It’s been two years since NASA’s Perseverance rover successfully landed on Mars, where its exploration of Jezero Crater continues. Perseverance rover’s primary surface mission was designed to last one Mars year, or 687 Earth days, beginning with its Feb. 18, 2021 landing. It reached that milestone on Jan. 6. As of Jan. 7, the rover has entered its extended mission phase.
We have been following the rover’s geologic fieldwork with its rich photo record as if we were standing at the outcrop on Mars. We last reported the rover’s progress in the September 2022 AAPG Explorer. As of Jan. 1 (SOL 664), Perseverance has traveled 13.9 kilometers and drilled 18 core samples out of 38 total sample tubes for the entire mission. The rover has returned more than 377,000 raw images that are publicly available in the mission multimedia catalog.
‘Intriguing’ Clues Consistent with Life
After exploring the basaltic crater floor, Perseverance reached the flat lying sedimentary rocks at Enchanted Lake in April 2022. The Perseverance team and legions of enthusiasts on Earth have waited years to get this close to the Jezero river delta. The objective is to explore these deltaic rocks in search of evidence of ancient life on Mars. The rover entered the Hawksbill Gap channel and began climbing the delta front on May 17, 2022 (SOL 441). Perseverance drilled and secured nine core tubes at select locations in the delta front.
Wildcat Ridge is the name given to a deltaic rock formed as mud and silt settled in an evaporating saltwater lake about 3.5 billion years ago. On July 20 (SOL 503), Perseverance abraded the surface of Wildcat Ridge to analyze the rock with the instrument named SHERLOC, for “Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals.” SHERLOC’s analysis indicated that the rock contained organic molecules that are found in context with sulfate minerals. This gives clues about the aqueous environments in which the minerals formed. This indicates that sediment and salts were deposited into the Jezero crater lake with conditions in which life could have existed. These organic detections were the strongest of the mission to date. Core samples 12 and 13 were taken in the Wildcat Ridge rock. Scientists eagerly wait for these samples to be returned to Earth for more detailed study as part of the future NASA/European Space Agency Mars Sample Return Mission.
This discovery in Jezero crater is analogous to the discovery in Gale Crater by the Curiosity rover. In June 2018, in situ detection of organic matter was reported in lacustrine mudstones, at the base of the 3.5-billion-year-old Murray Formation, by the Sample Analysis at Mars instrument on the Curiosity rover. Thiophenes, aromatic and aliphatic compounds were released by SAM pyrolysis and detected by analysis of evolved gasses. Thiophenes are an aromatic organic molecule containing sulfur (C4H4S). Thiophenes on Earth are primarily a result of biological processes. Thiophenes are often found in coal, crude oil, kerogen and stromatolites and microfossils. Scientists caution that this is not proof of fossil life on Mars but it is indeed intriguing.
Three Forks Sample Depot
The Perseverance rover has returned to the Three Forks area of Hawksbill Gap and reached another mission milestone by caching half of its sample tubes for return to Earth with the future NASA/ESA Sample Return Mission. The first sample tube was dropped on Dec.21, 2022 to begin the sample cache. The rest were dropped in a zigzag pattern with the 10 tubes placed between 5 and 15 meters apart from one another for retrieval by the future Mars Sample Return Mission. They are placed apart so that the planned retrieval helicopters can pick them up without disturbing other tubes in the cache. It is unlikely that the tubes will be lost by being covered with storm dust.
Mars Sample Return program principal scientist from Arizona State University, Meenakshi Wadhwa, said, “The samples for this depot – and the duplicates held aboard Perseverance – are an incredible set representative of the area explored during the prime mission. We not only have igneous and sedimentary rocks that record at least two and possibly four or even more distinct styles of aqueous alteration, but also regolith, atmosphere and a witness tube.”
In addition to 38 sample tubes, Perseverance carries five witness tubes to be opened on the Mars surface to “witness” the environment near sample collection sites. The witness tubes have a variety of materials that can capture molecular and particulate contaminants. When samples are returned to Earth, the witness tubes can reveal if Earth contaminants were present during sample collection.
The samples also contain two regolith soil samples. These will be studied not only for geology but to be scrutinized for hazards to future human explorers on Mars. It is known that dust from Earth’s moon is very abrasive to equipment and a hazard to be breathed. Mars regolith is known to have reactive perchlorates, but quantities and hazard levels are not known.
The strategy for the sample cache is “don’t put all of your eggs in one basket.” Most samples were taken in duplicate to provide redundancy. One of each set is being deposited in this first depot cache as a backup. There is no guarantee that Perseverance will be able to ferry its samples to the sample return lander at the end of the decade. Two small retrieval helicopters with the lander will fetch the sample tubes from the depot. With this hedge in mind, the mission team has been collecting two samples from each of its target rocks.
Three Forks will be the landing site for the sample Retrieval Lander. Michael Meyer, lead scientist of the Mars Exploration Program at NASA headquarters said, “One would be hard-pressed to imagine a more benign place. The terrain is flat with few rocks or other obstructions. The surface is like a pool table, really boring.”
After completing the depot at Three Forks, Perseverance will resume its science mission, heading to the top of the delta to the crater rim to collect additional samples. Caching the first depot will allow a change in sampling strategy for Perseverance. After completing the cache, Perseverance will switch to a single sample strategy to sample more locations and rock types.
Perseverance’s JPL project manager, Art Thompson, said, “We will still be working the sample depot deployment when our extended mission begins on Jan. 7, so nothing changes from that perspective. However, once the table is set at Three Forks, we’ll head to the top of the delta. The science team wants to take a good look around up there.”
Katie Stack Morgan, JPL deputy project scientist for Perseverance said, “The Delta Top Campaign is our opportunity to get a glimpse at the geological process beyond the walls of Jezero Crater. Billions of years ago a raging river carried debris and boulders from miles beyond the walls of Jezero. We are going to explore these ancient river deposits and obtain samples from their long-traveled boulders and rocks.”
Ingenuity Completes Flight 38
In our AAPG Explorer September 2022 update, we reported that the Ingenuity Mars helicopter made its 29th flight on June 11 and settled down to wait through the worst of the Martian winter with cold and limited sunlight for power. Ingenuity resumed operation on Aug. 20 with Flight 30 as a short test. It then worked progressively north and west to the delta front near Three Forks where the sample tubes have been cached. Ingenuity completed Flight 38 on Dec. 24 (SOL 656). Ingenuity was originally designed to make five flights in a 30-day demonstration of its capability as an exploration partner to the Perseverance rover. It has far exceeded expectations and will join Perseverance as an exploration companion in the climb to the delta top in the extended mission. Ingenuity has flown a total of 7.6 kilometers.
The sample recovery helicopters to be sent with the NASA/ESA Sample Return Mission are based on Ingenuity’s design but will have wheels instead of feet. They will also have a small manipulator arm with a two-fingered gripper to pick up the small, pencil-sized, titanium sample tubes. Testing of the sample recovery helicopters is ongoing.
The Sample Return Mission will launch in the 2026 or 2028 launch windows and return samples to Earth around 2033. Will one of the samples returned for detailed analysis in Earth labs reveal that ancient life did exist on Mars?