Melting probes at Lake Vostok and Europa

Signatures indicative of a subglacial ocean on the Jovian satellite Europa have been discovered by the Galileo spaceprobe. The structure and chemistry of this postulated ocean, have received considerable attention, and its exploration is seen as an important goal for the fields of comparative planetology and astrobiology. Terrestrial subglacial lakes (e.g., Lake Vostok) have been considered as analogues for several aspects of a Europan ocean and the means of exploring such an environment will be discussed. We review the concept of melting probes, i.e. small probes with a heated tip ("hot point"), that melt through the ice. Such devices can carry instruments for in-situ measurements, or act as sample-return probes by the new concept of melting "upwards" once the sampling in the liquid ocean has been performed. Experience with melting probes in Antarctica exists; a demonstration mission to, e.g., Lake Vostok is proposed, and a possible design for a mission to Europa is outlined. Although, for a Europan mission, a probe capable of in-situ analysis might differ substantially from the terrestrial 'sample-return' version.