Perseverance Reaches Rim of Jezero Crater

On December 10th, after nearly 4 years on Mars, NASA’s Perseverance rover reached the rim of Jezero Crater. From a place on the rim dubbed “Lookout Hill,” its view stretched as far as 60 kilometers (40 miles) across the Martian surface. The rim crest also marks a geologic transition from rocks that fell inside the crater after it formed 3.9 billion years ago to rocks thrown outside the crater by the impact and a new region for the rover to explore.  

Evidence that a lake formed in the crater floor after the impact made Jezero a tantalizing place to search for signs that the early Martian environment might have been able to support life — the mission’s top priority. The team’s geologists also wanted to investigate the ancient Martian crust, so they navigated Perseverance up the crater wall to a site from which the rover could access the ancient rocks they hoped to find on the outer edge of the rim.

Perseverance landed near a broad fan of sediment within Jezero on February 18, 2021, and began a series of four scientific campaigns examining different regions that had been inundated with water 3.7 billion years ago. The last of these examined a site called “Cheyava Falls,” where the delta’s rocks showed signs of wet chemical reactions considered possible biosignatures. The rover collected samples there, and elsewhere, that NASA hopes could be retrieved by a later mission and brought to Earth for more exhaustive analysis.

Climbing to the Rim

With its samples of Cheyava Falls safely stowed, Perseverance set off uphill toward the rim in August, seeking what might be the oldest rocks on Mars.

“The new campaign brings us completely new scientific riches as Perseverance roves into fundamentally new geology,” says project scientist Ken Farley (Caltech). For example, the rover spotted something entirely new in the “Pico Turquino Hills” en route to the rim. Brilliant white cobbles were seen scattered across a wider area covered with a diverse sampling of other volcanic rocks. They were cantaloupe-size chunks of pure-white quartz, a mineral never before seen on the Martian surface by satellites or previous landers.  

On Earth, quartz can form when water seeping through hot rock dissolves silicon, which crystalizes as quartz after the water evaporates. It’s the kind of hydrothermal environment that could have supported life, if any existed on the Red Planet billions of years ago. The cobbles were too small for Perseverance to sample with its drill and stash for sending back to Earth, but Farley hopes to find larger exposures of quartz in places later in the mission.

As Justin Maki (NASA) told a press conference at the annual meeting of the American Geophysical Union in Washington on December 12th, the 3½-month climb from the crater floor to Lookout Hill involved an ascend of 500 meters (1,640 feet). Perseverance tackled grades of up to 20% and some of the toughest terrain it has yet covered. The rough terrain challenged rover drivers, and the rover slipped in some places. But Maki pronounced Perseverance to be “in good health.”

The next stop will be at an outcrop called “Witch Hazel Hill” about 450 meters (1,500 feet (450 meters) away. Plans call for the rover to spend six months there studying an outcrop exposing more than 100 meters (330 feet) of layered structure. “As geologists, we love layered outcrops, each of which is like a page in the book of Martian history,” said Candice Bedford (Purdue).

Two more stops are scheduled. The first will start with a steep descent and cover about 3 km (2 miles) to “Lac de Charmes,” an area on the plains beyond the crater rim that have been less affected by the impact that gouged out Jezero. The second will require another trek of 1½ km (1 mile) to investigate a megabreccia, an outcrop of massive boulders. Scientists think this might be Martian bedrock shattered by an enormous impact 3.9 billion years ago that created the region’s 1,200-km-wide (745-mile) Isidis basin.

Perseverance has already collected and cached 25 samples for return to Earth, along with 13 more tubes available for future samples. NASA says it will complete revising plans for its problem-plagued sample-return mission in 2025.