Summary: DEEP SUB­SURFACE EXPLORATION OF COMETARY NUCLEI
M. J. S. Belton 1 and M. F. A'Hearn 2
1 National Optical Astronomy Observatories, 950 N. Cherry Ave, Tucson, AZ 84719, USA
2 Department of Astronomy, University of Maryland, College Park, MA 20742, USA
ABSTRACT
The surface regions of cometary nuclei are expected to be extensively modified by cosmic radiation and solar
insolation. Induced state changes and associated sublimation and phase­change boundaries are expected to
propagate deep into the interior. In the current exploration program a reconnaissance of the highly evolved upper
meter of the cometary surface is comprehensively covered. However, the relationship of evolved surface materials
to the pristine (i.e., unchanged since emplacement in the comet) materials that may exist at greater depths remains
to be explored. Except for the possibility of remote sensing by radar and microwave tomography, the problem of
sampling the properties of deep (1--100 m) sub­surface materials has received little attention. We consider a
concept for the scientific exploration of these deep sub­surface regions by means of excavation by hypervelocity
impact. A massive (approximately 500 kg) impactor is delivered at hypersonic speeds to a comet nucleus to
excavate a crater several tens of meters deep and over 100 m in diameter. We give two examples of such
missions: one to a suspected dormant comet, 3200 Phaethon, and one to a currently active comet, 9P/Tempel 1.
We show how a reconnaissance of the newly excavated crater structure from the flyby delivery spacecraft or an
associated lander can yield new information about the physical and compositional structure of the deep sub­
surface layers and about any lateral inhomogeneities that could be associated with the primordial cometesimal
structure of the nucleus.

Source: A'Hearn, Michael F. - Department of Astronomy, University of Maryland at College Park

Collections: Physics