Perseverance – the name says it all
On 18 February 2021, the Perseverance rover of NASA's Mars 2020 mission landed on Mars safe and sound. The research mission, initially scheduled to last two years, has begun. In this blog, DLR researcher Nicole Schmitz, together with her colleague Frank Preusker, will report regularly on the progress of the mission and the camera experiment in which they are involved. Both are part of the Science Team of the Mastcam-Z instrument, a stereo camera located on Perseverance's approximately two-metre-high mast.##markend##
Perseverance was certainly required during the three attempts to gather the first two rock samples from Mars
First attempt: Thursday, 5 August 2021, around 19:00, Gdynia, Poland
After about an eight-hour drive, I arrive at my hotel in Gdynia. I'm looking forward to spending a long weekend with friends on Poland's Baltic coast, but instead of heading straight to the seaside along with everyone else, I start by unpacking and setting up my work phone and laptop in my hotel room, dialling into the mission data portal and reporting for the daily Perseverance Science Discussion conference call via VPN. Today is a big day for Perseverance and for Mars research in general, as the rover is set to take its first rock sample. This sample will be part of a set of initial rock samples collected from another planet, and wil be transported to Earth in about 10 years' time.
After discussions that went on for days, a flat rock dubbed 'Roubion' was selected. Roubion is one of the many flat, weathered, polygonal rocks that the team has nicknamed 'pavers' because they resemble cobblestones. These pavers are typical of the part of the crater floor previously studied by the Perseverance rover on the NASA Mars 2020 mission. A rock sample from this geological unit, 'Cratered Floor Fractured Rough' (CFFR), would be an important clue in our efforts to decode the geological history of the Jezero Crater, as these are thought to be the oldest rocks in the crater. In the days leading up to this, Perseverance has been examining and recording Roubion and its immediate environment in detail using its scientific instruments.
There's a status report during the conference call. Everything's looking good. The Uplink team sent the drilling command to the rover in its previous transmission: the rover has been commanded to take a core sample from Roubion. The exact spot at which the rover should apply the drill has been precisely determined, having taken scientific and technical factors into account. We'll only know by tomorrow morning whether it's worked, as that’s when Perseverance's next data transmission will reach Earth.
Satisfied with the day's work, I join my friends for an evening stroll along the beach.
Friday, 6 August, 11:00, Gdynia
My partner, a scientist who is also involved in the mission, messages me with some welcome news: "We have a hole!" The data confirm that the core bit has drilled a seven-centimetre-deep hole, as planned. The images from Mastcam-Z, the Perseverance rover's main 'eyes' near the top of the mast, which I work on, show us the bore hole and missing drilled rock as expected. It's all crystal clear. Around it lies a conical heap of fine drilling dust.
I'm overjoyed. Within a couple of hours, we'll have received the next data transmission from Mars, so with any luck we'll have some photos of the sample container with the first core sample in it.
The next message comes through at 18:52. "The sample tube is empty." I write back, "What??" I let my friends go off to dinner without me and dial into the daily conference call. Everyone is scratching their heads. What just happened?
The telemetry data from the drilling and an image from the CacheCam in the Adaptive Caching Assembly (ACA) confirm that the sample container was transferred from the 'corer' to the ACA and that the sample container was sealed and successfully stowed in the rover – quite a success. Yet the volume measurement and an image of the unsealed sample container right after the drilling show that the vessel is empty. It takes a few minutes for us to digest this news, but then everyone goes right back into analysis mode.
Over the following days, we conduct extensive research into the possible cause. The rover selfie that had been planned to celebrate this success will have to be postponed for the time being. Our team of researchers command the rover to take new pictures of the area around Roubion. Could the core sample have fallen out of the sample container? No, there's no sign of it. Meanwhile, the NASA engineers are closely analysing the telemetry and comparing the measurement data with the results of drilling tests conducted on Earth. Slowly, the probable cause emerges: the rover technology worked exactly as it should, but the rock wasn’t firm enough, so it crumbled into powder and tiny fragments of material when it was drilled into, as there was no longer anything holding it together. Prior to the mission, NASA engineers had obtained over 100 drill cores from an array of test rocks on Earth, but in all their tests they’d never come across a rock that was too crumbly to extract a drill core. Martian rock 1 – Perseverance 0.
Now we need to look ahead and concentrate on working out the right steps to take next. Perseverance only has a limited number of sample containers for drill cores on board. It has to work next time. We need a more resistant rock for our next attempt at drilling. As one of my colleagues puts it, "It has to make a 'clonk' if you hit it with a hammer".
Fortunately, along the planned route to South Séítah there are long stretches of exposed rock of the same type as Roubion. Geologists refer to these as rock outcrops. The 400-metre-long ridge called 'Artuby' includes a small region that we have named 'Citadelle'. It has rock outcrops and metre-high boulders, some of which feature interesting layering patterns. Satellite images acquired from Mars orbit show that the boulders of Citadelle are part of an extensive outcrop on the summit and rear side of the ridge. We hope that the fact that the rock is still towering over the landscape after aeons of erosion indicates that it is solid enough to withstand the drilling.
Following in-depth consultations and investigations of possible targets, the team settles upon a dark rock, probably made of basalt, which we call 'Rochette'.
As always, we carry out a well-established series of tests before performing a core drilling on Rochette. After all, the basis for evaluating any samples obtained using the rover is an examination of their geological context within the terrain: where exactly have the samples been taken from and how are they related to the surrounding rock and geological units? The immediate vicinity of the selected rock is first documented in great detail with photographs in order to obtain such information. Using high-resolution images, the exact location for the sampling is also decided, along with an adjacent location, which serves as a 'geological twin'. The idea here is to obtain valuable data about the rock we want to sample by finding its geological twin and performing detailed analyses on site. The rover grinds the top layers of rock and dust of the geological twin with the abrasion tool in order to expose a fresh, unweathered surface. This surface is then carefully examined with all of the rover's scientific instruments (Mastcam-Z, SuperCam, SHERLOC, PIXL and Watson). In addition to the high-resolution images, these instruments provide data on the mineralogical and chemical composition of the rock. After these context measurements have been completed, the rover is given a break of one Mars-day (sol), so that it can fully charge its battery for the activities of the following day.
The day of sampling begins with Perseverance taking a sample container from the Adaptive Caching Assembly (ACA), heating it and then inserting it into the core drill. A device called a drill carousel transports the container and the drill bit to the rotating percussion drill on Perseverance's robotic arm. The pristine geological twin of the selected rock is drilled and the sample container is filled with a core sample the size of a piece of chalk. Perseverance then uses its robotic arm to transport the drill bit and sample container apparatus back into the drill carousel. The drill carousel transports the sample back to the ACA, where its volume is determined, it is photographed and lastly, its container is hermetically sealed. We will only see the contents of the sample container again when the sample is analysed on Earth in a cleanroom facility, with instruments that are much too big to be sent to Mars, but are also much more powerful.
The context measurements prior to drilling also provide us with new insights. The team had originally believed that Rochette was basalt, but high-resolution images of the geological twin before the drill core was removed show us textures that suggest that this rock is fine-grained material that could have been formed by an explosive volcanic eruption (caked volcanic ash) or possibly by an impact event. We will probably only know exactly what it is when it is on Earth and we can analyse it in high-tech laboratories.
The sampling from Rochette itself is scheduled for 1 September. After the failure of the first sampling, this time the team will perform a 'ground-in-the-loop' inspection after the drill core has been extracted. Before the sample container is sealed, the rover is supposed to acquire additional images of the still-open sample container with Mastcam-Z and send them back to Earth so that the team can confirm that a drill core has been collected. Only then is the robotic arm cleared to transfer the sample into the interior of the rover and seal the sample container.
Thursday, 2 September, 07:00, Berlin
My partner and I are sitting in front of the laptop, morning coffee in hand. This is today's first conference call. It's 22:00 in the JPL control centre in Pasadena, California. The Perseverance team has convened and is waiting to receive data from Mars. Everyone is eager to see the images of the second drilling attempt acquired by Mastcam-Z. The hope is that the images of the sample container will confirm that the sample has made it safely into the sample container this time. My colleague in San Diego who is responsible for the tactical image planning once again explains which Mastcam-Z images were ordered and from which angle. At around 08:00 we receive the first images, and it's looking good! Everyone cheers, and Mastcam-Z Principal Investigator Jim Bell (in Tempe, Arizona) praises the team, quipping, "Outstanding work, everyone. Thank you for flying with Mastcam-Z Airlines."
A couple of minutes later, another photo arrives, in which the container looks empty. People come up with a number of theories on why this could be the case. We decide that Perseverance should take more photos, which will arrive the next day. It turns out that, among other things, poor lighting conditions at the time of the exposure were to blame for the fact that the sample could not be seen in the second image.
On 5 September, following thorough analyses of all the data and images, the team is certain: it worked! On behalf of Perseverance, NASA posts, "Got it!" on Twitter, along with the best Mastcam-Z image of the sample in the sample container.
The team names the first successfully extracted core 'Montdenier'. On 8 September, Perseverance successfully takes another sample from Rochette, called 'Montagnac'.
Now it's time to celebrate: Perseverance is allowed to take the long-awaited selfie using the WATSON camera on the rover arm.
What are we looking to learn from these rock samples?
The geological history of the Jezero Crater has been shaped by volcanic activity and periods in which water was continuously present. Analysing the rocks from which the Montdenier and Montagnac samples were taken can help the team of researchers investigate the timing of this story.
The rock from which the mission's first core samples were taken is probably of volcanic origin. This could help the team precisely determine when it formed, as the presence of crystalline minerals in volcanic rock is particularly useful for radiometric dating. Each sample acts as a piece in a larger chronological puzzle. Putting them in the right order allows us to create a timeline of the most important events in the history of the Jezero Crater. These events include the formation of the crater, the covering of at least parts of the ground by igneous rocks, the appearance and disappearance of the crater lake, the deposition of different types of sediments and changes to the planet's climate in the past.
Perseverance has also discovered salts in these rocks. These salts could have formed when groundwater flowed through the rock, altering the original minerals, or more likely, when liquid water evaporated, leaving the salts behind. The salt minerals in the first two rock cores could also have trapped tiny bubbles of ancient Martian water. If present, these could serve as microscopic time capsules that shed light on Mars’ past climate. On Earth, salt minerals are also known for being able to preserve traces of life.
The rover has since left the Citadelle region. At the time of writing, in early October, it is in a region called South Séítah.
With the two rock samples safely stowed, Perseverance celebrated Sol 200 on 11 September 2021 by making a record-breaking 175-metre journey in a north-westerly direction along the Artuby outcrop. Perseverance navigated itself for most of the journey, covering 167 metres with the help of the autonavigation function (Autonav for short). This mobility software enables Perseverance to map the terrain itself and thus independently recognise and avoid hazards on longer journeys.
After acquiring a few more pictures of Artuby, Perseverance turned right (northeast) towards the Séítah region (from a Navajo phrase meaning 'amidst the sand'). Artuby ridge is a series of layered outcrops that outline the southern edge of the Séítah thumb and possibly represent a boundary between two geologic units.
Thanks to excellent remote sensing by the Ingenuity helicopter, we were able to take a look at Séítah before the trip and identify potential investigation and sampling targets. A thinly layered outcrop called 'Bastide' particularly caught our attention. The layering of Bastide suggests that it is a sedimentary rock that may have been deposited by water flow as a result of the activity of Lake Jezero more than three billion years ago. We got a close look at Bastide for the first time when we arrived at the outcrop on Sol 204 (15 September 2021), after a series of journeys. Since arriving there, Perseverance has abraded the rock to reveal a fresh surface and better study its composition using its sophisticated scientific instruments.
Key research questions when exploring South Séítah include: how do these rocks relate to those previously explored in the 'Cratered Floor Fractured Rough' unit? Do they represent a geologically different origin and period in the history of Jezero? The Bastide survey could provide answers to these questions, and this region may also yield a rock that will prove suitable for sampling, another clue that will help us decipher the history of the Jezero Crater.
But for now, Perseverance (and we) are enjoying a break. Earth and Mars are currently on opposite sides of the Sun (the exact conjunction is on 8 October), so communication with the rover is interrupted until mid-October. The rover was given a series of commands beforehand so it is able to conduct scientific activities during this time without the team having to check on its progress every day. Among other things, Perseverance will take images using Mastcam-Z, carry out weather measurements, keep an eye out for passing dust devils on the planet and listen to surrounding noises with its microphone.
This period of 'radio silence' is a good opportunity for us to calmly analyse the data collected so far and make plans for the next stages of the journey. Activities will resume as soon as Mars reappears from behind the Sun and becomes visible to us on Earth, and contact with Perseverance is re-established via the 70-metre antenna of NASA's Deep Space Network.