20 november 2006boston mercury observation workshop observational quests for mercury’s exosphere...
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20 November 2006 Boston Mercury Observation Workshop
Observational Questsfor Mercury’sExosphere
Ann L. SpragueLunar and Planetary Laboratory
University of ArizonaTucson, AZ 85721
20 November 2006 Boston Mercury Observation Workshop
Constituent Reference Column Abundance (atoms per cm2)
Hydrogen (H) Broadfoot et al. 1976 ~5x1010
Helium (He) Broadfoot et al. 1976 ~2x1013
Oxygen (O) Broadfoot et al. 1976 ~7x1012
Sodium (Na) Potter and Morgan 1985
~2x1012
Potassium (K) Potter and Morgan 1986
~1x1010
Calcium (Ca) Bida et al. 2000 ~1x107
Mercury’s Known Exospheric Species
Quest #1 What else?
20 November 2006 Boston Mercury Observation Workshop
Sprague et al. 1995
Predict S in Mercury’s Exosphere
From:
meteoritescometssulfides in regolith
Test this hypothesis withMESSENGER
20 November 2006 Boston Mercury Observation Workshop
Na and K
• Association with surface features• Diurnal wind• Distribution with true anomaly• Multiple release mechanisms• Relationship to the magnetosphere
Quest #2 Relationships to other physical parameters
20 November 2006 Boston Mercury Observation Workshop
The radar image thatshook the world ofplanetary science!!!
Ice at the polesOf Mercury!!!
Or…is it Sulfur?
Or…is it cold iron and titanium free silicate pyroclastics?
Or…is it somethingelse?
Slade et al. 1992, Harmon and Slade 1992, Butler et al. 1993
Quest #3 Relationship of exosphere to regions ofhigh radar albedo and coherent backscatter
20 November 2006 Boston Mercury Observation Workshop
Kuiper-Murasaki Crater Complex with seeing smear
20 November 2006 Boston Mercury Observation Workshop
Radar and Visible bright Spot BGeometry not quite right to show Spot A rotating aroundfrom the west.
Amateurs are imaging the surface of Mercury and finding high albedo regions
Na and K observations over these regions to look for sources would be useful
Image courtesy of Steve Massey
20 November 2006 Boston Mercury Observation Workshop
Image courtesy Frank Melillo, Holtsville, NY.
700nm
20 November 2006 Boston Mercury Observation Workshop
a. 55N, 27S; 6E, 354W
Spot B and Spot A
b. Same
c. Same,
also Kuiper-Murasaki
d. Spots B and A
e. Same
f. Same
g. Caloris Basin
h. 65N, 205E; 155W
0, 235E,125W
9S, 255E, 105W
i. 35S, 287-317E
43-73W
Filter Imaging andSpectroscopy (Na)
Sprague et al. 1998
20 November 2006 Boston Mercury Observation Workshop
Not observed over the
Surface like Na and K
Bida et al. 2000
Killen et al. 2004
Radiance of emission~ 2.5 kRay
High radial velocity (-2 km/s)indicates high energy
20 November 2006 Boston Mercury Observation Workshop
Test the hypothesis that exospheric O and Caare of solar wind origin.
At Mercury the Ca/O ~ 2.0 10-3 with a factor of 2 uncertainty in the O measurement (Broadfoot et al. 1976); there is small variability in the Ca measurements.
The ratio of Ca/O in the solar wind is ~ 1-4 10-3 (Wurz et al. 2001, 2003).
The similarity of the Ca/O ratio above the limb of Mercury (~ 2.0 10-3) to that of the solar wind, compels serious consideration that the source of Ca and O in Mercury's exosphere is originally the Sun via the delivery of O+6 and Ca+11 in the solar wind.
Koehn and Sprague, In Press, PSS, 2006
20 November 2006 Boston Mercury Observation Workshop
Model impact distribution of Ca+11 on the surface of Mercury for specific solar wind conditions Southern hemisphere impact sites dominate Color bar--the number of parcels impacting per site Each parcel represents ~1017 Ca ions Similar behavior, with more pronounced preference for
southern hemisphere impacts is seen for O+6
Mid- latitudeenhancements
20 November 2006 Boston Mercury Observation Workshop
Summary: Quests
Quest #1 What other constituents?
Quest #4 What is source for Ca and O?
Quest #2 Relationship to other physical parameters?
Quest #3 Relationship to regions ofhigh radar albedo, coherent backscatter,
and high visible albedo?