a persistent interplanetary magnetic field varying between 2 γ and 10 γ (nanotesla), which agrees with prior Pioneer 5 observations from 1960. This also means that interplanetary space is rarely empty or field-free. The magnetometer could detect changes of about 4 γ on any of the axes, but no trends above 10 γ were detected near Venus, nor were fluctuations seen like those that appear at Earth's magnetospheric termination. This means that Mariner 2 found no detectable magnetic field near Venus, although that didn't necessarily mean that Venus had none. However, if Venus had a magnetic field, then it would have to be at least smaller than 1/10 the magnetic field of the Earth. In 1980, the Pioneer Venus Orbiter indeed showed that Venus has a small weak magnetic field. The Anton type 213 Geiger-Müller tube performed as expected. The average rate was 0.6 counts per second. Increases in its counting rate were larger and more frequent than for the two larger tubes, since it was more sensitive to particles of lower energy. It detected 7 small solar bursts of radiation during September and October and 2 during November and December. The absence of a detectable magnetosphere was also confirmed by the tube; it detected no radiation belt at Venus similar to that of Earth. The count rate would have increased by 104, but no change was measured. It was also shown that in interplanetary space, the solar wind streams continuously, confirming a prediction by Eugene Parker, and the cosmic dust density is much lower than the near-Earth region. Improved estimates of Venus' mass and the value of the Astronomical Unit were made. Also, research, which was later confirmed by Earth-based radar and other explorations, suggested that Venus rotates very slowly and in a direction opposite that of the Earth. See also List of missions to Venus Microwave Radiometer (Juno), another microwave radiometer used in the 2010s on Jupiter References External links Mariner 2 Mission Profile by NASA's Solar System Exploration Full-scale engineering prototype of Mariner 2 in the Smithsonian Air and Space Museum, Washington, D.C. Mariner 2 Derelict satellites in heliocentric orbit Mariner program Missions to Venus Spacecraft launched in 1962 Derelict space probes Spacecraft launched by Atlas-Agena rockets Articles containing video clips de:Mariner#Mariner 1 und 2