More Surprises from Stardust

NASA’s Stardust probe continues to bring new knowledge about the nature of comets, nearly four years after it landed in western Utah following an epic space journey of almost 2.9 billion miles. In the far reaches of the solar system, the probe had gathered gas and dust blowing off comet Wild 2.

[Time exposure I took early morning of Jan. 15, 2006, showing the trail of Stardust sample package as it streaked over the old Wendover Air Base. Shortly afterward it landed intact on Dugway Proving Ground. In the photo, some stars look like little parachutes and part of the probe’s trail is jiggly because I moved the camera. The glaring object is a light on the tower.]

Who would have thought bits of a comet might taste sweet? Who would have believed that Stardust’s samples, which were supposed to be unaltered since the formation of the solar system, are less primitive than comet dust collected in Earth’s upper atmosphere?

A Sweet Comet

Since Stardust’s spectacular landing in Dugway Proving Ground on Jan. 15, 2006, scientists have been analyzing grains of material that were captured by the probe. An unusual finding is that dust from Wild 2 (pronounced Vilt 2) contains glycine, “a fundamental building block of life,” the space agency announced in August.

Glycine is a sweet-tasting amino acid; the body uses amino acids to manufacture proteins, which are essential for our type of life. Earlier, radio telescope astronomers discovered naturally-forming glycine in interstellar space, but this is the first time it has been detected in a comet.

James Elsila of the Goddard Space Flight Center, Greenbelt, Md., is quoted in a NASA press release as saying, “Our discovery supports the theory that some of life’s ingredients formed in space and were delivered to Earth long ago by meteorite and comet impacts.”

“The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare,” added Carl Pilcher, director of NASA’s Astrobiology Institute.

Not So Primitive

Stardust samples were expected to be primitive, unaltered material left over from the formation of the solar system 4.5 billion years ago and locked in the freezer of deep space. However, more of the dust was altered than scientists had anticipated.

On Monday, the Carnegie Institution for Science announced results of a study launched in 2003, using aircraft to collect comet dust in the upper atmosphere. High-altitude NASA planes scooped up dust shed by comet 26P/Grigg-Skjellerup when it passed near Earth that year.

The study found the material was less altered, more primitive, than the Stardust samples.

“The stratospheric dust includes minute grains that likely formed inside stars that lived and died long before the birth of our sun, as well as material from molecular clouds in interstellar space,” says a release by the institution, based in Washington, D.C. The grains are termed “ulta-primitive” dust particles.

They were shown to be that ancient because of their “extremely unusual isotopic compositions compared to anything else in the solar system,” the release adds.

Larry Nittler of the Carnegie Institution, a coauthor of the study, said the only other cometary material examined in labs are the Stardust samples. “Our samples seem to be much more primitive, much less processed, than the samples from Wild 2,” he said, “which might indicate that there is a huge diversity in the degree of processing of materials in different comets.”

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