Image of potential flat, smooth terrain on Ganymede imaged by NASA's Galileo spacecraft in 2000 that could be indicative of landslides. (Credit: NASA/JPL/Brown University)
The European Space Agency’s (ESA) recently launched Jupiter Icy Moons Explorer (JUICE) mission and NASA’s upcoming Europa Clipper mission could allow scientists to image landslides on the icy moons of Europa and Ganymede due to potential moonquakes on these small worlds. This comes after a recent study examined fault scarps on Europa and Ganymede orbiting Jupiter and Enceladus and Dione orbiting Saturn with the goal of drawing a connection between tectonic activity (quakes) and observed mass wasting (landslides) on these surfaces. The researchers “consider whether such smooth material can be generated by mass wasting triggered from local seismic shaking”, according to the study.
Global color mosaic of Neptune's largest moon, Triton, taken by NASA's Voyager 2 in 1989. (Credit: NASA/JPL-Caltech/USGS)
In a recent study submitted to the journal Icarus, a team of researchers at the International Research School of Planetary Science (IRSPS) located at the D’Annunzio University of Chieti-Pescara in Italy conducted a geological analysis of a region on Neptune’s largest moon, Triton, known as Monad Regio to ascertain the geological processes responsible for shaping its surface during its history, and possibly today. These include what are known as endogenic and exogenic processes, which constitute geologic processes occurring internally (endo-) and externally (exo-) on a celestial body. So, what new insights into planetary geologic processes can we learn from this examination of Monad Regio?
Lava flows in Mars' Elysium Planitia region have left a rather good likeness of a woolly mammoth or elephant. The region is known for some of the planet's youngest lavas - this one may formed in the past 100 million years.
Billions of years ago, Mars was a much different place than it is today. Its atmosphere was thicker and warmer, liquid water flowed on its surface, and the planet was geologically active. Due to its lower gravity, this activity led to the largest volcanoes in the Solar System (Olympus Mons and the Thetis Mons region) and the longest, deepest canyon in the world (Valles Marineris). Unfortunately, Mars’ interior began to cool rapidly, its inner core solidified, and geological activity largely stopped. For some time, geologists have believed that Mars was essentially “dead” in the geological sense.
However, recent studies have provided seismic and geophysical evidence that Mars may still be “slightly alive.” In a recent study, scientists from the University of Arizona (ASU) challenged conventional views of Martian geodynamic evolution by discovering evidence of an active mantle plume pushing its way through the crust, causing earthquakes and volcanic eruptions. Combined with some serious marsquakes recorded by NASA’s InSight lander, these finding suggests that there is still some powerful volcanic action beneath the surface of Mars.
Earth, seen from space, above the Pacific Ocean. Credit: NASA
Today, the Earth’s seven continents are distributed across the surface, with North and South America occupying one hemisphere, Africa, Europe, Asia, and Australia occupying the other, and Antarctica sitting alone around the South Pole. However, these continents were arranged in entirely different configurations throughout Earth’s history. On occasion, they formed supercontinents like Gondwana (ca. 550 to 180 million) and Pangaea (ca. 335 to 200 million years ago) that were surrounded by “superoceans.”
Eventually, the Earth’s tectonic plates will come together again to form the world’s next supercontinent. According to new research led by Curtin University in Bentley, Australia, this will happen roughly 200 to 300 million years from now. As they determined through a series of simulations, this will involve the Americas drifting westward until they collide with Australia and Asia (eliminating the Pacific Ocean) and Antarctica moving north to join them. This will give rise to the new supercontinent they have named “Amasia,” which will also have profound implications for life on Earth.
Mining asteroids might be necessary for humanity to expand into the Solar System. But what effect would asteroid mining have on the world's economy? Credit: ESA.
Plate tectonics have played a vital role in the geological evolution of our planet. In addition, many scientists believe that Earth’s geologically activity may have played an important role in the evolution of life – and could even be essential for a planet’s habitability. For this reason, scientists have long sought to determine how and when Earth’s surface changed from molten, viscous rock to a solid crust that is constantly resurfacing.
A 13-kilometer (8-mile) diameter crater being infilled by the Medusae Fossae Formation. Credit: High Resolution Stereo Camera/European Space Agency.
Scientists first observed the Medusae Fossae Formation (MFF) in the 1960s, thanks to the efforts of the Mariner spacecraft. This massive deposit of soft, sedimentary rock extends for roughly 1,000 km (621 mi) along the equator and consists of undulating hills, abrupt mesas, and curious ridges (aka. yardangs) that appear to be the result of wind erosion. What’s more, an unusual bump on top of this formation also gave rise to a UFO conspiracy theory.
Needless to say, the formation has been a source of scientific curiosity, with many geologists attempting to explain how it could have formed. According to a new study from Johns Hopkins University, the region was the result of volcanic activity that took place on the Red Planet more than 3 billion years ago. These findings could have drastic implications for scientists’ understanding of Mars’ interior and even its past potential for habitability.
Perspective view of Medusa Fossae looking south-east. Copyright: ESA/DLR/FU Berlin (G. Neukum)
Ojha’s past work includes finding evidence that water on Mars occurs in seasonal brine flows on the surface, which he discovered in 2010 as an undergraduate student. Lewis, meanwhile, has dedicated much of his academic carreer to the in-depth study of the nature of sedimentary rock on Mars for the sake of determining what this geological record can tell us about that planet’s past climate and habitability.
As Ojha explained, the study of the Medusa Fossae Formation is central to understanding Mars geological history. Much like the Tharsus Montes region, this formation was formed at a time when the planet was still geologically active. “This is a massive deposit, not only on a Martian scale, but also in terms of the solar system, because we do not know of any other deposit that is like this,” he said.
Basically, sedimentary rock is the result of rock dust and debris accumulating on a planet’s surface and becoming hardened and layered over time. These layers serve as a geological record, indicating what types of processes where taking place on the surface at the time that the layers were deposited. When it comes to the Medusae Fossae Formation, scientists were unsure whether wind, water, ice or volcanic eruptions were responsible for the deposits.
In the past, radar measurements were made of the formation that suggested that Medusae Fosssae had an unusual composition. However, scientists were unsure whether the formation was made of highly porous rock or a mixture of rock and ice. For the sake of their study, Ojha and Lewis used gravity data from various Mars orbiters to measure the formation’s density for the first time.
An isolated hill in the Medusae Fossae Formation. The effect of wind erosion on this hill is evident by its streamlined shape. Credit: High Resolution Stereo Camera/European Space Agency
What they found was that the rock is unusually porous and about two-thirds as dense as the rest of the Martian crust. They also used radar and gravity data to show that the Formation’s density was too great to be explained by the presence of ice. From this, they concluded that the heavily-porous rock had to have been deposited by volcanic eruptions when Mars was still geologically active – ca. 3 billion years ago.
As these volcanoes exploded, casting ash and rock into the atmosphere, the material would have then fallen back to the surface, building up layers and streaming down hills. After enough time, the ash would have cemented into rock, which was slowly eroded over time by Martian winds and dust storms, leaving the Formation scientists see there today. According to Ojha, these new findings suggest that Mars’ interior is more complex than previously thought.
While scientists have known for some time that Mars has some volatiles – i.e. water, carbon dioxide and other elements that become gas with slight increases in temperature – in its crust that allow for periodic explosive eruptions to occur on the surface, the kind of eruption needed to create the Medusa Fossae region would have been immense. This indicates that the planet may have massive amounts of volatiles in its interior. As Ojha explained:
“If you were to distribute the Medusae Fossae globally, it would make a 9.7-meter (32-foot) thick layer. Given the sheer magnitude of this deposit, it really is incredible because it implies that the magma was not only rich in volatiles and also that it had to be volatile-rich for long periods of time.”
According to Ojha and Lewis’ study, the eruption that created the Medusa Fossae Formation would have covered Mars in a global ocean. Image: ESO/M. Kornmesser, via N. Risinger
In addition, this activity would have had a drastic impact on Mars’ past habitability. Basically, the formation of the Medusae Fossae Formation would have occurred during a pivotal point in Mars’ history. After the eruption occurred, massive amounts of carbon dioxide and (most likely) methane would have been ejected into the atmosphere, causing a significant greenhouse effect.
In addition, the authors indicated that the eruption would have ejected enough water to cover Mars in a global ocean more than 9 cm (4 inches) in thickness. This resulting greenhouse effect would have been enough to keep Mars’ surface warm to the point that the water would remain in a liquid state. At the same time, the expulsion of volcanic gases like hydrogen sulfide and sulfur dioxide would have altered the chemistry of Mars’ surface and atmosphere.
All of this would have had a drastic impact on the planet’s potential habitability. What’s more, as Kevin Lewis indicated, the new study shows that gravity surveys have the potential to interpret Mars’ geological record. “Future gravity surveys could help distinguish between ice, sediments and igneous rocks in the upper crust of the planet,” he said.
Studying Mars surface features and geological history is a lot like peeling an onion. With every layer we peel back, we get another piece of the puzzle, which together adds up to a rich and varied history. In the coming years and decades, more robotic missions will be studying the Red Planet’s surface and atmosphere in preparation for an eventual crewed mission by the 2030s.
All of these missions will allow us to learn more about Mars warmer, wetter past and whether or not may have existed there at some time (or perhaps, still does!)
The surface of Venus has been a mystery to scientists ever since the Space Age began. Thanks to its dense atmosphere, its surface is inaccessible to direct observations. In terms of exploration, the only missions to penetrate the atmosphere or reach the surface were only able to transmit data back for a matter of hours. And what we have managed to learn over the years has served to deepen its mysteries as well.
For instance, for years, scientists have been aware of the fact that Venus experiences volcanic activity similar to Earth (as evidenced by lighting storms in its atmosphere), but very few volcanoes have been detected on its surface. But thanks to a new study from the School of Earth and Environmental Sciences (SEES) at the University of St. Andrews, we may be ready to put that particular mystery to bed.
The study was conducted by Dr. Sami Mikhail, a lecturer with the SEES, with the assistance of researchers from the University of Strasbourg. In examining Venus’ geological past, Mikhail and his colleagues sought to understand how it is that the most Earth-like planet in our Solar System could be considerably less geologically-active than Earth. According to their findings, the answer lies in the nature of Venus’ crust, which has a much higher plasticity.
Image of the “pancake volcanoes” located in the Eistla region, taken by the Magellan space probe. Credit: NASA/JPL
This is due to the intense heat on Venus’ surface, which averages at 737 K (462 °C; 864 °F) with very little variation between day and night or over the course of a year. Given that this heat is enough to melt lead, it has the effect of keeping Venus’ silicate crust in a softened and semi-viscous state. This prevents lava magmas from being able to move through cracks in the planets’ crust and form volcanoes (as they do on Earth).
In fact, since the crust is not particularly solid, cracks are unable to form in the crust at all, which causes magma to get stuck in the soft, malleable crust. This is also what prevents Venus from experiencing tectonic activity similar to what Earth experiences, where plates drift across the surface and collide, occasionally forcing magma up through vents. This cycle, it should be noted, is crucial to Earth’s carbon cycle and plays a vital role in Earth’s climate.
Not only do these findings explain one of the larger mysteries about Venus’ geological past, but they also are an important step towards differentiating between Earth and it’s “sister planet”. The implications of this goes far beyond the Solar System. As Dr. Mikhail said in a St. Andrews University press release:
“If we can understand how and why two, almost identical, planets became so very different, then we as geologists, can inform astronomers how humanity could find other habitable Earth-like planets, and avoid uninhabitable Earth-like planets that turn out to be more Venus-like which is a barren, hot, and hellish wasteland.”
Volcanoes and lava flows on Venus. Credit: NASA/JPL
In terms of size, composition, structure, chemistry, and its position within the Solar System (i.e. within the Sun’s habitable zone), Venus is the most-Earth like planet discovered to date. And yet, the fact that it is slightly closer to our Sun has resulted in it having a vastly different atmosphere and geological history. And these differences are what make it the hellish, uninhabitable place that is today.
Beyond our Solar System, astronomers have discovered thousands of exoplanets orbiting various types of stars. In some cases, where the planets exist close to their sun and are in possession of an atmosphere, the planets have been designated as being “Venus-like“. This naturally sets them apart from the planets that are of particular interest to exoplanet hunters – i.e. the “Earth-like” ones.
Knowing how and why these two very similar planets can differ so dramatically in terms of their geological and environmental conditions is therefore key to being able to tell the difference between planets that are conducive to life and hostile to life. That can only come in handy when we begin to study multiple-planet systems (such as the seven-planet system of TRAPPIST-1) more closely.
New research suggests that Mercury is still contracting and shrinking. Credits: NASA/JHUAPL/Carnegie Institution of Washington/USGS/Arizona State University
Mercury is a fascinating planet. As our Suns’ closest orbiting body, it experiences extremes of heat and cold, has the most eccentric orbit of any Solar planet, and an orbital resonance that makes a single day last as long as two years. But since the arrival of the MESSENGER probe, we have learned some new and interesting things about the planet’s geological history as well.
For example, images that were recently obtained by the NASA spacecraft revealed previously undetected landforms – small fault scarps – that appear to be geologically young. The presence of these features have led scientists to conclude that Mercury is still contracting over time, which means that – like Earth – it is tectonically active.
In geology, fault scarps refer to small step-like formations in the surface of a planet, where one side of a fault has moved vertically relative to the other. Previously, scientists believed that Mercury was tectonically dead, and that all major geological activity had taken place in the planet’s early history.
Images showing small fault scarps and trough (lower and upper white arrows) found on Mercury;s surface. Credits: NASA/JHUAPL/Carnegie Institution of Washington/Smithsonian Institution
This was evidenced by features spotted by the MESSENGER and Mariner 10 probes, both of which found evidence of large wrinkle ridges and fault scarps on the surface. The features were reasoned to be the result of Mercury contacting as it cooled early in its history (i.e. billion of years ago).
This action caused the planet’s crust to break, forming cliffs up to a kilometer and a half (about 1 mile) in height and hundreds of kilometers long. However, as the MESSENGER team noted, these small scarps were considerably younger, dating to about 50 million years of age.
They concluded that the scarps would have to be this young in order to survive bombardment by comets and meteoroids, a common occurrence on Mercury. They also noted their resemblance to similar features on the Moon, which also has young scarps that are the result of recent contraction.
“The young age of the small scarps means that Mercury joins Earth as a tectonically active planet, with new faults likely forming today as Mercury’s interior continues to cool and the planet contracts.”
The findings were made during the last 18 months of the MESSENGER mission, during which time the probe lowered its altitude to get higher-resolution images of the planet’s surface. The findings are also consistent with recent findings about Mercury’s global magnetic field, which appears to be powered by the planet’s slowly-cooling outer core.
As Jim Green, NASA’s Planetary Science Director, said of the discovery:
“This is why we explore. For years, scientists believed that Mercury’s tectonic activity was in the distant past. It’s exciting to consider that this small planet – not much larger than Earth’s moon – is active even today.”
All told, these findings have let scientists know that the planet is still alive, in the geological sense. It also means that that there is likely such as thing as Mercury-quakes, something which NASA is sure to follow up on if and when a lander mission (equipped with seismology instruments) is dispatched to the surface of the planet.
Where Should We Look for Life in the Solar System?
Emily Lakdawalla is the senior editor and planetary evangelist for the Planetary Society. She’s also one of the most knowledgeable people I know about everything that’s going on in the Solar System. From Curiosity’s exploration of Mars to the search for life in the icy outer reaches of the Solar System, Emily can give you the inside scoop.
In this short interview, Emily describes where she thinks we should be looking for life in the Solar System.
