The comparative study of planetary systems is a unique source of new scientific insight: following the six “key science questions” of the “Planetary Exploration, Horizon 2061” long-term foresight exercise, it can reveal to us the diversity of their objects (Question 1) and of their architectures (Question 2), help us better understand their origins (Question 3) and how they work (Question 4), find and characterize habitable worlds (Question 5), and ultimately, search for alien life (Question 6). But a huge “knowledge gap” exists which limits the applicability of this approach in the solar system itself: two of its secondary planetary systems, the ice giant systems of Uranus and Neptune, remain poorly explored.

Starting from an analysis of our current limited knowledge of solar system ice giants and their systems in the light of these six key science questions, we show that a long-term plan for the space exploration of ice giants and their systems will greatly contribute to answer these questions. To do so, we identify the key measurements needed to address each of these questions, the destinations to choose (Uranus, Neptune, Triton or a subset of them), the combinations of space platform(s) and the types of flight sequences needed.

We then examine the different launch windows available until 2061, using a Jupiter fly-by, to send a mission to Uranus or Neptune, and find that:

(1) an optimized choice of platforms and flight sequences makes it possible to address a broad range of the key science questions with one mission at one of the planets. Combining an atmospheric entry probe with an orbiter tour starting on a high-inclination, low periapse orbit, followed by a sequence of lower inclination orbits (or the other way around) appears to be an optimal choice.

(2) a combination of two missions to each of the ice giant systems, to be flown in parallel or in sequence, will address five out of the six key questions and establish the prerequisites to address the sixth one: searching for life at one of the most promising Ice Giant moons.

(3) The 2032 Jupiter fly-by window, which offers a unique opportunity to implement this plan, should be considered in priority; if this window cannot be met, using the 2036 Jupiter fly-by window to send a mission to Uranus first, and then the 2045 window for a mission to Neptune, will allow one to achieve the same objectives; as a back-up option, one should consider an orbiter + probe mission to one of the planets and a close fly-by of the other planet to deliver a probe into its atmosphere, using the opportunity of a future mission on its way to Kuiper Belt Objects or the interstellar medium;

(4) based on the examination of the habitability of the different moons by the first two missions, a third one can be properly designed to search for life at the most promising moon, likely Triton, or one of the active moons of Uranus.

Thus, by 2061 the first two missions of this plan can be implemented and a third mission focusing on the search for life can be designed. Given that such a plan may be out of reach of a single national agency, international collaboration is the most promising way to implement it.

行星系统的比较研究是获得新的科学见解的独特来源：遵循“远景2061号行星探索”长期预见运动的六个“关键科学问题”，它可以向我们揭示其物体的多样性（问题1）及其架构（问题2），帮助我们更好地了解它们的起源（问题3）以及它们的工作方式（问题4），找到并描述可居住世界的特征（问题5），并最终寻找外星生命（问题6） ）。但是，存在着巨大的“知识鸿沟”，这限制了这种方法在太阳系本身的适用性：它的两个次级行星系统，即天王星和海王星的冰巨星系统，仍未被很好地探索。

根据对这六个关键科学问题的分析，我们目前对太阳系冰巨人及其系统的有限知识的分析开始，表明对冰巨人及其系统进行太空探索的长期计划将极大地有助于解答这些问题。为此，我们确定了解决每个问题所需的关键度量，要选择的目的地（天王星，海王星，特里顿或其中的一个子集），空间平台的组合以及所需的飞行序列类型。

然后，我们使用木星飞越技术检查直到2061年可用的不同发射窗口，以向天王星或海王星发送任务，并发现：

（1）平台和飞行顺序的优化选择，使得在一个行星上执行一项任务就可以解决广泛的关键科学问题。最佳的选择是将大气进入探测器与从高倾角，低近视点轨道开始的轨道巡回飞行相结合，然后再进行一系列较低倾角的轨道（或相反方向）的组合。

（2）对两个冰巨系统分别进行并行或顺序飞行的两个任务的组合，将解决六个关键问题中的五个，并确定解决第六个关键问题的前提：在以下一个问题中寻找生命最有前途的冰巨人卫星。

（3）应优先考虑2032年木星飞越窗口，它为实施该计划提供了独特的机会；如果无法达到该窗口，则先使用2036年木星飞越窗口向天王星发送任务，然后再使用2045年对海王星执行任务，则将实现相同的目标；作为一种备用选择，应该考虑对一个行星进行一次轨道飞行器+探测任务，并考虑另一颗行星的近距离飞越，以向其大气层进行探测，并利用未来执行该任务的方式向柯伊珀飞行腰带物体或星际介质；

（4）根据前两个任务对不同卫星的可居住性的检查，可以适当地设计第三个任务，以在最有希望的卫星（可能是Triton或天王星的一个活跃卫星）上寻找生命。

因此，到2061年，可以执行该计划的前两个任务，并且可以设计出专注于寻找生命的第三个任务。鉴于这样一个计划可能是单个国家机构无法企及的，因此国际合作是实施该计划的最有希望的方式。