4 May 2009

Oppositions of Mars 2001-2014 Mars comes to opposition about every 25 or 26 months. Due to the ellipticity of the Martian orbit (e ~0.1) the Earth-Mars distance can vary quite a bit at different oppositions. The last close oppostion distance was in 2003 (which happened to be the closest opposition in 60,000 years, although others have been almost as close).

Mars in 2009-2010 Mars will be next at oppostion in early 2010. It will be about 14 arcsec diameter at closest approach. Not a very good opposition, but Mars will be in the northern part of sky, meaning it will pass almost directly overhead (where atmosphere is least bothersome) as seen from N. hemisphere.

Mars retrograde loops Relative to the background stars, Mars sometimes stops, reverses dierction, and make a "loop". This behavior drove early astronomers (who thought the Erath was at center of solar system) to the idea of epicycles.

Loops in heliocentric model Of course, these loops are easily understood in the heliocentric model- Earth is "lapping" Mars.

Schiaparelli drawing of Mars The late 19th c. Italian astronomer made drawing like this of Mars. Some of the features are real, most (particularly the linear "canali") are not.

Percival Lowells canals on Mars Around 1900, Percival Lowell ("self funded" astronomer from an old money Boston family) popularized the idea that there was a Martian civilzation that built "canals" to bring water from polar caps to crops. What was Lowell seeing?

Soap ad around 1900 In the early 20th c. , everyone "knew" there was a Martian civilization, mainly due to writings of Lowell. It was all nonsense, of course.

Earth and Mars to scale Mars has a radius about 0.53 that of Earth.

Mars from Earth Taken at the famous Lowell Observatory, in Flagstaff. Lowell was founded (and funded) by Percival Lowell. Lowell Observatory is one of the largest observatories not associated with a university or government, and part of its budget still comes from an endowment left by PL. So, even though PL was way wrong about Mars, he left an enduring positive legacy for astronomy.

Mars from Earth Mars around opposition in 2008. At closest, Mars was about 17 arcsec diameter. These images were taken with a small telescope. They were probably taken with the "take LOTS of images and throw out all but best" technique (which is really only useful for bright objects that you can image with short exposures!) Note the phase effects which cane be best seen in the top row of images.

Martian global topography Mars shows a global "hemispheric dichotomy". Spacecraft altimeter and gravity maps show that much of the northern hemisphere is on average 4 km lower than the southern hemisphere. New models hypothesize that this could be due to a giant impact about 4 Gyr ago that blasted a 10,000 x 8000 km basin. (See 26 June 2008 NATURE for details).

The Hellas Basin is the purple ellipse around -40 lat., 70 long. It is a 2300 km wide impact basin. A smaller impact basin, Argyre, can be seen at lat ~-50, long 320. Other large impact craters can be seen across planet. The large reddish blob centered at about 260 long on equator is the Tharsis Bulge, where all the large volcanoes are, as well as starting point for Valles Marineris.

Olympus Mons This is the largest shield volcano known in the solar system.

Valles Marineris A huge gash in Mars. This feature does NOT correspond to any of the features on Lowell's maps. It is of too low a contrast to be seen from Earth with current techniques. Named after the Mariner spacecraft.

Methane in Martian atmosphere Ground and space based spectroscopic observations detect methane in the Martian atmosphere. Methane is easily destroyed by solar UV photons, so any methane would only last a few hundred years in Martian atmosphere. So what is the source of this methane? Its either biological (bacteria or Martian cows) or non-biological (water- rock interactions?). Stay tuned, sports fans! This could turn out to be HUGE!

Sagan and Viking Carl Sagan next to Viking mockup in Death Valley. The two mid-1970s Viking landers (and also 2 orbiters) comprised a very ambitious and expensive set of missions to explore Mars and look for signs of life. Although the robotic chemistry lab that analyzed Martian soil (see picture of soil excavation trench below) found some unexpected chemical reactions, only a very few scientists think Viking found evidence for life. In 2008, the lander Phoenix found tentatve evidence for perchlorates in the Martian soil, a result which may help explain what Viking found.

After Viking failed to find definitive proof of life on Mars, interest in (and funding for) Mars missions waned for several decades.

Viking on Mars 1976

Viking on Mars 1976

Gamma rays from planets Some Mars orbiters have gamma ray and neutron detectors. Why? Cosmic rays (relativistic particles from Sun or farther away) hit the surface of Mars and can cause nuclear processes which result in the emission of gamma rays (high energy photons) or neutrons. Study of these can give info on types of atoms present in the surface layers of the planet.

Spacecraft maps of neutrons from Mars can be seen at APOD 15 March 2002.

Mars rovers The largest, MSL, will (we hope) be on Mars in 2011-13 time frame..

Mars rover mockups

Definitive proof of liquid water on Mars What can I say- an APOD from 1 April 2005.


One argument for existence of permafrost in high latitude areas of Mars is existence of patterned ground. These features, which suggest polygons, are found in permafrost on Earth. The next 3 pictures are of patterened ground- the first 2 on Mars, the last on Devon Island, in northern Canada:

Patterned ground from Phoenix Phoenix as in lander on Mars not Phoenix, AZ.

Patterned ground from MRO

Patterned ground Devon Island

Sublimating ice on Mars Phoenix dug a trench uncovering some white stuff. In a few days, it was gone, presumably sublimated away. See APOD 21 June 2008 for links- also see 12 November 20008 APOD.

Ice in crater This is a photo from Mars Express of a crater whose bottom is shielded from direct sunlight. For further info, see links at APOD for 20 July 2005.

Radar map of south pole on Mars Radar has been used to map the thickness of ice at pole. The thickness scale is in *kilo*meters , not meters! A press release describing this can be found at: http://jpl.nasa.gov/news/news.cfm?release=2007-030

Martian flow features Ancient flow features on Mars. What was flowing and when?

Phoenix descending, snapped by MRO One spacecraft imaging another around Mars! What amazing times we live in!! (See APOD 30 May 2008)

Martian avalanche See APOD 11 March 2008.

MRO images Opportunity Another instance of one tourist snapping a photo of another. Photo of rover Opportunity from orbiting Mars Reconnaissance Orbiter. APOD 9 October 2006.

Victoria Crater See APOD 22 Oct 2007 for a larger image.

Opportunity Mars Excursion Rover Opportunity found and imaged its own heat shield (or is that a fender from a Martian '37 Chevy?)

Like a rolling stone

A hole in Mars Opening to ???. The opening is about 125 meters across. See APOD 28 May 2007 for another image and links.

Mars and Earth Left side is Morocco, right side is Mars.

Martian sunset A dusty sunset on Mars.