Herschel Finds Olivine Crystals In Nearby Beta Pictoris
April Flowers for redOrbit.com – Your Universe Online
Beta Pictoris is 12 million years old, and resides a short 63 light-years from Earth. A gas giant planet and a dusty debris disc that has the potential to evolve into a torus of icy bodies like those of the Kuiper Belt found outside the orbit of Neptune are hosted by Beta Pictoris.
The composition of the dust on the outskirts of the Beta Pictoris system has been determined for the first time, thanks to the unique abilities of the Herschel observatory. Of particular interest to the ESA scientists is the mineral olivine. Olivine crystallizes out of the protoplanetary disc material close to newborn stars. It is eventually incorporated into asteroids, comets and planets.
“As far as olivine is concerned, it comes in different ‘flavors’,” explains Ben de Vries from KU Leuven.
“A magnesium-rich variety is found in small and primitive icy bodies like comets, whereas iron-rich olivine is typically found in large asteroids that have undergone more heating, or ‘processing’.”
The Herschel space observatory detected the pristine magnesium-rich variety in the Beta Pictoris system at 15 – 45 astronomical units (AUs) from the star, where temperatures are around -190 C.
To put that distance into perspective, the Earth is only 1 AU from the Sun, and the Kuiper Belt extends from the orbit of Neptune at about 30 to 50 AU from the Sun.
The study, published in Nature, found that the olivine crystals make up around 4% of the total mass of the dust found in this region of space. This led the team to conclude that the olivine was originally bound up inside comets and released into space by collisions between the comets.
“The 4% value is strikingly similar to that of Solar System comets 17P/Holmes and 73P/Schwassmann-Wachmann 3, which contain 2–10% magnesium-rich olivine,” says Dr de Vries.
“Since olivine can only crystallize within about 10 AU of the central star, finding it in a cold debris disc means that it must have been transported from the inner region of the system to the outskirts.”
Models of the evolution of swirling protoplanetary discs as they condense around new stars have shown the “radical mixing” transport mechanism previously. The mixing is stimulated by winds and heat from the central star of a system pushing materials away, along with temperature differences and the turbulent motion created in the disc during planet formation.
“Our findings are an indication that the efficiency of these transport processes must have been similar between the young Solar System and within the Beta Pictoris system, and that these processes are likely independent of the detailed properties of the system,” says Dr de Vries.
Beta Pictoris is over 1.5 times the mass of our Sun and eight times as bright. Its planetary system architecture is different from our Solar System.
“Thanks to Herschel, we were able to measure the properties of pristine material left over from the initial planet-building process in another solar system with a precision that is comparable to what we could achieve in the laboratory if we had the material here on Earth,” says ESA’s Herschel project scientist Göran Pilbratt.