Planetary Penetrators
Europa, Titan and Enceladus

ESA Cosmic Vision Proposals

Here is an overview of two mission concepts that were submitted by the UK Penetrator Consortium under the ESA Cosmic Vision program.

La Place Mission to Europa

On Jupiter's Moon of Europa, it is thought that there exists an ocean of liquid water beneath a crust of ice. Although estimates on the thickness of the ice vary from <1km to >30km, this would have profound consequences from an exobiological point of view, since if there is a warm ocean, protected from the radiation environment of Jupiter's Magnetosphere by the ice crust, it is not impossible that life may currently exist on Europa. Although radar mapping may some-day confirm the presence of sub-surface oceans, the only way to investigate the possibility of life is to land on the surface and make in-situ measurements.

A conventional soft Lander propelled by chemical rockets is on the very limits of technical feasibility. Any attempted mission would have to overcome two major obstacles. First is the substantial change in velocity required (4.3km/s) from interplanetary flight to a soft landing on the surface. This is further exacerbated by the second problem of the harsh radiation environment at Europa (7.5Mrad behind 40mm of Aluminium), requiring heavy radiation shielding. A micro-penetrator mission would be ideal, as the ice between the Penetrator and the surface reduce the amount of radiation shielding required.


Proposed Surface Science for a Europa Penetrator

The proposed instrumentation package for a Europa Penetrator includes

  • Beeping Transmitter
  • Accelerometer
  • Micro-Seismometers/tilt-meter
  • Chemical Sensor
  • Micro-camera
  • Radiation monitor

The Doppler-shift from a simple beeping transmitter would allow Earth-based very long base line determination of surface ice movement, deformation, and seismic vibrations. Data from an accelerometer during impact with the surface would allow a rough determination of the characteristics of the ice and the penetration depth. The seismometer would be used to detect seismic activity from either natural sources or meteoroid impact, and also determine the presence and size of an under-ice ocean. The chemical sensor package would look for the presence, extent and concentration of organic molecules, including possible indicators for life. The later could be achieved either through a detection of a uniform chirality of the molecules, or through a deviation from standard isotopic abundances. Another method would be the employment of an impact-hardened sub-surface camera to detect biological molecules that fluoresce under a small UV light source. Other experiments include a camera to characterise the landing site, and an instrument to measure the radiation environment on the surface of Europa.

"Tandem" Mission to Titan and Enceladus

One of the major discoveries of the Cassini mission to Saturn was that of a geologically active province at the south pole of Saturn's moon Enceladus. Geysers of water erupt out into space, possibly from sub-surface reservoirs of liquid water, supplying Saturn's E-ring with ice particles. ESA's Huygens Titan Lander discovered a world much like a primitive earth, whilst the Orbiter has discovered rich organic chemistry in the upper atmosphere, making return to the Saturnian moon a high priority.

Mission Architecture

The Tandem mission has been proposed under ESA's Cosmic Visions program to investigate both Titan and Enceladus. Its nominal architecture includes an orbiter and a carrier vehicle that would carry a Titan aerorover (balloon) and up to three Titan surface probes. Initially, the orbiter would be placed into a Titan – Enceladus cycling orbit for Penetrator release and surface science. At the conclusion of this phase of the mission, the orbiter is manoeuvred into orbit around Titan, and the carrier is released. Titan surface penetrators would be passively stabilized by fins.

Scientific Objectives

On both the worlds of Titan and Enceladus, seismological operations would characterise the interior (including the search for sub-surface oceans) and provide measurement of seismic / cryo-volcanical activity. The chemical sensor package would examine both the sub-surface geology and search for organic molecules of astrobiological importance.

On Enceladus, a potential target would be the “tiger stripes” observed from Cassini imagery. These are known to be hotter than the surrounding surface and are the sources of sub-surface out gassing. Penetrators would provide in-situ compositional information and study possible heat sources. On Titan, a three penetrator mission would allow for in-situ chemical analysis of a variety of terrain and surface features. These include icy surfaces, dunes, lake beds and mountains. A seismic network would investigate cryo-volcanic and tidal activity and probe the structure of Titan's Interior.

See the website of the penetrator consortium.