= Dawn spacecraft
{c}
The <Dawn spacecraft> was an orbital mission to <Vesta> and <Ceres>, two bodies in the main <asteroid belt>. Studying both with one instrument suite made their contrasting surfaces and internal evolution directly comparable. Its <ion propulsion> accelerated <Xenon> ions to provide a small thrust over long intervals, enabling prolonged orbital observations at two separate destinations.<Dawn by NASA>[Mission overview, targets and ion-propulsion description]{ref}
Its framing camera mapped landforms and surface textures; its visible/infrared spectrometer measured spectral features associated with surface minerals; and its gamma-ray and neutron detector constrained near-surface elemental composition. Radio tracking additionally constrained gravity through the spacecraft's orbital response.<Dawn by NASA>[Science Payload, instrument roles and radio tracking]{ref}
These instruments answer different questions. A bright patch in an image measures reflected light under a particular illumination geometry, not a unique composition. Combining spectral absorption features with imaging and nuclear-radiation measurements helps distinguish a compositional explanation from a change in grain size or viewing angle. The mission thus illustrates how complementary measurements make a geological inference more informative than a detailed photograph alone.
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