Figure 8-24 Comet Wild 2 (a) This picture shows two images combined. One is a high-resolution photograph showing the surprisingly heavily cratered comet. The other image is a longer photograph showing gas and dust jetting from the comet. Its tails are millions of kilometers long. (b) A substance called aerogel was used to capture particles from Comet Wild 2’s dust tail. A piece of space debris pierced the aluminum foil holding the aerogel and embedded in it, along with pieces of the foil. (c) A 2-μm piece of comet dust, composed of a mineral called forsterite. On Earth this mineral is used to make gems called peridot.