terça-feira, 17 de abril de 2012
Solar system mystery 'solved'
Planetary scientists claim they may have discovered how "chondrules", tiny particles found in meteorites, formed at the beginning of the solar system, thus solving the decades-old cosmic conundrum.
Chondrules are spherical particles of molten material found in meteorites but their origins have long been a mystery. No longer than about one millimetre in diameter, they melted at temperatures of more than 1,000 degrees Celsius, while the cooler materials surrounding them only experienced temperatures of a few hundred degrees Celsius.
Now, an international team, led by Australian National University, has cracked the mystery as to how "chondrules" could have actually formed in extreme heat, especially when the meteorite structure surrounding them remained cold.
"Most of the solar system is cold, so it's been unclear for decades what caused the chondrules to experience such extreme heat. We believe that chondrules formed in jets of material ejected from flattened discs, called 'protostellar discs', which encircle young stars.
"These discs are somewhat like the rings around the planet Saturn. The modern planets are the remnants of material of these discs clumping together. In observations of the formation of new stars, we can see jets of material accelerating out of protostellar discs.
"We show that as these jets shoot out of the discs, from about the Earth-Sun distance away, the materials brought with them are heated to the point of melting. The heavier items in them then drop back into the discs, where they cool and re- form," Raquel Salmeron, who led the team, said.
The scientists said that their theory challenged old assumptions about the formation of chondrules.
"For decades it has been assumed that jets could only form chondrules through the heating of materials in the vicinity of the Sun, followed by their transportation into protostellar discs," Salmeron said in a varsity release.
"We believe that our new theory explains how chondrules -- among the earliest materials in the solar system -- reached the temperatures required for melting, even though the early solar nebula was cold. It also explains the fairly uniform size of chondrules and provides a means for them to mix and combine with unheated material," Salmeron added.
Publicado por Jorge M. Gonçalves às 6:10 da tarde