Crystal formation in comets

Scientists have long wondered how small silicate crystals, which need very high temperatures to form, are present in cold comets that are born on the outer edge of the solar system. These crystals may initially be non-crystalline silicate particles, part of a mixture of gas and dust that forms the solar system.

A team of astronomers believed that they discovered a new explanation for where and how these crystals were created, using NASA's Spitzer Space Telescope to view Watch young stars like the sun. Their research, published in the May 14 issue of Nature, provides new insights into the formation of planets and comets.

Researchers from Germany, Hungary and the Netherlands found that silicates can be transformed into crystals from a star's explosion. They detected infrared signals of silicate crystals on gas disks and dust around the EX Lupi star in a conventional explosion observed by Spitzer in April 2008. These crystals were not excellent in previous observations. Spitzer's for the star's disk in the 'silent' period.

Attila Juhasz, one of the authors of the paper at the Academy of Astronomy Max-Planck, Heidelberg, Germany, said: 'We believe that we have for the first time observed the process of crystalline formation. The crystals are formed by heating the small particles on the surface layer of the inner disk of the star with heat from the explosion. This is a whole new case of how this material was created '.

Heat treatment is the process by which the material is heated to a certain temperature, but some connections break and re-form to change the physical properties of the material. It is also the way that silicate dust transforms into crystal form.

Scientists have previously considered two hypotheses that heat treatment can produce silicate crystals in young stars and comets. In the first case, long exposure to heat from a newly formed star can heat up some of the silicate dust inside the disc. In the second case, shock waves can suddenly heat silicate dust inside the disc to the temperature of crystalline formation, then the crystal cools quickly. The findings of Juhasz and colleagues did not match both of the above theories. The main author of the paper, Peter Abraham of the Konkoly Observatory of the Hungarian Academy of Sciences, Budapest, Hungary, said: 'We concluded arguing that this is the third way that silicate crystals can be formed '.

The image shows a star like the sun surrounded by gas and dust disks. Silicate, the main component of dust, may start in an unspecified non-crystalline form. (Photo: NASA / JPL-Caltech)

EX Lupi is a young star, probably similar to our sun 4 or 5 billion years ago. Every few years, the star experiences an explosion that astronomers think is the result of mass accumulation in the surrounding disks.These bursts have varying strengths and weaknesses, and the really big boom happens about every 50 years.
The researchers observed EX Lupi with Spitzer's infrared spectrometer in April 2008. Although the star is starting to fade away from the big boom discovered in January, it is still bright. 30 times more normal. When comparing this new observation Spitzer measurements taken in 2005 before the explosion began, many significant changes were observed.

In 2005, silicates on the surface of stellar disks in the form of crystalline dust. In 2008, spectroscopy showed the appearance of silicate crystals above the irregular shaped dust. These crystals are forsterite, materials commonly found in comets and planetary plates. They are also very hot, evidence that they were created during high temperatures, not by shock waves. If heated in that way, the crystals must have cooled to this point. Juhasz said: 'When it explodes, EX Lupi is 100 times brighter. The crystal forms at the surface of the disc, but only at a distance to the star where the temperature is high enough to heat silicate - about 1000 Kelvin (1 340 degrees F) - but still below 1 500 Kelvin (2 240 degrees F) '.

Michael Werner of NASA's Jet Laboratory, Pasadena, Calif, said: 'These observations for the first time show the formation of silicate crystals discovered in comets and meteors in the solar system of we. Therefore, what we observe in comets today can be generated from energy bursts when the sun is young. '

JPL manages the Spitzer space telescope for NASA's Science Board, Washington. Scientific activities are carried out at Spitzer Science Center, California, Pasadena Institute of Technology.