LOS ANGELES - NASA’s Perseverance rover has started its second science campaign on Mars, collecting rock-core samples in an area long considered by scientists to be a top prospect for finding signs of ancient microbial life on the Red Planet, NASA said on Thursday.

The rover has collected four samples from an ancient river delta in the Red Planet’s Jezero Crater since July 7, bringing the total count of scientifically compelling rock samples to 12, according to NASA.

“We picked the Jezero Crater for Perseverance to explore because we thought it had the best chance of providing scientifically excellent samples -- and now we know we sent the rover to the right location,” said Thomas Zurbuchen, NASA’s associate administrator for science in Washington.

“These first two science campaigns have yielded an amazing diversity of samples to bring back to Earth by the Mars Sample Return campaign,” he said. A key objective for Perseverance’s mission on Mars is astrobiology, including caching samples that may contain signs of ancient microbial life.

The rover will characterize the planet’s geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith, according to NASA.

   Subsequent NASA missions would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis.