The Mariner 5 spacecraft was launched in 1967 to carry a complement of experiments to probe Venus's atmosphere by radio occultation, measure the hydrogen hard ultraviolet spectrum, and sample the solar particles and magnetic field fluctuations above the planet. Data analyzed from Mariner 5 in 1971 found a small but irritatingly clear pattern in the turbulence perpendicular to both the direction of the travel and the magnetic field through which the solar wind was traveling. The effect was relatively small and has been essentially ignored by physicists until now.
Physicists' currently understand that turbulence in the solar wind should not be affected by the speed and direction of its travel, according to an article on Futurity. But when the first space probes attempted to measure the turbulence their observations didn’t quite match the physical law.
Recent space missions examining the solar wind with sensitive and highly-accurate modern instrumentation have found that the once small aberration was threatening to stand in the way of understanding solar wind—effectively the solar system’s largest and most interesting natural turbulence lab, according to the article.
Researchers at the University of Warwick have found a solution to this 40-year-old problem. The team viewed data from the recent Cluster mission and created a virtual model of how magnetohydrodynamic (MHD) turbulence builds up in the solar wind. They then flew a virtual space probe through that virtual model in a range of directions unlike the single direction of travel open to a probe such as Mariner 5. They reported their findings in the journal Physical Review Letters.
According to the article, researchers said the analysis clearly showed that when results were considered, correlation between changes in the turbulence in the solar wind and the direction of travel disappeared. The observed non-axisymmetric anisotropy may arise as a sampling effect of using just one probe taking a single particular path through the solar wind.