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Rock stars

Scientists around the world are waiting for a Halloween goodie bag from NASA and — unlike Charlie Brown, who would lament that he got a “rock” — these recipients could not possibly be more excited as they anticipate the arrival of their rocks.

NASA’s rocks are from outer space, collected by the wildly successful Stardust mission, launched seven years ago to gather comet debris. Stardust landed in January in a Utah desert. The capsule visited Comet Wild 2, a relatively recent arrival in the region of our solar system between Mars and Jupiter. In passing near this comet, Stardust’s “aerogel” collectors swept up material being ejected from the comet and brought it back to Earth. It is the most adventurous treasure hunt our species has ever conducted — a 2.9 billion-mile odyssey to gather a most impressive treasure.

Wild 2 is interesting because until recently it lived in the Kuiper Belt, a vast assemblage of comets orbiting way beyond Pluto, so far from our sun that almost no heat reaches them. In the icy recesses of the Kuiper Belt comets do little more than drift lazily about the sun — no long tails stream behind them, carrying away their surface material, erasing the telltale clues to their origins. Astronomers believe that Kuiper Belt comets are perfectly preserved fossils from the early days of our solar system — silent, unreachable eyewitnesses to the birth of our cosmic home.

Because the Kuiper Belt is so far away, visiting it is out of the question. But Comet Wild 2 got pulled by Jupiter’s gravity into a much closer orbit, essentially inviting us to meet it halfway, which NASA was only too willing to do. And, because Wild 2 had only been in our neighborhood for a short time, the increased heat from the sun had not had time to melt or otherwise disturb its primordial surface.

The rocks embedded in Stardust’s aerogel may have a truly interesting story to tell — our story — of how our solar system came to be. How did our planet get so rich in chemicals, from carbon to uranium, when these are astonishingly rare in our universe, making up a tiny fraction of its matter? Where did the building blocks of life on Earth come from? What kind of star exploded in this part of the Milky Way billions of years ago, creating the disc of interstellar material out of which our solar system formed? Why is there so much life-sustaining water on the Earth?

Missions like Stardust generally return little more than information for the billions of dollars it costs to run them. And those billions come from U.S. taxpayers. But surely they are worth every penny if they help us create the rich story of our origins.

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