# Presentation: 519492

## HYPERION: The Sponge Moon

- Dr. James Bauer, JPL
- Dr. Peter Thomas, Cornell University
- August 28, 2007

## Hyperion & the Saturnian System

## Hyperion from the Ground

**Hyperion from the Ground**

- Mommery et al. 2000

- R. H. Brown 85

- Hyperion

- Bauer et al. 97

- Saturn RPX

## Hyperion & Voyager

## Hyperion's Icy Surface

**Hyperion's Icy Surface**

- Brightest regions are exposed water ice in the rim of the crater that dominates the hemisphere in view (Hendrix & Hansen, 2007).

- UVIS

- ISS

- VIMS

- UVIS

## Spectra of bright and dark regions

## CO2 on high- and low-albedo  regions of Hyperion

- R. Clark, USGS

- Full spectrum with model,
- Cruikshank et al. 2007

## Compositional maps

- of Hyperion

- Iapetus

- The low-albedo material on Hyperion (in the craters) appears to be
- The same as that on Saturn’s other satellite, Iapetus.

## Origin of dark material?

**The IR spectra show that Phoebe dark material**
**is similar to Iapetus dark material, but the visual **
**spectra show that Hyperion and Iapetus are **
**more similar.**

- Buratti et al., 2001, *Icarus*
*(200-inch Hale telescope)*

**Origin of dark material?**

## Hyperion Composition

**Hyperion Composition**
**Map**

- Map by B. Dalton

_**Color code:**_
_**Blue **_**= H****2****O band depth**
_**Red**_** = CO****2**** band depth**
_**Green **_**= 2.42 ****μ****m band**
- Yellow = CO2 + 2.42 μm
- Magenta = H2O + CO2

- VIMS/ISS

- ISS

## CO2 bands on Iapetus and Hyperion compared.  

- CO2 bands on Iapetus and Hyperion compared.
- The shift of the Hyperion’s CO2 band center toward
- shorter wavelengths indicates that the CO2 molecules
- are somehow combined with, or attached to, other
- materials (possibly water ice molecules).

## Origin of the CO2

- Converted CO:   CO ↔ CO2  (Moore, Hudson, et al.)
- Product of H2O + carbonaceous material with UV
- Impact or shock-induced chemistry, e.g., H2O + CH3OH → CO2 ... (Naa Mvondo et al. 2007)
- Why is Hyperion’s CO2 complexed (when CO2 on other satellites is not) ?

- Original – requires re-supply to surface

- M. Brown, 2000

- S

- J

- U

- N

## Ubiquitous CO2?

**Ubiquitous CO2?**

- CO2  appears to be present on many outer Solar System surfaces including moons of Jupiter, Neptune &       Uranus, and Saturn

- Callisto, Hibbitts et al. 00

- Grundy et al . 03

- Clark et al. 05

## Hyperion, or

** ****what makes a space sponge?**

## 		        Hyperion

**Interesting because it has chaotic rotation,**
**is the largest irregularly-shaped satellite seen to date,**
**Voyager hinted at spotty albedo distribution.**
**Cassini made close flyby 26 September 2005, and**
**Several passes <500000 km at other times.**

- Voyager views
- of Hyperion

## Hyperion: the numbers

- Mean radius: 135 ± 4 km
- Range of diameters: 195 – 349 km
- Mean density 540 ± 50 km m-3
- (mass from NAV and RSS teams)
- Surface gravity ~ 2cm s-2

- Because of chaotic and slow rotation, the
- generation of the shape model required stitching
- data from several encounter together.

## Spin found from observing “control” points

## Hyperion: more numbers

- Instantaneous spin pole solutions:
-        UTC range                                          RA  Dec    rate  SS lat
- 2005,160/18:10:05 - 161/09:58:38   208.4, 35.3   75   -14.1
- 2005,161/16:43:20 - 162/15:22:01   210.8, 39.3    75   -13.3
- 2005,228/01:46:59 - 228/20:16:46   271.3, 35.6   72    27.0
- 2005,228/22:16:13 - 229/12:15:23   266.7, 39.1   72    22.1
- 2005,268/04:29:06 - 268/17:20:16   315.1, 56.6   72    13.3
- 2005,268/17:20:16 - 269/02:18:20   299.8, 58.7   72    11.3
- 2006,179/02:24:03 - 180/04:15:09   184.5, 34.8   72  -43.7
- Rate: spin rate in degrees per day
- SS lat = sub solar latitude: note drastic changes

## Hyperion: the numbers mean what?

- Mean density of 540 kgm-3, combined with probabililty
- of a lot of water ice, mean porosity is >40%.  If there are
- Denser components, porosity is even higher.
- Very small ring-related satellites have even lower densities.

## Slide 20

## The 

- Sponge

- Count obvious
-  craters; then,
- what’s left?
- Not much

## Phoebe, Hyperion

- Telesto at similar
- scale

## Craters on Hyperion and Phoebe

- Between 2-10 km,
- 2x craters on Hyperion
- as Phoebe.
- >10 km Saturated
- Small: more on Phoebe?

## Little fill or erosion in

-  old craters.
- Little sublimation
- Little ejecta fill

## Role of porosity?

- Housen and Holsapple, 2003 suggest
- Less ejecta for porosities >30%;
- and proportional 1/gD

- Very plausible,
- if...
- Effects of big
- impacts?

## Geology

**Central peaked**
**crater?**
**Barely...**

## Hyperion 

- Sponge-like appearance from lots of 2-10 km
- craters with good rim preservation.
- No suncup role.
- Scant evidence of ejecta, and some evidence
- for relative lack of ejecta.
- Dark material concentrated by downslope motion
- and/or some sublimation
- Porosity effects on craters?