PRE2019 1 Group2

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- Group -

  • Kasper Dols - 0953689
  • Marco Luijten - 1008931
  • Wouter Meekes - 1011988

Main tutor: Tijn Borghuis


Mission to Europa

Introduction

Europa is a very interesting, mysterious moon of Jupiter, discovered by Galileo Galilei in the year 1610. The moon raised a lot of interest in the past couple of decades, because there are some indications of liquid water on the moon. Since water is at the top of the list of ingredients that make life possible, the speculations for extraterrestrial life on Europa began to rise. Water dissolves nutrients for organisms to eat, transports important chemicals within living cells and allow those cells to get rid of waste. [1] But due to the circumstances at Europa, the water is believed to be hidden underneath a thick coat of ice. This coat is estimated to be 10 kilometers around the whole moon, with a deviation of 160. [2] Calculations will be performed using this 10 km; the 160 m deviation will be considered negligible with respect to 10 km.

Presence of liquid water on the surface

But can there be water present in liquid form somewhere at the surface of Europa? Probably not. One of the reasons to assume this, is based on the phase diagram of water, shown to the right. As can be seen in the image, the lowest pressure at which water can still exist in liquid form is its triple point at 611.73 Pa (0.0061 atm), at the usual temperature of 273.15 K (0 °C). Below that pressure, water has no liquid form. Since the pressure at Europa’s surface is about 10-10 atm, this means that liquid water can not stably exist on the surface of Europa. Some water may come to surface for a brief moment, but will almost instantaneously either freeze or boil, leaving no water remaining. It should be noted that indeed this diagram does not extend below 10-5 atm, and that based on this image it is thus technically not possible to say that water does not have a liquid form at such ultra-low pressures. However, it is first of all unlikely that such an out-of-place phase change exists based on this and other phase diagrams. Secondly, this ‘liquid’ may not be liquid as we know it and still be unable to support life. Much like solid water has different crystalline structures at different temperatures and pressures, so can this liquid water have very different properties based on the environment it is in. Hence based purely on physical grounds it is unlikely that liquid water in a familiar form exists on the surface of Europa. [3]

Presence of a sub-surface ocean

Why do researchers believe there is an sub-surface ocean? The first theories that the planet has a sub-surface ocean came after the fly-by mission of Voyager 1. This spacecraft was, in march 1979, the first spacecraft that made images in significant detail of Europa’s surface, with a resolution of about 2 kilometers per pixel. These images revealed a surprisingly smooth surface, brighter than that of earth’s moon, crisscrossed with numerous bands and ridges. Researchers noted that some of the dark bands had opposite sides that matched extremely well, comparable to pieces of a jigsaw puzzle. These cracks had separated, and dark, icy material appeared to have flowed into the opened gaps, suggesting that the surface had been active at some time in the past. The images also showed only a handful of big craters, which are expected to build up over billions of years as the planetary surface is bombarded by meteorites, until the surface is covered in craters. Thus, a lack of much craters suggested that Europa’s surface was relatively young and implied that something erased the craters, such as icy, volcanic flows. Next to that, scientists found patterns of some of the longest linear features in the images that did not match the predicted patterns of the features, created by tides as Europa orbits Jupiter. They determined that the found patterns would fit very well if Europa’s surface could move independently and was not locked to the rest of the interior. These interesting findings led to the next mission to Europa, Galileo. This spacecraft was launched in 1989 and entered orbit around Jupiter in 1995. Galileo eventually made 12 close flybys of the icy moon, including images of Europa at a range of scales, revealing new details about the surface and providing context for how those details were related to the moon as a whole. One important measurement made by the Galileo mission showed how Jupiter’s magnetic field was disrupted in the space around Europa, implying that a special type of magnetic field is being created within Europa by a deep layer of some electrically conductive fluid beneath the surface. Scientists believe, based on Europa’s icy composition, that the most likely material to create this magnetic signature is a global ocean of salty water. Above described are four strong indications of a sub-surface ocean on Europa, which is why the common belief under scientists is that the ocean really exists. [4]

Indications for life

The three basic requirements for life to be present are liquid water, chemical building blocks and a source of energy. The first requirement is explained in previous paragraph. The second requirement, the chemical building blocks, are also believed to be partly present. The ice and other materials on Europa’s surface are bombarded with radiation from Jupiter, that could alter them into some of the chemical building blocks of life, like oxygen (O2), hydrogen peroxide (H2O2), carbon dioxide (CO2) and sulfur dioxide (SO2). If these compounds reach the sub-surface ocean, they can be valuable nutrients to start and sustain life. Besides, the ocean water can react with the rocks and minerals of the subsurface ocean’s floor to liberate other nutrients to support life. The third requirement is a source of energy. Europa’s position in space is within the powerful gravitational field of Jupiter, causing the moon into an orbit with one hemisphere constantly facing Jupiter. This elliptical orbit takes Europa alternatingly closer to and further away from Jupiter. This constant increase and decrease of gravitational force on Europa results in elongating and relaxing of the moon with each trip around the planet. This internal movement, combined with gravitational forces caused by neighboring moons, produces internal friction and heat within Europa. This internal heat could be the energy source that keeps the subsurface ocean from freezing and sustains any life that exists there. Next to that, there could be hot water vents on the floor of the subsurface ocean that deliver energy and nutrients from the planet’s interior. On earth, organisms have been discovered in the subglacial lakes of Antarctica and in hot ion-rich waters of hydrothermal vents. Life in Europa’s sub-surface ocean could be supported in a similar way. [5] These indications for life in Europa’s ocean have led to a future mission of NASA to the moon. They planned to launch the Europa Clipper mission in 2025. The spacecraft will conduct an in-depth exploration of Europa, investigating whether the moon could harbor conditions suitable for life. [6]

The goal

The above described mission of NASA is of course very interesting, but with the strong indications for life as described above, the interest rises to search for life on the spot. Since the presence of liquid water at Europa’s surface is unlikely as explained, the goal of this project is as follows:

“Investigate whether it is possible to land on Europa, dig through the icy layer and send a submarine into the sub-surface ocean, to search for life, signs of life, or conditions that may support life in or on Europa.”

Users

The question who is helped by going to Europa starts by asking why anyone would want to go to Europa in the first place. Ultimately, the humanity wants to learn stuff. In particular, the search for life outside earth. This can teach the humanity about the origin of life, and help to answer the age-old question: “Is there other life in this universe?” The reason to go to Europa and not just any other satellite in the solar system (possibly much closer) is that Europa is very likely to contain liquid water, which is one of the prerequisites for biological life, like explained in the introduction. The first most obvious question to ask then: “Is there (the possibility of) life on Europa?” This is what the mission first and foremost should answer. Furthermore, knowledge about Europa can help to learn about other exoplanets. By comparing our long-distance observations of Europa to the on-site observations, long-distance observations of exoplanets can be translated to planetary conditions. This may allow a more accurate prediction whether an exoplanet may be habitable. Lastly, a mission to put a lander on a planetoid like Europa has never been undertaken, and hence going to Europa will be a proof of concept showing that it is possible to go such a hostile environment. This is convenient information for a possible similar mission to, for instance, Pluto or an exoplanet. In the end, it is unknown what will be found on Europa. Maybe it contains about as much life as the centre of the sun, maybe it will show that life would be possible but never sprung up, or perhaps it turns out that it is home of the Atlanteans, who sunk their city on earth when they found earth with its dense atmosphere and high temperatures would not make for a habitable colony. Either way, it is also important to take into account the lives that might be encountered on Europa. It would be a pity to find all new types of bacteria on Europa, only to kill them with a stowaway extremophile hidden on the lander. Sterilised equipment

The users can largely be divided into 3 categories:

  • Those executing this and other missions (SA’s)
  • Those processing and using the results (scientists)
  • Those potentially found during the missions (life)

The vehicle must be brought to Europa in the first place. SA’s will want a solution for that. Since direct communication over this distance is not possible, SA’s will want to be able to send commands to the vehicle such as ‘Go there’ or ‘Investigate this’, which the vehicle will carry out autonomously. For ‘investigate this’-commands, the vehicle should be able to recognise ‘this’ (‘this’ being whatever object it was instructed to investigate) and know how to investigate ‘this’. In ‘Go there’-commands, the vehicle should be able to know where it is on Europa and where its destination is. Furthermore, it should travel the distance and avoid or clear any obstacles it may come across. Furthermore, SA’s will want to be kept up-to-date on how the vehicle is doing. It should be capable of sending status updates to mission control about its own state. Furthermore, if something is found to be wrong, an ability to repair the vehicle could possibly save the mission. This updating will also give information to people planning a similar mission, about the feasibility and problems that are yet to be overcome. To avoid having to restart the mission on a monthly basis to accomplish the mission goals, some longevity on the vehicle is required. Both the energy and durability should last for a minimum t.b.d. period of time.

Scientists will want information on Europa itself; the chemical makeup of the crust, the atmosphere and the subsurface ocean, and the terrain of the crust. They will also want information on whether life exists there and/or could exist. This information will also help in the search for other habitable planets. For instance, measurements of Europa’s atmospheric density are done in terms of the column density (which counts the number of particles in a column with a particular ground surface area reaching all the way up into space), rather than the density of the atmosphere at surface level. Now, with a lander, the density of the atmosphere at surface level can be determined. This will yield a comparison between column density and surface density, which can be used for estimating the surface density of exoplanets based purely on column density. This may in the long run allow to find new planets to colonise, to redistribute the human load on the earth.

In case there is sentient life on Europa, they will most likely want to not be massacred. (This is deduced from the simple fact that if they are a civilization that would - for whatever reason - like to be massacred, they would’ve massacred themselves already.) Some form of communication is required. Furthermore, mission command will want them not to destroy the vehicle. For that, there is hope that they will not.

Space agencies:

  • People responsible for the journey to Europa
    • Vehicle operators
    • Executives for other missions
  • Scientists
    • Astronomers
    • Biologists
    • Biohistorians (that’s a profession now)
    • Humanity/ sociologists
  • Life
    • Civilizations

User Requirements

These are the requirements based on what the different users want.

External

  • 1 Get to Europa
  • 2 Build vehicle
    • 2.1 Assuming that the mission is paid for, the builders will build it, so long as it is legal

SA’s

  • 3 Command vehicle
    • 3.1 Autonomous execution of following category of commands
      • 3.1.1 Go there
      • 3.1.2 Investigate this
  • 4 Longevity
    • 4.1 Sufficient energy
    • 4.2 Sufficient durability

Scientists

  • 5 Info on Europa
    • 5.1 Atmosphere
      • 5.1.1 Ionosphere; plasma density, magnetic field, current
      • 5.1.2 Density and pressure
    • 5.2 Subsurface ocean
      • 5.2.1 Density
      • 5.2.2 Viscosity
      • 5.2.3 Salinity
    • 5.3 Crust
      • 5.3.1 Terrain
    • 5.4 All environments
      • 5.4.1 Chemical makeup
  • 6 Info on life
    • 6.1 Possibility
      • 6.1.1 Required chemicals
      • 6.1.2 Required environment
    • 6.2 Itself
      • 6.2.1 Chemical makeup
      • 6.2.2 Habitat (Link data of life to data of the habitat)
      • 6.2.3 Enzymes

Life

  • 7 Do not go all genocide on it
    • 7.1 Preserve habitat (as little perturbing as possible)
    • 7.2 Non-lethal research methods
    • 7.3 Sterilised equipment

User Preferences

These are the preferences based on what the different users would like, given unlimited resources.

  • Longevity
    • 4.3 Keep up-to-date on vehicle status
      • 4.3.1 Recognise and report on faulty equipment
      • 4.3.2 Possibly repair faulty equipment
  • 6 Info on life
    • 6.2 Itself
      • 6.2.4 DNA
      • 6.2.5 Complexity

Constraints

These are the constraints resulting from the implications of the user requirements and preferences. For instance, 'surviving Europa' implies being able to operate at temperatures between 86 and 132 K.

External

  • 1 Get maximum capacity with falcon heavy
    • 1.1 Must fit inside cylindrical capsule: (L=13.1 m, r=2.6 m)
    • 1.2 Must be under 3500 kg (possibly a bit more, but if at all it is negligible)
  • 2 Must be legal

SA’s

  • 3 Command
    • 3.1 Autonomous execution
      • 3.1.1 'Go there'
        • 3.1.1.1 Know current and destiny locations
        • 3.1.1.2 Move
        • 3.1.1.3 Recognise obstacles on the way
      • 3.1.2 Investigate this
        • 3.1.2.1 Recognise ‘this’
        • 3.1.2.2 Know how to and be able to investigate ‘this’ (possibly in the command)
  • 4 Longevity

Things prone to wear and tear or able to run out should run for at least 5 years.

    • 4.1 operate for preferably several years, Either:
      • 4.1.1 carry enough energy
      • 4.1.2 Produce energy there
    • 4.2 Durability
      • 4.2.1 Iono- & Magnetosphere

[7] Magnetic fields estimated at 5.0*10-7 T Electron densities of up to 1010 m-3 with energies up to 250 eV Ionospheric currents up to .42 A/m

      • 4.2.2 Low gravity

Calculations of non-uniform gravity Suggestions for zero-G car

      • 4.2.3 Low atmospheric pressure

Oxygen densities of around 10^-10 that of earth (~1.801*10^23 cm^-2)(see also calculation: Barometric formula) 3D-Plasma source-sink model Spectrometry model Monte Carlo model

      • 4.2.4 Low temperatures

86-132 K Europan temperature

      • 4.2.5 Possibly rough or slippery surface

Bases should be able to maintain their position on the surface

      • 4.2.6 Withstand tectonic activity

Life

  • 5 Do not kill
    • 5.1 Radioactive sources amply shielded
    • 5.2 Research methods that do not kill the subject
    • 5.3 No biological earthly life brought along on the mission
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