Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Planetary Science Vision 2050 Workshop 2017 (LPI Contrib. No. 1989) 8205.pdf OBSERVING OUTER PLANET SYSTEMS IN THE MID-21ST CENTURY. Matthew S. Tiscareno ([email protected]) and Mark R. Showalter ([email protected]) SETI Institute, 189 Bernardo Avenue #200, Mountain View CA 94043. Executive Summary: We offer several ideas on studying the outer solar system during the coming decades. Our particular interest is in ring systems and satellite systems, though surfaces and interiors and atmospheres are briefly touched upon. The technology of tomorrow will likely make basic hardware increasingly inexpensive, both for computing and for rocketry. Data transmission and storage will also become much more inexpensive, such that human attention rather than data will be the limiting factors in scientific endeavor. Automation and other data strategies will help us to grapple with this new reality [1]. These trends will enable better traditional spacecraft missions as well as entirely new kinds of spacecraft missions. We discuss some modest ideas for spacecraft missions in the second part of this abstract. On a parallel track, there is enormous potential in taking existing technology and multiplying it as it becomes more inexpensive, especially in the realm of space telescopes. We discuss some of the science return that could accrue in response to a major increase in time-domain observations. Finally, we close by discussing the scientific community of tomorrow, with hopes that it will be more diverse and welcoming. Space Telescopes: Studying the outer planets with space-based and ground-based telescopes will be essential in the near-term future, as no spacecraft will be operating in any outer planet system between the impending close of the Cassini and Juno missions and the arrival of the Europa and Juice missions around 2030. The Hubble Space Telescope continues to generate critically important science, and the James Webb Space Telescope will improve upon its capabilities in several ways. Particularly in regard to rings and small moons, JWST will discover new rings and moons that are beyond the sensitivity of Hubble, will conduct unprecedented spectroscopy of rings and moons, and will continue Hubble’s important work of time-domain science [2]. Time-domain science: Many aspects of the solar system are in constant flux, including planetary rings, satellite systems, and atmospheres. Examples include • Impacts and storms and cloud movements in giant planet atmospheres, all of which are transient events that are best studied frequently [3,4,5] • Jupiter’s Great Red Spot, which may be in the process of disappearing [6] • Volcanic activity at Io, with correlated changes in the Io Plasma Torus and in Jupiter’s aurorae [7] • The plumes of Enceladus [8] • “Propeller” moons embedded in Saturn’s rings [9] • The ring arcs of Neptune, post-Voyager movements of which have invalidated the prevailing model from the Voyager era [10] • The F ring of Saturn [11] • The spokes in Saturn’s rings; a seasonal pattern has been discerned [12], but we do not know how they vary on a climate-like scale from one Saturn year to another [2]. • The ring-moon system of Uranus, which shows signs of recent and frequent change [13] Heretofore, the study of such systems has involved periodically taking detailed snapshots and then using theory to figure out how the snapshots fit together. While that method has met with much success, the enormous increase in understanding that has come from Cassini’s extended time baseline in the Saturn system demonstrates how often nature surprises us when we fill in the gaps with more data, rather than with our own surmises. By the mid-21st century, it will have become vastly more inexpensive to launch a space telescope incurporating Hubble-class optics and electronics. Data transmission and storage will also become more and more affordable, to the point that they no longer exert limitations on our work. This will open an entirely new horizon with regard to time-domain science. It is not difficult to imagine a number of space telescopes, each focused on extended observations of one or a few targets. This will enable us to move beyond understanding basic structure and to focus our attention on weather and climate (and their analogues in other types of systems). Spacecraft Mission Concepts: Visiting Ocean Worlds. The currently planned missions to Europa (NASA) and Ganymede (ESA) will have concluded by 2050. As we continue to search for evidence of habitability on the “ocean worlds” of the solar system, perhaps the most compelling target is Enceladus, whose subsurface water reservoirs were recently shown by analysis of its rotation state to extend globally [14]. A more multifaceted target would Planetary Science Vision 2050 Workshop 2017 (LPI Contrib. No. 1989) be one or both of the Ice Giant planets, which feature complex ring systems wholly unlike those of Saturn, nearly unexplored icy moons that may well harbor oceans, and planets of a size class that is poorly understood yet known to be plentiful among exoplanets. Ice Giant orbiter missions have been proposed to ESA [15] and are under study by NASA [16]; a joint effort between the two agencies is likely the best solution. Returning to Saturn’s rings. Ring systems furnish the only accessible natural laboratory in which we can study disk processes, which are of high importance for understanding the origins of planetary systems [5,17]. The Cassini mission has returned a wealth of discoveries regarding Saturn’s rings and moons [18,19], opening a window onto a new set of more detailed science questions. Are the rings much younger than the planet and its moons, or indeed are many of the moons also younger than 100 Myr? How do disk processes such as self-gravity wakes and propeller moons shed light on the workings of proto-planetary systems? Spacecraft that specifically study Saturn’s rings in more detail, whether as dedicated missions or opportunistically, have the potential for high science return. Advances in propulsion technology may enable the Saturn Ring Observer mission concept [20] to be realized. By exerting a low but constant vertical thrust, such a spacecraft would “hover” over the rings and take detailed movies of individual particle interactions within the rings. Also, Keplerian trajectories that repeatedly skim above Saturn’s rings in a geometry similar to that of Cassini’s Saturn Orbit Insertion are in development and could be used for a variety of mission concepts, including low-cost ones. Cubesat/Chipsat concepts. As Moore’s Law runs aground due to physical limitations associated with heat flow and other factors [21], computer innovation will increasingly shift towards parallelization and towards making small components that are more capable and more affordable. Planetary scientists would do well to consider the new vistas opened up by large numbers of small components. Seeding Saturn’s rings with a swarm of “chipsats” may be more affordable than a hovering spacecraft as a way of studying the inter-particle interactions within disk systems [22]. Other problems amenable to swarms of chipsats might include mapping the magnetospheres, gravity fields, and/or atmospheres of the giant planets [23]. When they become sufficiently plentiful, “cubesats” may also be deployed inexpensively for focused studies of targets such as Iapetus or Chariklo that raise compelling science questions that are perhaps not broad enough to justify missions of even Discovery-class expense [23]. 8205.pdf Workforce Makeup and Climate: No less important than the goals we will pursue in the coming decades and the means we will use to get there is the scientific community that will undertake the work. Currently, several communities within the general population are severely underrepresented among planetary scientists, as are women [24], and members of those minoritized groups have reported various forms of harassment and other difficulties that hamper the advancement and flourishing of their careers [25]. To give one example, a recent study showed that spacecraft science teams and other paths to career advancement commonly lack women, even compared only to the pool of qualified applicants at the time the team was formed [26]. Far more research is needed to illuminate the magnitude of the problem, and the community must forge a courageous consensus to implement solutions. We particularly endorse the abstract submitted to this workshop by Rathbun et al. [24], which is dedicated to discussing this important topic. References: [1] Showalter MR et al. (2016), this workshop. [2] Tiscareno MS et al. (2016), Pub. Astron. Soc. Pac. 128, 018008. [3] Hueso R et al. (2010) Astrophys. J. 721, L129 [4] Sanchez-Lavega A et al. (2016), arXiv 1611.07669. [5] Sromovsky LA et al. (2015) Icarus 58, 192–223. [6] Simon-Miller A et al. (2002), Icarus 158, 249–266. [7] Yoshioka K et al. (2014), Science 345, 1581–1584. [8] Hedman MM et al. (2013), Nature 500, 182–184. [9] Tiscareno MS et al. (2010) Astrophys. J. 718, L92–L96. [10] de Pater I et al. (2005), Icarus 174, 263–272. [11] French RS et al. (2014), Icarus 241, 200–220. [12] Mitchell CJ et al. (2013), Icarus 225, 446–474. [13] Showalter MR and Lissauer JJ (2006), Science 311, 973–977. [14] Thomas PC et al. (2016), Icarus 264, 37–47. [15] Arridge CS et al. (2012), Exp. Astron. 33, 753–791. [16] Hofstadter MD et al. (2016), this workshop. [17] Burns JA and Cuzzi JN (2006), Science 312, 1753–1755. [18] Tiscareno MS and Murray CD, eds. (2017), Planetary Ring Systems: Properties, Structure, and Evolution, Cambridge UK: Cambridge Univ. Press, 650pp. [19] Tiscareno MS (2013), arXiv 1112.3305. [20] Spilker TR et al. (2010), J. Brit. Interplanet. Soc. 63, 345–350. [21] Waldrop MM (2016), Nature 530, 145–147. [22] Hedman MM et al. (2012), iCubeSat 1, B.1.1. [23] Tiscareno MS et al. (2012), iCubeSat 1, B.1.2. [24] Rathbun JA et al. (2016), this workshop. [25] Diniega S et al. (2016), Eos 97 (20), 11–13. [26] Rathbun JA et al. (2016), DPS 48, 332.01.