Let’s Explore Solar System Seismic Activity

Volcanoes: Io (which is slightly larger than the Earth

The U.S. Geological survey estimates that Earth experiences several million earthquakes and around 50 volcanic eruptions every year. But ours is not the only cosmic body that experiences seismic activity: ongoing exploration of the Solar System and the Universe by astronomers and other scientists indicates that volcanic eruptions and quakes (some similar to those on Earth and others vastly different) have been observed on our Moon as well as a growing list of planets, exo-moons, and stars within our galaxy.

The term seismic activity refers to the propagation and movement of elastic waves, called seismic waves, through a planetary body due to perturbations deep beneath its surface or in its upper layers. These waves cause quakes — the shaking and rolling motions that shifts a planet’s upper crust and surface. Quakes can have numerous causes; on Earth, movement of the tectonic plates that make up the planet’s surface, and the molten rock in the mantle beneath it, is the primary cause of earthquakes here at home.

On other bodies within the Solar System including our sun, seismic activity can be caused by other processes as well.  Tidal forces, pressures from cold gases and the roiling of the outer layers of a star can create movements which produce seismic waves, some capable of causing quakes and eruptions many times stronger than those observed on Earth.

The planets of our Solar System can be grouped according to their shared features and distance from the Sun.  The inner planets –Mercury, Venus, Earth and Mars — orbit close to the Sun and are composed primarily of rock, with a solid outer crust.  Beyond Mars, the “gas giants” Jupiter, Saturn, Uranus and Neptune consist largely of hydrogen, ammonia and methane gases around a small, solid core.

Because the inner planets, Earth’s closest neighbors in space, share a hard crust and an originally molten core, all show evidence of volcanic activity. Even tiny Mercury, closest to the Sun, reveals features characteristic of past eruptions.  Photographs and probes of Venus, with its hot cloudy atmosphere, and dry cold Mars also show fault lines, volcanic mountains and ancient lava flows indicating a seismically active past, when planetary cores were hotter and more liquid.

Composed largely of gasses, the outer planets lack a surface crust and a volatile molten core — key features necessary for large-scale planetary seismic activity.  However, in January 2011, advances in asteroseismology (the study of seismic activity on stars) delivered a surprise:  seismic waves were detected on Jupiter, whose composition – liquids and gases around a small rocky core – actually resembles that of the sun.

A variety of factors cause quakes on our moon and others in the Solar System, where evidence of past and present seismic activity has been captured in photographs.  Quakes on our own solitary Moon are caused not by movement of tectonic plates or lava, but by the pull of Earth’s gravity and the expansion of the moon’s cold crust when sunlight returns to its surface after the long lunar night, which lasts 14 Earth days.

Jupiter’s large moon Io experiences extensive seismic activity due to internal friction caused by Jupiter’s gravitational pull. Images of Io, Neptune’s moon Triton and Enceladus, a large moon of Saturn, also reveal evidence of massive cryovolcanic eruptions – explosions caused by pressures of cold or frozen gases beneath the moon’s surface.

Since stars consist primarily of gases, seismic waves observed on stars are believed to originate from turbulence in the outer, convective zone rather than the core. Some of these “star quakes” generate enough energy to cause the entire star to vibrate like a bell. Although our Sun is of course a star, helioseismology (from Greek, Helios: sun), a subspecialty of asteroseismology, focuses on the seismic activity detected there. A solar flare can generate sunquakes, some of which produce energy equivalent to earthquakes of magnitude 11 or stronger.

Beyond the orbit of Neptune, the Kuiper Belt is a region of small icy objects thought to be remnants from the formation of the Solar System. Although Kuiper Belt objects are composed largely of ices such as methane and ammonia, some hints of seismic activity can be observed even there. At 783 miles (1260 km) wide — large enough to have its own name — the Kuiper Belt Object Quaour has an observable surface area containing features suggestive of cryovolcanic changes.

Although conditions on our Earth are ripe for frequent quakes and eruptions, ongoing exploration and observation of the Solar System and the universe beyond reveal that, at least as far as seismic activity is concerned, we truly are not alone in the cosmos.

Image Credit: SOHO/NASA

Reference:

Martínez-Oliveros, J., Moradi, H., Besliu-Ionescu, D., Donea, A., Cally, P., & Lindsey, C. (2007). From Gigahertz to Millihertz: A Multiwavelength Study of the Acoustically Active 14 August 2004 M7.4 Solar Flare Solar Physics, 245 (1), 121-139 DOI: 10.1007/s11207-007-9004-8

A. Grigahcène, M.-A. Dupret, S. G. Sousa, M. J. P. F. G. Monteiro, R. Garrido, R. Scuflaire, & M. Gabriel (2011). Towards precise asteroseismology of solar-like stars Astrophysics and Space Science Proceedings series (ASSP) DOI: arXiv:1112.5961
Sibani, P., & Christiansen, S. (2008). Thermal shifts and intermittent linear response of aging systems Physical Review E, 77 (4) DOI: 10.1103/PhysRevE.77.041106

Sibani, P., & Christiansen, S. (2008). Thermal shifts and intermittent linear response of aging systems Physical Review E, 77 (4) DOI: 10.1103/PhysRevE.77.041106

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