Volcanism on Mercury

Today I am going to return to Mercury, and our trusty MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, better known as MESSENGER. Specifically, we are looking at evidence of volcanism; more specifically, explosive volcanism. Explosive volcanism is what most people think of when they think of volcanism; greatly dramatic eruptions that Hollywood loves to show. There is also effusive volcanism, in which lava steadily spills from the volcano. This kind of volcanism is responsible for the smooth plains that fill nearly a fifth (18%) of Mercury’s surface. On Mercury, explosive volcanism may have outlasted effusive volcanism.
Mercury shows evidence for explosive volcanism. This brings us to today’s article, “Spectroscopic properties of explosive volcanism within the Caloris basin with MESSENGER observations” by S. Besse, A. Doressoundiram, and J. Benkhoff. Published in 2015 in the American Geophysical Union’s Journal of Geophysical Research: Planets, the article takes a closer look at the explosive volcanism on Mercury. 
Specifically, the article focuses on Caloris Basin. Around 1500 kilometers (932 miles) in diameter, the interior is filled with smooth plains from effusive volcanism, at a near constant thickness. Pyroclastic deposits, signs of explosive volcanism, are mostly found in the southern area.
A color enhanced image of Caloris basin, created with MESSENGER Images. Astronomy Picture of the Day for 5 March, 2015. Credit to NASA, Johns Hopkins Univ. APL, Arizona State U., CIW.
A color enhanced image of Caloris basin, created with MESSENGER Images. Astronomy Picture of the Day for 5 March, 2015. Credit to NASA, Johns Hopkins Univ. APL, Arizona State U., CIW.
Investigating these pyroclastic deposits with the instruments onboard MESSENGER was not the easiest task. Due to the instruments and their sensitivities, as well as the angle at which the surface was viewed, tricky corrections had to be made to the data set. These corrections were also tested on lunar data, to verify the method used.
The data was spectroscopic. Spectroscopy is observing how the spectra given off by a material when it interacts with something on the electromagnetic spectrum (in this case, near-infrared, visible, and ultraviolet (UV) light). There are different types of spectra (i.e. emission, absorption) but what is important here is that they can be used to determine various properties of a material. In this case, that material was thirty-one pyroclastic deposits on the surface of Mercury. Spectrally speaking, the pyroclastic deposits are redder than Mercury’s standard terrain. There were also variations in the deposits that appeared in the UV spectra, which could be caused by a few different reasons. The variability could be a decrease in iron compared to the rest of Mercury, or a change in grain size–the results are consistent with either or both. Since the UV results change with the distance to the volcanic vents, it could be due to the thinning of the material (which could explain a change in grain size). Results are inconclusive, but understanding the volcanism that occurred at Caloris is a piece in the puzzle of Mercury’s history.
As has been mentioned, there was difficulty in the correction of the data, and there is insufficient data to do detailed investigations of how many spectral properties change with distance to the vent. Things could be made easier, and more data gathered, with the European Space Agency’s BepiColombo mission. The spacecraft is currently set to launch next year, arriving at Mercury in 2024.

 

Bibliography
Astronomy Picture of the Day. Nemiroff, Robert and Bonnell, Jerry, ed.. Enhanced Color Caloris. Astronomy Picture of the Day. 5 Mar 2015. Web.
The source of the image used.
Besse, S., A. Doressoundiramand J. Benkhoff (2015), Spectroscopic properties of explosive volcanism within the Caloris basin with MESSENGER observations, J. Geophys. Res. Planets120, 2102–2117, doi:10.1002/2015JE004819
Today’s main artile.
European Space Agency. BepiColombo. European Space Agency, n.d. Web.
A page with news for the upcoming BepiColumbo mission.
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