Astronomy Question: Mars, As Viewed From Earth
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HST image of Mars circa 1995. Image credit: NASA/Space Telescope Science Institute, (University of Toledo)
Matthew writes:
Dear Astronomer,
Before we ever sent any sort of probes to Mars, Earthbound astronomers spoke of Mars going through color changes as viewed through their telescopes, and that these color changes repeated with a regular periodicity.
This observation was what got a number of science fiction writers contemplating the existence of life on Mars.I’ve not heard of the periodic change of color of Mars as viewed from Earth for years.
Does it still change colors as viewed from Earth? If not, did Mars ever change colors as viewed from Earth, or was this an astronomical variety of ‘urban legend’?
If Mars did or does change colors periodically as observed from Earth, what is the cause of this color change? Noting a potential for Earth atmospheric effects, but also noting that this phenomenon was never reported for observations of any other planet.
Thanks!
Matthew,
Great question Matthew!
The image below can shed some light on your question. Essentially, Mars experiences seasonal “storms” that have varied intensity. While Mars’ atmosphere is pretty thin compared to Earth, Titan or Venus, it’s significant enough for uneven heat distribution from the sun to cause pockets of warm rising air and cooler sinking air (the same basic mechanism for weather on Earth too!). The winds generated throw dust into the martian atmosphere, and have at times created numerous dust storms (would they be called haboobs on Mars too?) across the surface of Mars.
In the image below, The wide angle cameras of the Mars Orbiter Camera were used to study changes in martian weather and surface frost patterns. Starting in June 2001, as southern winter transitioned to spring, dust storm activity began to pick up as cold air from the south polar cap moved northward toward the warmer air at the martian equator. By early July, dust storms had popped up all over the planet. Soon, the entire planet was enshrouded in dust. While the storms largely subsided by September of 2001, the atmosphere still had significant haze at the end of 2001.
The 2001 dust storm wasn’t the only occurrence of large-scale weather on Mars. Notably, in 1971, Mars was experiencing a large scale dust storm when Mariner 9 arrived during the later portion of that year. The Mars Exploration Rovers, Spirit and Opportunity, have had periodic “cleaning” events in which wind gusts actually blew the accumulated dust off of their solar panels and have, along with orbital cameras, imaged the martian equivalent of “dust devils”.
Mars Orbital Camera Image of the Tharsis and Valles Marineris region of Mars during June 2001 (left) and July 2001(right). Both images are of the same region, but details on the image to the right are obscured by dust. Image Credit: NASA/JPL
Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer
2012-12-04 08:06:26
Source: http://www.dearastronomer.com/2011/07/25/mars-as-viewed-from-earth/
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