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As one of the seven scientific payloads on board the Tianwen-1 orbiter, the Mars Orbiter Magnetometer (MOMAG) will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind. The instrument consists of two identical triaxial fluxgate magnetometer sensors, mounted on a 3.19 meter-long boom with a seperation of about 90 cm. The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads. The sensors are controlled by an electric box mounted inside the orbiter. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 10,000 nT per axis) with a resolution of 1.19 pT. Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz, but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.

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A well-resolved elliptical shell in the inner Orion Nebula has been investigated by monochromatic imaging plus high-and low-resolution spectroscopy.We find that it is of low ionization and the two bright ends are moving at -39 and -49 km s -1 with respect to OMC-1. There is no central object, even in the infrared J bandpass although H 2 emission indicates a possib!¢ association with the nearby very young prermain-sequence star J&W 352, which is one of the youngest pre-main-sequence stars in the inner Orion Nebula. Many of the characteristics of this object (low ionization, blue shift) are like those of the Herbig'Haro objects, although the symmetric form would make it an unusual member of that Class. 'L g NASA-CR-204652 1, L/_I'I'IKUIJ U IS'I'IUIN The basic structure of the Orion Nebula (NGC 1976; M42) is now understood to be thatof a blister of ionized gas (Zuckerman 1973;Balick et al. 1974; Meaburn 1975;Pankonin et al. 1979;Balick et al. 1980) on the near side of the Orion Molecular Cloud. The relatively thin layer of ionized material is the background to a highly dense nearby cluster of young stars (Herbig 1982) and both of these regions are viewed through a layer of material optically thick to ionizing radiation but marginally optically thick in visual wavelengths (van der Werf and Goss 1989; O'Dell et al. 1992). Astrophysical methods have been used to determine a threedimensional model of the ionized material (Wen and O'Dell 1995), which is a highly irregular concave form. The nebula is known to be populated by at least ten objects considered to be Herbig-Haro (HH) objects (Reipurth 1994) and numerous features resembling shock fronts which are blue shifted with respect to the main emitting layer (O'Dell et al. 1993a). The cluster of stars associated with M42 is no more than 2 million years old (Prosser et al. 1994) and contains a large range of stellar masses, the lower-mass stars still being in their pre-main-sequence contraction. Most of these lowermass stars are surrounded by circumstellar material which is likely to be distributed as disks, which may be protoplanetary. The facing side of most of these circumstellar disks, called proplyds, are photoionized by the same stars creating the ionized nebula. This causes local conditions of flow of the ionized material, which certainly occurs in the tails that point away from the sources of ionization (O'Dell et al. 1993b; O'Dell and Wen 1994) and may also occur on the cusps formed on the substellar sides (McCullough et al. 1994). Given the presence of these very young stars, whose formation is commonly believed to produce disks and jets as necessary components, it is hardly surprising that imaging and spectroscopy reveal numerous examples of compressed 1Guest Observer,