astroavani Posted March 22, 2016 Share Posted March 22, 2016 The graph above can be considered one of the most important diagrams of lunar science. This chart is the basis to estimate the ages of parts of the Moon where we have physical samples. Y-axis of the graph is shown the N number of impact craters in areas where the Apollo and Luna probes collected samples. In the laboratory we were determined were determined the ages of the samples and these data are shown in the X axis units for the X axis are easy to understand, age of formation of rocks in giga years, or billions of years. The units of the Y axis represents the cumulative number of craters equal to or greater than 1 km in diameter per square kilometer. remote sensing scientists use the best Moon images to count the number of primary impact craters in areas centered on where the samples of the Apollo missions and moon were collected. Normally this count craters covers areas of hundreds of square kilometers in order to ensure statistical significance to the value of N. This graph has been used for decades, but, for example, Copernicus data do not conform to it apparently there are also many subsequent craters compared with age assumed 0.8 Ga dating based on samples made in Apollo 12do which may be a radius of Copernicus. But now Harry Heisinger and his colleagues used high-resolution LRO images to retell the craters that formed on top of Copernicus and its ejecta, determining a value of N (red cross) that exactly fits with what was expected. The other red markings show that the new values N determined for the Tycho crater and the North Ray Crater Apollo 16 confirmed previous estimates. The power of this graph is that you can count craters for many areas of geological interest on the moon and extend a horizontal line of the calculated values of N on the Y axis to the right to intercept the curve. Arriving at the corner and down to the X axis you then have the age estimated from counts calibrated craters. Scientists from Kaguya mission used this technique when they determined that there were lavas aged 1.2 Ga in Oceanus Procellarum. This figure is also a history of bombing the moon suffered, with growth tail being responsible for the sharp drop in the value of N around 3.5 Ga. No one knows exactly why the cratering rate has stabilized with only a small decrease of 3.5 to 1 Ga, or that plunged since. But there are considerable uncertainties in this curve, the lunar samples were dated to determine ages for Nectaris, Copernicus and Tycho, but not if you have some evidence that the samples actually came from those features. Source: LPOD / Cienctec Adaptation: Avani Soareshttp://www.astrobin.com/full/242724/0/?real=&mod= 16 Link to comment Share on other sites More sharing options...
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