The endeavor to retrieve rock materials from Mars and analyze them for traces of past life is undergoing a significant reevaluation.

The US Space Agency has stated that the current plan cannot meet the deadline of returning the samples before 2040 within the allocated budget. The required $11 billion for the mission is deemed unsustainable.

Consequently, NASA is exploring alternative, more cost-effective approaches, seeking innovative ideas that can expedite the process. It aims to develop a new strategy later this year.

The retrieval of rock samples from Mars holds paramount importance in planetary exploration, akin to the significance of the Moon rocks brought back by Apollo astronauts, which revolutionized our understanding of the early Solar System.

Materials from Mars have the potential to reshape our understanding of the potential for extraterrestrial life.

However, NASA now acknowledges that the current approach to sample return is impractical given the current financial constraints. NASA Administrator Bill Nelson emphasized that $11 billion is prohibitively expensive, and delaying sample return until 2040 is unacceptable.

He is committed to safeguarding other scientific missions from being compromised by the Mars project and is therefore soliciting fresh perspectives from both within NASA and the industry.

While the existing mission framework is underway, with rock samples being collected and cataloged on Mars by NASA's Perseverance rover, the agency recognizes the need for a more feasible and sustainable path forward.

A dedicated follow-up mission was due to be launched later this decade that would carry a rocket to the surface of the Red Planet.

Once loaded into this ascent vehicle, Perseverance's samples would then be blasted skyward to rendezvous with a European-built spacecraft that could catch them and head for Earth.

It was envisaged that roughly 300g of Martian material would land in a capsule in the western US state of Utah in 2033.

However an independent review that was reported in September last year found faults with the way the mission design was being implemented. It doubted the schedule could be maintained and, even so, the cost was likely to balloon to somewhere between $8bn and $11bn.

In its response published on Monday, Nasa doesn't disagree with the assessment. The current architecture can be simplified somewhat but if the samples are to come home before 2040, a new approach is needed.

"We are looking at out-of-the-box possibilities that could return the samples earlier and at a lower cost," said Dr Nicola Fox, the director of Nasa's science directorate.

"This is definitely a very ambitious goal, and we're going to need to go after some very innovative new possibilities for design, and certainly leave no stone unturned."

Those new possibilities could include a smaller, simpler Mars rocket, she said.

Dr. Fox told BBC News that Esa remained central to the endeavor. Indeed, it's likely Europe's significant contribution - the Earth Return Orbiter (ERO) - will still be launched, albeit at a slightly later date than currently envisaged, possibly in 2030.

Dr. Orson Sutherland, Esa's Mars exploration group leader, said his organization would meticulously review Nasa's response plan.

"Our priority remains ensuring the best path forward to achieve MSR's ground-breaking scientific objectives and lay the groundwork for future human missions to Mars," he said.

Mr. Nelson emphasized that Nasa remained committed to MSR.

It needed, however, to fit within a sustainable budget envelope, which he described as somewhere between $5bn and $7bn.

The overwhelming scientific imperative behind MSR was underlined in recent days by the latest investigations of Perseverance.

The robot is working in a wide crater called Jezero, which looks to have held a large lake about 3.8 billion years ago - a highly promising scenario for the existence and preservation of microbial organisms.

Perseverance has been drilling and caching rocks that appear to have been laid down at the margin of the lake.

One of the rover's senior scientists, Prof Briony Horgan from Purdue University, said these samples were particularly exciting.

"Right now onboard Perseverance, we're carrying three samples of silica and carbonate-cemented rocks; and on Earth, both of those minerals can be fantastic for preserving ancient signatures of life," she told BBC News.

"We think it's possible that some of the samples are sandstones laid down in the ancient lake, but are still evaluating other origins as well. Either way, these rocks are the exact types of samples that we came to Mars to find, and we very much want to get them back to our labs on Earth."

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