Experiment Boom: A third type of boom, shorter and much more rigid, extended from the last side of the spacecraft, opposite the RTG. This was a hollow carbon-fiber tube, of 50 mm (2 in.) diameter. It can be seen in the photo as the silver rod stowed alongside the body. It carried four types of instruments: a solid-state X-ray instrument, composed of two silicon detectors, to study X-rays from solar flares and Jupiter's aurorae; the Gamma-Ray Burst experiment, consisting of two CsI scintillator crystals with photomultipliers; two different magnetometers, a helium vector magnetometer and a fluxgate magnetometer; and a two-axis magnetic search coil antenna measured AC magnetic fields.