The Perseverance rover is about to build the first depot of rock and soil samples on another planet. Establishing a cache site is a milestone in the complex preparation to return the first rocks and dirt from Mars to Earth by 2033.
Within days, the rover will start dropping some of its sample tubes, containing chalk-size cores of rock and sediment collected from the Martian surface, into the depot in an area nicknamed Three Forks in Jezero Crater.
The 10 tubes will fall about 2.9 feet (88.4 centimetres) from the rover's belly and land in different spots of level, rock-free terrain in Three Forks over the next 30 days.
The rover has been collecting pairs of samples from the rocks it has drilled into, stashing a backup set as a precaution.
The Mars Sample Return program, run jointly by NASA and the European Space Agency, will be an effort to land on Mars, retrieve the samples and return them to Earth over the next decade.
"The samples for this depot — and the duplicates held aboard Perseverance — are an incredible set representative of the area explored during the prime mission," said Meenakshi Wadhwa, the Mars Sample Return program principal scientist, in a statement.
"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," said Wadhwa, also director of the Arizona State University School of Earth and Space Exploration, referring to examples of volcanic and sedimentary rock, rocks that have been altered by water, surface dust and even the Martian atmosphere.
Perseverance is collecting rocks and soil as it investigates the site of an ancient lake that existed billions of years ago. This material could contain evidence of past microscopic organisms that would reveal whether life ever existed on Mars. Scientists will use some of the most sophisticated instruments to study these precious samples.
RETURNING SAMPLES TO EARTH
Initially, the plan was to launch a fetch rover, along with a Sample Retrieval Lander, in the mid-2020s. Once released on the Martian surface, the fetch rover would have retrieved samples from where Perseverance stashed them.
Now, Perseverance will be the primary transport vehicle to carry samples to the lander. The latest assessment of the rover shows it should still be in prime condition to deliver samples in 2030. Perseverance will back up to the lander, and the lander's robotic arm will transfer the samples.
The Sample Retrieval Lander will carry two sample recovery helicopters, similar in style to the Ingenuity helicopter currently on Mars — rather than a fetch rover.
Engineers have been impressed with Ingenuity's performance. The helicopter has survived more than a year beyond its expected life span and is about to perform its 37th flight. In case Perseverance can't return the samples to the lander, the little choppers will fly away from the lander, use arms to retrieve the samples and bring them back.
"Up to now, Mars missions required just one good landing zone; we need 11," said Richard Cook, Mars Sample Return program manager at NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement.
"The first one is for the Sample Retrieval Lander, but then we need 10 more in the vicinity for our Sample Recovery Helicopters to perform takeoffs and landings, and driving too."
The Mars Sample Return team is also focused on the pattern Perseverance will use to drop its samples.
"You can't simply drop them in a big pile because the recovery helicopters are designed to interact with only one tube at a time," Cook said.
The rover will drop the tubes in an intricate zigzag layout, allowing for enough space around each drop zone to make sure the helicopters can pick them up if necessary.
The Sample Retrieval Lander also carries the Mars Ascent Vehicle — the first rocket that will ever launch from the Martian surface, with the samples tucked safely inside. The spacecraft is set to launch from Mars in 2031. A separate mission will launch from Earth in the mid-2020s, called the Earth Return Orbiter, to rendezvous with the Mars Ascent Vehicle.
Onboard the Earth Return Orbiter is a system that will collect the container of samples from the Mars Ascent Vehicle while both vehicles are in orbit around the red planet.
The Earth Return Orbiter will then head back to our planet. Once the spacecraft is close to Earth, it will release a vehicle containing the cache of samples, and that spacecraft will touch down on Earth in 2033.
PERSEVERANCE'S FUTURE PLANS
Perseverance's prime mission will end on January 6 — nearly two years (and one Mars year) after it landed on the red planet. But the rover's journey isn't over yet.
"We will still be working the sample depot deployment when our extended mission begins on (January 7), so nothing changes from that perspective," said Art Thompson, Perseverance's project manager at JPL, in a statement. "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."
Perseverance will move into its new science operations, called the Delta Top Campaign, in the new year. The rover will finish climbing the steep bank of an ancient river delta that once emptied into Jezero Crater's lake billions of years ago and arrive at the upper surface of the delta in February.
For the next eight months, Perseverance will search for boulders and additional material that the river may have carried from other parts of Mars and deposited at the delta.
"The Delta Top Campaign is our opportunity to get a glimpse at the geological process beyond the walls of Jezero Crater," said Katie Stack Morgan, deputy project scientist for Perseverance at JPL, in a statement.
"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."
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