Pergamon www.elsevier.nl/locate/asr Adv. Space Res. Vol. 23, No. 11, pp. 1879-1886,1999 0 1999 COSPAR. published bv Elsevier Science zyxwvutsrqponmlkjihgfedc Ltd. All riahts reserved PII: SO273-1177(99)00271-Q Printed in &eat Britain 0273-I IT?/99 $20.00 + 0.00 zyxwvutsrq MGS MAGNETIC FIELDS AND ELECTRON REFLECTOMETER INVESTIGATION: DISCOVERY OF PALEOMAGNETIC FIELDS DUE TO CRUSTAL REMANENCE N.F. Ness’, M.H. Acufia2, J. Connerney 2, P. Wasilewski2, C. Mazelle3, J. Sauvaud3, D. Vignes3, C. d’Uston3, H. Reme3, R. Lin4, D.L. Mitchel14,J. McFadden4, D. Curtis4, P. Cloutie$, and S. J. Baue@ zyxwvutsrqponmlk 1 UDEL-Burt01Research Imtitute, Newark, DE 2NASA-GSFC7Greenbelt, MD 3CESWCMS, Toulouse, FR 4UC-Berkeley, Berkeley, CA SRice Univ., Houston, TX 6Univ. of Graz, Austria ABSTRACT The MGS MAC&R investigation provides vector measurements of the magnetic field and the ionospheric electron density near periapsis. The instrumentation consists of twin triaxial fluxgate magnetometers and a “top hat” electrostatic analyzer of electrons in the energy range of 1 eV to 20 keV. Results include extensive mapping of the detached bow shock wave in the solar wind, the nature and structure of the ionopause and magnetic pile-up boundaries. The most surprising result is the discovery of localized magnetic fields of planetary origin, presumably due to remanent crustal magnetization. Maximum fields measured while below the ionosphere exceed 300 nT. We present an initial study of one of these very localized fields and extrapolations to the Martian surface in the Acidalia planitia. 0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO 1999 COSPAR. Published by Elsevier Science Ltd. The Magnetometer-Electron Reflectometer (MAG/ER) experiment on the Mars Global Surveyor (MGS) has as its primary objective the detection and mapping of any intrinsic magnetic field of Mars and the continuation of studies of the nature of the solar wind interaction with the planetary ionosphere- atmosphere. Previous studies of these problems (Breus, 1992; Dolginov, 1987; Riedler et al. 1989; Schwingenschuh et al. 1990; Trotignon et al. 1993; and Verigin et al. 1993) has revealed the existence of a well-developed detached bow shock wave close to the planet and strong interaction with the atmosphere-ionosphere. But it had not been possible, because of the location of the measurements or their quality to make an accurate estimate of any global planetary magnetic field. Rather only an upper estimate of 2 x 1O22 Gauss- cm3 has been derived based upon similarity scaling considerations with Earth’s bow shock (Dolginov and Zhuzgov, 199 1). The MAG/ER instrumentation is identical to that developed and flown on the Mars Observer (MO) spacecraft (Acufia et al. 1992) that failed to be successfully injected into captured Martian orbit in 1993. 1879