Mars
Katrina Cain provides a concise answer to the question of why Mars s red in Universe Today: "For most of the planet, the red layer only covers a couple of millimeters and at its deepest, two meters.
"The red color comes from various oxides of iron (hematite mostly) in very, very fine particles, and trace amounts of other elements including titanium, chlorine and sulfur.
"One possible way the dust was created was by harder basalt rocks, which contain more feldspar, grinding against the softer basalt to create fine dust particles.
"All of that iron had to come from somewhere: volcanoes. The best information that we have is that the surface of mars below the red layer is made up of hardened, low viscose lava: basalt. The concentration of iron in Mars' basalt is higher than that of Earth, which is why Earth is much less red.
"And that is why Mars is red."
"The red color comes from various oxides of iron (hematite mostly) in very, very fine particles, and trace amounts of other elements including titanium, chlorine and sulfur.
"One possible way the dust was created was by harder basalt rocks, which contain more feldspar, grinding against the softer basalt to create fine dust particles.
"All of that iron had to come from somewhere: volcanoes. The best information that we have is that the surface of mars below the red layer is made up of hardened, low viscose lava: basalt. The concentration of iron in Mars' basalt is higher than that of Earth, which is why Earth is much less red.
"And that is why Mars is red."
Nancy Atkinson, also writing in Universe Today explains that the photography provided by the Mars Exploration Rovers is as much a work of artistry as it is of science: ..."scientists try and calibrate the rovers to see in "true color", but mostly, colors are chosen to yield the most science.
"Here's how scientists calibrate their amazing instruments, and the difference between true and false colors.
Atkinson poses the question: True or false: When we see the gorgeous, iconic images from" the rovers on Mars "those pictures represent what human eyes would see if they observed those vistas first hand."
Atkinson's answer: "The rovers provide a combination of so-called "true" and "false" color images. But, it turns out, the term "true color" is a bit controversial, and many involved the field of extraterrestrial imaging are not very fond of it.
"We actually try to avoid the term 'true color' because nobody really knows precisely what the 'truth' is on Mars," said Jim Bell, the lead scientist for the Pancam color imaging system on the Mars Exploration Rovers (MER). In fact, Bell pointed out, on Mars, as well as Earth, color changes all the time: whether it's cloudy or clear, the sun is high or low, or if there are variations in how much dust is in the atmosphere. "Colors change from moment to moment. It's a dynamic thing. We try not to draw the line that hard by saying 'this is the truth!'"
Bell likes to use the term "approximate true color" because the MER panoramic camera images are estimates of what humans would see if they were on Mars. Other colleagues, Bell said, use "natural color."
Atkinson poses the question: True or false: When we see the gorgeous, iconic images from" the rovers on Mars "those pictures represent what human eyes would see if they observed those vistas first hand."
Atkinson's answer: "The rovers provide a combination of so-called "true" and "false" color images. But, it turns out, the term "true color" is a bit controversial, and many involved the field of extraterrestrial imaging are not very fond of it.
"We actually try to avoid the term 'true color' because nobody really knows precisely what the 'truth' is on Mars," said Jim Bell, the lead scientist for the Pancam color imaging system on the Mars Exploration Rovers (MER). In fact, Bell pointed out, on Mars, as well as Earth, color changes all the time: whether it's cloudy or clear, the sun is high or low, or if there are variations in how much dust is in the atmosphere. "Colors change from moment to moment. It's a dynamic thing. We try not to draw the line that hard by saying 'this is the truth!'"
Bell likes to use the term "approximate true color" because the MER panoramic camera images are estimates of what humans would see if they were on Mars. Other colleagues, Bell said, use "natural color."
"True color would be an attempt to reproduce visually accurate color. False color, on the other hand, is an arbitrary selection of colors to represent some characteristic in the image, such as chemical composition, velocity, or distance. Additionally, by definition, any infrared or ultraviolet image would need to be represented with "false color" since those wavelengths are invisible to humans," Atkinson explained.
The cameras on ... MER do not take color pictures, however. Color images ... are assembled from separate black & white images taken through color filters. For one image, the spacecraft" must "take three pictures, usually through a red, a green, and a blue filter and then each of those photos gets downlinked to Earth. They are then combined with software into a color image. This happens automatically inside off-the-shelf color cameras that we use here on Earth. But the MER Pancams have 8 different color filters." Atkinson continues. "This gives the imaging teams infinitely more flexibility and sometimes, artistic license. Depending on which filters are used, the color can be closer or farther from "reality."
The cameras on ... MER do not take color pictures, however. Color images ... are assembled from separate black & white images taken through color filters. For one image, the spacecraft" must "take three pictures, usually through a red, a green, and a blue filter and then each of those photos gets downlinked to Earth. They are then combined with software into a color image. This happens automatically inside off-the-shelf color cameras that we use here on Earth. But the MER Pancams have 8 different color filters." Atkinson continues. "This gives the imaging teams infinitely more flexibility and sometimes, artistic license. Depending on which filters are used, the color can be closer or farther from "reality."
The same rock imaged in true and false color by the Mars Rover, Opportunity.
"(W)hen the MER Pancam team wants to produce an image that shows what a human standing on Mars would see," Atkinson asks; "how do they get the right colors? The rovers both have a tool on board know as the MarsDial which has been used as an educational project about sundials. "But its real job is a calibration target," said Bell. "It has grayscale rings on it with color chips in the corners. We measured them very accurately and took pictures of them before launch and so we know what the colors and different shades of grey are."
"One of the first pictures taken by the rovers was of the MarsDial. "We take a picture of the MarsDial and calibrate it and process it through our software," said Bell. "If it comes out looking like we know it should, then we have great confidence in our ability to point the camera somewhere else, take a picture, do the same process and that those colors will be right, too."
"One of the first pictures taken by the rovers was of the MarsDial. "We take a picture of the MarsDial and calibrate it and process it through our software," said Bell. "If it comes out looking like we know it should, then we have great confidence in our ability to point the camera somewhere else, take a picture, do the same process and that those colors will be right, too."
The rover Pancams are configured to produce the most scientific information as possibe.
""It turns out there is a whole variety of iron-bearing minerals that have different color response at infrared wavelengths that the camera is sensitive to," said Bell, "so we can make very garish, kind of Andy Warhol-like false color pictures." Bell added that these images serve double duty in that they provide scientific information, plus the public really enjoys the images.
And so, ...in "MER, color is used as a tool, to either enhance an object's detail or to visualize what otherwise could not be seen by the human eye. Without false color, our eyes would never see (and we would never know) what ionized gases make up a nebula, for example, or what iron-bearing minerals lie on the surface of Mars.
And so, ...in "MER, color is used as a tool, to either enhance an object's detail or to visualize what otherwise could not be seen by the human eye. Without false color, our eyes would never see (and we would never know) what ionized gases make up a nebula, for example, or what iron-bearing minerals lie on the surface of Mars.
"As for "true color," there's a large academic and scholarly community that studies color in areas such as the paint industry that sometimes gets upset when the term "true color" is used by the astronomical imaging group. "They have a well-established framework for what is true color, and how they quantify color. But we're not really working within that framework at that level. So we try to steer away from using the term 'true color'," Atkinson further explains.
"Levay noted that no color reproduction can be 100% accurate because of differences in technology between film and digital photography, printing techniques, or even different settings on a computer screen. Additionally, there are variations in how different people perceive color.
"Bell concluded, "What we're doing on Mars is really just an estimate, it's our best guess using our knowledge of the cameras with the calibration target. But whether it is absolutely 100% true, I think it's going to take people going there to find that out."
"Levay noted that no color reproduction can be 100% accurate because of differences in technology between film and digital photography, printing techniques, or even different settings on a computer screen. Additionally, there are variations in how different people perceive color.
"Bell concluded, "What we're doing on Mars is really just an estimate, it's our best guess using our knowledge of the cameras with the calibration target. But whether it is absolutely 100% true, I think it's going to take people going there to find that out."
Hadley Legget contributes a posting in WIRED NEWS that provides more detailed current scientific thought on why Mars appears red when it should actually be black in over all color..
Leggett writes: "Recent experiments show that regular sand, when combined with black Martian basalt, takes on a reddish hue as it’s crushed into dust, whether or not water or oxygen is present. Researchers from Aarhus University in Denmark claim that Mars’ red dust could have formed without the water that current hypotheses hold once covered the planet.
Panorama of Mars captured by Mars Pathfinder.
“Mars should really look blackish between its white polar caps, because most of the rocks at mid-latitudes are basalt,” said physicist Jonathan Merrison in a press release. “For decades we assumed that the reddish regions on Mars are related to the water-rich early history of the planet and that, at least in some areas, water-bearing, heavily oxidized iron minerals are present.”
"But when Merrison and his team mixed sand with a mineral called magnetite, found in Martian basalt, they found that mechanical stimulation alone produced a fine red dust. To simulate sand transport on Mars, the scientists tumbled pure quartz in a hermetically sealed flask for seven months, flipping each flask 10 million times. By the end of the experiment, 10 percent of the sand had turned to dust, and it became redder and redder with the addition of magnetite.
“Subsequent analysis of the flask material and dust has shown that the magnetite was transformed into the red mineral hematite, through a completely mechanical process without the presence of water at any stage of this process,” said Merrison, who presented the work yesterday at the European Planetary Science Congress in Germany.
"Although the scientists don’t understand how the black mineral converts into the red one, they think it’s due to a chemical reaction with the eroded sand. Because the experiment works not only in air, but also in a dry carbon dioxide atmosphere like the one on Mars, the researchers say simple grinding is a plausible explanation for how Mars got its striking color."
"But when Merrison and his team mixed sand with a mineral called magnetite, found in Martian basalt, they found that mechanical stimulation alone produced a fine red dust. To simulate sand transport on Mars, the scientists tumbled pure quartz in a hermetically sealed flask for seven months, flipping each flask 10 million times. By the end of the experiment, 10 percent of the sand had turned to dust, and it became redder and redder with the addition of magnetite.
“Subsequent analysis of the flask material and dust has shown that the magnetite was transformed into the red mineral hematite, through a completely mechanical process without the presence of water at any stage of this process,” said Merrison, who presented the work yesterday at the European Planetary Science Congress in Germany.
"Although the scientists don’t understand how the black mineral converts into the red one, they think it’s due to a chemical reaction with the eroded sand. Because the experiment works not only in air, but also in a dry carbon dioxide atmosphere like the one on Mars, the researchers say simple grinding is a plausible explanation for how Mars got its striking color."
Scientists say Mars should look black like the planet on the right, but may have turned red through a mechanical grinding process.
NASA/ESA/Hubble Team.
NASA/ESA/Hubble Team.
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