The US space agency's Mars rover Spirit has arrived at a large crater on the Red Planet called Bonneville and has taken a picture of its interior.
Bonneville crater is some 150m across
The rover is now perched on the south-west edge of Bonneville and will soon take measurements of the crater before heading towards high ground.
Spirit has also made observations of the night sky and has taken the first picture of Earth from another planet.
Scientists have no firm decisions about whether to drive into Bonneville.
The crater could tell scientists more about the underground geology of Mars.
"It was something no one had seen from a vantage point like this," said mission scientist Matt Golombek.
But driving into it could be dangerous for the rover and the Nasa team need to weigh up whether the crater is of sufficient scientific interest to warrant this risk.
"There has been absolutely no discussion with the science team about whether to go down; there has been no discussion with the rover drivers about what to do if we can't get out."
But Dr Golombek said there was no obvious evidence of layering - which is characteristic of sedimentary rocks laid down in water - in the upper tens of metres of the crater.
Spirit has been driving to the crater for over four weeks and has now travelled a total of more than 300 metres.
An image taken by Spirit of the night sky shows a bright streak that could either be a meteor or the Viking 2 orbiter, last heard from about 20 years ago.
Nasa also said it now understood the geology of Opportunity's landing site at Meridiani Planum a little better.
Scientists announced last week that they had found firm evidence of the past presence of water at the site through chemical and mineral analysis.
You are here: Earth as seen from the surface of Mars
These findings centred on the presence of sulphates and the hydroxide mineral jarosite in the outcrop of rock in Opportunity's crater. But the origin of the grey haematite, which covers the region outside the crater and can also form in the presence of water, was a mystery until now.
Mission scientist Professor Phil Christensen explained that the haematite at Opportunity's landing site came from rock that had been broken up into grains and then blown out in a blanket across Meridiani Planum.
He said he hoped to find vestiges of the original haematite formation out on Meridiani's plains.
Scientists recently made new estimates of the rovers' lifetime on the planet that extend their mission from 90 days to 240 days.