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.
|Europa as imaged by NASA's Galileo spacecraft in the 1990s. Credit: NASA|
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. 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 have flown on two missions, the Russian Mars 96 spacecraft that failed to leave Earth orbit and the two failed DeepSpace 2 Mars penetrators that were never heard from after their release from their mothercraft.)
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.)
You can read more about possible small lander designs in this blog post, this Science News article, or from this presentation.
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.
Note: My thanks to RL for informing that the Mars 96 mission also carried penetrators; the text has been corrected. However, there has been no successful use of penetrators on any planetary mission to date.