The Opportunity rover has failed in its first try at driving out of a crater it's been exploring since landing on Mars two months ago.
Mission crewmembers say the rover slipped while trying to go uphill out of the crater Sunday. Controllers plan to try a second way out.
The shallow crater is banked with dry and sandy slopes. Meantime, halfway around Mars, Opportunity's twin, Spirit, has been exploring the rim of a far larger crater.
NASA has scheduled a news conference for Tuesday in Washington to announce what it calls a "major scientific finding" made by the mission.