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Enceladus Flyby - 12 March 2008

Enceladus Flyby - 12 March 2008

12 March 2008

On 12 March 2008, Cassini visits Enceladus for the first time since the discovery of active geysers on this icy moon, two and a half years ago. The closest approach occurs at 19:06:12 UT at an altitude of just 52 kilometres above the surface and at a speed of 14.4 kilometres per second. This makes it Cassini's closest approach ever of Enceladus or any other Saturnian moon. The flyby occurs in orbit 61 of the mission.

Cassini will approach Enceladus on a fast, inclined trajectory over the northern hemisphere and after closest approach (at 20° S, 135° W) will depart over the southern hemisphere. Approximately 58 seconds after closest approach, Cassini will cross the centre of the moon's plume, at an altitude of approximately 641 km. The plume of ice, gas and dust particles originates from geysers erupting from giant fractures on the south pole of Enceladus and is thought to be continuously refreshed. This flyby offers unique in-situ observations of the plume's chemical composition.

Coincidently, Enceladus will be in eclipse (in Saturn's shadow) for just over two hours (19:05:16-21:18:08 UT) starting near closest-approach.

Science Highlights

  • Magnetospheric and Plasma Science (MAPS) group
    The different MAPS instruments will examine the particle environment at 50 km from the surface to determine the nature of the material coming form the surface and its relationship to Saturn's E-ring, and to distinguish between two potential populations of particles: plume particles and sputtered particles from elsewhere on the surface.
    -  Cassini Plasma Spectrometer (CAPS). CAPS will make measurements to understand Enceladus as a plasma source. Because Cassini will fly deeper into the plume than in July 2005, in situ instruments will measure a larger signal. The predicted increase in count rates suggests that INMS can provide new results on plume composition.
    -  Ion and Neutral Mass Spectrometer (INMS). One of the main science goals of INMS will be to try and determine the compositional differences in the plume gas versus the gas produced from E-ring bombardment at other latitudes. 
    -  Dual Technique Magnetometer (MAG). The close flyby distance will allow the magnetometer to determine whether Enceladus generates an induced magnetic field from a subsurface ocean. The magnetometer will also determine the composition of plume material from measurement of ion cyclotron waves in the magnetic field measurements
  • Visible and Infrared Mapping Spectrometer (VIMS)
    VIMS will perform compositional mapping to determine the identity of volatiles, organics, and minerals, and place them within a geologic context
  • Imaging Science Subsystem (ISS)
    ISS will image the surface of the cratered north polar terrain at up to 200 metre-scale resolution to determine the geologic history of Enceladus, including possible remnant tiger stripes; first good view of north polar regions (is all of it heavily cratered?)
  • Composite Infrared Spectrometer (CIRS)
    During the flyby Enceladus will pass through Saturn's shadow (solar eclipse as seen from Enceladus). CIRS will make observations of the warm-up after solar eclipse to determine the heat capacity and textural properties of the moon's regolith; observations of hot spots and determination of any changes from the previous flyby
  • Ultraviolet Imaging Spectrograph (UVIS)
    UVIS will obtain spectral images of Enceladus in the EUV (500-1100 Å) and FUV (1100-1900 Å) to map the surface composition, including water ice abundances and grain sizes, and will search for volatiles off the limb
  • Cassini Radar (RADAR)
    RADAR will perform scatterometry of both hemispheres to determine cm-scale roughness and radiometry to understand the energy balance

Table of events

16 February 2008

Time UTC

Time wrt
EN-61

Activity
11:51:00 -25d07h Start of Sequence S38 which contains Enceladus-61

10 March 2008

Time UTC

Time wrt
EN-61

Activity
01:06:00 -02d18h OTM #148 Prime. Enceladus-61 approach targeting manoeuvre

11 march 2008

Time UTC

Time wrt
EN-61

Activity
01:06:00 -01d18h OTM #148 Backup

12 march 2008

Time UTC

Time wrt
EN-61

Activity
02:36:00 -16h30m Start of the SOST Segment
03:31:12 -15h35m Inbound Enceladus ORS observations (distant). Images, compositional and temperature maps
14:36:12 -04h30m Inbound Enceladus RADAR
16:36:12 -02h30m Inbound ORS observations. Images and compositional maps
17:13:12 -01h53m Inbound ORS observations. Images and compositional maps
17:40:12 -01h26m ORS observations. Images, compositional maps
18:07:12 -00h59m ORS observations. Images, compositional and temperature maps
18:25:12 -00h41m ORS observations. Images and compositional maps of north pole region
18:44:42 -00h22m MAPS prime observations. In-situ INMS and CDA measurements
19:06:12 +00h00m Enceladus-61 Flyby Closest Approach Time. Altitude=52 km, speed=14.41 kms-1, high phase inbound, 136.5° phase at closest approach, mid phase outbound
19:11:12 +00h05m CIRS observations with Enceladus in Saturn's shadow
20:10:12 +01h04m Outbound Enceladus RADAR
20:54:12 +01h48m CIRS observations during and after eclipse (which ends at 21:18:08 UT)
22:01:12 +02h55m ORS observations (low-resolution). UVIS prime

13 march 2008

Time UTC

Time wrt
EN-61

Activity
00:14:12 +05h08m Deadtime, 5 minutes long. Used to accommodate changes in flyby time
00:20:00 +05h14m Turn to Earth
00:51:00 +05h45m 9 hr data downlink with Goldstone 70M

Observation Results

Instrument: Ion and Neutral Mass Spectrometer (INMS)

Date: 26 March 2008

Credit: NASA/JPL/SwRI

Image Notes: Mass spectrum showing the chemical constituents sampled in Enceladus' plume as the spacecraft flew through it

Instrument: Composite Infrared Spectrometer (CIRS)

Date: 26 March 2008

Credit: NASA/JPL/GSFC/SwRI/SSI

Image Notes: Southpolar map of thermal radiation between 12-16μm, revealing its distribution along the fractures. Plume jet locations are indicated with yellow stars

Instrument: Imaging Science Subsystem (ISS)

Date: 13 March 2008

Credit: NASA/JPL/Space Science Institute

Image Notes: Highest resolution view yet of Enceladus' north polar region, showing older and more cratered surface enclosed by younger terrain

Last Update: 1 September 2019
21-Apr-2021 11:59 UT

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https://sci.esa.int/s/AMej6XA

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