This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Saturday, May 5, 2012

Supermoon, Earth, Io and Enceladus

Tonight is a much publicized "supermoon,"a celestial event with the moon makes its annual closest approach to the earth and is opposite the sun giving a full moon.** The moon's orbit around the earth is elliptical, coming as close as 222,000 miles (perigee) and as far as 252,000 miles (apogee). It will appear bigger and brighter than other full moons. According to space.com, the moon will appear 14% larger and 30% brighter than other times of the year.

The moon will appear most spectacular right around moonrise, though this is largely due to an optical illusion rather than to its closer proximity. The exact cause of this illusion is debated. One theory is that the presence of objects, such as trees or buildings in the foreground, make the eye focus differently, and another holds that the brain interprets distant objects as wider.

Since the earth tides (both in the solid earth and in its oceans) are caused by the gravitational attraction of the moon and sun (mostly the moon), tides are expected to be higher than normal, but not by enough to get all excited about. NASA estimates about 1" higher than usual, possibly somewhat higher depending on local geography, and also amplified if there are storms in the area.

Example of amplified tides due to supermoon. This record,
extracted  from a NASA video of a longer time-record.
There is a lot of speculation on the WWW about possible supermoon effects on earthquakes and volcanic eruptions (good grief--including the Tohoku earthquake in 2011. For a debunking of this, see here.) There is no scientific evidence to suggest any dramatic effects associated with supermoons. There are, however, two other places in the solar system where moons do cause spectacular effects.

One is on Io, a satellite of Jupiter. The gravity of Jupiter and its largest moon Ganymede, with help from two other moons Europa and Ganymede, cause tides over 300 feet, as high as a 30 story building. This deformation causes such heating in the interior of Io that it spouts fiery volcanoes of sulfur and sulfur dioxide. The other is on Enceladus, a frigid satellite of Saturn. Enceladus is only 80 K, 80 degrees above absolute zero, at its equator, but at its south pole, temperatures as high as 180 K have been measured. In that region, icy plumes of water ice spurt out into the vacuum of space. The tides on Io and their effect in producing volcanism were figured out by three scientists***  even before the Voyager spacecraft arrived there and observed the volcanism. The tides on Enceladus and their relation to the plumes are still not fully understood. Two different satellites, two different manifestations of tidal energy.

**Here is an excellent article about the event from EarthSky.org.
***Peale, Cassen, Reynolds, Science, 203, 4383, pp. 892-894, 1979

1 comment:

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