A more general definition of 'sky' allows for skies as seen on other worlds. At right is a 360° panorama of the horizon on Mars as perceived in the visual true-color range of the NASA Mars Exploration Rover 'Spirit' on November 23-8, 2005.
"In antiquity the classical planets were the non-fixed objects visible in the sky, known to various ancient cultures. The classical planets were therefore the Sun and Moon and the five non-earth [[planets] of our solar system closest to the sun (and closest to the Earth); all easily visible without a telescope. They are Mercury, Venus, Mars, Jupiter, and Saturn."
"Mars is the fourth planet from the Sun in the Solar System. Named after the Roman god of war, Mars, it is often described as the "Red Planet" as the [iron(III) oxide] iron oxide prevalent on its surface gives it a reddish appearance. ... The red-orange appearance of the Martian surface is caused by iron(III) oxide, more commonly known as hematite, or rust. ... Much of the surface is deeply covered by finely grained iron(III) oxide dust."
"NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has observed two unexpected phenomena in the Martian atmosphere: an unexplained high-altitude dust cloud and aurora that reaches deep into the Martian atmosphere."
“If the dust originates from the atmosphere, this suggests we are missing some fundamental process in the Martian atmosphere.”
"MAVEN’s Imaging Ultraviolet Spectrograph (IUVS) observed what scientists have named “Christmas lights.” For five days just before December 25th, MAVEN saw a bright ultraviolet auroral glow spanning Mars’ northern hemisphere. Aurora, known on Earth as northern or southern lights, are caused by energetic particles like electrons crashing down into the atmosphere and causing the gas to glow."
“What’s especially surprising about the aurora we saw is how deep in the atmosphere it occurs — much deeper than at Earth or elsewhere on Mars. The electrons producing it must be really energetic.”
"The source of the energetic particles appears to be the Sun. MAVEN’s Solar Energetic Particle instrument detected a huge surge in energetic electrons at the onset of the aurora. Billions of years ago, Mars lost a global protective magnetic field like Earth has, so solar particles can directly strike the atmosphere. The electrons producing the aurora have about 100 times more energy than you get from a spark of house current, so they can penetrate deeply in the atmosphere."
"A comet that flew close to Mars showered the red planet with fine cometary dust, according to observations by a trio of spacecraft."
"Comet C/2013 A1 Siding Spring passed within 139,500 kilometres of the red planet on 19 October, the closest a comet has ever been seen to come to a planet without actually colliding with it. To avoid being damaged by the comet dust, all spacecraft orbiting Mars moved to the far side of the planet for 20 minutes while the comet dust was at its most intense, but this did not prevent them from studying the effects it had on Mars’ atmosphere."
“They call this comet encounter a once-in-a-lifetime event, but it’s more like once in a million years.”
"The European Space Agency’s Mars Express spacecraft detected an increase in electrons in Mars’ upper atmosphere, partly ionising it. This was attributed to fine cometary dust penetrating the atmosphere, which led to a meteor storm of thousands of meteors per hour. The increase in electrons led to the creation of a temporary new layer of charged particles in the ionosphere, which runs from an altitude of 120 kilometres to several hundred kilometres above. This is the first time such an event has been seen, even on Earth the extra density of electrons was measured to be five to ten times higher than normal by NASA’s Mars Reconnaissance Orbiter. Another NASA spacecraft, MAVEN, which also observed the new layer in the ionosphere, will monitor for any long-term events as it goes about its regular duties of studying Mars’ atmosphere."
"MAVEN’s Imaging Ultraviolet Spectrograph was able to ascertain the species of ions that flooded into the ionosphere from the comet, the first time a comet that has come direct from the distant Oort Cloud has been sampled in this way. It detected the signal of magnesium, iron and sodium ions following the meteor shower, a signal that dominated Mars’ ultraviolet spectrum for hours afterwards, taking two days to dissipate."
"The results show that dust from the comet, which has a nucleus two kilometres across, according to high resolution images from the Mars Reconnaissance Orbiter, had a dramatic effect on Mars’ atmosphere."
“Observing the effects on Mars of the comet’s dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harm’s way.”
- "Classical planets, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. 15 February 2014. Retrieved 2014-02-15.
- "Mars, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. 15 February 2014. Retrieved 2014-02-15.
- "The Lure of Hematite". Science@NASA. NASA. March 28, 2001. Retrieved 2009-12-24.
- Mark Peplow. "How Mars got its rust". BioEd Online. MacMillan Publishers Ltd. Retrieved 2007-03-10.
- Philip R. Christensen, et al. (June 27, 2003). "Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results". Science 300 (5628): 2056–61. doi:10.1126/science.1080885. PMID 12791998.
- Matthew P. Golombek (June 27, 2003). "The Surface of Mars: Not Just Dust and Rocks". Science 300 (5628): 2043–2044. doi:10.1126/science.1082927. PMID 12829771.
- NASA GSFC (19 March 2015). "Mysterious Martian dust cloud and aurora detected by NASA spacecraft". Greenbelt, Maryland USA: NASA. Retrieved 2015-05-17.
- Laila Andersson (19 March 2015). "Mysterious Martian dust cloud and aurora detected by NASA spacecraft". Greenbelt, Maryland USA: NASA. Retrieved 2015-05-17.
- Arnaud Stiepen (19 March 2015). "Mysterious Martian dust cloud and aurora detected by NASA spacecraft". Greenbelt, Maryland USA: NASA. Retrieved 2015-05-17.
- Keith Cooper (10 November 2014). "Comet dust ionises Mars’ atmosphere". United Kingdom: Astronomy Now. Retrieved 2015-05-18.
- Nick Schneider (10 November 2014). "Comet dust ionises Mars’ atmosphere". United Kingdom: Astronomy Now. Retrieved 2015-05-18.
- Jim Green (10 November 2014). "Comet dust ionises Mars’ atmosphere". United Kingdom: Astronomy Now. Retrieved 2015-05-18.
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