By Paul Rincon
BBC News Online science staff, in Paris
The US space agency's Mars rovers will be given another seven months to explore the Red Planet, says Nasa.
The rovers on Mars have more time to explore
Dr Firouz Naderi, director of Solar System exploration at the US space agency's Jet Propulsion Laboratory, told BBC News Online that he had recommended the missions be extended.
Spirit and Opportunity were given an initial work phase of 90 Martian days.
But back in April, Nasa announced that it would be extending the rovers' mission until September.
Although Nasa headquarters has said the project will not get any new money, Dr Naderi - who manages the rover finances - says the money will be found from elsewhere within the organisation.
"We were doing about $5m a month during the primary mission, and during the first extended mission we were doing about $3m a month," he said here at the Committee on Space Research (Cospar) scientific assembly.
"Maybe there is another couple of hundred thousand dollars we can [shave off].
He added that the extension was both good and bad news for the mission.
An extended stay does not mean more spending money
"The good news is that they're lasting far longer than we had anticipated.
"The bad news is that we had not planned for it to go on this long so we have to squeeze other things to come up with the money."
The rover team would be carrying out an operational experiment, with rover scientists back at their home institutions working five days a week through distributed processing, Dr Naderi said.
Opportunity is now about 10 to 12m (32-39ft) inside Endurance Crater, a 130m-wide (426ft) depression at Meridiani Planum on Mars.
The rover will continue to proceed deeper into the crater until the gradient approaches 30 degrees, the limit at which scientists think it will become difficult to back out of the crater.
When it gets out of the crater, it will examine the spacecraft's heat shield, which is thought to have excavated a deep hole when it slammed into Mars during descent.
After this, the rover will head for the "etched terrain", a site some kilometres to the south, which contains large exposed outcrops of the same bedrock that Opportunity has been examining near its landing site.
Spirit is currently still at the base of Columbia Hills. It is due to proceed to about 30m (98ft) up the hills and then hibernate to endure the harsh Martian winter.