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NASA Solar System Treks

Jun 30 2017 00:00:00 UTC

Dec 27 2017 00:00:00 UTC

Ganymede

Giant Moon of a Giant Planet

Jupiter's biggest Moon is also the Solar System's largest, greater in diameter than the planet Mercury. Ganymede's icy crust displays a mixture of terrain dominated by impact craters, and mysterious landscapes covered by gigantic ridges and grooves. Beneath its crust and above a rocky mantle is a large ocean of liquid water, leading to speculation about chances for alien biology. Convecting, molten metal in Ganymede's core generates a global magnetic field that helps to create aurorae in Ganymede's sky.

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Ganymede

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Solar System Treks?

The Solar System Treks are online, browser-based portals that allow you to visualize, explore, and analyze the surfaces of other worlds using real data returned from a growing fleet of spacecraft. You can view the worlds through the eyes of many different instruments, pilot real-time 3D flyovers above mountains and into craters, and conduct measurements of surface features. The portals provide exciting capabilities for mission planning, planetary science, and public outreach.

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NASA needs your help spotting changes on the surface of Earth's nearest neighbor – the Moon! Join MoonDiff, our newest volunteer science project, and help scientists learn about the Moon’s dynamic surface.

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PhobosTrek with data from Mars Express and Viking
GanymedeTrek with data from Voyager and Galileo
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EuropaTrek with data from Voyager and Galileo
BennuTrek with data from OSIRIS-REx
RyuguTrek with data from JAXA's Hayabusa2

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Figure 1: Volcanic landforms on the western flank of the Cauchy Shield. B and C are classic low-profile lunar domes. The object labeled A is a small cluster of volcanic cones. Merge of LOLA and Kaguya TC altimetry data, emphasizing surface topography.

Feature of the Month - August 2024

Lunar Volcanic Cones In the July 2024 article in this series, we looked at how the kind of volcanic fire fountain eruptions that typically build up cinder cones here on Earth, usually result in widely distributed blankets of volcanic ash rather than localized cones. On the moon, erupted droplets experience much less gravity than what similar droplets experience here on Earth. The flying lunar droplets also experience no atmospheric drag. The result is that instead of quickly dropping and piling up near the site of the eruption, lunar pyroclastic ash can fly out over great distances.

But the Moon is not completely without features resembling cinder cones. They are, however, far less common than what we find here on Earth. Most lunar volcanoes are low, flat, pancake-like domes with slopes of only about one degree. This is due to most lunar lava erupting with very low viscosity, being very thin and runny. Many lunar eruptions were effusive in nature, with lava oozing from cracks in the ground and flowing out across the landscape. But some lunar eruptions were pyroclastic in nature. Lava charged with dissolved gasses under great pressure was shot as jets into the lunar sky in a way similar to the explosive release when opening a soda that has been shaken.

An excellent example volcanic variety is seen on the western flank of the Moon's great Cauchy shield volcano in Mare Tranquillitatis. Two very typical lunar domes are labeled B and C in figure 1. But a small cluster of cones, labeled A, looks very different. These resemble pyroclastic cones that we commonly see on Earth.

Why would pyroclastic deposits pile up locally to form cones in some cases, and spread out widely as ash deposits in other cases? There could be several reasons. Lower amounts of dissolved gas could lead to lower pressure, shooting erupted lava for shorter distances. A variety of factors including pressure, the rate of lava being erupted, and the viscosity of the lava could influence whether the pyroclastic eruption takes the form of a spray of small droplets or large molten blobs that, due to being heavier, do not travel as far from the vent. While true cinder cones are made of small pieces of volcanic material that solidify before hitting the ground, larger flying globs of molten material that remain at least partially molten when they fall back to the ground can become welded together and pile up around the vent to form a spatter cone. Spatter cones can somewhat resemble cinder cones in shape, but tend to be denser and more consolidated.

A bird's-eye view of Mons Latreille (labeled as A) and two irregular cones (labeled as B and C) (shown in Moon Trek)

Figure 2: Mons Latreille (A) and two unnamed irregular cones labeled B and C.

Other fine examples of volcanic cones occur in Mare Crisium (figure 2). One particularly dramatic instance takes the form of a breached cone, labeled A in the figure. We see this kind of structure frequently here on Earth. Pyroclastic debris piles up around the vent as a cone in the early stage of an eruption. As the eruption continues, less gas remains dissolved in the erupted lava, and it erupts as more of a liquid that can build up and break through part of the cone as a liquid flow. The breached cone here has been known in the past by the informal name of “Horseshoe Crater” for obvious reasons. The area right next to the cone has been designated as the planned landing site for the Firefly commercial landing carrying NASA experiments to this fascinating area. The International Astronomical Union gave the former Horseshoe Crater the now formal name of “Mons Latreille.” Near Mons Latreille, we can see two smaller and somewhat more irregularly-shaped nameless cones, labeled B and C in figure 2.

A bird's-eye view of lunar cones Isis (labeled as A) and Osiris (labeled as B) (shown in Moon Trek)

Figure 3: Lunar cones Isis (A) and Osiris (B).

Many lunar cones are anonymous. But two cones, Isis and Osiris, found near the intersection of Mare Serenitatis and Mare Tranquillitatis have earned formal names as features on the Moon (figure 3). Isis has an irregular shape with a breach to the northwest. It appears that lava may have flowed from the vent and out through the breach. Osiris is circular in shape and could easily be mistaken for an impact crater were it not for the exaggerated height off the rim formed by the cone surrounding the crater. It is interesting to note that Osiris lies near the intersection of several straight rilles. Such straight rilles are interpreted as being faulted terrain wedged apart by magma rising through cracks in the lunar crust. In many locations, we see volcanic landforms associated with straight rilles, providing evidence of magma having made it up to the surface. Osiris may be another such example.

A bird's-eye view of the Fra Mauro region of a spatter rampart and volcanic ash (shown in Moon Trek)

Figure 4: A spatter rampart located along a straight rille in the Fra Mauro region stretches diagonally through the center of this image. A dark blanket of volcanic ash stretches out from the rampart.

When pyroclastic eruptions occur along the length of an extended fissure rather than a single vent, a string of spatter cones can form next to the fissure, forming a spatter rampart. We see examples of this here on Earth in the famous “curtain of fire” eruptions that form from fissures breaking out on Hawaii's Mauna Loa volcano. On the Moon, we see what looks to be a convincing example in the Fra Mauro region (figure 4). A merged line of spatter cones looks to have formed along a straight rille. Further convincing evidence comes from the blanket of dark volcanic ash that can be seen around the rampart and rille.

A high-resolution birds-eye view of the Marius Hills (shown in Moon Trek)

Figure 5: The Marius Hills seen via a merge of LOLA and Kaguya TC altimetry data.

The Marius Hills (figure 5) is a particularly noteworthy collection of a large number of steep-sided volcanic domes and cones. These features are definitely steeper than typical mare domes. Why would that be? Many researchers believe that the difference here may be due to a difference in the composition of the lava that was erupted. Lava that is higher in silica content is more viscous or pastier, and therefore can pile up in steeper slopes. Measurements from orbit indicate that the lava of the Marius Hills is basalt, a low-silica form of lava. But basalt can have a range of silica content. It will be interesting to sample the lava of the Marius Hills to see if it is higher in silica than typical mare basalt, and if that might provide answers to questions about the steepness of domes and the frequency of cones here.

An angled view of Mairan T (shown in Moon Trek)

Figure 6: Mairan T, a beautiful silicic cone.

One especially famous cone on the Moon is Mairan T (figure 6). This is one of a series of volcanic features that we examined in the January 2019 article in this series. Composition certainly plays a key role in this cone's form. Spectrometry from instruments in orbit around the Moon reveal that this cone is composed of lava that is especially high in silica content, too high for the lava to be considered basalt. Such lava, if not erupted with too much force from too much dissolved gas, could easily pile up around the vent, forming this beautiful volcanic cone.

These are just a few selected examples. But from this list, we can see that lunar volcanic cones are a diverse group, and diverse stories likely come together in explaining how they formed.

Did You Know?

Touring the Lunar South Pole

Craters of Bennu

The Connected Solar System

Ryugu, A Near-Earth Asteroid

Lacus Mortis on the Moon

Mercury Tour

Volcanoes of the Moon

Mars Mid-Latitude Glaciers

Ceres' Active Geology

Disaster on Vesta

Virtual Reality Library

You can use the “Experience TrekVR” tool in many of the Trek portals to create your own virtual reality flyovers of terrain that interests you. We’ve also created a list of pre-made VR flyovers of some of the more popular sites to help get you started in your VR explorations. Use your smart phone to scan the QR code associated with each flyover, put your phone in a pair of cardboard-compatible goggles, and start flying. Keep an eye on this page! We’ll be updating it with new flyovers.

These flyovers use data from the Wide Angle Camera aboard the Lunar Reconnaissance Orbiter to provide a broad view of the fascinating geography that led to these sites being selected for the first stages of human exploration on the Moon. For each site, we provide a screenshot map from Moon Trek showing the flyover path marked in yellow and a red X marking the landing site. We also include a QR code or browser link for you to use in viewing the flyover.

Apollo 11
Sea of Tranquility

The site of humanity’s first steps on the Moon was chosen for its flat, level, safe terrain. We can see this as we fly from the rugged highlands to the south to the smooth plains of Tranquility to the north.

Apollo 12
Ocean of Storms

Another flat landing site was provided by Oceanus Procellarum – the Ocean of Storms, actually the Moon’s greatest plain of solidified lava. We fly south to north in this view.

Apollo 14
Fra Mauro

The landscape for this mission was much trickier, with lots of rolling hills to deal with. These were formed from rock debris blasted out by a distant asteroid impact on the Moon. In this view, we fly north over the area.

Apollo 15
Hadley Rille

At the base of the towering Apennine Mountains, Apollo 15 landed on the edge of Hadley Rille, a great channel carved long ago by flowing lava. Here we fly northward along the range of mountains and the lava channel.

Apollo 16
Descartes Highlands

This was the first human mission to the Moon to land in the rugged, rough, ancient highlands of the Moon. In this view, we fly south to north.

Apollo 17
Taurus-Littrow Valley

The final Apollo mission to the Moon made a spectacular descent into the Taurus-Littrow valley, deeper than Earth’s Grand Canyon. Here we fly over the valley from east to west.

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Virtual Reality

Have Google Cardboard or a set of VR goggles? Open the Tools panel to draw a path to float along with full 360 views, or get started with some of our favorite fly-alongs in our Virtual Reality Library. If you are unfamiliar with QR codes, watch the short video below to see how it works with Trek Virtual Reality.

Currently not available in Titan or Icy Moons Trek.

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