NASA’s Planetary Geology, Geophysics and Geochemistry Laboratory

Mercury North Polar Topography

The Mercury Laser Altimeter (MLA) was a laser altimeter onboard the NASA MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging) mission. MESSENGER was the first spacecraft to orbit Mercury and it observed the Mercury surface and environment for more than four years. MLA obtained millions of laser altimetric measurements giving the distance between the spacecraft and the surface. Given spacecraft pointing and position information, these could be geolocated in the Mercury body-fixed frame. The MLA team at GSFC analyzed the MESSENGER radio tracking data and MLA altimetric data to obtain maps of topography that have proved a fundamental dataset for Mercury data analysis. Due to the very eccentric orbit of MESSENGER, with a periapsis near the north pole, MLA could only obtain altimetric ranges between ~18°S and the north pole.

Since the archival of the MLA topographic maps to the PDS in 2016, analysis of the MESSENGER data has continued. Some examples of recent studies that used MLA data are Hamill et al. (2020) and Barker et al. (2022), focused on the polar craters that host volatiles, and Bertone et al. (2021), making the first measurement of tidal deformation of Mercury.

Here we present improved topographic maps of the polar regions. The MLA tracks were iteratively adjusted to minimize mismatch, following a methodology is similar to Zuber et al. (2012) and Barker et al. (2021). These maps are in the latest Mercury reference frame, which used the MESSENGER data to update the previous IAU definition (see here for a SPICE PCK kernel). In particular, note that the datum reference is 2439.4 km, not 2440 km as previously.
These maps are higher-quality than the ones archived on the PDS in 2016, but did not benefit from supplemental MDIS data (with the shape-from-shading technique, as in Hamill et al. 2020 and Barker et al. 2022).
In addition to the topographic maps (HDEM), we provide the MLA data count maps (HDEC) which can be used to better understand the (sparse) coverage of the MLA data in the northern hemisphere.

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