NASA originally expected they’d only last a few months, but the plucky Martian rovers are still crawling across the surface of Mars – more than 3 years later. So the agency has gone ahead and extended their missions… again. This is the fifth time NASA has extended their mission, keeping them operational potentially through 2009.
The twin rovers landed on the surface of Mars in January, 2004. Mission planners expected that it would only take a few months before dust coated the rovers’ solar panels so thickly that they wouldn’t be able to generate power any more. But the Martian weather had a trick; dust devils and wind gusts came by often enough to keep the solar panels relatively clear of dust. Without the loss of power looming, the rovers have been able to keep going, and going, and going.
Their accomplishments to date have been staggering. So far, Spirit has driven a total of 7.26 kilometers (4.51 miles) and has returned more than 102,000 images. Opportunity has driven 11.57 kilometers (7.19 miles) and has returned more than 94,000 images.
Opportunity turned up evidence of the planet’s watery past, when oceans affected rocks for long periods of time, and deposited layers of material. Spirit also found that water altered the mineral composition of the rocks and soil in its surroundings. The rovers have been instrumental in helping scientists understand the Martian dust devils. And both have discovered metallic meteorites sitting the surface of the Red Planet. One of these has a similar composition to the meteorite that reached Earth from Mars.
Seen one Martian crater and you’ve seen them all right? Well, check this one out. It’s an image of Maunder Crater on the surface of Mars, captured by ESA’s Mars Express. Although the crater is large, 90 km (56 miles) across, it’s very shallow – less than a kilometre. It used to be much deeper, but some geologic process has since filled it in.
The images of Maunder crater were captured in late 2005 by Mars Express at a resolution of roughly 15 metres per pixel. The crater, named after British astronomer Edward W. Maunder, is located about halfway between Argyre Planitia and Hellas Planitia on the southern Highlands of Mars.
It once looked like a more traditional crater, but then something happened on the west side to make it cave in. A large landslide pushed material from the crater wall to the inner portion. The edges of the crater that remain show gullies that could have been created when large amounts of material was flowing down into the crater.
One intriguing discovery: there are gullies along the upper side of the trough in the middle of the crater that have been caused by seeping water.
Mission planners for the Mars Science Laboratory have quite a challenge on their hands. Where should they land the rover in 2010? They’ve got a whole planet to choose from. Well, they’ve narrowed the field of prospective landing sites down to about 30 intriguing candidates. And now NASA’s Mars Reconnaissance Orbiter has delivered high resolution images of each and every potential landing site… in colour!
We’ve got Spirit and Opportunity currently crawling across the surface of Mars. The Phoenix Mars Lander is on its way now. But when NASA’s Mars Science Laboratory arrives in 2010, the science is really going to get rolling. This SUV-sized robotic explorer will bring its own nuclear power source, and a suite of science instruments, giving it the range and capabilities to find life on the surface of the Red Planet.
But where should it land? The University of Arizona’s HiRISE team delivered 143 images captured by NASA’s Mars Reconnaissance Orbiter to the researchers this week, showcasing each location in false and enhanced colour.
Normally the spacecraft captures its images in black-and-white. It’s relatively simple to grab a single image of the Martian surface with one of its filters. When you’re trying to get colour, though, things become more complicated. The spacecraft moves so quickly above Mars that it’s very difficult to capture several images of the same area in different wavelengths of light and then merge them together into a single colour image.
Researchers with the HiRISE team have developed a computer program that can process data from different colour filters and merge them into a single image. Of course, to process each 20,000 by 50,000 pixel region can take several hours.
Mission planners for the Mars Science Laboratory will be meeting at a workshop later this month to try and narrow down the field of choices. These colour photographs will help them make a decision.
You can browse all the images yourself if you like. Click here to see them. You can also access the movie that pans across a potential landing site at Nili Fossae. The animation shows a range of enhanced colours that reveal rocks that might have been altered by water in the past.
Carina Nebula. Image credit: Hubble Space Telescope/NASA.
When you look at the amazing pictures captured by the Hubble Space Telescope, or the Mars Exploration Rovers, do you ever wonder: is that what you’d really see with your own eyes? The answer, sadly, is probably not. In some cases, such as with the Mars rovers, 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.
So, to start off, let’s put this in the form of a true or false question: T or F: When we see the gorgeous, iconic images from Hubble or the stunning panoramas from the Mars rovers, do those pictures represent what human eyes would see if they observed those vistas first hand?
Answer: For the Hubble, mostly false. For the rovers, mostly true, as 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 in 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.”
Zolt Levay of the Space Telescope Science Institute produces images from the Hubble Space Telescope. For the prepared Hubble images, Levay prefers the term “representative color.”
“The colors in Hubble images are neither ‘true’ colors nor ‘false’ colors, but usually are representative of the physical processes underlying the subjects of the images,” he said. “They are a way to represent in a single image as much information as possible that’s available in the data.”
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.
The cameras on Hubble and MER do not take color pictures, however. Color images from both spacecraft are assembled from separate black & white images taken through color filters. For one image, the spacecraft have to 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 while Hubble has almost 40, ranging from ultraviolet (“bluer” than our eyes can see,) through the visible spectrum, to infrared (“redder” than what is visible to humans.) 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.”
Stone mountain rock outcrop in true and false colour. Image credit: NASA/JPL
The same rock imaged in true and false color by Opportunity.
In the case of the Hubble, Levay explained, the images are further adjusted to boost contrast and tweak colors and brightness to emphasize certain features of the image or to make a more pleasing picture.
But when the MER Pancam team wants to produce an image that shows what a human standing on Mars would see, how do they get the right colors? The rovers both have a tool on board known 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.”
Hubble can also produce color-calibrated images. Its “UniverseDial” would be standard stars and lamps within the cameras whose brightness and color are known very accurately. However, Hubble’s mission is not to produce images that faithfully reproduce colors. “For one thing that is somewhat meaningless in the case of most of the images,” said Levay, “since we generally couldn’t see these objects anyway because they are so faint, and our eyes react differently to colors of very faint light.” But the most important goal of Hubble is produce images that convey as much scientific information as possible.
The rover Pancams do this as well. “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 both Hubble and 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, Bell explained.
“They have a well-established framework for what is true color, and how they quantify color,” he said. “But we’re not really working within that framework at that level. So we try to steer away from using the term ‘true color’.”
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.
“What we’re doing on Mars is really just an estimate,” Bell said, “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.”
For more information see http://hubblesite.org/ or check out Jim Bell’s 2006 book “Postcards From Mars.”
When last we saw our plucky rover, it was tentatively crawling down into the massive Victoria crater on the surface of Mars. Well, NASA’s Mars Opportunity rover has been making some serious progress since then. In fact, it’s already gotten down to do some science. The rover is currently several metres down inside the rim of Victoria crater, balancing on a steep slope, and peering at an ancient slab of exposed bedrock.
Opportunity is now slowly descending down into the 800-metre-wide Victoria Crater; slowly, and carefully. Its first stop is a patch of exposed bedrock. Even though it’s still on the slope, Opportunity was able to reach over with its robotic arm and use some of its tools to examine the bright outcropping.
Controllers had Opportunity make a few extra safety checks, since it’s currently driving down a 25-degree slope, and stretching out the arm too far could unbalance it. The rover drove down 2.25 metres (7.38 feet) to get the rock within easy – and safe – reach. This was the third drive the rover has made since it entered the crater on September 13th.
NASA is watching the rover’s traction very carefully. This 25-degree angle is the steepest the rover is going to see. And so far, the worst slippage has only been about 10%. So it should be able to get down into the crater, and still be able to crawl back out again. Fortunately, Victoria crater won’t be Opportunity’s final home on Mars.
Researchers are hoping the rover will find older and older patches of rock, exposed when an asteroid impacted the surface of Mars millions of years ago. These ancient rocks will tell a story of Martian history much older than the fragmented pieces scientists have been able to put together so far. Were there long periods where the planet was covered by liquid water?
It’s your job Opportunity. Don’t come out of your hole until you’ve got some answers.
You know the cliche, wherever we find water here on Earth, we find life. But what if the environment is really hostile? So hostile that any living creature would almost never see water. And even when there was water, they were constantly being blasted with radiation. Amazingly, there’s a microbe out there, Deinococcus geothermalis, that can handle some of the harshest environments on the planet – favoured habitats include nuclear power plants. Scientists once suspected that microbes like this might have evolved on Mars. Nope, they’re homegrown.
Of all the different strains of bacteria on Earth, those in the genus Deinococcus are a hardy bunch. They’re extremely resistant to ionizing radiation, they laugh at ultraviolet light, extreme, heat, cold and they don’t mind being completely dried out for long periods. Bathed in acid? Boring.
D. geothermalis is actually a cousin of another microbe called Deinococcus radiodurans. D. radiodurans is capable of withstanding 500 times the radiation that will kill a human – with no loss of viability. The Guiness Book of World records calls D. radiodurans the toughest bacteria in the world, and some scientists have proposed that it actually evolved on Mars and somehow journeyed to Earth.
Researchers have recently sequenced the bacteria’s cousin, D. geothermalis’ entire genome sequence, providing some valuable clues into how a microbe can be so tough, and how they two are related (no Martian explanation necessary).
Their paper describing the results of their sequencing efforts, entitled Deinococcus geothermalis: The Pool of Extreme Radiation Resistance Genes Shrinks will be published in the September 26th issue of the journal Public Library of Science.
The microbe was first discovered in a hot pool at the Termi di Agnano, in Naples, Italy. Other scientists have turned it up in other nasty locations, such as industrial paper machine water, deep ocean subsurface environments, and subterranean hot springs in Iceland.
While working with the microbe, the researchers noted, “the extraordinary survival of Deinococcus bacteria following irradiation has also given rise to some rather whimsical descriptions of their derivation, including that they evolved on Mars.”
In fact, the US Department of Energy is considering D. geothermalis as a possible solution to break down radioactive waste. Which would be good, since it’s often a pest; adhering to the surface of steel, and causing problems in nuclear power plants.
Currently, scientists have no idea why bacteria like D. geothermalis are so hardy to radiation. They’re just as susceptible to normal bacteria to have their DNA broken up by radiation, but they use some kind of efficient repair mechanism to fix the damage quickly.
The big surprise with this research is that it overturns previously held theories about how D. radiodurans protects itself. The two strains of bacteria are both extremely resistant to radiation, and yet D. geothermalis lacks the genes that scientists thought D. radiodurans was using. By comparing genome sequences between the two strains, the researchers were able to narrow down the genes which are likely contributing to the microbes’ tolerance.
This research also overturns the intriguing possibility that D. radiodurans comes from Mars; evolving on the Cosmic Ray blasted surface of the Red Planet. These two strains have enough in common, with traceable evolutionary steps, that the researchers can see how they evolved right here on Earth.
Here’s Dr. Michael J. Daly, an associate professor at the Uniformed Services University of the Health Sciences in Bethesda, “the thermophile Deinococcus geothermalis is an excellent organism in which to consider the potential for survival and biological evolution beyond its planet of origin, as well as the ability of life to survive extremely long periods of metabolic dormancy in high-radiation environments. The current work reinforces the notion that resistance to radiation and desiccation readily evolved on Earth, and that the underlying resistance systems are based on a universal set of repair genes. The work underscores the vulnerability of potential life-inhabiting environments on Mars to contamination by human exploration; and how the efficiency of ordinary DNA repair proteins could be increased, which might be important to astronauts. The growing awareness that there is hardly a habitat on Earth not harboring life is now changing our consensus of consequences for possible life on Mars.”
More Mars news… NASA’s Mars Odyssey spacecraft has turned up what look like the entrances to caves along the slope of a Martian volcano. If these turn out to be actual tunnels or caves, they could be a scientific goldmine, offering future explorers protection and a unique region to study – perhaps even life could be hiding away from hostile Martian surface environment.
The seven possible cave entrances are dark, and nearly circular, ranging in size from 100 to 250 metres (328 to 820 feet) across. They were discovered by NASA’s Mars Odyssey and Mars Global Surveyor spacecraft. Follow up observations with Odyssey’s infrared cameras confirmed that they could very well be cavernous entrances into underground regions on Mars.
The infrared evidence showed that the temperatures inside the holes changed less than the surrounding regions. “They are cooler than the surrounding surface in the day and warmer at night,” said Glen Cushing of the U.S. Geological Survey’s Astrogeology Team and of Northern Arizona University, Flagstaff, Ariz. “Their thermal behavior is not as steady as large caves on Earth that often maintain a fairly constant temperature, but it is consistent with these being deep holes in the ground.”
One of the downsides of these caves is their altitude. They’re located near the top of a massive Martian volcano called Arsia Mons. At this high altitude, life would have a difficult time coping with the extreme cold and lower air pressure.
Planetary geologists think the caves might have been formed by underground stresses around the volcano. The caves are inline with with other bowl-shaped pits that appear to have been formed when material collapsed. There could be long networks of tunnels and stress fractures. In some cases, the roof just collapsed in completely, and in other places, you might get a cave entrance instead.
The next step is to bring the much more powerful Mars Reconnaissance Orbiter’s camera in to image the regions better. It might be able to shed some light on the mystery.
I’ll warn you right now, it’s raining Mars news today. Take cover. First up, we’ve got this interesting story. Planetary scientists at MIT have estimated that Mars’ southern pole contains the largest quantity of frozen water in the inner solar system (apart from the Earth, of course). Many people believed that frozen carbon dioxide was the predominant substance in the south pole’s cap, but nope, it’s water.
The research was led by Maria Zuber, MIT professor of geophysics, and the lead investigator for gravity for the Mars Reconnaissance Orbiter. The project is funded by the NASA Mars Program.
Scientists have long suspected that the Martian southern pole was mostly ice and dust, covered by a thin coating of carbon dioxide, but they didn’t have a firm estimate. Zuber and her colleagues used topographical and gravitational data by three Mars spacecraft to find the volume and mass of the ice cap.
Once they had the volume and mass, they were able to calculate the density. The density of water ice is 1,000 kg per cubic metre, while the density of solid carbon dioxide (aka dry ice) is 1,600 kg per cubic metre. Their estimates calculated that the Martian southern pole is about 1,220 kg per cubic metre. That indicates that it’s mostly water, with about 15% silicate dust mixed in.
This makes the southern polar region of Mars the largest body of water in the inner solar system, outside of the Earth. Just in case that’s not clear, we’re talking about Mercury, Venus and Mars.
One thing that’s still puzzling astronomers is the fact that the polar cap doesn’t reflect as much as you would expect from a coating of ice. It’s believed that the silicate dust mixed in dulls down the cap’s reflectivity.
Zuber and her team are planning to estimate the northern polar cap.
The polar ice caps on Mars have been there for a long time; although, they haven’t always stayed the same size, or shape. They cover the surface between the poles and approximately 60° latitude today, but Norbert Schorghofer of the Institute for Astronomy and NASA Astrobiology Institute in Hawaii has shown that Mars has had at least forty major ice ages during the past five million years.
The Martian ice caps are divided into three layers: a massive bottom sheet, a porous middle layer and a thin, dry, dusty top layer. The makeup and extent of the ice coverage has varied over its long history due to both precipitation of water vapor from the atmosphere, and the diffusion and condensation of water from pores in the ice.
“Although neither of the two mechanisms by itself could simultaneously account for the mass fraction and latitudinal boundary of the observed ice, their combination provides just enough ice at the right places,” Schorghofer said.
Unlike the Earth, Mars doesn’t have a Moon to keep its tilt in check. Instead, the planet is able to tilt as much as 10-degrees from its current angle. This can create tremendous variation in the size of its ice sheets.
Earlier studies of the ice showed that the shifting of the ice was due largely to Mars’ varying tilt (obliquity), and thus changes in global and local temperatures affecting the humidity levels of the entire planet. Schorghofer used computer modeling that takes into account thermal and atmospheric conditions, as well as the growth and retreat of the ice sheets. His research shows that the transfer of water vapor from the ice into the atmosphere, and the condensation of this water back into the ice profoundly altered the way in which the ice caps melted and re-froze.
Closer to the poles, the amount of ice changes very little over time. But near the edges of the sheets, the volume of ice has varied by as much as 100,000 cubic km during each ice age. Mars’ icy love handles have each also shrunk an overall depth of 60cm over the past 2.5 million years.
Understanding the cause for ice ages on Mars may help us learn more about the climate history of other planets, including Earth.
“The dynamic nature of the ice sheets makes Mars an ideal system in which to test and expand our knowledge of astronomical climate forcing. A great deal could be learned about terrestrial ice ages from the study of Martian ice stratigraphy – a longer, cleaner and simpler record than Earth’s,” Schorghofer said.
When the Phoenix Mars Lander arrives at the Red Planet in 2008, it might just see the different kinds of ice layers that Schorghofer is predicting.
With the powerful Martian dust storms dissipating, the Mars Exploration Rovers are ready to resume their duties, apparently no worse for wear. When we last met our heroes, Opportunity was about to climb down into Victoria Crater to look for evidence of ancient water. Now it took its first tentative steps into the crater, putting all six wheels onto the slope. And then it crawled back out again. Easy does it…
Victoria Crater measures 800 metres (half a mile) across, and it’s the largest impact crater either of the rovers have encountered during their travels on Mars. Since the crater cuts down through Martian rock, it gives scientists an unprecedented opportunity to peer back in time, when layers of rock were put down – ideally when there was liquid water present.
The rover team commanded Opportunity to drive just far enough on September 11, 2007 that all six of its wheels got onto the inner slope. The rover was then asked to come back out again, so the team could measure the amount that its wheels slipped on the slope. Right at the end, as Opportunity was just crawling out, its wheels slipped further than the rover team wanted, so they had it stop, with its front wheels still on the slope.
Now that they’ve gathered data on Opportunity’s traction on this angle, the rover team will analyze it to understand if entering or exiting the crater is going to pose a hazard.
