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NASA scientists said they might have identified the first specks of interstellar dust in materials collected by the agency's Stardust spacecraft.

The interstellar dust is comprised of tiny particles that take part in making stars and planets. The Stardust spacecraft's primary job was to catch dust streaming from Comet Wild 2 and return it to Earth for analysis. However, scientists also hoped to collect particles of interstellar dust.

The material was collected in a 2.9 billion mile journey during the Stardust probe's seven-year mission. The spacecraft used a retractable device containing cells filled with a material called aerogel, a porous substance that is designed to trap dust molecules. The capsule that contained the samples landed back on Earth in January 2006.

Team members now say that there might be two contemporary interstellar dust grains in the Stardust Interstellar Dust Collector (SIDC) deployed during the mission.

Dr. Andrew Westphal of the University of California announced the discovery at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas.

"There are two particles, but they are in the same track. So when they hit the aerogel, they were together - they are two components of the same particle," Westphal told BBC News. "But they are very different from each other. That in itself is interesting, because if this does turn out to be interstellar dust, then it is a bit more heterogeneous than people thought."

Bruce Hudson found the first speck. After discovering he named the particle "Orion."A group of scientists later discovered another grain, which Hudson donned "Sirius."

However, Westphal said that the find "could be a false alarm."

"The right way to say it is we're cautiously excited," he said. "We have very limited data on it so far and the reason is deliberate. The analyses we are doing have the potential to do some minor damage to the particles. We don't think it will and we'll be careful to limit our analyses."

"So far this particle is unique... if we drop it on the floor, it will cost $300m to get another one."

Scientists said they have found 28 definite impact "tracks" in the interstellar dust collector. However, most of these are from angles that show little particles of debris from impacts with Stardust's solar panels.

Interstellar dust is formed by gas ejecting from stars and then condensing to form grains. The grains were gathered as Stardust traveled throughout the interstellar dust stream, which passes through our Solar System.

Dr. Don Brownlee, the spacecraft's chief scientists, told BBC News, "All the heavy atoms in this room were in interstellar dust...so we want to know what this stuff is." He added: "This dust, once it's formed, and once it's heated or changed [initially] it is set for billions of years.

Westphal told BBC News: "It is very fine-grained material, which is what you'd expect for interstellar dust. It has an elemental composition which is consistent with what you would expect for interstellar dust. And it has a composition for other elements which are not inconsistent, but a bit surprising."

So far, the researchers have analyzed magnesium, aluminum, iron, chromium, manganese, nickel, copper and gallium from the particles.

Interstellar dust can be a nuisance in optical astronomy because it can obscure objects in regions of the sky targeted for observation.