Itokawa’s Muses Sea (the smooth area near the center), where
HAYABUSA collected its sample Optical microscope photo of
Itokawa dust particles supported by 5-µm-diameter carbon fibers
(courtesy: Osaka University/JAXA) For me, it’s the amazing
amount of information such tiny samples hold about the heating
history of the asteroid. The first analysis shows that the
sample of Itokawa heated to 800 degrees Celsius. The asteroid
formed from smaller objects; each of these impacts made the
asteroid larger and larger and caused heat to accumulate inside
the asteroid, changing kinetic energy to thermal energy. So as
the asteroid was growing, it was heating up. And the minerals in
the samples returned by HAYABUSA record every stage of this
heating process, and also the cooling, down to the present
temperature today. All those steps are recorded in different
minerals. And by careful analysis of these tiny mineral grains
in the HAYABUSA samples, you can map out the heating history and
then the cooling history of the astero