The first priority is to examine the rocks there, and Perseverance is stuffed to the gills with scientific instruments to do just that. But there's no way JPL c

The first priority is to examine the rocks there, and Perseverance is stuffed to the gills with scientific instruments to do just that. But there's no way JPL can squeeze every kind of instrument from every kind of lab on Earth into one rover. If we want to get the most out of our trip to Jezero, we need a way to bring some rocks back here. And yes that does mean a second trip to the same place. We could send human geologists to bring the samples back (though they could obviously pick up rocks themselves), but sending humans to Mars is both more expensive and more uncertain (it's been on the agenda many times but is always vulnerable to budget cuts due to the price tag and long duration of the program). The only other way to do it is to send a robotic sample return mission. Why do it as two missions to the same place instead of one? Because a fully kitted-out scientific rover and an ascent stage together would be very heavy, requiring a larger rocket and probably a different entry, descent, and landing (EDL) mode. Mars EDL is hard: gravity too high for an easy powered descent like the Moon, atmosphere too thin for an easy aerobraked descent like Earth. The current "sky crane" EDL mode does not scale well to heavier vehicles. So we can't just send an ascent stage with Perseverance, and a near-future there-and-back-again mission couldn't feature a rover as capable as Perseverance. The best compromise is to find the most interesting samples with a top-of-the-line scientific rover, then send the ascent stage to get them later. And yes, this uncrewed return mission is planned by NASA/JPL and ESA [1]. The current concept involves two launches: one sends a lander with an ascent stage (and possibly a small rover to fetch the samples, or Perseverance could do it--it depends how soon the ascent mission gets there) and the second sends an Earth return stage to bring the samples the rest of the way home. [1] https://www.nasa.gov/press-release/nasa-moves-forward-with-campaign-to-return-mars-samples-to-earth https://www.nasa.gov/press-release/nasa-moves-forward-with-c...