Sunday, October 18, 2009

Impactor plume photographed!

Shaun Saunder sends in an article from Newscientist that show the first image, taken by the trailing spacecraft, of lunar material kicked up by the impact of NASA's LCROSS mission.

Initially it was hoped that the impactor would kick up a plum that could be seen by telescopes on Earth. No plume was visible to Earth based scopes or even Hubble. Ejecta from the impact would have had to rise better than a half mile above the surface for it to be visible but most of the material stayed well below that altitude. Luckily the LCROSS craft was flying right behind the imactor stage. As such the ejecta had only to rise half as high.

Of course there was some bad communication as well. From the article:
  • ...mission members said they expected the plume to reach no higher than about 10 km. But projectile experiments carried out on Earth weeks before the impact suggested the plume might reach far lower altitudes.
What possibly may not have been taken into account initially was that the impactor was hollow giving it a very of very low density. Therefor far less energy than expected was transfered to the site. A large portion of that energy was transferred back into the impactor , crumpling it. (as the article puts it, much like the crumple zones in today's cars)

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