NASA has chosen for a solid rocket for the Mars Ascent Vehicle.
https://spaceflightnow.com/2020/04/20/nasa-narrows-design-for-rocket-to-launch-samples-off-of-mars/
https://spaceflightnow.com/2020/04/20/nasa-narrows-design-for-rocket-to-launch-samples-off-of-mars/