Earth’s magnetic field is one of the most mysterious features of our planet. It is also essential to life as we know it, ensuring that our atmosphere is not stripped away by solar wind and shielding life on Earth from harmful radiation. For some time, scientists have theorized that it is the result of a dynamo action in our core, where the liquid outer core revolves around the solid inner core and in the opposite direction of the Earth’s rotation.
In addition, Earth’s magnetic field is affected by other factors, such as magnetized rocks in the crust and the flow of the ocean. For this reason, the European Space Agency’s (ESA) Swarm satellites, which have been continually monitoring Earth’s magnetic field since its deployment, recently began monitoring Earth’s oceans – the first results of which were presented at this year’s European Geosciences Union meeting in Vienna, Austria.
The Swarm mission, which consists of three Earth-observation satellites, was launched in 2013 for the sake of providing high-precision and high-resolution measurements of Earth’s magnetic field. The purpose of this mission is not only to determine how Earth’s magnetic field is generated and changing, but also to allow us to learn more about Earth’s composition and interior processes.
Artist’s impression of the ESA’s Swarm satellites, which are designed to measure the magnetic signals from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere. Credit: ESA/AOES Medialab
Beyond this, another aim of the mission is to increase our knowledge of atmospheric processes and ocean circulation patterns that affect climate and weather. The ocean is also an important subject of study to the Swarm mission because of the small ways in which it contributes to Earth’s magnetic field. Basically, as the ocean’s salty water flows through Earth’s magnetic field, it generates an electric current that induces a magnetic signal.
Because this field is so small, it is extremely difficult to measure. However, the Swarm mission has managed to do just that in remarkable detail. These results, which were presented at the EGU 2018 meeting, were turned into an animation (shown below), which shows how the tidal magnetic signal changes over a 24 hour period.
As you can see, the animation shows temperature changes in the Earth’s oceans over the course of the day, shifting from north to south and ranging from deeper depths to shallower, coastal regions. These changes have a minute effect on Earth’s magnetic field, ranging from 2.5 to -2.5 microtesla. As Nils Olsen, from the Technical University of Denmark, explained in a ESA press release:
“We have used Swarm to measure the magnetic signals of tides from the ocean surface to the seabed, which gives us a truly global picture of how the ocean flows at all depths – and this is new. Since oceans absorb heat from the air, tracking how this heat is being distributed and stored, particularly at depth, is important for understanding our changing climate. In addition, because this tidal magnetic signal also induces a weak magnetic response deep under the seabed, these results will be used to learn more about the electrical properties of Earth’s lithosphere and upper mantle.”
By learning more about Earth’s magnetic field, scientists will able to learn more about Earth’s internal processes, which are essential to life as we know it. This, in turn, will allow us to learn more about the kinds of geological processes that have shaped other planets, as well as determining what other planets could be capable of supporting life.
Be sure to check out this comic that explains how the Swarm mission works, courtesy of the ESA.
As a species, we humans tend to take it for granted that we are the only ones that live in sedentary communities, use tools, and alter our landscape to meet our needs. It is also a foregone conclusion that in the history of planet Earth, humans are the only species to develop machinery, automation, electricity, and mass communications – the hallmarks of industrial civilization.
But what if another industrial civilization existed on Earth millions of years ago? Would we be able to find evidence of it within the geological record today? By examining the impact human industrial civilization has had on Earth, a pair of researchers conducted a study that considers how such a civilization could be found and how this could have implications in the search for extra-terrestrial life.
Carbon dioxide in Earth’s atmosphere if half of global-warming emissions are not absorbed. Credit: NASA/JPL/GSFC
As they indicate in their study, the search for life on other planets has often involved looking to Earth-analogues to see what kind conditions life could exist under. However, this pursuit also entails the search for extra-terrestrial intelligence (SETI) that would be capable of communicating with us. Naturally, it is assumed that any such civilization would need to develop and industrial base first.
This, in turn, raises the question of how often an industrial civilization might develop – what Schmidt and Frank refer to as the “Silurian Hypothesis”. Naturally, this raises some complications since humanity is the only example of an industrialized species that we know of. In addition, humanity has only been an industrial civilization for the past few centuries – a mere fraction of its existence as a species and a tiny fraction of the time that complex life has existed on Earth.
For the sake of their study, the team first noted the importance of this question to the Drake Equation. To recap, this theory states that the number of civilizations (N) in our galaxy that we might be able to communicate is equal to the average rate of star formation (R*), the fraction of those stars that have planets (fp), the number of planets that can support life (ne), the number of planets that will develop life ( fl), the number of planets that will develop intelligent life (fi), the number civilizations that would develop transmission technologies (fc), and the length of time these civilizations will have to transmit signals into space (L).
This can be expressed mathematically as: N = R* x fp x ne x fl x fi x fc x L
The Drake Equation, a mathematical formula for the probability of finding life or advanced civilizations in the universe. Credit: University of Rochester
As they indicate in their study, the parameters of this equation may change thanks to the addition of the Silurian Hypothesis, as well as recent exoplanets surveys:
“If over the course of a planet’s existence, multiple industrial civilizations can arise over the span of time that life exists at all, the value of fc may in fact be greater than one. This is a particularly cogent issue in light of recent developments in astrobiology in which the first three terms, which all involve purely astronomical observations, have now been fully determined. It is now apparent that most stars harbor families of planets. Indeed, many of those planets will be in the star’s habitable zones.”
In short, thanks to improvements in instrumentation and methodology, scientists have been able to determine the rate at which stars form in our galaxy. Furthermore, recent surveys for extra-solar planets have led some astronomers to estimate that our galaxy could contains as many as 100 billion potentially-habitable planets. If evidence could be found of another civilization in Earth’s history, it would further constrain the Drake Equation.
They then address the likely geologic consequences of human industrial civilization and then compare that fingerprint to potentially similar events in the geologic record. These include the release of isotope anomalies of carbon, oxygen, hydrogen and nitrogen, which are a result of greenhouse gas emissions and nitrogen fertilizers. As they indicate in their study:
“Since the mid-18th Century, humans have released over 0.5 trillion tons of fossil carbon via the burning of coal, oil and natural gas, at a rate orders of magnitude faster than natural long-term sources or sinks. In addition, there has been widespread deforestation and addition of carbon dioxide into the air via biomass burning.”
Based on fossil records, 250 million years ago over 90% of all species on Earth died out, effectively resetting evolution. Credit: Lunar and Planetary Institute
They also consider increased rates of sediment flow in rivers and its deposition in coastal environments, as a result of agricultural processes, deforestation, and the digging of canals. The spread of domesticated animals, rodents and other small animals are also considered – as are the extinction of certain species of animals – as a direct result of industrialization and the growth of cities.
The presence of synthetic materials, plastics, and radioactive elements (caused by nuclear power or nuclear testing) will also leave a mark on the geological record – in the case of radioactive isotopes, sometimes for millions of years. Finally, they compare past extinction level events to determine how they would compare to a hypothetical event where human civilization collapsed. As they state:
“The clearest class of event with such similarities are the hyperthermals, most notably the Paleocene-Eocene Thermal Maximum (56 Ma), but this also includes smaller hyperthermal events, ocean anoxic events in the Cretaceous and Jurassic, and significant (if less well characterized) events of the Paleozoic.”
These events were specifically considered because they coincided with rises in temperatures, increases in carbon and oxygen isotopes, increased sediment, and depletions of oceanic oxygen. Events that had a very clear and distinct cause, such as the Cretaceous-Paleogene extinction event (caused by an asteroid impact and massive volcanism) or the Eocene-Oligocene boundary (the onset of Antarctic glaciation) were not considered.
Artistic rendition of the Chicxulub impactor striking ancient Earth, with Pterosaur observing. Credit: NASA
According to the team, the events they did consider (known as “hyperthermals”) show similarities to the Anthropocene fingerprint that they identified. In particular, according to research cited by the authors, the Paleocene-Eocene Thermal Maximum (PETM) shows signs that could be consistent with anthorpogenic climate change. These include:
“[A] fascinating sequence of events lasting 100–200 kyr and involving a rapid input (in perhaps less than 5 kyr) of exogenous carbon into the system, possibly related to the intrusion of the North American Igneous Province into organic sediments. Temperatures rose 5–7?C (derived from multiple proxies), and there was a negative spike in carbon isotopes (>3%), and decreased ocean carbonate preservation in the upper ocean.”
Finally, the team addressed some possible research directions that might improve the constraints on this question. This, they claim, could consist of a “deeper exploration of elemental and compositional anomalies in extant sediments spanning previous events be performed”. In other words, the geological record for these extinction events should be examined more closely for anomalies that could be associated with industrial civilization.
If any anomalies are found, they further recommend that the fossil record could be examined for candidate species, which would raise questions about their ultimate fate. Of course, they also acknowledge that more evidence is necessary before the Silurian Hypothesis can be considered viable. For instance, many past events where abrupt Climate Change took place have been linked to changes in volcanic/tectonic activity.
Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill
Second, there is the fact that current changes in our climate are happening faster than in any other geological period. However, this is difficult to say for certain since there are limits when it comes to the chronology of the geological record. In the end, more research will be necessary to determine how long previous extinction events (those that were not due to impacts) took as well.
Beyond Earth, this study may also have implications for the study of past life on planets like Mars and Venus. Here too, the authors suggest how explorations of both could reveal the existence of past civilizations, and maybe even bolster the possibility of finding evidence of past civilizations on Earth.
“We note here that abundant evidence exists of surface water in ancient Martian climates (3.8 Ga), and speculation that early Venus (2 Ga to 0.7 Ga) was habitable (due to a dimmer sun and lower CO2 atmosphere) has been supported by recent modeling studies,” they state. “Conceivably, deep drilling operations could be carried out on either planet in future to assess their geological history. This would constrain consideration of what the fingerprint might be of life, and even organized civilization.”
Two key aspects of the Drake Equation, which addresses the probability of finding life elsewhere in the galaxy, are the sheer number of stars and planets out there and the amount of time life has had to evolve. Until now, it has been assumed that one planet would give rise to one intelligent species capable of advanced technology and communications.
But if this number should prove to be more, we may a find a galaxy filled with civilizations, both past and present. And who knows? The remains of a once advanced and great non-human civilization may very well be right beneath us!
Billions of years ago, Earth’s environment was very different from the one we know today. Basically, our planet’s primordial atmosphere was toxic to life as we know it, consisting of carbon dioxide, nitrogen and other gases. However, by the Paleoproterozoic Era (2.5–1.6 billion years ago), a dramatic change occurred where oxygen began to be introduced to the atmosphere – known as the Great Oxidation Event (GOE).
Until recently, scientists were not sure if this event – which was the result of photosynthetic bacteria altering the atmosphere – occurred rapidly or not. However, according to a recent study by a team of international scientists, this event was much more rapid than previously thought. Based on newly-discovered geological evidence, the team concluded that the introduction of oxygen to our atmosphere was “more like a fire hose” than a trickle.
Thanks to the many missions that have been studying Mars in recent years, scientists are aware that roughly 4 billion years ago, the planet was a much different place. In addition to having a denser atmosphere, Mars was also a warmer and wetter place, with liquid water covering much of the planet’s surface. Unfortunately, as Mars lost its atmosphere over the course of hundreds of millions of years, these oceans gradually disappeared.
When and where these oceans formed has been the subject of much scientific inquiry and debate. According to a new study by a team of researchers from UC Berkeley, the existence of these oceans was linked to the rise of the Tharis volcanic system. They further theorize that these oceans formed several hundred millions years earlier than expected and were not as deep as previously thought.
The early ocean known as Arabia (left, blue) would have looked like this when it formed 4 billion years ago on Mars, while the Deuteronilus ocean (right), about 3.6 billion years old, had a smaller shoreline. Credit: Robert Citron/UC Berkeley
As Michael Manga explained in a recent Berkeley News press release:
“The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later. We’re saying that the oceans predate and accompany the lava outpourings that made Tharsis.”
The debate over the size and extent of Mars’ past oceans is due to some inconsistencies that have been observed. Essentially, when Mars lost its atmosphere, its surface water would have frozen to become underground permafrost or escaped into space. Those scientists who don’t believe Mars once had oceans point to the fact that the estimates of how much water could have been hidden away or lost is not consistent with estimates on the oceans’ sizes.
What’s more, the ice that is now concentrated in the polar caps is not enough to create an ocean. This means that either less water was present on Mars than previous estimates indicate, or that some other process was responsible for water loss. To resolve this, Citron and his colleagues created a new model of Mars where the oceans formed before or at the same time as Mars’ largest volcanic feature – Tharsis Montes, roughly 3.7 billion years ago.
A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University
Since Tharsis was smaller at the time, it did not cause the same level of crustal deformation that it did later. This would have been especially true of the plains that cover most the northern hemisphere and are believed to have been an ancient seabed. Given that this region was not subject to the same geological change that would have come later, it would have been shallower and held about half the water.
“The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later,” said Manga. “We’re saying that the oceans predate and accompany the lava outpourings that made Tharsis.”
In addition, the team also theorized that the volcanic activity that created Tharsis may have been responsible for the formation of Mars’ early oceans. Basically, the volcanoes would have spewed gases and volcanic ash into the atmosphere that would have led to a greenhouse effect. This would have warmed the surface to the point that liquid water could form, and also created underground channels that allowed water to reach the northern plains.
Their model also counters other previous assumptions about Mars, which are that its proposed shorelines are very irregular. Essentially, what is assumed to have been “water front” property on ancient Mars varies in height by as much as a kilometer; whereas on Earth, shorelines are level. This too can be explained by the growth of the Tharsis volcanic region, roughly 3.7 billion years ago.
A map of Mars today shows where scientists have identified possible ancient shoreline that may have been etched by intermittent oceans billions of years ago. Credit: Robert Citron/UC Berkeley.
Using current geological data of Mars, the team was able to trace how the irregularities we see today could have formed over time. This would have began when Mars first ocean (Arabia) started forming 4 billion years ago and was around to witness the first 20% of Tharsis Montes growth. As the volcanoes grew, the land became depressed and the shoreline shifted over time.
Similarly, the irregular shorelines of a subsequent ocean (Deuteronilus) can be explained by this model by indicating that it formed during the last 17% of Tharsis’ growth – roughly 3.6 billion years ago. The Isidis feature, which appears to be an ancient lakebed slightly removed from the Utopia shoreline, could also be explained this way. As the ground deformed, Isidis ceased being part of the northern ocean and became a connected lakebed.
“These shorelines could have been emplaced by a large body of liquid water that existed before and during the emplacement of Tharsis, instead of afterwards,” said Citron. This is certainly consistent with the observable effect that Tharsis Mons has had on the topography of Mars. It’s bulk not only creates a bulge on the opposite side of the planet (the Elysium volcanic complex), but a massive canyon system in between (Valles Marineris).
This new theory not only explains why previous estimates about the volume of water in the northern plains were inaccurate, it can also account for the valley networks (cut by flowing water) that appeared around the same time. And in the coming years, this theory can be tested by the robotic missions NASA and other space agencies are sending to Mars.
This artist’s concept from August 2015 depicts NASA’s InSight Mars lander fully deployed for studying the deep interior of Mars. Credit: NASA/JPL-Caltech
Consider NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission, which is scheduled for launch in May, 2018. Once it reaches Mars, this lander will use a suite of advanced instruments – which includes a seismometer, temperature probe and radio science instrument – to measure Mars interior and learn more about its geological activity and history.
Among other things, NASA anticipates that InSight might detect the remains of Mars’ ancient ocean frozen in the interior, and possibly even liquid water. Alongside the Mars 2020 rover, the ExoMars 2020, and eventual crewed missions, these efforts are expected to provide a more complete picture of Mars past, which will include when major geological events took place and how this could have affected the planet’s ocean and shorelines.
The more we learn about what happened on Mars over the past 4 billion years, the more we learn about the forces that shaped our Solar System. These studies also go a long way towards helping scientists determine how and where life-bearing conditions can form. This (we hope) will help us locate life it in another star system someday!
For some time, scientists have known that the Moon and Mars have some fascinating similarities to Earth. In addition to being similar in composition, there is ample evidence that both bodies had active geological pasts. This includes stable lava tubes which are very similar to those that exist here on Earth. And in the future, these tubes could be an ideal location for outposts and colonies.
However, before we can begin choosing where to settle, these locations need to be mapped out to determining which would be suitable for human habitation. Luckily, a team of speleologists (cave specialists), geologists and ESA astronauts recently created the largest 3D image of a lava tube ever created. As part of the ESA’s PANGAEA program, this technology could one day help scientists map out cave systems on the Moon and Mars.
The lava tube in question was the La Cueva de Los Verdes, a famous tourist destination in Lanzarote, Spain. In addition to ESA astronaut Matthias Mauer, the team consisted of Tommaso Santagata (a speleologist from the University of Padova and the co-founder of the Virtual Geographic Agency), Umberto Del Vecchio and Marta Lazzaroni – a geologists and a masters student from the University of Padova, respectively.
Testing out the Leica BLK360 in La Cueva de los Verdes lava tube in Lanzarote, Spain. Credit and Copyright: ESA – Alessio Romeo
For five days in November 2017, this campaign mobilized 50 people, four space agencies and 18 organizations in five different locations. The La Cueva de los Verdes lava tube was of particular importance since it is one of the world’s largest volcanic cave complexes, measuring roughly 8 km in length. Some of these caves are even large enough to accommodate residential streets and houses.
During the campaign, Mauer, Santagata, Vecchio and Lazzaroni relied on two instruments to map the lava tube in detail. These included the Pegasus Backpack, a wearable mapping solution that collects geometric data without a satellite ad synchronizes images collected by five cameras and two 3D imaging laser profilers, and the Leica BLK360 – the smallest and lightest imaging scanner on the market.
In less than three hours, the team managed to map all the contours of the lava tube. And while the results of the campaign continue to be analyzed, the team chose to use the data they obtained to produce a 3D visual of all the twists and turns of the lava tube. The scan that resulted covers a 1.3 km section of the cave system with an unprecedented resolution of a few centimeters.
Santagata and the Virtual Geography Agency also turned their 3D visual into a lovely video titled “Lave tube fly-through”, which beautifully illustrates the winding and organic nature of the lava tube system. This video was posted to the ESA’s twitter feed on Tuesday, March 13th (shown above). This video, like the scans that preceded it, represent a breakthrough in geological mapping and astronaut training.
While lava tubes have been mapped since the 1970s, a clear view of this subterranean passage has remained elusive until now. Beyond being the first, the scans the team conducted could also help scientists to study the origins of the cave system, its peculiar formations, and assist local institutions in protecting the subterranean environment. As intended, the scans could also assist future space exploration and colonization efforts.
Pangaea-X arrives at the entrance to La Cueva de los Verdes lava tube. Credit and Copyright: ESA–Robbie Shone
For instance, the 8 km lava tube has both dry and water-filled sections. In the six-kilometer dry section, the lava tube has natural openings (jameos), that are aligned along the top of the cave pathway. These formations are very similar to “skylights” that have been observed on the Moon and Mars, which are holes in the surface that open into stable lava tubes.
Such structures are considered to be a good place for building outposts and colonies since they are naturally shielded from radiation and micrometeorites. Lava tubes also have a constant temperature, therefore offering protection against environmental extremes, and could provide access to underground sources of water ice. Some sections could also be sealed off and pressurized to create a colony.
As such, exploring such environments here on Earth is a good way to train astronauts to explore them on other bodies. As all astronauts know, mapping an environment is the first step in exploration, especially when you are looking for a place to establish a base camp. And in time, this information can be used to establish more permanent settlements, giving rise to eventual colonization.
It’s been a time of milestones for Mars rovers lately! Last month (on January 26th, 2018), NASA announced that the Curiosity rover had spent a total of 2,000 days on Mars, which works out to 5 years, 5 months and 21 days. This was especially impressive considering that the rover was only intended to function on the Martian surface for 687 days (a little under two years).
But when it comes to longevity, nothing has the Opportunity rover beat! Unlike Curiosity, which relied on a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) for power, the solar-powered Opportunity recently witnessed its five-thousandth sunrise on Mars. This means that the rover has remained in continuous operation for 5000 sols, which works out to 5137.46 Earth days.
This five-thousandth sunrise began on Friday, Feb. 16th, 2018 – roughly 14 Earth years (and 7.48 Martian years) after the rover first landed. From its position on the western rim of the Endeavour Crater, the sunrise appeared over the basin’s eastern rim, about 22 km (14 mi) away. This location, one-third of the way down “Perseverance Valley”, is more than 45 km (28 mi) from Opportunity’s original landing site.
Mosaic view looking down from inside the upper end of “Perseverance Valley” on the inner slope of Endeavour Crater’s western rim. Credit: NASA/JPL/Cornell/Marco Di Lorenzo/Ken Kremer/kenkremer.com
This is especially impressive when you consider that the original science mission was only meant to last 90 sols (92.47 Earth days) and NASA did not expect the rover to survive its first Martian winter. And yet, the rover has not only survived all this time, it continues to send back scientific discoveries from the Red Planet. As John Callas, the Opportunity Project Manager at NASA’s Jet Propulsion Laboratory, explained in a NASA press release:
“Five thousand sols after the start of our 90-sol mission, this amazing rover is still showing us surprises on Mars… We’ve reached lots of milestones, and this is one more, but more important than the numbers are the exploration and the scientific discoveries.”
For instance, the rover has provided us with 225,000 images since its arrival, and revealed that ancient Mars was once home to extensive groundwater and surface water. Beginning in 2008, it began working its way across the Endeavour Crater in order to get a glimpse deeper into Mars’ past. By 2011, it had reached the crater’s edge and confirmed that mineral-rich water once flowed through the area.
At present, researchers are using Opportunity to investigate the processes that shaped Perseverance Valley, an area that descends down the slope of the western rim of Endeavour Crater. Here too, Opportunity has learned some fascinating things about the Red Planet. For instance, the rover has conducted observations of possible “rock stripes” in the valley, which could be indicative of its valley’s origin.
Textured rows on the ground in this portion of “Perseverance Valley” are under investigation by NASA’s Mars Exploration Rover Opportunity. Credits: NASA/JPL-Caltech
These stripes are of interest to scientists because of the way they resemble rock stripes that appear on mountain slopes here on Earth, which are the result of repeated cycles of freezing and thawing on wet soil. On Mauna Kea, for example, soil freezes every night, but is often dry due to the extreme elevation. This causes soils that have high concentrations of silt, sand and gravel to expand, pushing the larger particles up.
These particles then form stripes as they fall downhill, or are moved by wind or rainwater, and cause the ground to expand less in this space. This process repeats itself over and over, creating a pattern that leads to distinct stripes. As Opportunity observed, there are slopes within the Perseverance Valley where soil and gravel particles appear to have formed into rows that run parallel to the slope, alternating between rows that have more and less gravel.
In the case of the Perseverance Valley’s stripes, scientists are not sure how they formed, but think they could be the result of water, wind, downhill transport, other processes, or a combination thereof. Another theory posits that features like these could be the result of changes in Mars tilt (obliquity) which happen over the course of hundreds of thousands of years.
“One possible explanation of these stripes is that they are relics from a time of greater obliquity when snow packs on the rim seasonally melted enough to moisten the soil, and then freeze-thaw cycles organized the small rocks into stripes. Gravitational downhill movement may be diffusing them so they don’t look as crisp as when they were fresh.”
Stone stripes on the side of a volcanic cone on Mauna Kea, Hawaii, which are made of small rock fragments that are aligned downhill. These are formed when freeze-thaw cycles lift them out of the finer-grained regolith and move them to the sides, forming stone stripes. Credits: Washington University in St. Louis/NASA
Having the chance to investigate these features is therefore quite the treat for the Opportunity science team. “Perseverance Valley is a special place, like having a new mission again after all these years.” said Arvidson. “We already knew it was unlike any place any Mars rover has seen before, even if we don’t yet know how it formed, and now we’re seeing surfaces that look like stone stripes. It’s mysterious. It’s exciting. I think the set of observations we’ll get will enable us to understand it.”
Given the state of the Martian surface, it is a safe bet that wind is largely responsible for the rock stripes observed in Perseverance Valley. In this respect, they would be caused by sand blown uphill from the crater floor that sorts larger particles into rows parallel to the slope. As Robert Sullivan, an Opportunity science-team member of Cornell University, explained:
“Debris from relatively fresh impact craters is scattered over the surface of the area, complicating assessment of effects of wind. I don’t know what these stripes are, and I don’t think anyone else knows for sure what they are, so we’re entertaining multiple hypotheses and gathering more data to figure it out.”
Despite being in service for a little over 14 years, and suffering its share of setbacks, Opportunity is once again in a position to reveal things about Mars’ past and how it evolved to become what it is today. Never let it be said that an old rover can’t reveal new secrets! If there’s one thing Opportunity has proven during its long history of service on Mars, it is that the underdog can make some of the greatest contributions.
When robotic missions first began to land on the surface of Mars in the 1970s, they revealed a harsh, cold and desiccated landscape. This effectively put an end generations of speculation about “Martian canals” and the possibility of life on Mars. But as our efforts to explore the Red Planet have continued, scientists have found ample evidence that the planet once had flowing water on its surface.
In addition, scientists have been encouraged by the appearance of Recurring Slope Lineae (RSL), which were believed to be signs of seasonal water flows. Unfortunately, a new study by researchers from the U.S. Geological Survey indicates that these features may be the result of dry, granular flows. These findings are another indication that the environment could be too dry for microorganisms to survive.
This inner slope of a Martian crater has several of the seasonal dark streaks called “recurrent slope lineae,” or RSL, which were caputred by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter. Credits: NASA/JPL-Caltech/UA/USGS
For the sake of their study, the team consulted data from the High Resolution Image Science Experiment (HiRISE) camera aboard the NASA Mars Reconnaissance Orbiter (MRO). This same instrument was responsible for the 2011 discovery of RSL, which were found in the middle latitudes of Mars’ southern hemisphere. These features were also observed to appear on Martian slopes during late spring through summer and then fade away in winter.
The seasonal nature of these flows was seen as a strong indication that they were the result of flowing salt-water, which was indicated by the detection of hydrated salt at the sites. However, after re-examining the HiRISE data, Dundas and his team concluded that RSLs only occur on slopes that are steep enough for dry grains to descend – in much the same way that they would on the faces of active dunes.
“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand. This new understanding of RSL supports other evidence that shows that Mars today is very dry.”
Using pairs of images from HiRISE, Dundas and his colleagues constructed a series of 3-D models of slope steepness. These models incorporated 151 RSL features identified by the MRO at 10 different sites. In almost all cases, they found that the RSL were restricted to slopes that were steeper than 27° and each flow ended on a slope that matched the patterns seen in slumping dry sand dunes on Mars and Earth.
Dark, narrow streaks flowing downhill on Mars at sites like the Horowitz Crater are inferred to be due to seasonal flows of water. Credit: NASA/JPL-Caltech/Univ. of Arizona
Basically, sand flows end where a steep angle gives way to a less-steep “angle of repose”, whereas liquid water flows are known to extend along less steep slopes. As Alfred McEwen, HiRISE’s Principal Investigator at the University of Arizona and a co-author of the study, indicated, “The RSL don’t flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can’t be a coincidence.”
These observations is something of a letdown, since the presence of liquid water in Mars’ equatorial region was seen as a possible indication of microbial life. However, compared to seasonal brine flows, the present of granular flows is a far better fit with what is known of Mars’ modern environment. Given that Mars’ atmosphere is very thin and cold, it was difficult to ascertain how liquid water could survive on its surface.
Nevertheless, these latest findings do not resolve all of the mystery surrounding RSLs. For example, there remains the question of how exactly these numerous flows begin and gradually grow, not to mention their seasonal appearance and the way they rapidly fade when inactive. On top of that, there is the matter of hydrated salts, which have been confirmed to contain traces of water.
To this, the authors of the study offer some possible explanations. For example, they indicate that salts can become hydrated by pulling water vapor from the atmosphere, which might explain why patches along the slopes experience changes in color. They also suggest that seasonal changes in hydration might result in some trigger mechanism for RSL grainflows, where water is absorbed and release, causing the slope to collapse.
NASA’s Mars Reconnaissance Orbiter investigating Martian water cycle. Credit: NASA/JPL/Corby Waste
If atmospheric water vapor is a trigger, then it raises another important question – i.e. why do RSLs appear on some slopes and not others? As Alfred McEwen – HiRISE’s Principal Investigator and a co-author on the study – explained, this could indicate that RSLs on Mars and the mechanisms behind their formation may not be entirely similar to what we see here on Earth.
“RSL probably form by some mechanism that is unique to the environment of Mars,” he said, “so they represent an opportunity to learn about how Mars behaves, which is important for future surface exploration.” Rich Zurek, the MRO Project Scientist of NASA’s Jet Propulsion Laboratory, agrees. As he explained,
“Full understanding of RSL is likely to depend upon on-site investigation of these features. While the new report suggests that RSL are not wet enough to favor microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized. In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues.”
In the coming years, NASA plans to carry out the exploration of several sites on the Martian surface using the Mars 2020 rover, which includes a planned sample-return mission. These samples, after being collected and stored by the rover, are expected to be retrieved by a crewed mission mounted sometime in the 2030s, and then returned to Earth for analysis.
The days when we are finally able to study the Mars’ modern environment up close are fast approaching, and is expected to reveal some pretty Earth-shattering things!
Beneath the Antarctic ice sheet, there lies a continent that is covered by rivers and lakes, the largest of which is the size of Lake Erie. Over the course of a regular year, the ice sheet melts and refreezes, causing the lakes and rivers to periodically fill and drain rapidly from the melt water. This process makes it easier for Antarctica’s frozen surface to slide around, and to rise and fall in some places by as much as 6 meters (20 feet).
According to a new study led by researchers from NASA’s Jet Propulsion Laboratory, there may be a mantle plume beneath the area known as Marie Byrd Land. The presence of this geothermal heat source could explain some of the melting that takes place beneath the sheet and why it is unstable today. It could also help explain how the sheet collapsed rapidly in the past during previous periods of climate change.
Glaciers seen during NASA’s Operation IceBridge research flight to West Antarctica on Oct. 29, 2014. Credit: NASA/Michael Studinger
The motion of Antarctica’s ice sheet over time has always been a source of interest to Earth scientists. By measuring the rate at which the ice sheet rises and falls, scientists are able to estimate where and how much water is melting at the base. It is because of these measurements that scientists first began to speculate about the presence of heat sources beneath Antarctica’s frozen surface.
The proposal that a mantle plume exists under Marie Byrd Land was first made 30 years ago by Wesley E. LeMasurier, a scientist from the University of Colorado Denver. According to the research he conducted, this constituted a possible explanation for regional volcanic activity and a topographic dome feature. But it was only more recently that seismic imaging surveys offered supporting evidence for this mantle plume.
However, direct measurements of the region beneath Marie Byrd Land is not currently possible. Hence why Seroussi and Erik Ivins of the JPL relied on the Ice Sheet System Model (ISSM) to confirm the existence of the plume. This model is essentially a numerical depiction of the physics of the ice sheet, which was developed by scientists at the JPL and the University of California, Irvine.
To ensure that the model was realistic, Seroussi and her team drew on observations of changes in altitude of the ice sheet made over the course of many years. These were conducted by NASA’s Ice, Clouds, and Land Elevation Satellite (ICESat) and their airborne Operation IceBridge campaign. These missions have been measuring the Antarctic ice sheet for years, which have led tot he creation of very accurate three-dimensional elevation maps.
A view of mountains and glaciers in Antarctica’s Marie Byrd Land seen during the Nov. 2nd, 2014, IceBridge survey flight. Credit: NASA / Michael Studinger
Seroussi also enhanced the ISSM to include natural sources of heating and heat transport that result in freezing, melting, liquid water, friction, and other processes. This combined data placed powerful constrains on the allowable melt rates in Antarctica, and allowed the team to run dozens of simulations and test a wide range of possible locations for the mantle plume.
What they found was that the heat flux caused by the mantle plume would not exceed more than 150 milliwatts per square meter. By comparison, regions where there is no volcanic activity typically experience a feat flux of between 40 and 60 milliwatts, whereas geothermal hotspots – like the one under Yellowstone National Park – experience an average of about 200 milliwatts per square meter.
Where they conducted simulations that exceeded 150 millwatts per square meter, the melt rate was too high compared to the space-based data. Except in one location, which was an area inland of the Ross Sea, which is known to experience intense flows of water. This region required a heat flow of at least 150 to 180 milliwatts per square meter to align with its observed melt rates.
In this region, seismic imaging has also shown that heating might reach the ice sheet through a rift in the Earth’s mantle. This too is consistent with a mantle plume, which are thought to be narrow streams of hot magma rising through the Earth’s mantle and spreading out under the crust. This viscous magma then balloons under the crust and causes it to bulge upward.
Temperature changes in the Antarctic ice sheet over the last 50 years, measured in degrees Celsius. Credit: NASA/GSFC Scientific Visualization Studio
Where ice lies over top of the plume, this process transfers heat into the ice sheet, triggering significant melting and runoff. In the end, Seroussi and her colleagues provide compelling evidence – based on a combination of surface and seismic data – for a surface plume beneath the ice sheet of West Antarctica. They also estimate that this mantle plume formed roughly 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence.
Roughly 11,000 years ago, when the last ice age ended, the ice sheet experienced a period of rapid, sustained ice loss. As global weather patterns and rising sea levels began to change, warm water was pushed closer to the ice sheet. Seroussi and Irvins study suggests that the mantle plume could be facilitating this kind of rapid loss today, much as it did during the last onset of an inter-glacial period.
Understanding the sources of ice sheet loss under West Antarctica is important as far as estimating the rate at which ice may be lost there, which is essentially to predicting the effects of climate change. Given that Earth is once again going through global temperature changes – this time, due to human activity – it is essential to creating accurate climate models that will let us know how rapidly polar ice will melt and sea levels will rise.
It also informs our understanding of how our planet’s history and climate shifts are linked, and what effect these had on its geological evolution.
Sixty-six million years ago, an asteroid struck Earth in what is now the Yucatan Peninsula in southern Mexico. This event, known as the Chicxulub asteroid impact, measured 9 km in diameter and caused extreme global cooling and drought. This led to a mass extinction, which not only claimed the lives of the dinosaurs, but also wiped out about 75% of all land and sea animals on Earth.
However, had this asteroid impacted somewhere else on the planet, things could have turned out very differently. According to a new study produced by a team of Japanese researchers, the destruction caused by this asteroid was due in large part to where it impacted. Had the Chicxulub asteroid landed somewhere else on the planet, they argue, the fallout would not have been nearly as severe.
Satellite views of the Chicxulub impact site in the Yucutan Peninsula, southern Mexico. Image credit: NASA/JPL
Dr. Kaiho and Dr. Oshima began by considering recent studies that have shown how the Chicxulub impact heated the hydrocarbon and sulfur content of rocks in the region. This is what led to the formation of stratospheric soot and sulfate aerosols which caused the extreme global cooling and drought that followed. As they state in their study, it was this (not the impact and the detritus it threw up alone) that ensured the mass extinction that followed:
“Blocking of sunlight by dust and sulfate aerosols ejected from the rocks at the site of the impact (impact target rocks) was proposed as a mechanism to explain how the physical processes of the impact drove the extinction; these effects are short-lived and therefore could not have driven the extinction. However, small fractions of stratospheric sulfate (SO4) aerosols were also produced, which may have contributed to the cooling of the Earth’s surface.“
Another issue they considered was the source of the soot aerosols, which previous research has indicated were quite prevalent in the stratosphere during the Cretaceous/Paleogene (K–Pg) boundary (ca. 65 million years ago). This soot is believed to coincide with the asteroid impact since microfossil and fossil pollen studies of this period also indicate the presence of iridium, which has been traced to the Chicxulub asteroid.
Previously, this soot was believed to be the result of wildfires that raged in the Yucatan as a result of the asteroid impact. However, Kaiho and Oshima determined that these fires could not have resulted in stratospheric soot; instead positing that they could only be produced by the burning and ejecting of hyrdocarbon material from rocks in the impact target area.
When an asteroid struck the Yucatan region about 66 million years ago, it wiped out the dinosaurs, and most of life on Earth. If it had hit elsewhere, the dinosaurs might well have survived. Credit: NASA/Don Davis
The presence of these hydrocarbons in the rocks indicate the presence of both oil and coal, but also plenty of carbonate minerals. Here too, the geology of the Yucatan was key, since the larger geological formation known as the Yucatan Platform is known to be composed of carbonate and soluble rocks – particularly limestone, dolomite and evaporites.
To test just how important the local geology was to the mass extinction that followed, Kaiho and Oshima conducted a computer simulation that took into account where the asteroid struck and how much aerosols and soot would be produced by an impact. Ultimately, they found that the resulting ejecta would have been sufficient to trigger global cooling and drought; and hence, an Extinction Level Event (ELE).
This sulfur and carbon-rich geology, however, is not something the Yucatan Peninsula shares with most regions on the planet. As they state in their study:
“Here we show that the probability of significant global cooling, mass extinction, and the subsequent appearance of mammals was quite low after an asteroid impact on the Earth’s surface. This significant event could have occurred if the asteroid hit the hydrocarbon-rich areas occupying approximately 13% of the Earth’s surface. The site of asteroid impact, therefore, changed the history of life on Earth.”
Mass extinction only occurred when the asteroid having 9-km diameter hit the orange areas. Credit: Kunio Kaiho
Basically, Kaiho and Oshima determined that 87% of Earth would not have been able to produce enough sulfate aerosols and soot to trigger a mass extinction. So if the Chicxulub asteroid struck just about anywhere else on the planet, the dinosaurs and most of the world’s animals would have likely survived, and the resulting macroevolution of mammals probably would not have taken place.
In short, modern hominids may very well owe their existence to the fact that the Chicxulub asteroid landed where it did. Granted, the majority of life in the Cretaceous/Paleogene (K–Pg) was wiped out as a result, but ancient mammals and their progeny appear to have lucked out. The study is therefore immensely significant in terms of our understanding of how asteroid impacts affect climatological and biological evolution.
It is also significant when it comes to anticipating future impacts and how they might affect our planet. Whereas a large impact in a sulfur and carbon-rich geological region could lead to another mass extinction, an impact anywhere else could very well be containable. Still, this should not prevent us from developing appropriate countermeasures to ensure that large impacts don’t happen at all!
Mars modern landscape is something of a paradox. It’s many surface features are very similar to those on Earth that are caused by water-borne erosion. But for the life of them, scientists cannot imagine how water could have flown on Mars’ cold and desiccated surface for most of Mars’ history. Whereas Mars was once a warmer, wetter place, it has had a very thin atmosphere for billions of years now, which makes water flow and erosion highly unlikely.
In fact, while the surface of Mars periodically becomes warm enough to allow for ice to thaw, liquid water would boil once exposed to the thin atmosphere. However, in a new study led by an international team of researchers from the UK, France and Switzerland, it has been determined that a different kind of transport process involving the sublimation of water ice could have led to the Martian landscape becoming what it is today.
The study, which was led Dr. Jan Raack – a Marie Sklodowska-Curie Research Fellow at The Open University – was recently published in the scientific journal Nature Communications. Titled “Water Induced Sediment Levitation Enhances Downslope Transport on Mars”, this research study consisted of experiments that tested how processes on Mars’ surface could allow water transport without it being in liquid form.
Reull Vallis, the river-like structure captured by the ESA’s Mars Express probe, is believed to have formed when running water flowed in the distant martian past. Credit and copyright: ESA/DLR/FU Berlin (G. Neukum)
To conduct their experiments, the team used the Mars Simulation Chamber, an instrument at The Open University that is capable of simulating the atmospheric conditions on Mars. This involved lowering the atmospheric pressure inside the chamber to what is normal for Mars – about 7 mbar, compared to 1000 mbar (1 bar or 100 kilopascals) here on Earth – while also adjusting temperatures.
On Mars, temperatures range from a low of -143 °C (-255 °F) during winter at the poles to a high of 35 °C (95 °F) at the equator during midday in the summer. Having recreated these conditions, the team found that when water ice exposed to the simulated Martian atmosphere, it would not simply melt. Instead, it would become unstable and begin violently boiling off.
However, the team also found that this process would be capable of moving large amounts of sand and sediment, which would effectively “levitate” on the boiling water. This means that, compared to Earth, relatively small amounts of liquid water are capable of moving sediment across the surface of Mars. These levitating pockets of sand and debris would be capable of forming tje large dunes, gullies, recurring slope lineae, and other features observed on Mars.
In the past, scientists have indicated how these features were the result of sediment transportation down slopes, but were unclear as to the mechanisms behind them. As Dr. Jan Raack explained in a OUNews press release:
“Our research has discovered that this levitation effect caused by boiling water under low pressure enables the rapid transport of sand and sediment across the surface. This is a new geological phenomenon, which doesn’t happen on Earth, and could be vital to understanding similar processes on other planetary surfaces.”
Illustration of the ESA Exomars 2020 Rover, which will explore the Red Planet in search for signs of ancient life. Credit:ESA
Through these experiments, Dr. Raack and his colleagues were able to shed light on how conditions on Mars could allow for features that we tend to associate with flowing water here on Earth. In addition to helping to resolve a somewhat contentious debate concerning Mars’ geological history and evolution, this study is also significant when it comes to future exploration missions.
Dr. Raack acknowledges the need for more research to confirm their study’s conclusions, and indicated that the ESA’s ExoMars 2020 Rover will be well-situated to conduct it once it is deployed :
“This is a controlled laboratory experiment, however, the research shows that the effects of relatively small amounts of water on Mars in forming features on the surface may have been widely underestimated. We need to carry out more research into how water levitates on Mars, and missions such as the ESA ExoMars 2020 Rover will provide vital insight to help us better understand our closest neighbour.”
