A faulty battery has emerged as one of the likeliest causes for the crash-landing of the Genesis sample capsule.
The Genesis capsule crash-landed in Utah
Scientists have been removing pieces of dirt and mud that lodged in the damaged canister after it smashed at high speed into the Utah desert on Wednesday.
They remain optimistic that something can be salvaged from the mission, aimed at capturing solar wind particles.
Engineers are looking into the theory that a battery overheating early in the mission may have led to the crash.
The battery was designed to detonate explosive charges that would release the craft's parachutes, helping to slow its descent to Earth.
It was then supposed to be caught in midair by a Hollywood helicopter stunt pilot.
Instead, the parachutes failed to open and the capsule struck the ground at the Air Force's Utah Test and Training Range, southwest of Salt Lake City, at 310km/h (193mph).
The 205kg (420lbs)capsule is now in a specially built clean-room at the nearby US Army Dugway Proving Ground.
"We have a mangled mess of a spacecraft. The sample canister broke open," said Nasa project scientist David Lindstrom.
"We have been lucky in that it's only dirt - we did not have a problem with liquid water in there, so we're very hopeful of getting good science out of this."
The capsule was removed to a clean-room at the nearby army base
Both the outer protective canister and the inner science canister were breached in the impact.
Scientists say some of the plates designed to collect solar wind particles appear to be more or less intact, although others have crumbled to dust.
"Overall, the science community is optimistic because the particles are implanted within the collectors," said Lindstrom.
Ultimately the solar samples will be taken to the Johnson Space Center in Houston, Texas, for study and preservation.
Scientists are going through all the debris in a methodical manner
The precise nature of these particles could tell scientists how the Sun and the planets grew out of a huge cloud of gas and dust 4.5 billion years ago.
The $260m Genesis mission was launched in August 2001. The main spacecraft travelled to a location 1.5 million km (1 million miles) from Earth where, for more than 800 days, it hung delicate collecting wafers in the stream of particles blowing off the surface of the Sun.
The collectors were then stored inside a sample-return capsule which was jettisoned into the Earth's atmosphere as the main Genesis spacecraft flew past the Earth.
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