Planetary scientists are rearranging Apollo-era moonquake data to ensure that these valuable measurements carry over into new generations.
Fifty years ago, during the Apollo moon landing program, astronauts left more than footprints on the moon before returning to Earth. For long-term scientific research, they placed seismograph equipment on the moon to measure the tiny displacements on the ground caused by seismic waves inside the moon. The instruments were placed at a distance from each other and still worked well with the technology of the time. After waiting patiently, the five lunar seismometers (set up by the Apollo 11, 12, 14, 15 and 16 missions) have recorded numerous moonquakes and meteor impacts. Geological rock blocks are easily fractured and arranged in a disorderly manner.
It is not easy to obtain data from seismometers successfully, because it is not only dependent on the equipment in space, but also the analysis of the logistics equipment on the earth side is equally important. Seismographs cannot store data. When they detect seismic waves, they will transmit radio signals immediately, which are received by NASA’s Deep Space Network (DSN) and recorded on ranging tapes. Data digitization.
Multi-layer conversion, the chance of error is relatively increased. First, the measurement speed of the seismometer is unstable, which means that the instrument is very sensitive to the temperature of the lunar surface, and there is an uneven distribution of density during measurement. Second, the time parameter on the working tape is based on the time when the earth received the data, but the number of receiving antennas in the deep space network will affect the data transmission. lost. Over the decades, every time a tape was copied, a small portion of the data was corrupted. After this batch of seismograph data was digitized, it was found that there were many loopholes, repetitions, and slight deviations in the time records. Although it can be used in scientific analysis, it cannot be integrated into modern seismic data analysis software. Personnel also need to be very familiar with the mission at the time to know how to use the data, but this is not the same operation that most planetary scientists are familiar with.
Dr. Ceri Nunn (NASA JPL) and the collaborating team carried out the restoration of the scientific data this time, and took on the heavy responsibility of re-storage. Fix timekeeping issues from tape and convert files into modern data formats. It is hoped that the new data archive will make it easier for a new generation of young seismologists to use the data to understand the structure of the moon. A detailed record of the restoration has been published in the Journal of Planetary Science by the first author, Dr. Nunn, and the newly restored data of the Apollo-era moonquakes are made public.
▲ Seismic profile of a shallow moonquake. The X-axis is time (seconds), and the Y-axis is the vertical displacement of the surface (meters). Documenting the instruments deployed on Apollo 12. (Source: IOPscience, the same below)
▲ Comparison before and after restoration of the same earthquake record. (top) before sorting; (bottom) repaired by the author’s team.
(This article is reproduced with permission from the Taipei Planetarium; the first picture shows the astronauts placing a seismometer on the moon, source: NASA)
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