Venusian Volcanism?

It is known that the planet Venus had been volcanically active in the past. In addition to previously discussed resurfacing, there is evidence of more recent volcanoes and rift zones (areas of radial cracks stretching away from a volcano, from which lava may arise). While this is a definite change in volcanism type from Venus’s past, one question remains: what about volcanism now?
There is a rather logical reason to expect Venus to be geologically active in some way. Venus is approximately the same size as Earth. Geologic activity requires heat from the inside; smaller bodies, like the Moon and Mercury, cooled long ago and are geologically ‘dead’; since the Earth and Venus are comparable in size, their internal heat should be as well. Most likely, geological activity on Venus would not be the same as Earth. Venus’s lithosphere (the outer crust and upper part of the molten mantle) appears to be a solid ‘shell’; no plate tectonics. In more contrasts to Earth, the surface of Venus is hot and at a high pressure, mostly due to the carbon dioxide in its thick atmosphere. Recent observations have shown anomalies in the amount of sulfur dioxide in this atmosphere.
Venus' surface as revealed by radar. Image credit Magellan Project/JPL/NASA.
Venus’ surface as revealed by radar. Image credit Magellan Project/JPL/NASA.
This brings us to today’s article, Active Volcanism on Venus in the Ganiki Chasma Rift Zone, by E. V. Shalygin, W. J. Markiewicz, A. T. Basilevsky, D. V. Titov, N. I. Ignatiev, and J. W. Head. Published in the American Geophysical Union’s publication Geophysical Research Letters in May 2015, these authors looked for evidence of volcanism on present-day Venus.
The authors used the European Space Agency’s Venus Express mission to complete this task. This spacecraft, which was in orbit around Venus from 2006 to 2014, had an instrument capable of detecting the temperature of Venus’s surface and any ‘thermal anomalies’–places that are hotter or colder than one would expect. Such an anomaly, or ‘bright spot’ as it would appear in the data, does not necessarily mean volcanism: it could be an effect of natural atmospheric variations, or the presence of clouds.
The average surface temperature on Venus is 740 Kelvin (872 Fahrenheit, 467 Celcius), and four spots warmer than this were found in instrument data that were not explainable from an atmospheric viewpoint. They were dubbed A through D. Three of these were visible for days, then later vanished, A and B slowly ebbing away over a few days. The exact behavior is difficult to determine due to the timing of observations. All the bright spots appeared near an area called Ganiki Chasma–specifically, near fault lines in the rift zone. In a terrestrial analog, Earth has its own rift zones often active as well, which strengthens the idea that these transient bright spots are volcanic in origin. Thermal anomalies of Earth found near volcanoes often last years, but are also supported by groundwater circulation that would not be present on Venus, and the atmosphere may also play a role in the difference in duration.
Most likely, the source of these bright spots was an effusive eruption (lava coming up through the rifts instead of the center of the volcano) and likely recent. The determination on age is because the areas of the bright spots are superimposed on remnants of a recent crater, shows lava over old faults, and new faults. If this is the case, this may explain the aforementioned variations in sulfur dioxide seen in the atmosphere, as well as demonstrate modern day volcanism on Venus, though there is certainly more to learn.

 

Bibliography
Astronomy Picture of the Day. “APOD: 2005 September 3 – Venus Unveiled.” N.p., 3 Sept. 2005. Web.
The picture used in the middle of the paper, illustrating Venus’ surface.
Bennett, Jeffrey O., ed. The Cosmic Perspective. 7th ed. Boston: Addison-Wesley, 2014. Print.
One of my astronomy textbooks, used for reference on what we know of Venus and its geologic history.
European Space Agency. Venus Express. European Space Agency, 2015. Web.
The home page for a site devoted to Venus Express and its science. This and the links it provided gave me the years the spacecraft was orbiting around Venus.
Marshak, Stephen. Earth: Portrait of a Planet. 3rd ed. W.W. Norton & Company. Print.
My geology textbook, used for reference on rift zones and volcanism in general.
Shalygin, E. V., W. J. Markiewicz, A. T. Basilevsky, D. V. Titov, N. I. Ignatiev, and J. W. Head (2015), Active volcanism on Venus in the Ganiki Chasma rift zone, Geophys. Res. Lett., 42, doi:10.1002/2015GL064088
Today’s main article.
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