Mars: A Big and Bright Geological Ghost

Thursday, October 20th, 2005 at 01:35 PM by Juan

Mars has been in the news recently for two reasons. The first being that Mars will be “Big and Bright” at the end of this month. The second reason is that there is now clear evidence that Mars, a geologically dead world, was once a much more geologically active planet. In either case, Mars is set to make this Halloween rather interesting astronomically speaking. You are welcome to SCSU’s Astronomy Public Nights for a chance to view this “big and bright geological ghost” through a telescope for yourself. The Planetarium shows will run as scheduled but telescopic viewing will only occur on clear nights. Reservations are needed for the Planetarium show but not for the telescopic viewing.^[1] See you there!

Big and Bright
On the night of October 29-30, Mars will be at its closest point to the Earth. It will be at 43.1 million miles (69.4 million kilometers) from our planet. Although it will not be as close as it was two years ago it will be a nice view through a telescope. This approach of Mars will be the closest until the summer of 2018.

The apparent size of Mars will only be 20 arcseconds (1/3 of an arcminute), about equal to the apparent size of a penny at 620 feet away. The full Moon, by contrast, appears to have a diameter of 30 arcminutes or about 90 times larger than Mars. The remainder of this year and next, the Earth-Mars distance will increase as the Earth passes Mars up and speeds away from Mars.

(Click on image for full-size version.) This amazing image of Mars was posted on SpaceWeather.com earlier today. It was taken by Larry Owens of Atlanta, GA using a 14-inch telescope. Among other things, it captures a sandstorm working its way up the Valles Marineris.

Current images of Mars barely show the polar ice caps on Mars. This is due to seasonal changes on Mars and the current tilt of Mars. We do, however, see a bright orange disk with distinct areas of light and dark (or in the amazing image shown here, we can even see the geological features of Mars).

Geological Ghost
We often teach students that Mars is a geological ghost, a world on which geological activity was initially vigorous enough to create the largest canyon (the Valles Marineris) and volcanoes (Olympus Mons) in the solar system but which today is a geologically dead world. This month, several planetary scientists published the first high-resolution map of Mars’ magnetic field using the Mars Global Surveyor. The features seen in the map are important because

Mars currently has no global magnetic field of internal origin but must have had one in the past, when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like magnetic field. … Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes and Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and support the notion that the Mars crust formed during an early era of plate tectonics.^[2]

(Click on image for full-size version.) A map of the magnetic fields of Mars from Connerney, et al. (2005). The full-size version clearly shows that the magnetic features seem to line up perpendicular to those (known) faults (which are represented by dashed lines).

In other words, this map of Mars’ magnetic field reveals something many planetary geologists had suspected, that Mars once experienced plate tectonics like those that drive earthquakes and continental drift on Earth. However, due to its small size, Mars cooled off quickly and stopped its plate tectonics more than 3 billion years ago. To quote Dr. Ness, one of the authors of this discovery:

That would make Mars less likely to develop life [because the loss of a magnetic field] may, in turn, cause the loss of the protection of the magnetosphere, which helps with blocking the solar wind, and which may have stripped away the oxygen and water that used to be there.^[3]

I think this discovery is also interesting in that it illustrates one of the key features that sets science apart from idle speculation. Planetary scientists have had a theory to explain the formation of the planets for quite some time. However, a scientific theory is only as strong as the predictions it makes that can be verified observationally. One of the predictions for the current theory is that there must have been tectonic activity on Mars in the distant past if planets formed at the same time through similar processes. Our confidence in our understanding of planetary geology has received a boost from this discovery.

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