The Perseverance Rover and Sample Return Mission is the Next Step in NASA's Journey Toward Mars. Credit: NASA.
In July 2020, NASA is launching the next era of Mars Exploration with the Perseverance Rover. The Perseverance Rover, formally known as Mars 2020, will make the eight-month journey to Mars and kick off a multi-decade long effort to collect and return samples from the Red Planet in the search for life. Perseverance is the first part of a three mission Mars Sample Return Program that will collect, launch, and return geologic samples that might just contain evidence of past life on Mars. The three missions of sample return will first collect and cache the samples (the job of the Perseverance Rover), then the second mission will launch a rocket to Mars to collect this sample cache and launch it into Mars orbit for safekeeping and easy of capture, the third mission will rendezvous with these samples in Mars orbit and rocket them back to Earth for study. We are on the verge of the launch of the first step of this ambitious effort with the Perseverance Rover.
The three mission plan that will return samples from Mars. Credit: Nature/Images of Earth and Mars surface: NASA.
NASA has been exploring Mars for decades, ever since the Mariner 4 spacecraft flew by the planet in 1965. In that time, we have mapped the surface, identified the minerals, and unlocked the history of the planet. We have discovered grand volcanoes, dynamic polar caps, and a very complex history of water and geologic evolution. NASA is dedicated to exploring the universe for life, and Mars, especially early Mars, has all of the conditions we think life would need. The only step left is to find evidence of this life. Unfortunately, finding evidence of life is not easy. It will require us to search the planet for just the right samples which have all the conditions to support and preserve evidence of past life and the specialized instrumentation sensitive enough to detect it. Current technology does not allow us to send the laboratory equipment needed for life detection to Mars. Instead, the Mars Sample Return Program is designed to pick up the best samples on Mars and return them to the best instruments on Earth.
Picking up samples from space is not easy. Most missions are one way and only return their data. Landing and launching from Mars is particularly difficult. It is the largest planet that we have ever tried to return samples from. Large planets and their gravity make it difficult to launch from the surface. To return samples from Mars, we will need to launch a rocket from Earth that will carry a rocket to Mars that will then launch samples into the Martian orbit. This means that the largest rocket we can send to Mars will only have the power to launch about 100 grams of Martian samples back. This becomes the next challenge as scientists must carefully select the perfect samples to return.
The Jezero Delta that will be the target of the Perseverance Mission. Altered minerals are shown in blues and greens. Credit: NASA.
There has been a nearly continuous, 25 year-long effort to understand where we should land on Mars. NASA’s Pathfinder mission landed on Mars in 1997 to jumpstart the modern era’s effort to explore the surface of Mars. Since then, we have landed the Spirit (2004), Opportunity (2004), Curiosity (2012) and soon to be launched Perseverance ( landing in 2021), all of which went through a long series of workshops by the Mars community to scour the latest satellite images of Mars and combine them with our best understanding of astrobiology to decide where each mission should land. Before looking at the science, each landing site had to meet three basic engineering requirements. It had to be below 500 meters in elevation to allow for enough atmosphere for the parachutes to open, it had to be within 30° of the equator to stay warm enough to survive the winter, and finally, the science needs to be close to a 10 km wide flat plain that is safe enough to land on. Once those engineering requirements are met, the scientist got to work debating the science of where to land. The science goals of the mission required several specific types of samples. The most important samples are ones that have the potential to preserve evidence of life as biosignatures (the Mars science term for fossils of alien life) and have the ability to explore the most ancient rocks on Mars (more than 4 billion years old, when Mars was warm and wet). The best of both of these needs was found in the Jezero Crater Basin. Jezero is an ancient impact crater that once held a deep lake. We see a stream channel leading to the crater and then forming a delta deposit that only occurs when sediment filled rivers flow into a deep lake. Satellite analysis of the delta and surrounding terrains show extensive suites of altered minerals that indicate that the environments needed for life are all around. The Perseverance Rover will be sent to explore and collect the best samples it can find in Jezero to understand this ancient history of Mars and search for evidence of life. We will then have to wait for the next two missions to return these samples to know what they have found.
Artist concept of the Perseverance Rover on Mars. Credit: NASA.
The Perseverance Rover was built on the technology that created the Curiosity Rover that has been exploring Gale Crater since 2012. Perseverance is a similar size rover and will land with a similar sky-crane system, however, this new rover will feature some important upgrades. Perseverance will have a range trigger and hazard avoidance capability that will allow for the selection of a much smaller landing ellipse that allows the mission to get much closer to the targets of interest, this alone may save years of driving on the surface. Perseverance will also carry a small helicopter, named Ingenuity. The thin Martian atmosphere makes flying very difficult, but Ingenuity will test if flying a drone on Mars is possible and have the potential to return some new perspectives on the Martian surface. The primary objective of Perseverance is to characterize and collect samples that will be returned later to Earth. This requires a robust sample collection and caching system. Perseverance will cache samples in 30 tubes that can be left somewhere safe when they are ready. This will allow the mission to collect the first set of samples as quickly as possible and store them someplace safe so that they can be collected later before undertaking a longer and more risky extended mission to get more interesting samples but at the risk that rover might break or be stuck in a place that we can not reach to retrieve the samples.
Perseverance Rover's Payload for exploring Mars and selecting samples. Credit: NASA.
The instrument suite of Perseverance gets to be completely different from Curiosity’s as well. Perseverance does not need to complete the analysis with an on-board laboratory the way that Curiosity does, instead, it needs to quickly find, characterize and collect the best samples that will then be fully studied on Earth. These instruments include a high-resolution camera (Mastcam-Z) to find good samples and take beautiful images of the planet. A laser (SuperCam) that can tell the elemental composition of the surface rocks. A radar (RIMFAX) for peering below the surface of the planet. Spectrometers (SHERLOC, PIXL) for finding organics and getting a close-up view of the planet’s surface and a weather station (MEDA) to monitor the planet’s climate and improve future landing efforts. One of the most exciting of the Perseverance payloads is a device called MOXIE. MOXIE is an experiment designed to test if we can separate out the oxygen from the thin Martian CO2 atmosphere to use as rocket fuel. One of the most challenging parts of the whole Sample Return Effort comes in the second step when we send a mission to Mars to rocket the samples into Martian orbit. If MOXIE is successful, that mission will carry a much bigger version of the experiment to fuel that rocket with oxygen sourced on Mars and save us the hassle of launching the fuel all the way from Earth. If MOXIE works, it will revolutionize the role that Mars can play as an exploration hub around the solar system.
The Perseverance Rover's main objective is to find and cache important samples to be returned to Earth. Credit: NASA.
Once the Perseverance Rover lands on Mars in February 2021, it will begin a mad dash to search for the best samples to understand the Jezero Crater geology and find biosignatures. Even though the rover is expected to last for years, it is based on the engineering of Curiosity which has been exploring Mars for eight years and counting, a single part failure could end the mission at any time. The key samples must be found, put in tubes, and deposited on the surface, ready to be collected by the next mission whenever this failure occurs. Until filled, there will be a lot of pressure to understand and collect the best samples as fast as possible. Once these samples are collected, the Rover team can breathe a bit and work on their extended mission. They can explore more of the Jezero Delta, they can drive up to the crater walls and even into the ancient crustal environments exposed just west of the crater. Here the rover will encounter some of the oldest planetary rocks in the solar system and get a first-hand look at the geologic record of the earliest years on Mars and possibly a sense about what the oldest rocks on Earth would have looked like, before being eroded away on our much more active planet. This part of the mission may yield more samples in a second depot that may be stored for later retrieval as well. Once all the samples have been collected and cached somewhere safe, Perseverance will still have a very capable rover and will use its instruments to keep on unraveling the mysteries of ancient Mars.