Clark%20R.%20Chapman%20(SwRI),%20S.C.%20Solomon%20(CIW),%20R.%20L.%20McNutt,%20Jr.%20(APL),%20B.%20J.%20Anderson%20(APL),%20L.%20G.%20Evans%20(CSC),%20R.%20E.%20Gold%20(APL),%20J.W.%20Head%20(Brown%20Univ.),%20S.%20M.%20Krimigis%20(APL),%20S.%20L.%20Murchie%20(APL),%20L.%20R.%20Nittler%20(CIW),%20R.%20J.%20Phillips%20(SwRI),%20J.%20A.

1
Mercury after Three MESSENGER Flybys

• Clark R. Chapman (SwRI), S.C. Solomon (CIW), R.
  L. McNutt, Jr. (APL), B. J. Anderson (APL), L. G.
  Evans (CSC), R. E. Gold (APL), J.W. Head (Brown
  Univ.), S. M. Krimigis (APL), S. L. Murchie
  (APL), L. R. Nittler (CIW), R. J. Phillips
  (SwRI), J. A. Slavin (GSFC), M. T. Zuber (MIT),
  and the MESSENGER Team

11. Mission Highlights and Prize Presentations
DPS 2009, Fajardo, Puerto Rico 6 October 2009
2
Payload Instruments
3
Flyby Geometries
M1
M2
M3
- 3
4
M3 Gravity Assist

• Closest approach was 227.8 km above Mercury
  surface
• Spacecraft flew only 218 m below the targeted
  altitude.
• Next scheduled trajectory-correction maneuver
  will likely not be needed.
• Next maneuver will be the fifth (and final) Deep
  Space Maneuver on 24 November.

5
M3 Data Return
M3 WAC image (750 nm), 4.8 km/pixel resolution

• Safe-hold aborted collection of closest-approach
  and departure data
• Images were acquired for 6 of surface for the
  first time
• Useful approach-science data were obtained from 6
  of 7 instruments plus radio science
• 441 images were collected on approach
• Data collection resumed on 3 October, with
  another 817 images planned

6
M3 Magnetic Field and Plasma Protons
Magnetopause
Bow shock

• Passage across magnetotail dusk to midnight
• Highly dynamic tail magnetic field factor of 5
  variation in magnitude
• Field variations anti-correlate with protons
  suggests motion of tail structure

7
Internal Field Model
Smooth inversions of MESSENGER and M10
observations, after correcting for external
fields and accounting for noise contributions,
yield harmonic fields.
Uno et al., 2009
Field is dominantly dipolar (215 nT RM3, 2
tilt), with substantial higher-order structure.
Anderson et al., LPSC, 2008
- 7
8
Mercurys Exosphere and Neutral Tail
9
Tail Species Comparison, M2
Variations in the observed distributions
constrain the combination of source processes
involved.
10
Mercury Imaging Coverage
11
Mercury Imaging Coverage
12
Terminator Views M2 vs. M3
M3
M2
- 12
13
Mercury Laser Altimeter Topography
14
Evidence of Surface Contraction
Beagle Rupes
M3 scarp
Puerto Rico (to scale)
Mariner 10 revealed an abundance of lobate
scarps, reflecting crustal shortening on
surfaces ranging from ancient intercrater plains
to the youngest smooth plains. Many more have
been seen on all 3 flybys.
15

• Rembrandt
• The Rembrandt basin represents an intermediate
  stage of filling by volcanic plains, between the
  largely unfilled lunar Orientale basin and the
  nearly completely filled Caloris basin and lunar
  Imbrium basin.

Orientale
16
Detail of Rembrandt Basin
17
Extensional Faults in the Outer Caloris Basin
Floor
18
Extensional Tectonics at the Center of Caloris
Pantheon Fossae

• Radial graben complex located near the center of
  Caloris, discovered during M1
• Individual graben can extend for hundreds of
  kilometers

19
Rare evidence of surface extension
Caloris
Rembrandt
Watters et al., 2009
Raditladi
20
Raditladis Twin, Imaged on M3
Raditladi
Newly-imaged basin
50 km
The extremely low density of small craters on
Raditladi suggested that it might be just 1 Gy
old. The newly-imaged basin during M3 may have
even fewer craters inside its peak-ring,
suggesting unexpectedly recent volcanism.
21
Morphology and Color Variations Imply Volcanic
Activity
Well come back to this feature in a moment
100 km
22
Simplified crustal cross-section
Origin of Smooth Plains
Denevi et al., 2009
M1
23
Mercury Surface Spectra
McClintock et al., 2008

• Mercury is spectrally similar to lunar highlands
  (without FeO band).
• Spatial variations in spectra are resolvable and
  reflect differences in maturity and composition.

Distance (Radii)
Sample of M1 spectra
- 23
24
Possible Volcanic Vents
newly-imaged basin
20 km
25
Crater Size-Frequency Distributions
Strom et al., 2008 Fassett et al., 2009
26
100 km

100 km

Interesting impact features imaged on the M3 flyby
27

Orbital Mission Phase
Mercury Orbit Insertion 18 March 2011
Three flybys down, 730 to go!
- 27
28
Summary of M3 Results

• Imaged 6 of Mercurys surface never before
  viewed by spacecraft
• Relatively young double-ring basin found that is
  very similar to Raditladi
• Additional examples of volcanism seen
• Imaging completed of region of MLA profile on M1
• Doppler filtering of thermal neutrons is being
  used to determine average surface composition of
  neutron-absorbing elements (Fe Ti)
• Significant magnetic field activity different
  from first two flybys
• Exosphere and tail searched for new species
• No energetic particles seen

- 28
29
Density
30
M3 Flyby Anomaly

• At 555 pm EDT on 29 September the MESSENGER
  spacecraft flew by Mercury and achieved its
  needed gravity assist.
• Minutes before closest approach, MESSENGER
  entered an anticipated eclipse, and power
  switched to the battery.
• Autonomy detected an unexpected power
  configuration and sent the spacecraft into
  safe-hold, halting data collection but preserving
  already collected data.
• Review of telemetry after the eclipse and later
  conjunction revealed the anomaly but showed that
  all systems (including power) were behaving
  normally.
• MESSENGER was quickly restored to operational
  mode, and all stored data were downlinked on 30
  September.
• Detailed investigation of the root cause of the
  anomaly is ongoing.
• On the basis of performance data from this event,
  modifications to flight operational set points
  will be implemented to eliminate the potential
  for recurrence of this event.

- 30