The mission's Perseverance rover is only weeks away from emerging from the 28-mile-wide Jezero Crater to explore new terrain. It's a point in the mission Horgan set her sights on following the rover's landing in the crater four years ago.

"The crater rim is like the edge of the world, and it feels like we're so close to going over the edge," said Horgan, co-investigator and long-term planner on the Perseverance mission and professor of planetary science in the College of Science. "We're going to be getting our first views of some of the oldest rocks we're going to see on the mission. These are more than 4 billion years old and dug up from the deep crust of Mars and exposed by this impact crater."

Briony Horgan, a planetary scientist at Purdue, says Earth rocks can only provide some historical data. She sees every rock on Mars like a time capsule, potentially holding information from billions of years ago about the history of environmental conditions on the planet.

Perseverance is climbing a small mountain range as it progresses, with the top of the crater rim about a 1/2 mile vertically from the original landing site. Additional areas of the red planet's rocks and terrain potentially will be accessible for the mission once the rover clears the top of the crater and descends the other side.

To Horgan, every rock on Mars is like a time capsule, potentially holding information from billions of years ago that could help answer questions about the potential for microbial life and the history of environmental conditions on the planet. Finding evidence of microbial life, even from billions of years ago, would open the door to new research in understanding how common simple life forms are in the universe.

The Mars rover's crater exit is the latest stage of the mission, which began with a July 2020 launch and 300-million-mile trip through space. The rover successfully landed in February 2021 in Jezero Crater, just north of the Martian equator. The crater used to contain a lake about the size of two Lake Tahoes. Before the rover launched, Horgan led a study of the mineralogy of the site, which produced one of the results that contributed to the selection of Jezero Crater for the mission.

Hogan's involvement in NASA's Perseverance rover mission extends beyond her planetary science research. She was involved in designing Mastcam-Z, part of the rover's system of cameras that can record images in color, 3D and video. It also has zoom capability strong enough to view a housefly at the far end of a soccer field.

Rolling over the crater's edge will give the car-sized Perseverance and the mission team members their first view of the wide-open Isidis Planitia impact basin, an ancient watershed created by a much larger impact almost 4 billion years ago. It is crisscrossed by riverbeds, including a river that fed Jezero Crater's lake. Some of the rock outcroppings in the basin predate Jezero Crater itself.

"Rocks that are this old are very rare on Earth," Horgan said. "They've been eroded or destroyed by plate tectonics and water. So, this is really a great chance to see what the building blocks of Earth-like planets look like."

Horgan said there is excitement about the age of the rocks that are potentially from deep in the upper mantle of Mars, forced to the surface by the impacts that created Jezero Crater and the Isidis Planitia basin. Hydrothermal environments may have been created by the water and heat in the larger impact basin with warm water moving through cracks in the rock offering a great opportunity for life to survive if it ever arose on Mars.

Horgan characterized where the rover goes after emerging from Jezero Crater as "a moving target." Plans for the samples Perseverance has collected take priority, possibly dictating whether the rover remains on the Jezero rim or descends back into the crater itself. More concrete plans for a future sample return mission could come by early next year.

"We know that regardless of what happens, we're going to get time to explore the crater rim and get additional really exciting ancient samples," she said.

The suite of samples taken by the Mars rover could reveal details ranging from the red planet's own history to potential keys in the formation of planets and habitable environments. Horgan said some samples could provide insight into how water interacted with different kinds of rocks and minerals, which trap potential biosignatures that may have been formed by life.

Discoveries by Perseverance this year have broken the stereotype of Mars being a red, dusty planet. A field of blue-colored volcanic basalt stones was among the reveals for Mars earlier this year, as well as a unique black-and-white zebra-striped rock. Horgan said the rock is an example of weird crustal rock and is unlike anything the rover has come across in Jezero Crater.

As of the end of November, the rover has driven close to 20 1/2 miles and has collected 25 rock and regolith samples and one atmosphere sample.

Related Links
Mars 2020: Perseverance Rover
Mars News and Information at MarsDaily.com
Lunar Dreams and more