Geodynamics Science Highlight
NASA GSFC Geodynamics 921

SCIENCE HIGHLIGHT

Geodynamics Branch, Code 921

SEPTEMBER 2003

Sanchez Study Shows Effects of Atmospheric Torques on Mars
Paper Published in Journal of Geophysical Research (Planets)

picture of Braulio Sanchez
In a paper recently published in Journal of Geophysical Research (Planets), Braulio Sanchez studied “Atmospheric Rotational Effects on Mars Based on the NASA Ames General Circulation Model”. His analysis evaluated the topographic, stress and pressure torques in changes in the length of the day (LOD) of Mars and on the motion of its pole. Surface values of stress and pressure were taken from the NASA Ames General Circulation Model, provided by co-author Bob Haberle. Sanchez developed separate time series for both the moments of inertia of the ice caps and the axial component of atmospheric angular momentum. He found that stress dominates the torque budget on Mars, which is different from the Earth where pressure effects dominate.

Power spectrum of polar motion for Mars

Above: Power spectrum of polar motion for Mars. Below: Motion of the pole from atmospheric torques, dominated by stress

Motion of the pole from atmospheric torques, dominated by stress

The annual and semi-annual changes in LOD amplitudes from the ice caps and axial torque were found to be 0.747 and 0.121 milliseconds respectively. The torque-induced polar motion on Mars reaches a maximum of 16.26 mm in the second half of the Martian Northern Hemisphere winter (see Figure at right, bottom). Calculated changes in LOD using the angular momentum approach are smaller, 0.187 and 0.136 milliseconds for the annual and semi-annual harmonics.

The expected precision of the planned but now delayed ESA NetLander Ionospheric and Geodesic Experiment (NEIGE) could detect the main harmonics in the LOD time series, which could be used to test the results based on the model. Annual and semi-annual polar motion harmonics induced by atmospheric torques are below the level of NEIGE detection.

color bar

Contact: Braulio Sanchez, GSFC, Code 921 (bsanchez@santafe.nasa.gov)

small earth image Back to Geodynamics Science Highlights

Responsible NASA official: Dr. Herbert Frey

This page maintained by Jim Roark (SSAI)
Last modified on September 29, 2003