Jupiter – Saturn Magnetospheres Meeting

Atlanta, 31 May 2015

2Proximal +/- 1 hr Priorities June 5, 2014 314 Dec 2014

F-ring and Proximal Orbit Mission PhaseF-ring Orbits

• 20 orbits• Nov 30, 2016 - April 23, 2017

3Proximal +/- 1 hr Priorities June 5, 2014

• 22 orbits

• April 23, 2017 - Sept. 15, 2017

414 Dec 2014

Proximal Orbits

4Proximal +/- 1 hr Priorities June 5, 20144

5Proximal +/- 1 hr Priorities June 5, 2014 3

Proximal Orbits 271 - 281

6Proximal +/- 1 hr Priorities June 5, 2014 3

Proximal Orbits 282 – 292

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Cool/cold orbits

8Proximal +/- 1 hr Priorities June 5, 2014

RPWS Science Questions (+/- 1 hr in blue)

1. How, and to what extent, is the ionosphere and magnetosphere connected to the rings?

2. What is the true rotation period of Saturn’s interior, and how is this decoupled from the magnetosphere?

3. Does lightning interact with the ionosphere, magnetosphere, and rings?

4. How much ring material lies below the D-ring?

5. What is the nature of Saturn’s noon, equatorial exosphere, thermosphere, and ionosphere?

6. Are there wave-particle interactions associated with the inner radiation belt?

7. What is the nature of the SKR source region?

9Proximal +/- 1 hr Priorities June 5, 2014

F-ring orbit geometry relative to auroral field lines

10Proximal +/- 1 hr Priorities June 5, 2014

• Very interesting region where Saturn is ‘connected’ to the rings via the planetary magnetic field

• Unexplored except for a brief period during SOI

• Direct access to field lines carrying lightning whistlers.

• Is there a connection between lightning and ring features like spokes?

• Are there sprite-like phenomena associated with lightning that might accelerate electrons toward the rings?

• Explore a mechanism to explain similar periodicities in the rings and magnetosphere

• Revisit VLF emissions associated with ring impacts

• Is there undetected material between Saturn and inner edge of D-ring?

• Best opportunity to explore Saturn’s exosphere, thermosphere, and ionosphere

• Are there wave-particle interactions in inner radiation belt (chorus)?

Opportunities provided by the proximal orbit geometry

11Proximal +/- 1 hr Priorities June 5, 2014

Gurnett et al., GRL, 2010.Kurth et al., PRE-VII, 2011.

• The F-ring orbits provide the best opportunity to revisit auroral field lines at low altitudes and perhaps another opportunity to explore the SKR source region.

• These orbits also afford passes along auroral field lines in order to map these into the distant magnetosphere (magnetotail) to understand these connections.

• Campaigns have been proposed for HST auroral imaging (and other Earth-based observations during this portion of the Cassini mission.

12Proximal +/- 1 hr Priorities June 5, 2014

Brief bursts of VLF emissions were detected during SOI when Cassini was over the main ring system.

Hypothesis was that these bursts were indications of cm-sized impactors on the rings, excited by the ionized gas generated by the impact.

VLF Emissions due to impacts on rings

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• Does lightning in Saturn’s atmosphere interact with the rings?

• Are there sprite-like phenomena that accelerate electrons out of the ionosphere?

Saturn – ring interactions related to lighting

14Proximal +/- 1 hr Priorities June 5, 2014

RPWS Contributions to Science Priorities in F-Ring and Proximal Orbits

• MC1b - Observe Saturn’s magnetosphere over a solar cycle, from one solar minimum to the next.

• MN1b - Conduct in situ studies of Saturn’s ionosphere and inner radiation belt.

• MN1c - Investigate magnetospheric periodicities, their coupling to the ionosphere, and how the SKR period is imposed from close to the planet (3-5 Rs) out to the deep tail.

• MN2a - Determine the coupling between Saturn’s rings and ionosphere.

• SC1b - Observe seasonal changes in the winds at all accessible altitudes coupled with simultaneous observations of clouds, temperatures, composition, and lightning.

• SC2a - Observe the magnetosphere, ionosphere, and aurora as they change on all time scales - minutes to years - and are affected by seasonal and solar cycle forcing.

• SN1a - Determine Saturn's rotation rate and internal structure despite the planet's unexpected high degree of axisymmetry.

• SN2a - Observe Saturn's newly discovered lightning storms

15Proximal +/- 1 hr Priorities June 5, 2014

Backup

RPWS Team Science Priorities (+/- 1 hr)

16Proximal +/- 1 hr Priorities June 5, 2014

RPWS Observational Requirements (Periapsis ± 1 Hour)

1. Lightning whistler search should be done on thrusters – couple with periapses that require thrusters to offset atmospheric torque: minimum two passes +/- 40 minutes, three desired

2. Langmuir probe interferometry observations of the ionosphere can ride along with an INMS-friendly attitude: Periapsis +/- 30 minutes with NEG_X to Dust Ram, ≥ 2 periapses at each of the 3 different periapsis altitudes

3. Whistler, dust, wave-particle interactions, ring impact signatures, all require wideband observations, hence, data volume.

4. All but INMS/LP observations require no special attitude and can ride along with virtually any other science

5. Desire to have empty SSR and science telemetry for atmospheric entry – quasi-RT science data as feasible

17Proximal +/- 1 hr Priorities June 5, 2014

Mitchell et al., Icarus, 2013

• Periodicities observed in the occurrence of spokes in the rings appear to include such magnetospheric periods as those for Saturn kilometric radiation and magnetic fields.

• The proximal orbits take Cassini through magnetic fields which connect Saturn to the rings; this would seem to be an obvious place to look for linkages.

An opportunity to explore sources for ring periodicities