Enceladus – Overview

For the next major project, me and my teammates have decided to create a vehicle capable of traveling a 10 kilometer round trip while combating low temperatures (~-201 degrees Celsius) [1], water geysers [2], low visibility caused by brightness [3], and weak gravitational pull (0.113 m/s²) on Enceladus [4]. In the following text, I will discuss Enceladus’s environment, the reason behind the choice of Enceladus, the possible opportunities for a surface vehicle, the possible difficulties, design implications, and possible vehicles designs.

PT.1: ENCELADUS’ LOOKS & OPPORTUNITIES

Enceladus, with multiple traits that make it an attractive planet to study, is chosen as our target for multiple reasons. To begin with, the Cassini mission has shown the existence of traits relate with the existence of life, such as liquid water, organic molecules, and hydrothermal vents [5-7]. The detection of plumes on the South Pole of Enceladus’s surface hinted at the existence of water underneath Enceladus [5]. Then, with the Cassini mission flyby, the detection of sodium and potassium salts in the ice ejected from surface plumes confirmed that there is a large salt water reservoir underneath Enceladus. Liquid water existing under surface ice layers hints at the possibility of life [5] due to water being a possible catalyst for the creation of life, as water plays many key roles for life on Earth. This possibility is further strengthened by evidence of organic molecules, including those with molecular masses exceeding 200u, detected by the Cosmic Dust Analyzer (CDA) and the Ion and Neutral Mass Spectrometer (INMS) during the Cassini flyby and pointed out by scientists Postberg et. al [6]. Another indicator of the possibility of life could be the hydrothermal vents in Enceladus, revealed by nanometer level SiO2 (silica) particles in ice particles ejected by plumes that indicate the existence of high temperature hydrothermal activity that ejects ocean floor silica into the plumes in Enceladus [7]; hydrothermal vents are an important characteristic as it could act as an energy source for living things. To continue, a probe could easily sample grains of ice and water vapor from surface geysers on Enceladus [2] using instruments similar to that of the INMS on the Cassini probe for data that could reveal more about the composition of the planet’s inner sea without drilling holes into Enceladus’s thick ice layer.

PT.2: DIFFICULTIES & IMPLICATIONS

There are multiple difficulties and design implications involved with a vehicle on Enceladus, due to low gravity [4] and low temperatures [1]. As a result of low gravitational field force on Enceladus, it is difficult to make the vehicle have enough grip to the ground. As conventional forms of movement require friction to propel a vehicle, the low gravity situation would make wheels, for example, to have a tendency to slip on the surface of the planet that it is traversing. Slipping could result in extremely low levels of efficiency while also decreasing driver control over the vehicle. A possible solution to this problem is the incorporation of NASA’s new design for its mars rover, a soft wheel that results in more grip for terrain. Another difficulty is cold weather, as common batteries such as lithium ion batteries fail to function at low temperatures [8]. Also, many materials become brittle at temperatures of about -201 degrees Celsius [1].

PT.3: POSSIBLE SOLUTIONS

Possible modes of transportation on Enceladus include rovers, rocket propelled vehicles, and submarines. Rocket propelled vehicles is a possibility on Enceladus, as it could be determined using the equation a=v^2/r that an object only needs to reach around 19.00 m/s, or 68.4 km/h, to orbit Enceladus. An electric motor could be used to speed up the vehicle to that speed, and then rocket engines could help maintain the orbit of the vehicle around Enceladus. This is an extremely efficient use of energy, as very little energy is needed to lift the vehicle off the ground and from point A to point B. However, fuel could be difficult to obtain after it runs out, and the overall weight and complexity of the vehicle would make it difficult for maintenance and missions that require landing in terrain. Another, more classic, approach is building an electric powered rover like vehicle. Not only are these vehicles less complex, the energy source used in the vehicle is completely renewable by solar panels. Solar panels would also be extremely advantageous, as there is no atmosphere blocking light energy from the sun. It could also be a great solution for missions requiring the sampling of surface geysers due to better mobility. However, the rate of energy consumption would be far greater than the rate of recharge of solar panels, making it difficult for the vehicle to make full utilization of the time it has on the surface of Enceladus. Movement speed is also extremely limited, as it has to travel around terrain at a speed lower than 68.4 km/h, and even lower on inclined surfaces or hills; braking is also extremely limited due to low grip levels. Submarines could also be used, as they would provide a lot insight into Enceladus’s inner ocean, and could also be used to investigate hydrothermal vents on the bottom of the ocean. However, the ice shell on Enceladus, ranging from 5km to 30 km thick [9], would be extremely difficult to drill through.

SUMMARY

To summarize, the planet of Enceladus was chosen due to the possibility of life on Enceladus and the ease of collection of data on Enceladus. However, designing a vehicle for Enceladus also has the difficulties of low temperature and low gravity, causing low levels of grip for vehicles travelling on land and decreased battery performance. As a solution there are many different types of vehicles that could be designed for Enceladus, including rocket propelled vehicles, a rover, or a submarine.

[1]: Robert H. Brown et al. Composition and Physical Properties of Enceladus’ Surface.Science311,1425-1428(2006).DOI:10.1126/science.1121031

[2]: Wanying Kang, John Marshall, Tushar Mittal, Suyash Bire, Ocean dynamics and tracer transport over the south pole geysers of Enceladus, Monthly Notices of the Royal Astronomical Society, Volume 517, Issue 3, December 2022, Pages 3485–3494, https://doi.org/10.1093/mnras/stac2882

[3]: Spencer, J.R. et al. (2009). Enceladus: An Active Cryovolcanic Satellite. In: Dougherty, M.K., Esposito, L.W., Krimigis, S.M. (eds) Saturn from Cassini-Huygens. Springer, Dordrecht.

[4]: Park, R. S., Mastrodemos, N., Jacobson, R. A., Berne, A., Vaughan, A. T., Hemingway, D. J., et al. (2024). The global shape, gravity field, and libration of Enceladus. Journal of Geophysical Research: Planets, 129, 2023JE008054. https://doi.org/10.1029/2023JE008054

[5]: Čadek, O., et al. (2016), Enceladus’s internal ocean and ice shell constrained from Cassini gravity, shape, and libration data, Geophys. Res. Lett., 43, 5653–5660, doi:10.1002/2016GL068634.

[6]: Postberg F, Khawaja N, Abel B, Choblet G, Glein CR, Gudipati MS, Henderson BL, Hsu HW, Kempf S, Klenner F, Moragas-Klostermeyer G, Magee B, Nölle L, Perry M, Reviol R, Schmidt J, Srama R, Stolz F, Tobie G, Trieloff M, Waite JH. Macromolecular organic compounds from the depths of Enceladus. Nature. 2018 Jun;558(7711):564-568. doi: 10.1038/s41586-018-0246-4. Epub 2018 Jun 27. PMID: 29950623; PMCID: PMC6027964.

[7]: Hsu, HW., Postberg, F., Sekine, Y. et al. Ongoing hydrothermal activities within Enceladus. Nature 519, 207–210 (2015). https://doi.org/10.1038/nature14262

[8]: J. Jaguemont, L. Boulon, Y. Dubé, A comprehensive review of lithium-ion batteries used in hybrid and electric vehicles at cold temperatures, Applied Energy,Volume 164, 2016, Pages 99-114,ISSN 0306-2619, https://doi.org/10.1016/j.apenergy.2015.11.034.

[9]: Ondřej Čadek, Ondřej Souček, Marie Běhounková, Gaël Choblet, Gabriel Tobie, Jaroslav Hron, Long-term stability of Enceladus’ uneven ice shell,
Icarus, Volume 319, 2019, Pages 476-484, ISSN 0019-1035, https://doi.org/10.1016/j.icarus.2018.10.003.