Mars the Red Planet
On December 24th Mars (image at right) will be in opposition, or in non astronomical jargon directly opposite to the position of the Sun as viewed by an observer on Earth. However, six days prior to this Mars will be as close to Earth as it is going to get during this opposition.
 "Hang on a minute, that doesn't make sense!"
Well, at least that's what I said when I first read about the orbits of Mars and Earth. The reason for this apparent discrepancy is the inclination of Mars's orbital plane with respect to the ecliptic. Unfortunately it is difficult to describe the concept linguistically or diagrammatically in a two dimensional media like this but the net result for this particular opposition means the date and time of the closest approach happens slightly before the actual opposition.
There are a couple of really good animations on the Windows on the Universe and Illumination web sites that show the relationship between the orbits of Earth and Mars reasonably well and are worth having a look at and play with.
This approach will see a minimum separation of 88,115,332 km which is considerably further than the 2003 opposition when Mars came within 55,758,006 km of Earth. Actually the 2003 opposition is believed to have been the closest since 12th September 57,617 BC but it is estimated that over the next two millennia the 2003 record will be surpassed on at least 22 occasions.
The table below shows the minimum distance between Mars and the earth between 2003 and 2018.
With a current orbital eccentricity of around 9% Mars has the greatest eccentricity of the major planets. Pluto does have a much greater eccentricity at almost 25% which is not only nearly three times that of Mars, but brings it closer to the Sun than Neptune for a large proportion of its orbit. Unfortunately for Pluto in 2006 the International Astronomical Union decided that Pluto did not fit the definition of a planet and demoted it to the status of dwarf planet. There has been considerable debate over this decision. However, Pluto is smaller (diameters 52 km smaller ) and less massive (3.65 Yg less) than Eris so there was definitely an inconsistency that needed to be addressed.
Until the second half of the 1970's we knew surprisingly little about Mars and many believed it was still possible that there was some kind of life there.
Mars has long been the fictional source of aliens, invaders, ancient civilizations and cultures and host of other "out of this world" ideas. Certainly until the last quarter of the 20th century relatively little was know about our red neighbor. This all changed in the last quarter of the 20th century when NASA and other space agencies sent surveying and mapping satellites as well as several landers and automated rovers to explore Mars.
 In 1976 when NASA's Viking space craft took the image at right it wasn't long before somebody claimed that it was a face that was too close to that of the sphinx in Egypt to be a coincidence. Theories of ancient civilizations with the capacity for interplanetary exchange of information as well as interplanetary travel abounded and it wasn't long before people were claiming it was proof of an ancient Martian society.
Later high resolution images like the one below, revealed that the face was nothing more than an optical illusion most likely caused by the way our brains try and look for patterns within images. If you have a pair of red-blue 3D glasses then you may wish to go to the NASA Astronomy Picture of the Day site and look at the stereoscopic composite image of the now infamous Face on Mars.
There have been three successful missions to land small autonomous rovers on the surface of Mars with the later two Spirit and Opportunity being far more successful than anyone could have hoped. They were originally designed to explore the surface for 90 days but have now been operating for well over 1,000 days. They have survived more than a full Martian year including a winter and a massive dust storm. By obscuring the Sun the rovers were unable to use their solar cells to generate the electricity they needed not only to operate but to keep the electronics from being destroyed by the cold. All that could be done was to park them in a sheltered place where there was plenty of sunlight and shut down everything but the system that kept the internal temperature within safe limits. When the dust settled the rovers started up again and there was a great sigh of relief when it was found they had survived with little damage.
Mars is roughly 80 Gm further from the Sun than Earth but its day is only about 38 minutes longer than the Earthly equivalent. The Martian axis is inclined by 29.19° to the plane of its orbit and as a result it experiences seasons all be it on a 668.60 sols (686.96 earth days) cycle, in a similar way to the Earth's seasons. It is however considerably smaller, less dense and less massive than Earth and consequently only has a gravity that is 37.6% that of Earth's or slightly more than twice that of the Moon.
 Mars has two moons, Phobos and Deimos as shown in the image on the right. They are nothing like Earth's Moon being much smaller and irregularly shaped. It is believed that they are actually asteroids that have been trapped by Mars's gravity and ended up in orbit rather than crashing into the surface.
In subsequent articles we will look at the wealth of information that has and is coming from the spacecraft that are studying Mars from orbit as well as on the surface. If you have some time to spare on a clear night over the next couple of weeks have a look at Mars through a telescope or pair of binoculars because that's about as good as it's going to get till at least 2016. The image below shows Mars's path during the current opposition in daily steps. With any luck I will have my astronomical imaging system working in the next week or so and have some pictures of Mars.
As usual you can find out more about Mars by following these links.
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_07914C2F-03E6-EA6A-A1B74455BF257290.jpg "MaSu on Machines, Meteors & Mozzies"){kind=logo}
