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Crystals rain
onto forming star

Posted: 27 May 2011

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NASA's Spitzer Space Telescope has found evidence for tiny green crystals of olivine raining down onto a forming star from the clouds of dust and gas swirling around it.

The observations of proto-star HOPS-68, which resides in the constellation of Orion, are the first time that these crystals have been seen in the cold outer reaches of a star's accretion disc, and are a surprising find since temperatures as hot as lava – some 700 degrees Celsius – are required to form them.

Artist's impression of the olivine crystals being transported from the hot forming star by jets to the cool outer proto-planetary disc (top), where the crystals then rain back down on the swirling planet-forming disc (bottom). Image: NASA/JPL-Caltech/University of Toledo.

The scientists deciphering the findings speculate that jets blasting out from the proto-star are transporting the crystals from the fiery furnace of the forming star to the cold, -170 degrees Celsius reaches of the outer disc where they have been seen falling back down towards the star.

“We propose that the crystals were cooked up near the surface of the forming star, then carried up into the surrounding cloud where temperatures are much colder, and ultimately fell down again like glitter,” says Tom Megeath of the University of Toledo and principal investigator of the research.

The crystals are in the form of forsterite, which is very common on Earth, and have been reported before in planet-forming discs around young stars, although not at such distances from the newborn star as seen at HOPS-68. The same breed of crystal has also been seen close-up on comets, and the new theory has implications for how they became incorporated into such frigid objects.

One popular theory says that these materials were mixed together in the early planet-forming disc, with those forming near the Sun eventually migrating outwards to the cold reaches of the Solar System. The new suggestion is that jets from the young proto-Sun could have blasted the crystals into the outer regions of our Solar System to later make up the building-blocks of comets.