Mercury in the middle of a meteor shower


The measurements made by the Mercury Atmospheric and Surface Composition Spectrometer aboard NASA’s Messenger revealed seasonal peaks of calcium in the exosphere. The researchers believe it is due to a meteor shower, a constant siege for the first planet of the Solar System.


Credit: NASA

Mercury, the first planet of the solar system and the closest to the Sun, is going through a period of being really busy, at least as suggested by the data sent by NASA’s Messenger (Mercury Surface, Space Environment, Geochemistry, and Ranging), in the middle of a meteor shower. This event, also common around our planet, is probably associated with the passage of an asteroid or comet and its trail of debris, dust and gas: the smallest particles of dust, rock and ice undergo the influence of solar radiation that pushes them away, creating the famous comet tail (which in fact is only visible during the approach to the Sun).
“The possible discovery of a meteor shower on Mercury is really exciting and particularly important because the environment of plasma and dust around the planet is relatively unexplored,” said Rosemary Killen, a planetologist at the NASA Goddard Space Flight Center in Maryland, and lead author of the study published in Icarus. Specifically, NASA talks about Encke, the second periodic comet to be named after the much more famous Halley’s Comet. It is an object of about 2/3 kilometers in diameter ending its orbit around the Sun every three and a half years. Encke generates during the year two meteor showers visible from Earth, the Taurids of November and the Beta Taurids between June and July.
As said, the phenomenon of meteor showers also occurs around the Earth. During the summer nights can often happen to see, especially if the sky is clear, a meteor shower (the famous Perseids) generated by a passing comet. Messenger has shown that the rocks that are encountering Mercury are not very different from those whizzing around Earth, even during the winter (as the Geminid meteor shower, which reached their peak last weekend and that derive from the fragments left from 3200 Phaethon asteroid). However, the visual impact is different on Mercury, owing to the peak of calcium that is produced when passing a comet in the “vicinity” exosphere, that thin layer of low-density particles, and therefore, contains only light atoms (traces of hydrogen, helium, oxygen, sodium, calcium, potassium, and water vapor). Measurements made by the Mercury Atmospheric and Surface Composition Spectrometer aboard Messenger revealed seasonal peaks of calcium that occurred regularly during the first nine years (the probe began orbiting the planet in March 2011).


Credit: NASA

For the NASA researchers, the increase in regular calcium is caused by the arrival of a huge amount of dust particles that strike the planet freeing calcium molecules. It is a process (called evaporation from impact) that allows the renewal of the gas and the particles in the exosphere. But experts doubt that alone interplanetary dust present in the inner solar system can cause periodic spikes of calcium.
Think, then, to Mercury as a huge “vacuum” space, a planet that attracts dust and debris. Joseph Hahn explained: “The planet is under constant siege from interplanetary dust and then regularly passes through this another sandstorm, which we believe is from comet Encke. “The planet is under constant siege of interplanetary dust and then regularly passes through this dust storm, which we believe comes from the comet Encke.” In support of their hypothesis, the researchers brought the detailed computer simulations. However, data on the peaks of calcium collected by the probe Messenger are slightly different from the results of the simulations, this due to the gravitational force of Jupiter and other planets that changed slightly the orbit of the comet.

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