Magsat reenters atmosphere



NASA's magnetic-field-mapping satellite, Magsat, reentered the atmosphere north of the Arctic Circle and burned up on reentry at 0720 UT, June 11, after a longer-than-expected (7 1/2-month) lifetime (see ‘Magsat to Reenter Soon,’ EOS, 61, 475, May 27, 1980). The objectives of the mission were to provide a global vector survey of the main geopotential field and low-altitude measurements of crustal anomalies. Data were obtained nearly up to the time of reentry. The Figure shows ‘quick-look’ data from a 3000-km-long pass taken at 1940 UT on June 10, about 12 hours before reentry. The satellite was over the western Pacific, near the Mariana trench. The data were obtained at altitudes of 187 to 191 km, which is believed to be the lowest altitude at which magnetic field data have been obtained from a satellite. The quantity plotted is δB, i.e., the difference between the measured field magnitude and the field which is calculated from a 13th-degree spherical harmonic model that is derived from Magsat data. The variations are probably due to crustal sources. If confirmed, the data will represent the highest resolution of crustal magnetic anomalies that has been achieved from satellite measurements.