Slide 1 - School of Mathematical Sciences School of Mathematical by pengxiuhui


									                              Cassini Imaging at Saturn
                                    (from a QMUL perspective)

2005 JUL 22 M.W. Evans QMUL
                      What is Cassini doing right now?

Excerpt from sequence S12 SPASS (Spacecraft Attitude SpreadSheet)
2005-203 is Day Of Year 203 in the year 2005 i.e. July 22 2005.
                         What is Cassini seeing right now?

Output from CASPER
visualisation tool for
2005 Jul 22 08:05:00
Cassini highlights from a purely QMUL perspective
        (observations that the Queen Mary group have been directly involved in)

   In no particular order

   1. Discovery of new satellites
   2. Interactions between F ring and Prometheus
   3. Mutual events between saturnian satellites
   4. High resolution observations of features in the rings
   5. Ongoing campaign of satellite orbit determination
                           Mutual Events

A mutual event is when one satellite passes in front of another.
The event can be timed to high accuracy and used in the determination
of the orbits of the two satellites.
With this type of observation no information about where the camera is
pointed is needed .
Several such observations have already been made
Dione-Rhea Mutual Event
Mimas-Janus Mutual Event
Dione-Helene Mutual Event
                  Interaction between the F ring and Prometheus
 2004 June

Re-projected image of the F ring. In the bottom left a faint stream of material, or streamer, connects the ring to
the satellite Prometheus.

Streamer probably formed when Prometheus moved into the F ring and locally disrupted material in the ring.

2005 July 1

Region of Wide Angle
                                       F ring
camera image

Dark lanes, or striations,
in F ring are clearly
visible but no streamer of
material between the F
ring and Prometheus             A ring outer edge

The white square
indicates the approximate                       Prometheus
region simultaneously
imaged by the Narrow
Angle camera shown in
the following slide.

Narrow Angle camera
image N1467350440
taken at same time as
Wide Angle camera
image on previous
4 striations can be
clearly seen.

               Longitude-radius re-projection of SOI WAC image

Location of Prometheus apocentre passages showing alignment with F ring striations
(image from SOI, 2004 July 1). Arrows indicate the location in longitude of positions
at which Prometheus was at its apoapse (A for the core and B for a ring 140 km interior
to the core). “B” arrows separated by 2.8 deg. In inner dust sheet striations are
approximately linear and their gradients are entirely consistent with the Keplerian shear
of an initially radial feature formed when Prometheus is at apoapse.
    During apoapse passage Prometheus pulls a streamer of material from the F ring --
the dark lanes or striations are the regions from which material has been removed at
previous apoapse passages
Prometheus a streamer and striations in the same image
                  Discovery of new satellites

To date there have been 4 confirmed discoveries of new
satellites by Cassini

S/2004 S 1 (Methone) - 2004 June 1
S/2004 S 2 (Pallene) - 2004 June 1
S/2004 S 5 (Polydeuces) - 2004 October 21
S/2005 S 1 - 2005 May 1

Which brings the current number of saturnian satellites to 35
S/2004 S 5 (Polydeuces)

Cassini WAC image 1477086063.
The first of the 4 S/2004 S 5 discovery images
The same image with star & satellite locations added
S/2004 S 5 discovery. Pair of images shuttered on 2004 October 21
                 (Small sections of full images)
       S/2004 S 5 (Polydeuces) discovery movie

                 QuickTime™ and a
            Photo - JPEG decompre ssor
           are neede d to se e this picture.

Movie consists of small sections of 4 consecutive images
S/2005 S 1 discovery sequence. Satellite in the Keeler Gap

                        QuickTime™ an d a
                   Photo - JPEG decompressor
                  are need ed to see this picture.
  High resolution image of the                                               Pandora 12:11 ILR
  325 km wide Encke gap in
  the A ring taken during SOI.                                               Prometheus 17:16 ILR
  The gap is maintained by the
  satellite Pan (not in this

  Clearly visible are 3 ringlets
  in the gap, edge waves on                           Prometheus 15:14 ILR
  the inner edge and
  associated wakes caused by
  the passage of Pan and
  resonance features either
  side of the gap due to mean
  motion resonances with the
  satellites Prometheus and

Prometheus 15:14 ILR radius 133,163 km
Pandora   12:11 ILR radius 133,793 km
Prometheus 17:16 ILR radius 133,901 km

                                         Image N1467351325
                                   Satellite in a ring gap and edge waves

The gravitational interaction between a satellite and ring particle (in the frame rotating with the satellite). Each ring
particle receives a “kick” as it drifts past the satellite which increases its eccentricity and it then proceeds on a
sinusoidal path.
It can be shown that

Where        is satellite mass/planet mass
                                  Cassini websites

ISS Team homepage

JPL Cassini homepage

         publicly available jpegs of all images (usually everything up to the
         previous day)

The full science quality Cassini images (launch through September 2004)

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