Best evidence yet for active volcanism on Venus?

Overview

In an article from Geophysical Research Letters, a team led by Eugene Shaygin used images taken by the Venus Monitoring Camera (VMC) aboard Venus Express to identify transient hot spots on the surface. These hot spots are located near very young (~10 Mya) volcanoes and rifts, and are suggestive of active lava flows.

Even though the surface is generally obscured from view by the thick clouds, there is a transparent window through which light can pass in the near infrared wavelengths, and the VMC can capture images near 1 μm.

What Did They Find?

Examining VMC images of the Atla Regio region, the research team identified bright spots, i.e., areas where the local emissivity was significantly higher. These hot spots were first seen in VMC images from June 2008, and were gone again by October.

VMC images of Ganiki Chasma showing transient hot spots

They believe they have eliminated other possible sources for these hot spots, and they are confident the spots represent an increase in the surface temperature.

As additional supporting evidence, they point to Magellan spacecraft radar imagery.  Radar-dark parabolas are seen around impact craters on Venus, and are understood to represent deposited ejecta from the impact (more here in this paper by Campbell et al.). These parabolas are associated with the youngest impact craters, and believed to be among the youngest visible features on the planet. Magellan images of the same location show that the ejecta parabola associated with crater Stillwell is interrupted by what could be lighter colored lava flows that would post-date the fairly recent ejecta.

The authors believe these hot spots are volcanic in origin, and the body of evidence suggests that Venus is currently geodynamically active.

Why Is It Important?

If there are active volcanoes on Venus, it would be invaluable for future comparative studies of rocky worlds with ongoing volcanism. It could shed light on why the Earth and Venus evolved so differently, and help us learn more about the Earth in the process.

References:

Shalygin, E., Markiewicz, W., Basilevsky, A., Titov, D., Ignatiev, N., & Head, J. (2015). Active volcanism on Venus in the Ganiki Chasma rift zone Geophysical Research Letters, 42 (12), 4762-4769 DOI: 10.1002/2015GL064088

Campbell, B., Campbell, D., Morgan, G., Carter, L., Nolan, M., & Chandler, J. (2015). Evidence for crater ejecta on Venus tessera terrain from Earth-based radar images Icarus, 250, 123-130 DOI: 10.1016/j.icarus.2014.11.025

Searching for volcanic eruptions on Venus: Nothing yet

Eugene Shalygin and colleagues report on their ongoing attempts to detect volcanic activity on Venus. The Venus Monitoring Camera (VMC) carried by the Venus Express orbiter is capable of making observations in the near-infrared centered around 1.01 microns, a wavelength at which thermal emissions from the planet's surface can be detected on the night side.  They are making observations in likely locations, specifically the area around the Maat Mons, Sapas Mons, and Ozza Mons volcanoes (Messenger spacecraft SAR data showed recent volcanism here, geologically speaking), with the hope of detecting localized bright spots in the images.

To get an idea of how often Maat Mons might erupt, the team reviewed the eruption history of Mauna Loa on Earth since 1900.  They found that even though it is an active volcano, there are only eruption events on 1.6% of the days during the 100 years they evaluated.  Accounting for the length of observation on Venus, the authors calculated a probability of seeing an eruption during any particular observation at 8.6%.

Ultimately, the series of observations made with the VMC, 12 passes in all, did not reveal any suspicious hot spots that could be interpreted as volcanic events.  This does not preclude the possibility that eruptions occurred during this time, but did so while Venus Express was not looking.

They recommend that they keep looking, of course (I concur).

REFERENCES:

Shalygin, E., Basilevsky, A., Markiewicz, W., Titov, D., Kreslavsky, M., & Roatsch, T. (2012). Search for ongoing volcanic activity on Venus: Case study of Maat Mons, Sapas Mons and Ozza Mons volcanoes Planetary and Space Science, 73 (1), 294-301 DOI: 10.1016/j.pss.2012.08.018


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Variations in sulphur dioxide at the cloud tops of Venus: due to volcanoes? maybe not

A recent article in Nature Geoscience, Variations of sulphur dioxide at the cloud top of Venus's dynamic atmosphere, has caused the science press to get excited about the possibility of active volcanoes on Venus.

Every news headline I saw over the last few weeks that referred to this article wondered aloud if there are active volcanoes.  Even the ESA website poses the news as a question.  So, does Venus have active volcanism?  First, let's talk about the paper and what it reports.

Emmanuel Marcq and colleagues used ultraviolet spectrometer data  collected from 2007 to 2012 using the SPICAV instrument aboard the Venus Express spacecraft to examine the density of sulphur dioxide above the clouds of Venus.  They found that SO2 column densities increased prior to 2007, and then decreased by a factor of 5 over the next five years.

This finding is quite similar to observations made by the Pioneer Venus Orbiter in the 1970s and 1980s, which revealed a ten-fold decrease in  SO2 column density.  At the time, Larry Esposito (1984) of the Laboratory for Atmospheric and Space Physics in Boulder interpreted this decline to have occurred following an episode of volcanogenic upwelling from the lower atmosphere (it is important to note that SO2 is abundant and ubiquitous in the lower atmosphere of Venus).

Marcq, et al. conclude that the SO2 variability observed from the 1970s to the present is the result of long-timescale fluctuations in upward transport from the troposphere to the mesosphere.

What they do not know is whether this is the result of 1) episodic increased buoyancy from volcanic plumes, or 2) intrinsic dynamic variability in the upward component of the global circulation.

Back to our original question: Does Venus possess active volcanoes?  This study cannot answer that question.  The authors seem to want it to be so, but say in their conclusion: "By Occam's razor, we are inclined to think that this variability originates from intrinsic dynamical variability in the ascending sub-solar branch of the global circulation at cloud-top level on a decennial timescale rather than from an external forcing such as extra buoyancy caused by volcanic eruptions, but we cannot dismiss a volcanic forcing through our study alone."

It's pretty clear that most people want active volcanoes on Venus, but the jury is still out, I'm afraid.



REFERENCES:

Esposito, L. W. (1984). Sulfur dioxide: Episodic injection shows evidence for active venus volcanism. Science (New York, N.Y.), 223(4640), 1072-1074. doi: 10.1126/science.223.4640.1072

Marcq, E., Bertaux, J., Montmessin, F., & Belyaev, D. (2012). Variations of sulphur dioxide at the cloud top of Venus’s dynamic atmosphere Nature Geoscience DOI: 10.1038/NGEO1650