Herschel Discovers Cometary Crystals around Beta Pictoris
We all know about comets in our own solar system. They’re conglomerates of ices mixed with dust and rock. As they get close to the Sun their gases sublimate, the dust is freed and that action creates dust and plasma tails streaming out behind the comet. Astronomers see comets as repositories of information (in the form of those ices and dust particles) about conditions in the early solar system, since those materials have survived until this time. In particular, comets often contain materials that formed close to the Sun in the early history of the solar system, but then were somehow transported out to colder regions where comets seem to thrive.
So, it’s rather cool that astronomers have now found cometary particles in another solar system, the young star Beta Pictoris. The European Space Agency’s Herschel space telescope detected pristine materials in the dust disk surrounding this star. Those materials match the makeup of comets in our own solar system.
Beta Pictoris hosts a gas giant planet, in addition to a dusty debris disk that will likely spawn the formation of some icy bodies similar to the worldlets that astronomers are finding in our own Kuiper Belt.
So, what’s the material made of that Herschel found? First, the mineral olivine is present in the disk around Beta Pic. Olivine forms in protoplanetary disk material close to newly formed stars. In our solar system we find it in asteroids and comets, and of course it’s found on Earth, too.
The data collected by the Herschel telescope allowed astronomers to calculate that the olivine crystals in the Beta Pic disk make up about 4% of the total mass of the dust found in a region that lies between 15 to 45 astronomical units from the star. In our solar system, that extends from well beyond the orbit of Saturn out beyond the inner limit of the Kuiper Belt. The 4% number is quite similar to such solar system comets as 17P/Holmes and 73P Schwassmann-Wachmann 3.
Astronomers concluded that the olivine was originally bound up inside comets and released into space by collisions between the icy objects. And, since since olivine can only crystallize at a distance of not more than 10 astronomical units 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 out to colder areas. A process called “radial mixing” could help push materials out away from the central star, and that could explain how the olivine crystals made it to the deep freeze of the Beta Pic system. Want to read more about this find? Check out ESA’s Herschel Web page for the full story.
Get Your Stargazing On for October!
This month’s edition of “Our Night Sky”, the star gazing video I produce for AstroCast.tv is now up for your viewing pleasure! Check it out!