NASA’s Perseverance rover successfully landed on Mars on Feb. 18, 2021, which AAPG celebrated with a live watch party. Perseverance has since explored the Séítah region and is currently at the delta front of Jezero Crater on Mars using an enhanced autonomous navigation system and under guidance from NASA/JPL controllers. As of May 13, 2022, Sol 436, Perseverance has traveled 11.4 kilometers and drilled eight core samples. The rover has returned more than 249,000 raw images that are publicly available in the mission multimedia catalog.
Shortly after landing, Perseverance obtained invaluable SuperCam images of the western fan using the Mastcam-Z camera and the remote micro-imager. These long-distance telephoto images help reveal the stratigraphy and sedimentology of the delta deposits. From this, investigators have gleaned some history of the ancient lake in Jezero crater. Now, with the rover at the delta front, controllers and mission geologists look for the opportunity to drill core samples of the delta deposits for future return and detailed study on Earth.
The SuperCam imaged a prominent butte located about 2.6 kilometers west of the landing zone and one kilometer south of the main delta front (introduced in the June 2021 EXPLORER and pictured in accompanying photograph to this article). It has been informally named “Kodiak Butte.”
Investigators are able to infer ancient sedimentary processes from this erosional remnant of the delta. The accompanying images of Kodiak show two distinct outcrop areas with three sedimentary layer types revealing the original deltaic depositional geometry.
As published in the journal Science in October 2021, Kodiak Butte reveals outcrop sections that define distinct deltaic stratigraphic units of topsets, foresets and bottomset units. This corroborates the remote orbital reconnaissance interpretation of the fluvial delta sediments in the northwest quadrant of Jezero Crater. The bottomset layers consist of horizontal-to-low-angle, thinly bedded and fine-grained mudstones and sandstones. Overlying this is the ten-meter thick foreset unit composed of steeply inclined beds with steep dip angles. The foreset units appear to be sandstone with scattered cobbles. The thickness of the foreset units indicates a rising water depth in the Jezero lake basin which stabilized at 10 meters water depth. At this stage, the delta was truncated by topset units. The uppermost topset beds contain boulder conglomerates, implying episodic, high-energy floods. Kodiak Butte sedimentation demonstrates sustained fluvial input to a lake environment punctuated with high-energy, short-duration floods.
“Never before has such well-preserved stratigraphy been visible on Mars,” said Nicolas Mangold, Perseverance scientist and lead author of the Science report. “This is the key observation that enables us to once and for all confirm the presence of a lake and river delta at Jezero. Getting a better understanding of the hydrology months in advance of our arrival at the delta is going to pay big dividends down the road. We saw distinct layers in the scarps containing boulders up to 1.5 meters across that we knew had no business being there.”
They estimate that floodwater velocities needed to transport the boulders many kilometers from their provenance would have been 6 to 30 kilometers per hour.
Sanjeev Gupta, co-author of the Science paper said, “These results also have an impact on the strategy for the selection of rocks for sampling. The finest-grained material at the bottom of the delta probably contains our best bet for finding evidence of organics and biosignatures. And the boulders at the top will enable us to sample old pieces of crustal rocks. Both are main objectives for sampling and caching rocks before Mars Sample Return.”
While we are looking at variations in water depth on the 10-meter scale, we should put this in context of the probable high-water level of the ancient Jezero lake. Jezero is 45 kilometers wide and 500 meters deep. The morphology of the delta from orbital remote sensing indicates the crater was filled to its rim at maximum. The observed sedimentation in Kodiak Butte occurred with lake levels 100 meters below the rim.
With the sedimentary clinoforms so beautifully displayed at Kodiak looking very Earth-like, this presents us something to ponder. Should the difference between Earth gravity, 1 g, and Martian gravity, 0.38 g, make a difference in the angle of repose? They are remarkably similar, apparently. The angle of repose of deltaic foresets on Earth is about 15-30 degrees. The measured angle of the Kodiak Butte foresets in Jezero Craters is 30-35 degrees. For loose outcrop sediments on Earth, the angle of repose of dry sand is 34 degrees. On Mars, it is about 30 degrees as observed in craters. On Earth, due to cohesion, the angle of repose increases to up to 45 degrees. On Mars, the angle of repose of crater slopes apparently saturated with brine is about 40 degrees.
Perseverance’s first science campaign gathered valuable geologic data from the floor of Jezero Crater in the Séítah area (see map). Perseverance JPL deputy project scientist Katie Stack Morgan, as quoted in the December 2020 EXPLORER, reported that Perseverance landed farther from the Jezero delta front than planned. Perseverance landed 2.2 kilometers from the southeast-facing scarp of the western fan deposits, a primary objective of the mission. This has given the opportunity to study the crater floor and return some interesting results. There is abundant evidence for habitable conditions on Mars before 3.5 billion years ago. Few rocks remain on Earth from this time when life first evolved on our planet.
The Séítah area appears to be dominated by mafic volcanic lava flows on crater floor. SuperCam has returned the signature of olivine absorption in spectral data. We observe areas of what appear to be crumbly, rubbly volcanic “paver stones.” The Perseverance team attempted a core sample of a rock named “Rubion.”
Perseverance moved on and encountered a rock named “Rochette” that appeared to be competent. It was grooved and fluted from winds over billions of years. Perseverance performed an abrasion test and spectral analysis. Close inspection revealed dark and white mineral grains determined to be calcium sulfate, magnesium sulfate, sodium chloride and possible carbonates. The rock was significantly altered in presence of water indicating past conditions favorable to supporting microbial life.
During the Séítah campaign, Perseverance obtained rock, soil and atmosphere samples. Currently, out of 43 sample tubes, the rover has taken eight rock core samples, one atmosphere sample tube and one control witness tube.
The Ingenuity Mars helicopter completed its amazing first flight on Mars on April 19, 2021. It is still operating as the Perseverance rover’s exploration companion. Ingenuity fills a gap between orbital imagery and rover perspective. The pre-launch experimental test plan was for three flights in 45 days. As of April 29, 2022, it has made 28 successful flights. Ingenuity’s 25th flight on April 8, 2022 set new records for highest speed and distance traveled during a single flight. Ingenuity carries two cameras but no scientific instruments and communicates with Earth via a base station onboard Perseverance.
The Delta Front Campaign
The delta is the focus for the rover team’s upcoming second science campaign.
“The delta in Jezero Crater is the main astrobiology target of Perseverance,” Stack Morgan reported in the December 2021 EXPLORER.
Perseverance continues to look for rocks that formed in, or were altered by, water which may have supported microbial life. The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals, or “SHERLOC” instrument will scan for organic molecules to improve the chances of finding ancient traces of microbial life. After leaving the Séítah area, Perseverance began “rapid traverse” mode to get to the delta front and arrived there on April 18, 2022, (Sol 415). The following day, Ingenuity made its 26th flight and found Perseverance’s backshell and parachute where it was jettisoned in Jezero Crater. The Perseverance team then began the second campaign of the mission, the Delta Front Campaign. Over the next few months, they will use the entire suite of Perseverance instruments to explore the delta. They expect to find sediments different from the basaltic rocks of the crater floor.
The Delta Front Campaign will take about six months. Perseverance will climb 40 meters up and over the delta and select drill sites along the way, and characterize the 3-billion-year-old deltaic sediments. Perseverance has maneuvered itself to an “on ramp” to the delta named “Hawksbill Gap.” This is a gentle incline that will take the robot to an elevation of a few tens of meters above the crater floor.
On May 17, 2022, Sol 441, Perseverance began the climb up the ancient delta. It will examine rocks that appear to have the best chance of revealing evidence of past life that may have evolved on Mars. Then Perseverance will make its way back down the delta front to drill core samples. They will be cached at the base of the delta to be retrieved and returned to Earth on a later mission in the early 2030s.
When the Delta Front Campaign concludes, Perseverance will begin its third campaign, the Delta Top.
Curiosity Rover Discovery at Gale Crater
Meanwhile, the Curiosity rover has been operating in Gale Crater since 2012, some 3,700 kilometers from its brother, Perseverance. Curiosity used its tunable laser spectrometer instrument to analyze 24 samples from geologically diverse locations in Gale Crater. Results were published in the Proceedings of the National Academy of Sciences journal on Jan. 18, 2022. Included in these data are 10 measured δ13C values less than -70 parts per thousand found for six different sampling locations. Enrichment in carbon-13 on Earth is associated with biological processes. This carbon-13 enrichment has not been observed in Mars meteorites studied on Earth. There are multiple possible explanations for the anomalously depleted carbon-13 observed in Curiosity samples, but no single explanation can be accepted without further research. This underscores the importance of studying Mars geology and the urgency to return Perseverance Mars samples to Earth labs.