The Solar System Treks are online, browser-based portals that allow you to visualize, explore, and analyze solar system bodies....
Welcome to Mojave! Not the desert in California, but the crater on Mars. Mojave is over 50 kilometers across and about 1.5 kilometers deep. This view, looking south, was generated using Mars Trek combining data from the THEMIS instrument aboard the Mars Odyssey spacecraft and the MOLA laser altimeter aboard the Mars Reconnaissance Orbiter. Even more than its terrestrial namesake, the area surrounding this crater is very arid. But it wasn’t always. Look at the lobate ejecta blanket extending from the crater into the foreground on this view. This is characteristic of a rampart crater, and tells us that the impactor that created Mojave hit in an area with a large amount of subsurface water, possibly in the form of ice. The pasty ejecta around the crater very appropriately evokes images of throwing a rock into mud. Now take a look at the terrain behind the crater. It was extensively sculpted by massive outflow channels emptying huge volumes of water north into the great bay that occupied the area now known as Chryse Planitia. Close examination of the terrain in and around Mojave reveals the presence of classic alluvial fans. Here on Earth, alluvial fans just like these form as a result of heavy desert downpours, typically thundershowers. So did Mars experience drenching rains in the past? We see evidence in Mojave that this may have been the case. Clusters of small, closely-shaped pits on the floor of Mojave have been interpreted as resulting from the eruption of steam released when deposits of subsurface water or ice were heated by the energy of the impact that formed the crater. We see examples of this in other regions on Mars, and even on other worlds. (For an asteroidal example, take a look at the pitted terrain on Vesta north of the crater Marcia and highlighted in Vesta Trek). Mojave and its surroundings tell us amazing stories of Mars’ watery past, and of the large amounts of water that may be found even today beneath Mars’ surface. But those are far from the only stories that Mojave has to tell. A team led by Stephanie Werner of the University of Oslo has proposed Mojave as the source for the shergotties, Martian meteorites that have fallen to the Earth and into the collections of many meteorite enthusiasts (including me). They base this on comparing the estimated age of the crater with the time that the shergottites spent exposed to cosmic rays during their flight through space, along with similarities between the mineralogy of the Mojave area and the composition of the shergotties. So did the impact that formed Mojave cause pieces of Mars to rain down upon the Earth? Mojave’s role as the source of the shergotties is far from settled, and continues to be energetically debated in the journals and at planetary science conferences. But this just adds to the fascinating aspects of this remarkable crater.
The Straight Wall, formally known as Rupes Recta, is the finest example of a fault on the Moon. It stretches for a distance of 120 km across the floor of Mare Nubium. The flat floor of the mare takes a dramatic step up here with the ground being 200 to 400 meters higher on the east side of the fault than on the west. This is a favorite feature among amateur astronomers, being easily visible even in small telescopes. When the Sun’s illumination comes from the east, the fault casts a dark shadow westward across the flat floor of Mare Nubium. When the sunlight comes from the west, as in this LRO Wide Angle Camera view, the fault’s face becomes brightly illuminated. Moon Trek’s Elevation Profile Tool lets you explore this fascinating feature’s height and slope. Use Moon Trek’s Search feature, and look for ͞Rupes Recta͟ to find it. Another very interesting feature can be seen about 40 km to the west of the Straight Wall. Rima Birt is an example of a sinuous rille. It runs roughly parallel to the Straight Wall for a distance of about 30 km. This is apparently a channel carved by lava flowing across the surface of the Moon. At each end, the rille terminates in a small pit.
There’s a lot to learn from the stories told by the amazing lunar landforms of Hyginus crater and Hyginus Rille. Hyginus Rille is the sharp, 220 km long depression stretching left to right (west to east) in this Moon Trek visualization using data from the WAC camera aboard the Lunar Reconnaissance Orbiter. Hyginus Crater is seen at the elbow-like bend in the rille near the center of the image. Hyginus Rille apparently formed when magma from the Moon’s mantle forced its way up through a crack in the lunar crust. As the intruding magma widened the crack, parallel faults were formed on the surface above. As the faults pulled away from each other due to the extensional forces below, the land between them dropped down forming a graben. Beneath the widening Hyginus Rille, chambers of pressurized foam formed at the top of the dike of molten rock, as dissolved gasses bubbled out of the rising magma. The faults above provided a path for that pressure to be relieved through what must have been spectacular pyroclastic volcanic eruptions. A dark blanket of volcanic ash from these eruptions can be seen surrounding Hyginus Crater. As the pressurized chambers were evacuated by the eruptions, they collapsed, resulting in volcanic pit craters on the surface. Hyginus Crater is the largest of those seen here, but a string of smaller pit craters can be seen extending to the northwest along the rille. Such pit craters are notable for their lack of raised rims. You can explore something similar here on Earth by driving along the Chain of Craters Road in Hawaii Volcanoes National Park. There was an intense debate for many years as to whether the Moon’s craters formed through volcanic eruptions or meteoroid impacts. We now know that the vast majority of lunar craters formed as a result of impacts. But as these examples along Hyginus Rille demonstrate, volcanic craters can also be found on the Moon. There’s another very curious aspect to this region. The floor of Hyginus Crater is an example of an Irregular Mare Patch or IMP. The Ina Caldera, about 325 km to the north, is the best-known of these IMPs. These mysterious features exhibit erupted volcanic material. Nothing special there. But the technique of crater counting leads to an estimate of very young ages for these areas, indicating eruptions that are far too recent to be consistent with our current thermal modeling of the Moon. But as Jim Head presented at the 2016 meeting of the Lunar Exploration Analysis Group, the foamy nature of the erupted material could lead us to seriously underestimate the ages of these features based on crater counts. Finally, take a look at the branching of the rille at the far right of this image. The upper branch actually connects Hyginus to another of the Moon’s great straight rilles, the Ariadaeus Rille.
South is up in this Mars Trek view of the southern portion of Chryse Planitia. The MGS MOLA and Mars Express HRSC, Color Hillshade Blend layer used here represents different surface elevations as different colors, blue being low, progressing through shades of green, yellow, and orange as we move to progressively higher elevations. This technique is particularly effective in making surface topography really stand out. In this view, we can readily appreciate Mars’ distant watery past, with many features streamlined by the flow of water and a number of great outflow channels being clearly seen. Mawrth Vallis, made famous in Andy Weir’s story ͞The Martian͟, is the relatively narrow channel with two right-angle bends seen on the left. Chryse Chaos is seen at top, with the long channel of Ares Vallis to its left, and the bifurcated channel of Shalbatana Vallis to its right. On the far right, we see the multiple large, braided channels of Kasei Valles. In Mars’ distant past, great floods of water flowed through these channels and into the basin of Chryse Planitia, which may have been a large bay opening up into a great northern ocean on Mars.
A field of barchan dunes with their distinctive crescent shapes marches across the floor of McLaughlin Crater in this view from Mars Trek using data from the CTX camera aboard the Mars Reconnaissance Orbiter. The orientation of the dunes here indicates that the prevailing winds here are blowing from the far side of the crater toward our vantage point. The rim of the 95-km diameter crater rises in the distance. McLaughlin Crater is of particular interest as the apparent site of an ancient lake filled by upwelling groundwater rather than inflowing surface water. Abundant carbonate deposits on the floor of the crater indicate that the water here lasted for a prolonged time, and was not too acidic for possible life. This was among the reasons why McLaughlin Crater was chosen in 2015 as one of the Exploration Zone candidates for human missions to Mars.
Take a look at the crater in the center foreground of this Mars Trek visualization using THEMIS data from Mars Odyssey. Aside from the central peak, the crater’s floor is largely covered by alluvial fans. Note the fan radiating out from the canyon on the crater’s rim above and to the right of the central peak. Notice the smooth slopes stretching down from the rim on the left and the fan emerging from the canyon on the lower right. These look remarkably similar to the same kinds features here on Earth, and like the fans on Earth, they seem to tell a story of rocky debris washed down from high, steep slopes during intense precipitation. Imagine a deluge of water, sand, and rock flooding down from the crater rim during an intense Martian cloudburst. The size of these fans seems to indicate that they likely built up over millennia. All of this tells us something fascinating about past climate on Mars. The unnamed crater here is 63km across, and can be found at latitude -23.5 and longitude 74.3. Fans like this can be found in numerous craters across bands of specific latitudes on Mars. The Alluvial Fans static layer in Mars Trek can help you find more examples.
Moon Trek 1.0 Overview
Mars Trek 3.0 Overview
Vesta Trek 1.0 Overview
Volcanoes of the Moon
Mars Mid-Latitude Glaciers
Disaster on Vesta
Phobos Trek (Coming Soon) Overview