The phrase "twin rovers" refers to two robotic vehicles that are exactly the same and designed to explore and collect information about different places, usually on other planets or moons. Full definition
With twin rovers still making tracks on Mars, plans are already underway for the next robotic mission to set foot on the Red Planet. (sciencemag.org)
NASA had earlier considered to fly an orbiter in 2018, but later decided to supply equipment for the European probes, expand its current Mars missions and develop the Curiosity twin rover for launch in 2020. (ibtimes.com)
Certainly the twin rovers on Mars and the intrepid Cassini spacecraft dodging around Saturn's rings have generated a powerful sense of wonder, yet those are exactly the kinds of projects that are at risk as Griffin places his bet on human voyagers, not mechanical surrogates. (discovermagazine.com)