Mars is still quite mysterious, despite all we’ve learned about the planet in recent years. We still have a lot to learn about its interior and surface evolution and how changes affected the planet’s history and habitability. Fortunately, an impact on the red planet sent clues to Earth in the form of meteorites.
The geological information contained in these meteorites would be even more valuable if we knew exactly where they came from. A team of researchers say they’ve figured it out.
Every year during Mars’ summer solstice, a cloud of water ice forms on the leeward side of Arsia Mons, one of Mars’ largest extinct volcanoes. The cloud can grow to be up to 1800 km (1120 miles) long. It forms each morning, then disappears the same day, only to reappear the next morning. Researchers have named it the Arsia Mons Elongated Cloud (AMEC).
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.
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.
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.
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.
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 decades, Mars has been the focal point of intense research. Beginning in the 1960s, literally dozens of robotic spacecraft, orbiters and rovers have explored Mars’ atmosphere and surface, looking for clues to the planet’s past. From this, scientists now know that billions of years ago, Mars was a warmer, wetter place. Not only did liquid water exist on its surface, but it is possible life existed there in some form as well.
Granted, some recent findings have cast some doubt in this, indicating that Mars’ surface may have been hostile to microbes. But a new study from an international team of scientists indicates that evidence life could be found in volcanic deposits. Specifically, they argue that within the massive geological structure known as Valles Marineris, there may be ancient volcanoes that have preserved ancient microbes.
The team began by examining the Coprates Chasma canyon, one of the lowest points in Valles Marineris, which is home to over 130 volcanoes and solidified lava flows. This consisted of analyzing high-resolution images of the region that were taken by NASA’s Mars Reconnaissance Orbiter (MRO), which revealed cones of basaltic lava (aka. scoria) and ash that measured around 400-meters (1300 ft) high.
After examining the cones’ surface patterns and morphological details, they confirmed that these were indeed the remains of lava volcanoes (and not mud volcanoes, which was another possibility). In addition, they also noted similarities between these cone and others on Mars where mud volcanism is not possible – as well as similarities with volcanic cones here on Earth.
“The spatial distribution of the cones also suggests their volcanic origin. They appear to occur more frequently along tectonic fractures that formed the trough in the surface and whose fracture interfaces continue into the subsurface, creating pathways for the magma to ascend.”
Even more surprising was the apparent age of the volcanoes, which was very young. On Mars, the main period of volcanic activity ended during Mars’ Hesperian Period – which ran from 3.7 to approximately 3.0 billion years ago. And while images acquired by the Mars Express mission have shown indications of younger volcanoes (occurring 500 million years ago), these tend to be located in volcanic provinces.
A good example of this is the Tharsis Bulge, which is located several thousand km from the Coprates Chasma canyon. It is here that the Tharses Montes mountain chain is located, which consists of the shield volcanoes of Ascraeus Mons, Pavonis Mons and Arsia Mons. Olympus Mons, the tallest mountain in the Solar System (with an elevation of 22 km or 13.6 mi), is located at the edge of this region.
In contrast, the volcanic cones spotted in the Coprates Chasma canyon were estimates to be between 200 and 400 million years of age, placing them in the most recent geological period known as the Amazonian (3.0 billion years ago to the present day). This effectively demonstrates that these volcanoes formed late in Mars’ history and far away from volcanic areas like Tharsis and Elysium.
It also demonstrates that these volcanoes were not part of the original formation of Valles Marineris, which is believed to be related to the formation of the Tharsis Bulge. This all took place between the Noachian to Late Hesperian periods of Mars (ca. 3.5 billion years ago), which was the last time Mars experienced widespread geological activity.
Last, but not least, the team used the Compact Reconnaissance Imaging Spectrometer (CRISM) aboard the MRO to learn more about the mineral compositions of the region’s lava and volcanic cones. Once again, their findings proved to be surprising, and could indicate that the Coprates Chasma region is a suitable location to search for evidence of ancient life on Mars.
Essentially, the CRISM data indicated the presence of high-silica content minerals in the volcanic rock, which included opaline-like substances at one of the peaks. Opaline silicates, it should be noted, are water-bearing materials that are often produced by hydrothermal processes – where silicate structures form from supersaturated, hot solutions of minerals that cool to become solid.
On Earth, microorganisms are often found within opal deposits since they form in energy and mineral-rich environments, where microbial lifeforms thrive. The presence of these minerals in the Coprates Chasma region could therefore mean that ancient microorganisms once thrived there. Moreover, such organisms could also be fossilized within the mineral-rich lava rock, making it a tempting target for future research.
As Hauber indicated, the appeal of Coprates Chasma doesn’t end there, and future mission will surely want to make exploring this region a priority:
“Coprates Chasma is not just interesting with regard to the question of previous life on Mars. The region would also be an excellent landing site for future Mars Rovers. Here we could investigate many scientifically important and interesting topics. Analyzing samples for their elemental isotopic fractions would allow us to determine with far greater precision when the volcanoes were actually active.
“On the towering, steep walls, the geologic evolution of the Valles Marineris is presented to us almost like a history book – gypsum strata and layers of old, crustal rocks can be observed, as well as indications for liquid water trickling down the slopes even today during the warm season. That is as much Mars geology as you can get!”
In other words, this low-lying region could be central to future studies that attempt to unlock the history and geological evolution of the Red Planet. The payoffs of studying this region not only include determining if Mars had life in the past, but when and how it went from being a warmer, wetter environment to the cold, dessicated landscape we know today.
In the future, NASA, the ESA, the China National Space Agency (CNSA) and Roscosmos all hope to mount additional robotic missions to Mars. In addition, NASA and even SpaceX hope to send crewed missions to the planet in the hopes of learning more about its past – and possibly future – habitability. Between its geological history, greater atmospheric pressure, and the possibility of fossilized life, one or more of these missions may be headed to Valles Marineris to have a look around.