NEAR's Magnetometer

Magnetometer

The magnetometer (MAG), one of the instruments on the NEAR spacecraft, is mounted on a tripod off the high gain antenna. It will measure the strength and direction of Eros' magnetic field, and may be capable of detecting variations in the field depending on their magnitude and scale. The major purpose of determining the strength of the magnetic field is to help indicate the origin of Eros. If a small magnetic field is detected, this may indicate that Eros is composed of tiny, stable rocks or particles clumped together creating no circulation of matter. A small magnetic field could also mean that Eros contains magnetized particles, but because they are pointing in different directions, they cancel each other out. If a larger magnetic field is detected, this may indicate that a heat source, possibly composed of liquid iron and nickel, is present. Presence of a magnetic field in conjunction with data collected from other instruments, such as the Near Infrared Spectrometer and the Multispectral Imager, can further indicate the composition of Eros.

The Earth's magnetic field is generated in the mobile outer core composed of liquid iron and nickel. The source of the magnetic field cannot be permanently magnetized material, because the interior of the Earth is too hot for any material to retain its magnetism. This means that the Earth's magnetism must be generated electromagnetically. The Earth behaves much like that of a bar magnet. Think of the Earth as having a giant bar magnet passing from one pole to the other pole through its center.

Magnetism of an iron magnet is caused by electric currents associated with the spinning motion of atomic electrons. If the magnetometer indicates a large magnetic field for Eros then it could be assumed that there is a current circulating Eros causing the field. To get a general idea of what a magnetic field looks like, think of iron filings sprinkled around a bar magnet. The iron filings would take on the appearance of the characteristic dipole pattern. A magnetic field might exist in the space around a magnet, similar to the way an electric field surrounds a charged body.

The magnetometer fluxgate sensor and electronics

The magnetometer antenna
dish assembly

Lesson Plan on Magnetism

Magnetometer Overview on NEAR Web Server

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Contact Steve Bowser (slbowser@umd5.umd.edu) or
Joy Maloney (jmaloney@umd5.umd.edu) for further information.