A view of the interior of an impact crater on Mars shows prominent bright layer of bedrock. Credit: NASA/JPL/UArizona
Impact craters have been called the “poor geologists’ drill,” since they allow scientists to look beneath to the subsurface of a planet without actually digging down. It’s estimated that Mars has over 600,000 craters, so there’s plenty of opportunity to peer into the Red Planet’s strata – especially with the incredible HiRISE (High Resolution Imaging Science Experiment) camera on board the Mars Reconnaissance Orbiter which has been orbiting and studying Mars from above since 2006.
The tiny black speck in the lower left corner of this image within the red circle is a cluster of recently formed craters spotted on Mars using a new machine-learning algorithm. This image was taken by the Context Camera aboard NASA's Mars Reconnaissance Orbiter in a region called Noctis Fossae, located at latitude -3.213, longitude: 259.415. Image Credit: NASA/JPL-Caltech/MSSS
Does the life of an astronomer or planetary scientists seem exciting?
Sitting in an observatory, sipping warm cocoa, with high-tech tools at your disposal as you work diligently, surfing along on the wavefront of human knowledge, surrounded by fine, bright people. Then one day—Eureka!—all your hard work and the work of your colleagues pays off, and you deliver to humanity a critical piece of knowledge. A chunk of knowledge that settles a scientific debate, or that ties a nice bow on a burgeoning theory, bringing it all together. Conferences…tenure…Nobel Prize?
Well, maybe in your first year of university you might imagine something like that. But science is work. And as we all know, not every minute of one’s working life is super-exciting and gratifying.
An artist's illustration of an asteroid shower on the Earth-Moon system. Image Credit: Murayama/Osaka Univ.
Natural processes here on Earth continually re-shape the planet’s surface. Craters from ancient asteroid strikes are erased in a short period of time, in geological terms. So how can researchers understand Earth’s history, and how thoroughly it may have been pummeled by asteroid strikes?
Scientists can turn their attention to our ancient companion, the Moon.
A meteorite struck Mars sometime between February and July 2005 and formed this crater. It's the HiRise Picture of the Day for February 5, 2020. Image Credit: NASA/JPL/UoArizona.
NASA has repeatedly imaged the Martian surface, and sometimes a feature appears that wasn’t there in prior images. That’s what happened when a meteorite survived the plunge through Mars’ thin atmosphere sometime between February and July, 2005. It created this impact crater north of Valles Marineris.
New Horizons image of the small craters on Pluto's moon Charon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
In 2015, the New Horizons mission became the first robotic spacecraft to conduct a flyby of Pluto. In so doing, the probe managed to capture stunning photos and valuable data on what was once considered to be the ninth planet of the Solar System (and to some, still is) and its moons. Years later, scientists are still poring over the data to see what else they can learn about the Pluto-Charon system.
For instance, the mission scienceteam at the Southwest Research Institute (SwRI) recently made an interesting discovery about Pluto and Charon. Based on images acquired by the New Horizons spacecraft of some small craters on their surfaces, the team indirectly confirmed something about the Kuiper Belt could have serious implications for our models of Solar System formation.
The HiRISE camera on NASA's Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique "Swiss cheese" like appearance. Image:NASA/JPL/University of Arizona
The HiRISE camera on NASA’s Mars Reconnaissance Orbiter captured this unusual crater or pit on the surface of Mars. Frozen carbon dioxide gives the region its unique “Swiss cheese” like appearance. Image:NASA/JPL/University of Arizona
During late summer in the Southern hemisphere on Mars, the angle of the sunlight as it strikes the surface brings out some subtle details on the planet’s surface.
In this image, the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter (MRO) captured an area of frozen carbon dioxide on the surface. Some of the carbon dioxide ice has melted, giving it a swiss-cheese appearance. But there is also an unusual hole or crater on the right side of the image, with some of the carbon dioxide ice clearly visible in the bottom of the pit.
NASA scientists are uncertain what exactly caused the unusual pit. It could be an impact crater, or it could be a collapsed pit caused by melting or sublimation of sub-surface carbon dioxide ice.
MRO has been in orbit around Mars for over 10 years, and has completed over 50,000 orbits. The MRO has two cameras. The CTX camera is lower resolution, and has imaged over 99% of the Martian surface. HiRISE is the high-resolution camera that is used to closely examine areas and objects of interest, like the unusual surface pit in this image.
Asteroid impacts on Mars could have generated supersonic winds that shaped the surface, according to a new study. Credit: geol.umd.edu
The study of another planet’s surface features can provide a window into its deep past. Take Mars for example, a planet whose surface is a mishmash of features that speak volumes. In addition to ancient volcanoes and alluvial fans that are indications of past geological activity and liquid water once flowing on the surface, there are also the many impact craters that dot its surface.
In some cases, these impact craters have strange bright streaks emanating from them, ones which reach much farther than basic ejecta patterns would allow. According to a new research study by a team from Brown University, these features are the result of large impacts that generated massive plumes. These would have interacted with Mars’ atmosphere, they argue, causing supersonic winds that scoured the surface.
These features were noticed years ago by Professor Peter H. Schultz, a professor of geological science with the Department of Earth, Environmental, and Planetary Sciences (DEEPS) at Brown University. When studying images taken at night by the Mars Odyssey orbiter using its THEMIS instrument, he noticed steaks that only appeared when imaged in the infrared wavelength.
Artist’s conception of the Mars Odyssey spacecraft. Credit: NASA/JPL
These streaks were only visible in IR because it was only at this wavelength that contrasts in heat retention on the surface were visible. Essentially, brighter regions at night indicate surfaces that retain more heat during the day and take longer to cool. As Schultz explained in a Brown University press release, this allowed for features to be discerned that would otherwise not be noticed:
“You couldn’t see these things at all in visible wavelength images, but in the nighttime infrared they’re very bright. Brightness in the infrared indicates blocky surfaces, which retain more heat than surfaces covered by powder and debris. That tells us that something came along and scoured those surfaces bare.”
Along with Stephanie N. Quintana, a graduate student from DEEPS, the two began to consider other explanations that went beyond basic ejecta patterns. As they indicate in their study – which recently appeared in the journal Icarus under the title “Impact-generated winds on Mars” – this consisted of combining geological observations, laboratory impact experiments and computer modeling of impact processes.
Ultimately, Schultz and Quintana concluded that crater-forming impacts led to vortex-like storms that reached speeds of up to 800 km/h (500 mph) – in other words, the equivalent of an F8 tornado here on Earth. These storms would have scoured the surface and ultimately led to the observed streak patterns. This conclusion was based in part on work Schultz has done in the past at NASA’s Vertical Gun Range.
An infrared image revealing strange bright streaks extending from Santa Fe crater on Mars. Credit: NASA/JPL-Caltech/Arizona State University.
This high-powered cannon, which can fire projectiles at speeds up to 24,000 km/h (15,000 mph), is used to conduct impact experiments. These experiments have shown that during an impact event, vapor plumes travel outwards from the impact point (just above the surface) at incredible speeds. For the sake of their study, Schultz and Quintana scaled the size of the impacts up, to the point where they corresponded to the impact craters on Mars.
The results indicated that the vapor plume speed would be supersonic, and that its interaction with the Martian atmosphere would generate powerful winds. However, the plume and associated winds would not be responsible for the strange streaks themselves. Since they would be travelling just above the surface, they would not be capable of causing the kind of deep scouring that exists in the streaked areas.
Instead, Schultz and Quintana showed that when the plume struck a raised surface feature – like the ridges of a smaller impact crater – it would create more powerful vortices that would then fall to the surface. It is these, according to their study, that are responsible for the scouring patterns they observed. This conclusion was based on the fact that bright streaks were almost always associated with the downward side of a crater rim.
IR images showing the correlation between the streaks and smaller craters that were in place when the larger crater was formed. Credit: NASA/JPL-Caltech/Arizona State University
As Schultz explained, the study of these streaks could prove useful in helping to establish that rate at which erosion and dust deposition occurs on the Martian surface in certain areas:
“Where these vortices encounter the surface, they sweep away the small particles that sit loose on the surface, exposing the bigger blocky material underneath, and that’s what gives us these streaks. We know these formed at the same time as these large craters, and we can date the age of the craters. So now we have a template for looking at erosion.”
In addition, these streaks could reveal additional information about the state of Mars during the time of impacts. For example, Schultz and Quintana noted that the streaks appear to form around craters that are about 20 km (12.4 mi) in diameter, but not always. Their experiments also revealed that the presence of volatile compounds (such as surface or subsurface water ice) would affect the amount of vapor generated by an impact.
In other words, the presence of streaks around some craters and not others could indicate where and when there was water ice on the Martian surface in the past. It has been known for some time that the disappearance of Mars’ atmosphere over the course of several hundred million years also resulted in the loss of its surface water. By being able to put dates to impact events, we might be able to learn more about Mars’ fateful transformation.
The study of these streaks could also be used to differentiate between the impacts of asteroids and comets on Mars – the latter of which would have had higher concentrations of water ice in them. Once again, detailed studies of Mars’ surface features are allowing scientists to construct a more detailed timeline of its evolution, thus determining how and when it became the cold, dry place we know today!
This colorful image of Martian bedrock, punctuated in the center by dunes, is courtesy of the HiRise camera aboard NASA's Mars Reconnaissance Orbiter. Image: NASA/JPL/University of Arizona
For a supposedly dead world, Mars sure provides a lot of eye candy. The High Resolution Imaging Science Experiment (HiRise) aboard NASA’s Mars Reconnaissance Orbiter (MRO) is our candy store for stunning images of Mars. Recently, HiRise gave us this stunning image (above) of colorful, layered bedrock on the surface of Mars. Notice the dunes in the center. The colors are enhanced, which makes the images more useful scientifically, but it’s still amazing.
HiRise has done it before, of course. It’s keen vision has fed us a steady stream of downright jaw-dropping images of Elon Musk’s favorite planet. Check out this image of Gale Crater taken by HiRise to celebrate its 10 year anniversary orbiting Mars. This image was captured in March 2016.
HiRise captured this image of unusual textures on the floor of the Gale Crater, the same crater where the Curiosity rover is working. Image: NASA/JPL-Caltech/Univ. of Arizona
The MRO is approaching its 11 year anniversary around Mars. It has completed over 45,000 orbits and has taken over 216,000 images. The next image is of a fresh impact crater on the Martian surface that struck the planet sometime between July 2010 and May 2012. The impact was in a dusty area, and in this color-enhanced image the fresh crater looks blue because the impact removed the red dust.
This color-enhanced image of a fresh Martian crater was captured by the HiRise camera. Image: NASA/JPL-Caltech/Univ. of Arizona
These landforms on the surface of Mars are still a bit of a mystery. It’s possible that they formed in the presence of an ancient Martian ocean, or perhaps glaciers. Whatever the case, they are mesmerizing to look at.
These odd ridges are still a mystery. Were they formed by glaciers? Oceans? Image: NASA/JPL-Caltech/Univ. of Arizona
Many images of the Martian surface have confounded scientists, and some of them still do. But some, though they look puzzling and difficult to explain, have more prosaic explanations. The image below is a large area of intersecting sand dunes.
What is this? A vast area of Martian rice paddies? Lizard skin? Nope, just an area of intersecting sand dunes. Image: NASA/JPL-Caltech/Univ. of Arizona
The surface of Mars is peppered with craters, and HiRise has imaged many of them. This double crater was caused by a meteorite that split in two before hitting the surface.
This double impact crater was caused by a meteorite that split into two before hitting Mars. Notice how the eroding force of the wind has shaped each crater the same, smoothing one edge and creating dunes in the same place. Image: NASA/JPL-Caltech/Univ. of Arizona
The image below shows gullies and dunes at the Russell Crater. In this image, the field of dunes is about 30 km long. This image was taken during the southern winter, when the carbon dioxide is frozen. You can see the frozen CO2 as white on the shaded side of the ridges. Scientists think that the gullies are formed when the CO2 melts in the summer.
These gullies are on the dunes of Russell Crater on Mars. This image was taken during winter, and the frozen carbon dioxide on the shaded slopes. Credit: NASA/JPL/University of Arizona
The next image is also the Russell Crater. It’s an area of study for the HiRise team, which means more Russell eye candy for us. This images shows the dunes, CO2 frost, and dust devil tracks that punctuate the area.
This image of the Russell Crater, an area of study for HiRise, shows the area covered in dunes, with some frost visible in the lower left. The larger, darker markings are dust devil tracks. Image: By NASA/JPL/University of Arizona – HiRISE, Public Domain, https://commons.wikimedia.org/w/index.php?curid=12015650
One of the main geological features on Mars is the Valles Marineris, the massive canyon system that dwarfs the Grand Canyon here on Earth. HiRise captured this image of delicate dune features inside Valles Marineris.
These delicate dune features formed inside the Valles Mariners, the massive canyon system on Mars. Image: NASA/JPL/University of Arizona
The Mars Reconnaissance Orbiter is still going strong. In fact, it continues to act as a communications relay for surface rovers. The HiRise camera is along for the ride, and if the past is any indication, it will continue to provide astounding images of Mars.
A brand new crater on the Moon! This new 12 meter (39 foot) diameter impact crater formed between 25 October 2012 and 21 April 2013 Credit: NASA/GSFC/Arizona State University].
Animation of a temporal pair of the new 39-foot (12-meter) impact crater on the moon photographed by NASA’s Lunar Reconnaissance Orbiter Credit: NASA/GSFC/Arizona State University
We often hear how the Moon’s appearance hasn’t changed in millions or even billions of years. While micrometeorites, cosmic rays and the solar wind slowly grind down lunar rocks, the Moon lacks erosional processes such as water, wind and lurching tectonic plates that can get the job done in a hurry.
One of a series of photos Apollo 11 astronaut Edwin Aldrin made of his bootprint in the dusty, sandy lunar soil, called regolith. Based on a newy study, the impression may disappear in a few tens of thousands of years instead a few million. Credit: NASA
Remember Buzz Aldrin’s photo of his boot print in the lunar regolith? It was thought the impression would last up to 2 million years. Now it seems that estimate may have to be revised based on photos taken by the Lunar Reconnaissance Orbiter (LRO) that reveal that impacts are transforming the surface much faster than previously thought.
This map shows the distribution of new impact craters (yellow dots) discovered by analyzing 14,000 narrow-angle camera (NAC) temporal pairs. The two red dots mark the location of the March 17, 2013 and September 11, 2013 impacts that were recorded by Earth-based video monitoring. LRO’s mission was recently extended an addition two years through September 2018. Credit: NASA/GSFC/ASUThe LRO’s high resolution camera, which can resolve features down to about 3 feet (1-meter) across, has been peering down at the Moon from orbit since 2009. Taking before and after images, called temporal pairs, scientists have identified 222 impact craters that formed over the past 7 years. The new craters range from 10 feet up to 141 feet (3-43 meters) in diameter.
By analyzing the number of new craters and their size, and the time between each temporal pair, a team of scientists from Arizona State University and Cornell estimated the current cratering rate on the Moon. The result, published in Nature this week, was unexpected: 33% more new craters with diameters of at least 30 feet (10 meters) were found than anticipated by previous cratering models.
LRO before and after images of an impact event on March 17, 2013. The newly formed crater is 59 feet (18 meters) in diameter. Subsurface regolith not exposed to sunlight forms a bright halo around the new crater. There also appears to be a larger nimbus of darker reflectance material visible much further beyond but centered on the impact. Credit: NASA/GSFC/Arizona State University
Similar to the crater that appeared on March 17, 2013 (above), the team also found that new impacts are surrounded by light and dark reflectance patterns related to material ejected during crater formation. Many of the larger impact craters show up to four distinct bright or dark reflectance zones. Nearest to the impact site, there are usually zone of both high and low reflectance. These two zones likely formed as a layer of material that was ejected from the crater during the impact shot outward to about 2½ crater diameters from the rim.
An artist’s illustration of a meteoroid impact on the Moon. Impacts dig up fresh material from below as well as send waves of hot rock vapor and molten rock across the lunar landscape, causing a much faster turnover of the moon soil than previously thought. Credit: NASA
From analyzing multiple impact sites, far flung ejecta patterns wrap around small obstacles like hills and crater rims, indicating the material was traveling nearly parallel to the ground. This kind of path is only possible if the material was ejected at very high speed around 10 miles per second or 36,000 miles per hour! The jet contains vaporized and molten rock that disturb the upper layer of lunar regolith, modifying its reflectance properties.
How LRO creates temporal pairs and scientists use them to discover changes on the moon’s surface.
In addition to discovering impact craters and their fascinating ejecta patterns, the scientists also observed a large number of small surface changes they call ‘splotches’ most likely caused by small, secondary impacts. Dense clusters of these splotches are found around new impact sites suggesting they may be secondary surface changes caused by material thrown out from a nearby primary impact. From 14,000 temporal pairs, the group identified over 47,000 splotches so far.
Here are two examples of a low reflectance (top) and high reflectance (bottom) splotch created either by a small impactor or more likely from secondary ejecta. In either case, the top few inches of the regolith (soil) was churned Credit: NASA/GSFC/Arizona State UniversityBased on estimates of size, depth and frequency of formation, the group estimated that the relentless churning caused by meteoroid impacts will turn over 99% of the lunar surface after about 81,000 years. Keep in mind, we’re talking about the upper regolith, not whole craters and mountain ranges. That’s more than 100 times faster than previous models that only took micrometeorites into account. Instead of millions of years for those astronaut boot prints and rover tracks to disappear, it now appears that they’ll be wiped clean in just tens of thousands!
A depression on Ceres is possibly what’s left of one of the largest craters from Ceres’ earliest collisional history. Credit: SwRI/Simone Marchi.
Scientists have found a bit of a mystery at the dwarf planet Ceres. Yes, there are those intriguing bright spots inside numerous craters, which is a mystery that has mostly been solved (the bright areas likely made of bright salts leftover from the sublimation of a briny solution of sodium carbonate and ammonium chloride; read more details in this NASA article.)
But a new puzzle involves the craters themselves. In the rough and tumble environment of the asteroid belt, ancient Ceres was certainly pummeled by numerous large asteroids during its 4.5 billion-year lifetime. But yet, there are just a few large craters on Ceres.
How could that be?
“It is as though Ceres cures its own large impact scars and regenerates new surfaces, over and over,” said Dr. Simone Marchi, a senior research scientist at the Southwest Research Institute.
Scientists with NASA’s Dawn mission were surprised to find that Ceres has no clear signs of truly giant impact basins. This image shows both visible (left) and topographic (right) mapping data from Dawn. Credit: NASA/JPL-Caltech/SwRI.
Ceres has lots of little craters, but the Dawn spacecraft, orbiting Ceres since early 2015, has found only 16 craters larger than 100 km, and none larger than 280 km (175 miles) across. Scientists who model asteroid collisions in our Solar System predicted Ceres should have amassed up to 10 to 15 craters larger than 400 kilometers (250 miles) wide, and at least 40 craters larger than 100 km (62 miles) wide.
By comparison, Dawn’s other target of study, the smaller asteroid Vesta, has several large craters, including one 500 kilometers (300 miles) in diameter, covering almost the entire south pole region.
While they aren’t visible now, the scientists say there are clues that large impact basins may be hidden beneath Ceres’ surface.
“We concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, likely the result of Ceres’ peculiar composition and internal evolution,” Marchi said.
The top of this false-color image includes a grazing view of Kerwan, Ceres’ largest impact crater. This well-preserved crater is 280 km (175 miles) wide and is well defined with red-yellow high-elevation rims and a deep central depression shown in blue. Kerwan gradually degrades as one moves toward the center of the image into an 800-km (500-mile) wide, 4-km (2.5-mile) deep depression (in green) called Vendimia Planitia. This depression is possibly what’s left of one of the largest craters from Ceres’ earliest collisional history. Credit: SwRI/Simone Marchi.
There are hints of about three shallow depressions around 800 km (500 miles) wide, and Marchi said they could be what are called or planitiae, or ancient impact basins, left over from large collisions that took place early in Ceres’ history.
There are a few possible reasons why the big craters have been erased, and the scientists now have to figure out which reason or combination of reasons best explain their findings. One reason could be because of large amounts of water or ice in Ceres’ interior, which has long been suspected. Does the absence of large craters lend any insight into Ceres’ water content?
“It might,” Marchi said via email. “There is evidence for ice locally at the surface but it is not clear how much water ice there is in the subsurface.”
Marchi said the craters allow scientists to “probe” down to different depths, depending on their sizes, and that the missing large craters (greater than 100 km in diameter) can provide information on the properties on just the upper 100-200 km or so of Ceres’s outer shell.
Because ice is less dense than rock, the topography could “relax” over time — like what happens if you push on your skin, then take the pressure off, and it relaxes back to its original shape, although this happened extremely more slowly on Ceres. The scientists said that over geological timescales of several million years the water or ice would slowly flow and the craters would smooth out.
Additionally, recent analysis of the center of Ceres’ Occator Crater — where the largest bright areas are located — suggests that the salts found there could be remnants of a frozen ocean under the surface, and that liquid water could have been present in Ceres’ interior.
A recent paper constrains the amount of subsurface ice to be no more than 30-40%.
“However, the lack of large craters cannot be solely explained by the presence of 30-40% of water,” Marchi told Universe Today.
Another reason for the lack of large craters could be hydrothermal activity, such as geysers or cryovolcanoes, which could have flowed across the surface, possibly burying pre-existing large craters. Smaller impacts would have then created new craters on the resurfaced area. Hydrothermal activity has been linked to bright areas on Ceres, as well.
A close look at some of the craters on Ceres show cracked-like surfaces and other areas that looks like there was flow of the surface that “softened” some of the features. Marchi said the team is still working to clarify the Ceres’ peculiar composition and how cryolava or “low viscous material” could have caused the crater rims and bowls to “relax.”
The bright central spots near the center of Occator Crater are shown in enhanced color in this view from NASA’s Dawn spacecraft. The view was produced by combining the highest resolution images taken in February 2016 (at image scales 115 feet (35 meters) per pixel of 35 meters with color images obtained in September 2015 at a lower resolution. Click for a highest-res view. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI
“This is still work in progress,” he told Universe Today. “Ceres is far more richer than Vesta in terms of smooth, flow features. Given that they are in the same environment (e.g. similar impact speed with asteroids), one would think that the production of impact melts would be the same. Thus the fact that we see more flow features on Ceres is a confirmation of its peculiar composition. This may facilitate production of impact “melt” (or ‘mud’ if there is enough water and clays).”
Another reason for the lack of large craters is that smaller, later impacts could have erased the bigger older impact basins. But if that were the case, the older basins would seemingly be more visible than they are now.
But the answer to this puzzle might all come back to the intriguing bright areas on Ceres.
“The presence of ammoniated phyllosilicates, carbonates and salts is truly amazing,” Marchi said. “I think this peculiar composition and Ceres’ internal structure are responsible for the lack of large craters, although we do not know precisely what the obliteration mechanism is.”
Marchi said the large crater obliteration was active well after the late heavy bombardment era, or about 4 billion year ago, so the resurfacing is inextricably linked to Ceres itself and its internal evolution, not impact events.
“All this shows over and over how peculiar Ceres is,” Marchi said. “Beside being a transition object (at inner/outer solar system boundary), it is peculiar in composition, and now also in cratering record.”
Finding out more about Ceres’ interior is one of the more intriguing aspects of Dawn’s continued mission there.
![Distribution of new impact craters (yellow dots) discovered by analyzing 14,000 NAC temporal pairs. The two red dots mark the location of the 17 March 2013 and the 11 September 2013 impacts that were recorded by Earth-based video monitoring [NASA/GSFC/Arizona State University]](https://www.universetoday.com/wp-content/uploads/2016/10/Moon-new-crater-distribution-NASA-GSFC-ASU.jpg)
![Example of a low reflectance (top) and high reflectance (bottom) splotch created either by a small impactor or more likely from secondary ejecta. In either case, the top few centimeters of the regolith (soil) was churned [NASA/GSFC/Arizona State University].](https://www.universetoday.com/wp-content/uploads/2016/10/Moon-craters-splotches-NASA.gif)
