NASA's Mission to Europa May Get More Interesting Still
SpaceFlightNow.com has published an article reporting that NASA officials have asked their European counterparts if they would like to propose contributing a small probe to NASA's Europa mission planned for the mid-2020s.
If the Europeans are interested, the probe could carry out any of several possible missions. Two mentioned in the article would be a small lander or a craft that could fly through and study any plumes found erupting from the moon's surface.
NASA / JPL-Caltech
Europa as imaged by NASA's Galileo spacecraft in the 1990s
Another possibility, not discussed by the article, might be a small spacecraft that could repeatedly flyby the moon to make magnetic field and gravity measurements. Both studies are key to understanding the size of this moon's ocean and the structure of its rocky core. The main Europa Clipper flyby craft will make these measurements during each of its flybys. Both studies, however, improve with the number of passes by the moon, so a second craft would add substantially to these measurements. I'm told that one or more of the CubeSat studies NASA is separately funding as possible augments to the mission would do this.
British scientists and engineers have studied small penetrator landers that would be shaped roughly like a cannon shell that would use the force of impact to dive a meter or two into the icy surface. Penetrators have been used on the Earth to deploy probes from planes and have been proposed several times for planetary missions. (The failed DeepSpace 2 Mars penetrators were the only two ever flown so far as I know.) Penetrators avoid many of the complications involved in a soft landing. The penetrator would need an avionics module to keep its orientation and likely would need a retro rocket to reduce the approach speed, both of which add considerable complexity to the design.
Penetrators would not be the only possible small lander design. All approaches, though, would involve small probe that would carry one to a few small instruments such as a seismometer/geophone and one or more chemistry experiments. Even simple measurements could provide information that would complement the measurements made by the main spacecraft. (As a side note, the same would be true of a small lander for Ganymede added to Europe's JUICE mission that will orbit this moon of Jupiter in the early 2030's. I don't know if that design would still be open to adding a small lander that might be a near duplicate of one carried on NASA's Europa craft.)
If the European Space Agency's managers decide they might like to participate, then European scientists could propose specific probe plans as part of a future Medium Class mission competition, where it would compete against other planetary and astrophysics proposals.