The finger-sized core will be packed into a sealed tube to return to Earth later.
Scientists say their best chance of finding out if Mars once harbored life is to study its surface materials in a sophisticated home lab.
Perseverance landed on the Red Planet in February in a 45-kilometer-wide crater called Jezero.
Satellite images show that this deep depression once contained a lake fed by a delta-like river.
It is therefore considered a perfect candidate for preserving ancient microbes if they ever existed.
The NASA robot has moved about 1 km (3,000 feet) south from the spot where it dramatically landed five months ago.
It is now resting on what is called a “cobble” or “rough break”.
This is a collection of light-colored rocks that the mission team believes represent the base or floor of Jezero.
The scientists want to find out if the boulders are sedimentary or volcanic in origin. Lead scientist Ken Farley said both are interesting, but the special thing about volcanic rocks is that they can be dated in the lab with very high precision and accuracy.
This will really determine the timing of a lot of things we’re looking for on Mars,” he told reporters.
Trail will first clean the surface of a selected cobblestone section to remove the dust that obscures it on Mars, and then use its powerful instruments to examine the site.
These instruments are attached to the end of its robotic arm. They are able to determine the chemical composition, mineralogy, and texture of the rock’s interior so that it can be clearly identified.
Finally, in early August, the robot will secure a borehole core.
Over the course of its mission, the rover will store about 40 of these small sample tubes. Afterward, Nasa and European Space Agency (ESA) projects will arrive on Mars, appropriate them and bring them home.
Professor Farley said he expects there are four unique samples hidden in the area of the crater currently being studied. The rock lies at about 600 meters and appears to contain very thinly layered sediments, possibly deposited by the system of lakes and river deltas that once populated Jezero.
“This is exactly the kind of rock we would most like to study for possible biological features in this ancient rock record,” Caltech researchers said.
NASA was pleased with the Trailblazer’s performance.
One particular success is the driving mode, which now achieves a high degree of autonomy.
While previous vehicles required extensive guidance from controllers on Earth or could only navigate slowly under their own power, Perseverance can map the terrain and plan its route with great efficiency while moving at high speed. The rover can travel 100 metres or more, negotiating difficult obstacles such as large rocks or cracks in the ground.
The rover is supported in its reconnaissance by the mini-helicopter it carries to Mars.
The small helicopter, called “Smart”, has flown ahead of the Trailblazer to survey the terrain.
“We just completed the ninth flight (of Ingenuity),” said Nasa project manager Jennifer Trosper.
“It broke all our records. The duration was 2 minutes and 46 seconds, the speed was 5 m/s, we quadrupled the flight distance and flew about 625 meters.”