NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Impact Vaporization as a Possible Source of Mercury's Calcium ExosphereMercury's calcium exosphere varies in a periodic way with that planet's true anomaly. We show that this pattern can be explained by impact vaporization from interplanetary dust with variations being due to Mercury's radial and vertical excursions through an interplanetary dust disk having an inclination within 5 degrees of the plane of Mercury's orbit. Both a highly inclined dust disk and a two-disk model (where the two disks have a mutual inclination) fail to reproduce the observed variation in calcium exospheric abundance with Mercury true anomaly angle. However, an additional source of impacting dust beyond the nominal dust disk is required near Mercury's true anomaly (ν) 25deg +/-5deg. This is close to but not coincident with Mercury's true anomaly (ν=45deg) when it crosses comet 2P/Encke's present day orbital plane. Interestingly, the Taurid meteor storms at Earth, which are also due to Comet Encke, are observed to occur when Earth's true anomaly is +/-20 or so degrees before and after the position where Earth and Encke orbital planes cross. The lack of exact correspondence with the present day orbit of Encke may indicate the width of the potential stream along Mercury's orbit or a previous cometary orbit. The extreme energy of the escaping calcium, estimated to have a temperature greater than 50000 K if the source is thermal, cannot be due to the impact process itself but must be imparted by an additional mechanism such as dissociation of a calcium-bearing molecule or ionization followed by recombination.
Document ID
20150010116
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Killen, Rosemary M.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Hahn, Joseph M.
(Texas Univ. Austin, TX, United States)
Date Acquired
June 8, 2015
Publication Date
April 2, 2015
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
GSFC-E-DAA-TN19659
Funding Number(s)
CONTRACT_GRANT: NNX07AR78G
CONTRACT_GRANT: AST-1313013
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Dust
Interplanetary
Exosphere
No Preview Available