Nasa scientists are considering whether to send the Mars rover Opportunity into an impact crater the buggy has spent the last three weeks travelling to.
Opportunity is now sitting at the edge of the 130m-wide Endurance Crater on the Martian Meridiani Planum.
Professor Steve Squyres said the crater contained rocks that were likely to be of huge scientific interest.
But the problem facing Nasa is that the rover could have difficulty getting out of the depression once inside.
"By looking deeper, we can look back in time. It's a spectacular crater, many metres of the history of Mars. We can see an enormous outcrop," said Professor Squyres, who heads the US space agency's rover science team.
Multiple layers of exposed bedrock line the inside of much of the crater.
"There is a rock unit below what we saw at Eagle Crater," Professor Squyres said. "It looks fundamentally different from anything we've seen before. It's big. It's massive. It has a story to tell us."
He said that if it was decided the rover should descend into the depression, it might carry out more science on the plain beforehand.
Endurance Crater is more than 20m (66ft) deep, from the highest point on its rim. This is 10 times as deep as Eagle Crater, where the rover found evidence for a large body of liquid water at Meridiani at some point in the past.
By looking deeper into the Martian bedrock, scientists might be able to tell much more about the history of water on the Martian surface.
The rover is now perched on the western rim of the crater. Nasa scientists are currently identifying interesting science targets and assessing how difficult it would be for the rover to descend into the crater and get back out.
Professor Squyres said it was possible the rover would be sent in even if there was a risk it might not get out again.
"I could imagine doing that if there's stuff in there that's scientifically important," he said.
"But before we would make such a move, there's an awful lot of science out on the plains. There's the heatshield, the fractures, the ripples; we may make a trip down south and back again, I don't know."