Apollo 12 solar wind data from Lunar surface

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Apollo 12 solar wind data from Lunar surface

Apollo program has huge impact on human beings. Humans for the first time reached the other world, touched the lunar surface. Astronauts had tasks to take samples of the lunar surface and take them back to the Earth. Among Apollo digging instruments were placed also scientific instruments.

Apollo 12 project had a special meaning to me. And that is the exploration of the Solar wind. Astronauts set the instruments on the lunar surface and the data are available in the CDAWeb (Coordinated Data Analysis Web: CDAWeb), which is a public database from the current and past space physics missions. It is possible to download the original data, or ascii files, or plot the data in the way as I did.  

Apollo 12: 28 second resolution data on March 24, 1976 09 - 12 UT: Density 1/cm^3, Bulk SW speed km/s, V_thermal km/s (SW solar wind, UT universal time)

 The solar wind is a constant stream of plasma and charged particles from the upper atmosphere of the Sun, called Corona, spreading into the space. The interplanetary magnetic field is embedded within the solar wind plasma. The solar wind varies in density, speed and temperature over the time and over the solar latitude. The speed of the solar wind ranges from slow solar wind 300 - 500 km/s to fast solar wind 500 - 1000 km/s and temperature between 10^6 K to 10^5 K. Slow solar wind is almost twice denser than the fast solar wind. The fast solar wind originates from coronal holes, which is the region of open magnetic field lines. The slow solar wind originates from the streamer belts over the closed magnetic field lines. The typical solar wind magnetic field is about 5 nT.

 On the upper figure are shown 28s resolution plasma parameters observed on the lunar surface by Apollo 12 from November 24, 1976 09:00 UT until 12:00 UT (chosen randomly from data which were available online at the moment).

 The Earth's Moon has no real atmosphere or intrinsic magnetic field. The lunar surface is directly hit by the solar wind. The Apollo program deployed aluminium foil sheet to measure the solar wind properties and the lunar surface soil. The study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. The experiment was deployed by the astronauts and the foil was taken later back for farther analysis. On top of it Apollo 12 carried a SWS (solar wind spectrometer) which was left on the lunar surface. 
credit NASA

 The IMP-8 spacecraft (NASA) was launched in October 1973 and was providing data of the solar wind properties until 2006 in a distance of 1 AU from the Sun (distance between Sun and Earth). It was instrumented for interplanetary and magnetotail studies of cosmic rays, energetic solar particles, plasma, electric and magnetic fields of the solar wind. And the data from this spacecraft can be compared to what was received from Apollo project on the lunar surface. 
IMP8: B [nT] magnetic field by IMP8 in 1 AU

IMP8: Solar wind speed V [km/s], thermal speed [km/s], proton density [1/cm^3]
The first separated panel shows the averaged magnetic field B [nT] in 15 s resolution. It showed averaged solar wind without any strong fluctuations, between 4.5 and 5 nT. That cannot be compared to Apollo 12 data, because I do not have the data available. The solar wind speed V [km/s] in order of 380 km/s didn't differ from the both measurements and clearly shows that the Moon is directly hit by the solar wind. The proton density in the third panel was in half compared to what was observed in the solar wind by IMP8 and Apollo 12 on the lunar surface. 





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