Geologists love field research. They love getting their special hammers and chisels into the seams of the rock, exposing unweathered surfaces and working out the secrets of the rock. Mars would be the ultimate excursion for many, but unfortunately that is not possible.
Instead, we sent the Perseverance rover on the excursion. But if a geologist went along, what would it be like for them?
Geologists tell us that there is no substitute for field research. Perseverance is making its excursion in Jezero Crater, and luckily the crater has been explored in different ways by different satellites. For a geologist, the crater is a gold mine.
NASA chose Jezero crater for the Perseverance mission, also because of its geology. Although geology is primarily concerned with the physical structure of a planet, understanding how a planet could have supported life is becoming increasingly important. Biology is inextricably linked with geology. With its collection of sediments and its ancient coastline, Jezero crater is a prime target for modern planetary geology.
Jezero crater has been a lake once in the past, and possibly twice, according to some research. Scientists studying Jezero say the lake likely formed during a period of continuous surface runoff. Two incoming streams fed the lake, and an overflow carved a canal out of the lake.
The Perseverance Rover is on the ground in Jezero Crater. The outlet gorge carved by overflow flooding is visible in the top right of the crater. Ancient rivers carved the bays on the left side of the crater. Photo credit: NASA / Tim Goudge.
The picture above shows the Jezero crater in detail. Endurance landed near the west side of the crater, near the clearly visible river delta. This river sediment contains ancient clays that are particularly good at capturing and conserving organic matter. If a real living geologist were with Perseverance, he would likely be heading straight for these clays.
NASA’s Mars Reconnaissance Orbiter has examined the Jezero crater. One of his instruments is an imaging spectrometer called the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). It is especially good at identifying clays. The picture below shows some of the clays in Jezero.
This image of the Jezero crater on Mars is from the CRISM instrument on the MRO. CRISM is an imaging spectrometer for the detection of clays on Mars. In this picture, the clays appear green. Photo credit: NASA / JPL-Caltech / ASU
The river sediment is piled so high that its edge is like a cliff. Perseverance will move along the base of this cliff before working its way up and across the delta, hopefully reaching the old coast. Depending on the length of the mission, the rover then climbed Jezero’s 610-meter-high crater rim and explored some of the plains that surround the crater. Perseverance’s main mission is roughly a Martian year (roughly two Earth years), and NASA believes it could complete roughly half of that traverse in that time.
While a geologist – or really any other scientist or scientifically minded person – would poke fun at the secrets of Jezero Crater, this would only be a start. If all goes well and persistence leaves the crater towards the highlands, our fictional geologist will be alive in amazement at the geological richness of the region surrounding the crater.
This image shows with a green dot where NASA’s Perseverance rover landed in Jezero Crater on Mars on February 18, 2021. The base image was captured with the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter (MRO). Together with the Mars Express Orbiter, the MRO has mapped Jezero in detail. Photo credit: NASA / JPL-Caltech / University of Arizona
The German Aerospace Center (DLR) operates a special camera on ESA’s Mars Express Orbiter. It is called a high resolution stereoscopic camera (HRSC). The HRSC is a powerful unit whose job it is to map and study the surface of Mars. His tasks include characterizing the geological development of the planet. Part of his job is to create high resolution digital terrain models (DTM) of Mars, including the region around Jezero.
DLR recently published two images of the Jezero crater and the surrounding area, highlighting the geological context and topography. The pictures explain the geological diversity of the area and why it was chosen as a target area by Perseverance.
As the pictures show, the Jezero crater is located on the boundary between different geological areas of different ages. The highland region of Terra Sabaea contains rocks from the Paleozoic of Mars (Noachian: 4.1 to 3.7 billion years ago). The Isidis Impact Basin is from the same period. The Isidis Planitia Plain is much younger and dates back to the Hesperians (3.7-3.0 billion years ago) and Martian modernism (the Amazon-3.0 billion years to date). The result is that rocks and other debris around Jezero Crater are from each of Mars’ three geological epochs. To a geologist, this is a great rocky gold mine.
The nearby Syrtis Major is a volcanic province whose lava flows also originate from the Hesperian. The Nili Fossae region is a trough system created by the shocks of the Isidis impact. This is a geologist’s dream excursion. If persistence can do its main task, it will explore some regions outside the Jezero crater.
Of particular interest are agglomerate debris, so-called megabreccia, which formed during the Isidis impact. They are located west of Jezero in the Noachian bedrock, in the igneous bedrock and in the lava flows of Syrtis Major. Megabreccias can be very large, up to a kilometer in diameter, and contain valuable clues about the early history of Mars.
Another picture from the HRSC. Terra Sabea is approximately 4.1 to 3.7 billion years old and the Isidis Impact Basin dates from the same period, approximately 3.9 billion years ago. Syrtis Major is around 3.7 to 3 billion years old, and Isidis Planitia is younger, forming around 3 billion years ago to modern times. This gives Perseverance the opportunity to view rocks from the entire geological history of Mars. Photo credits: ESA / DLR / FU Berlin, BY-SA 3.0 IGO
While perseverance can function as a kind of field geologist in some ways, it has its limits. His drill can only reach shallow depths. All life that existed on Mars probably dates from 3.7 to 3.4 billion years ago when life appeared on Earth. Any near-surface evidence of microscopic life was likely destroyed by UV radiation, although some may be retained in the sediments and clays.
Perseverance will collect its samples and hopefully a future mission will bring them back to Earth for a deeper and more thorough study. This is also in line with the way geologists work. Field samples are subjected to rigorous testing in laboratories.
Perseverance will teach us a lot about the geological history of Mars and how life might have existed there. Now that it is safe on the surface of Mars, its mission is almost a success. But it’s not the only rover to take a field trip to Mars in the 2020s.
An artist’s impression of the ExoMars / Rosalind Franklin rover on Mars. Photo credits: ESA / ATG medialab
ESA’s Rosalind Franklin Rover makes its own journey to Mars. It will end up in Oxia Planum, a region that is rich in clayey rock. It is also a very geologically diverse region. The Rosalind Franklin can take samples up to two meters deeper than Perseverance.
But we are ahead of ourselves.
Someday a real human geologist might very well set foot on Mars. Maybe several. But until then, our rover geologists have to do that for us.
If past missions are any indication, persistence will go well beyond your primary mission. NASA’s MSL Curiosity landed on Mars in August 2012 and is still in operation thanks to its Multi-Mission Radioisotope Thermoelectric Generator (RTG). Perseverance has the same type of energy source. Breakdowns aside, it’s reasonable to hope that the rover will get into the area from Jezero Crater and look at and extract stones from across the geological history of Mars.
In this case, not only is our imaginary geologist on an excursion of a lifetime. Probably every geologist on earth will experience this journey on a representative basis.