“如果存在生物，那么火星上也有可能存在过文明？”麦冬问。
“麦冬小姐，这个可不好说。”老猫耸耸肩，“智慧和文明从来都不是进化的目标，生物进化的目的是为了更好地适应环境，而非长出更发达的大脑，你何必一定要把智慧视作高等生命的标准？在进化和生物学的角度上，最成功的生物从来都是最适应环境的，而非脑容量最大的——在中生代的地球，大型爬行动物智商不高，但这不妨碍它们霸占全球。”
“我只是觉得，如果火星上也存在过文明的话，那么这一切就变得很浪漫了。”女孩说，“我们面对的就不再是一颗没有生机的死寂星球，而是某个古代文明留下的遗迹。”
唐跃一愣，低头往脚下看，他想象着火星车驶过的地表之下，埋藏着如古罗马万神殿那样巨大而宏伟的建筑，他们正在经过某条宽广笔直的大道，而在数万年前，火星文明的居民们在这里朝拜自己的神明。
“就算存在文明，我们也很难看到他们的遗迹。”老猫悠悠地说，“唐跃，你往左边看。”
唐跃依言，站起来往车子的左边眺望。
在荒原的尽头，有层层叠叠的深红色山丘，它们犬牙交错，遍布沟壑。
“你看到了什么？”
“沙子，荒原，还有线形排列的山丘。”
“那是雅丹地貌。”老猫问，“你们知道什么是雅丹地貌么？”
“风蚀地貌？”麦冬说。
“就是风蚀地貌，你们所看到的那些像龙背一样起伏的岩石山峦，都是风蚀的结果，在这个星球上，没有什么力量比风沙流水更强大，无论什么文明建立起多么高大坚固的建筑，都会在漫长的时光中被刀割一样的气流侵蚀破碎，最终化作漫天的黄沙。”老猫淡淡地说，“最缓慢最无声的力量向来都是最强大的。”
“这世上没什么可以敌得过时间，一个发展了万年的文明，一千万年就能抹平它的一切痕迹。”老猫接着说，“但在地质年代的巨大尺度上，我们一般都用亿为单位来计算时间……什么王朝霸业什么文明硕果，最后都是沙子。”
唐跃和麦冬都陷入了沉默。
他们不知道该说什么，以人类的渺小去丈量时间的尺度，总是让人心生敬畏。
老猫顿了顿，开口高声吟诵:
“客自海外归，曾见沙漠古国。
有石像半毁，唯余巨腿，蹲立沙砾间。
像头旁落，半遭掩埋，人面依旧可畏。”
唐跃一愣，不知道老猫在说什么，麦冬在他耳机中小声提醒这是雪莱的诗句，出自著名的《奥西曼提斯》。
老猫拔高了声音。
“那冷笑，那发号施令的高傲，
足见工匠看穿主人的内心，
才把石像刻得神情惟肖，
而石像之手与石像之心，早已化作灰烬！
底座之上大字在目:
吾乃万王之王是也，盖世功业，敢叫天公折服！”
火星流浪狗在死寂的茫茫荒漠上前行，沙砾遍地，老猫的声音变得苍茫浩瀚，唐跃望着满眼风沙，心中也顿起苍凉。
但老猫的声音又缓缓低落下来，如泣如诉，如一曲挽歌。
“此外无一物，但见废墟周围，
寂寞平沙空莽莽，
伸向荒凉四方。”
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第一百日（1）作屎的老猫
翌日。
老猫和唐跃花了一上午的时间，在一平方公里的区域内再次取了二十个样本。
昆仑站坐落在火星北半球的伊希地平原中，这是一个直径一千五百公里的圆形盆地，在三十九亿年前被一颗陨石撞了出来，昆仑站的地址之所以设置在此处，是因为火星登陆任务的专家们怀疑伊希地平原中存在大量水冰，昆仑站的后期任务就是寻找并发掘这些潜在的水资源，为进一步的登陆计划做准备。
下一次火星登陆任务中，地球方面会带来有能力支持长途行驶的改进型火星车，接下来的科考队员们就能驾着车子奔驰在广袤的平原上。
不过很不幸，地球消失了，整个计划也就戛然而止，到此中断了。
唐跃在实验舱内捣鼓了一下午，终于在二十个土壤样本中找到了合格品。
“这个是到目前为止条件最好的土质，唐跃你看，这个样本的主要成分是斜长石和高钙单斜辉石，高硅玻璃的含量较低，含铁以及镁硅酸盐的黏土非常丰富，这种土质和地球上的土壤成分比较接近，PH值比较居中。”麦冬很欣喜。
“能用来种西红柿么？”唐跃问。
“先做一个Vis-NIR光谱检测，看看结果。”麦冬指示。
唐跃点点头，他把土壤样本浸入溶液中，过滤提取出浸出液，放进光度计里。
结果很快就出来了。
“嗯……看这个近红外光谱的数据结果，指标很理想！”麦冬盯着图谱看了许久，慢慢地点头，“唐跃，这个样本是在哪儿采到的？”
唐跃端起玻璃皿看标签，“E2，是一条古河道的河床上，距离我们不远，老猫挖了很深才取的样本。”
“对，伊希地平原是形成于诺亚纪（Noachian）晚期的陨石坑，这个时期有大量的硫酸盐和水合化合物通过火山喷发沉积在了地表上，你们真厉害，就这个！”麦冬拍板，“唐跃，这个可以用作种植番茄的基质！”
唐跃大喜，转身朝着车头大喊:
“老猫！掉头回去掉头回去！咱们找到合适的土壤啦！”
话音刚落，车身一震，唐跃的身子也跟着一歪。
老猫扭过头来，闷闷地说:“叫毛叫啊，车轮陷坑里啦。”
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老猫和唐跃用塑料密封袋取了十几公斤的泥土回来，取土的位置距离昆仑站大概一公里左右，是一条早已干涸的古河道，老猫扫除了表面积累的沙子和砾石，用铲子往下深刨了一米，才找到了这些合格的泥土。
他们用火星流浪狗把泥土运回昆仑站。
唐跃气喘吁吁地把袋子堆在车库门前，拍拍巴掌。
“这些泥土起码有十五六公斤，够不够？如果不够我们可以再去挖。”
“用于初步实验性的种植应该足够了。”麦冬说，“不过这些泥土不能直接用来种番茄，它们只是基质，缺乏植物生长所必须的营养成分，所以接下来我们还得给它加入……”
“金坷垃！”唐跃眼睛一亮。
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肥料是个很神奇的东西，它是人类自学会刀耕火种之后最重要的发明，通过人工手段改善土壤的性质，提高土壤的肥力，以此极大地提升农作物的产量——在人类漫长的农耕历史上，学会使用肥料是一个革命性的进步，它是农耕社会得以发展壮大的基础。
肥料是农业科学中永恒不变的重要课题，社会与科技的进步，特别是化学工业的发展，让人们可以定量地分析农作物所需的营养成分，并人为地为它们提供这些基本元素，这些技术最终催生出了现代农业中最重要的组成部分，化肥。
现代社会人口得以如此迅速地膨胀，究其根本原因之一是化肥的使用，通过科学地为农作物供给其所必需的矿质元素，让农业生产迅速工业化，促进粮食产量的逐年攀升，粮食产量的提高是人口增长的基础。
当然，金坷垃也是一个很神奇的东西。
俗话说肥料掺了金坷垃，一袋能抵两袋……
昆仑站内很显然是没什么东西可以用来当肥料的，但好在唐跃就是一台有机肥制造机，这大概就是唐跃存在的意义——早在数千年前，中国人的老祖宗们就学会了如何使用有机肥料来提高土壤的肥力，促进庄稼的生长，这大概是根植在中国人骨子里的先天技能。
千年的农耕文明把对土地的热爱深深地镌刻在了每个人的基因中。
要不然怎么那么多人喜欢看种田文呢。
老猫和唐跃把废弃物收集箱内的干燥粪便全部都翻了出来，这些大便全部经过马桶的干燥和抽吸，干硬得像是石头，用真空包装包好了——按照规定，昆仑站内产生的一切垃圾都不允许随意扔在火星表面，必须全部带回地球。
不过现在这条规定已经作废。
唐跃想去哪拉屎，就去哪拉屎。
两人把所有的粪便都带进了车库，这种捣屎的活肯定不能在主站内干，否则昆仑站还住不住人了。
唐跃把干燥粪便倒在车库地板上，随意清点了一下，发现他这三个月以来，排便还算均匀顺畅，这里所有的大便都是他自己的，再往前其他人的粪便和垃圾都已经被猎户座一号带走了。
老猫蹲下来，手中捏着一根不知道哪儿找来的棍子，饶有趣味地戳了戳地板上包装好的大便，“唐跃，我觉得你可能严重便秘且大便干燥，你看你拉的翔硬得跟大理石似的。”
唐跃戴上口罩，并不想搭理老猫这个话痨。
老猫还在戳地上的大便，翻过来覆过去地戳。
“唐跃你看，这坨翔像不像一颗真空包装的茶叶蛋？你是怎么拉出这么圆的屎蛋蛋来的？能不能演示一下？”
“还有这个，这坨翔大，我估计一下，起码得有五两重吧……”
“这坨很有艺术气息，看上去像是梵高的星空。”
“哎唐跃！你来看这个，这坨翔长得很像你诶！简直就是一个模子里刻出来的，你们真是一对父子……”
唐跃恼怒地抄起一块干燥的大便砸了过去。
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对火星轨道变化问题的最后解释
作者君在作品相关中其实已经解释过这个问题。
不过仍然有人质疑——“你说得太含糊了”，“火星轨道的变化比你想象要大得多！”
那好吧，既然作者君的简单解释不够有力，那咱们就看看严肃的东西，反正这本书写到现在，嚷嚷着本书BUG一大堆，用初高中物理在书中挑刺的人也不少。
以下是文章内容：
Long-term integrations and stability of planetary orbits in our Solar system
Abstract
We present the results of very long-term numerical integrations of planetary orbital motions over 109 -yr time-spans including all nine planets. A quick inspection of our numerical data shows that the planetary motion， at least in our simple dynamical model， seems to be quite stable even over this very long time-span. A closer look at the lowest-frequency oscillations using a low-pass filter shows us the potentially diffusive character of terrestrial planetary motion， especially that of Mercury. The behaviour of the eccentricity of Mercury in our integrations is qualitatively similar to the results from Jacques Laskar's secular perturbation theory (e.g. emax∼ 0.35 over ∼± 4 Gyr). However， there are no apparent secular increases of eccentricity or inclination in any orbital elements of the planets， which may be revealed by still longer-term numerical integrations. We have also performed a couple of trial integrations including motions of the outer five planets over the duration of ± 5 × 1010 yr. The result indicates that the three major resonances in the Neptune–Pluto system have been maintained over the 1011-yr time-span.
1 Introduction
1.1Definition of the problem
The question of the stability of our Solar system has been debated over several hundred years， since the era of Newton. The problem has attracted many famous mathematicians over the years and has played a central role in the development of non-linear dynamics and chaos theory. However， we do not yet have a definite answer to the question of whether our Solar system is stable or not. This is partly a result of the fact that the definition of the term ‘stability’ is vague when it is used in relation to the problem of planetary motion in the Solar system. Actually it is not easy to give a clear， rigorous and physically meaningful definition of the stability of our Solar system.
Among many definitions of stability， here we adopt the Hill definition (Gladman 1993): actually this is not a definition of stability， but of instability. We define a system as becoming unstable when a close encounter occurs somewhere in the system， starting from a certain initial configuration (Chambers， Wetherill & Boss 1996; Ito & Tanikawa 1999). A system is defined as experiencing a close encounter when two bodies approach one another within an area of the larger Hill radius. Otherwise the system is defined as being stable. Henceforward we state that our planetary system is dynamically stable if no close encounter happens during the age of our Solar system， about ±5 Gyr. Incidentally， this definition may be replaced by one in which an occurrence of any orbital crossing between either of a pair of planets takes place. This is because we know from experience that an orbital crossing is very likely to lead to a close encounter in planetary and protoplanetary systems (Yoshinaga， Kokubo & Makino 1999). Of course this statement cannot be simply applied to systems with stable orbital resonances such as the Neptune–Pluto system.
1.2Previous studies and aims of this research
In addition to the vagueness of the concept of stability， the planets in our Solar system show a character typical of dynamical chaos (Sussman & Wisdom 1988， 1992). The cause of this chaotic behaviour is now partly understood as being a result of resonance overlapping (Murray & Holman 1999; Lecar， Franklin & Holman 2001). However， it would require integrating over an ensemble of planetary systems including all nine planets for a period covering several 10 Gyr to thoroughly understand the long-term evolution of planetary orbits， since chaotic dynamical systems are characterized by their strong dependence on initial conditions.
From that point of view， many of the previous long-term numerical integrations included only the outer five planets (Sussman & Wisdom 1988; Kinoshita & Nakai 1996). This is because the orbital periods of the outer planets are so much longer than those of the inner four planets that it is much easier to follow the system for a given integration period. At present， the longest numerical integrations published in journals are those of Duncan & Lissauer (1998). Although their main target was the effect of post-main-sequence solar mass loss on the stability of planetary orbits， they performed many integrations covering up to ∼1011 yr of the orbital motions of the four jovian planets. The initial orbital elements and masses of planets are the same as those of our Solar system in Duncan & Lissauer's paper， but they decrease the mass of the Sun gradually in their numerical experiments. This is because they consider the effect of post-main-sequence solar mass loss in the paper. Consequently， they found that the crossing time-scale of planetary orbits， which can be a typical indicator of the instability time-scale， is quite sensitive to the rate of mass decrease of the Sun. When the mass of the Sun is close to its present value， the jovian planets remain stable over 1010 yr， or perhaps longer. Duncan & Lissauer also performed four similar experiments on the orbital motion of seven planets (Venus to Neptune)， which cover a span of ∼109 yr. Their experiments on the seven planets are not yet comprehensive， but it seems that the terrestrial planets also remain stable during the integration period， maintaining almost regular oscillations.
On the other hand， in his accurate semi-analytical secular perturbation theory (Laskar 1988)， Laskar finds that large and irregular variations can appear in the eccentricities and inclinations of the terrestrial planets， especially of Mercury and Mars on a time-scale of several 109 yr (Laskar 1996). The results of Laskar's secular perturbation theory should be confirmed and investigated by fully numerical integrations.
In this paper we present preliminary results of six long-term numerical integrations on all nine planetary orbits， covering a span of several 109 yr， and of two other integrations covering a span of ± 5 × 1010 yr. The total elapsed time for all integrations is more than 5 yr， using several dedicated PCs and workstations. One of the fundamental conclusions of our long-term integrations is that Solar system planetary motion seems to be stable in terms of the Hill stability mentioned above， at least over a time-span of ± 4 Gyr. Actually， in our numerical integrations the system was far more stable than what is defined by the Hill stability criterion: not only did no close encounter happen during the integration period， but also all the planetary orbital elements have been confined in a narrow region both in time and frequency domain， though planetary motions are stochastic. Since the purpose of this paper is to exhibit and overview the results of our long-term numerical integrations， we show typical example figures as evidence of the very long-term stability of Solar system planetary motion. For readers who have more specific and deeper interests in our numerical results， we have prepared a webpage (access )， where we show raw orbital elements， their low-pass filtered results， variation of Delaunay elements and angular momentum deficit， and results of our simple time–frequency analysis on all of our integrations.
In Section 2 we briefly explain our dynamical model， numerical method and initial conditions used in our integrations. Section 3 is devoted to a description of the quick results of the numerical integrations. Very long-term stability of Solar system planetary motion is apparent both in planetary positions and orbital elements. A rough estimation of numerical errors is also given. Section 4 goes on to a discussion of the longest-term variation of planetary orbits using a low-pass filter and includes a discussion of angular momentum deficit. In Section 5， we present a set of numerical integrations for the outer five planets that spans ± 5 × 1010 yr. In Section 6 we also discuss the long-term stability of the planetary motion and its possible cause.
2 Description of the numerical integrations
（本部分涉及比较复杂的积分计算，作者君就不贴上来了，贴上来了起点也不一定能成功显示。）
2.3 Numerical method
We utilize a second-order Wisdom–Holman symplectic map as our main integration method (Wisdom & Holman 1991; Kinoshita， Yoshida & Nakai 1991) with a special start-up procedure to reduce the truncation error of angle variables，‘warm start’(Saha & Tremaine 1992， 1994).
The stepsize for the numerical integrations is 8 d throughout all integrations of the nine planets (N±1，2，3)， which is about 1/11 of the orbital period of the innermost planet (Mercury). As for the determination of stepsize， we partly follow the previous numerical integration of all nine planets in Sussman & Wisdom (1988， 7.2 d) and Saha & Tremaine (1994， 225/32 d). We rounded the decimal part of the their stepsizes to 8 to make the stepsize a multiple of 2 in order to reduce the accumulation of round-off error in the computation processes. In relation to this， Wisdom & Holman (1991) performed numerical integrations of the outer five planetary orbits using the symplectic map with a stepsize of 400 d， 1/10.83 of the orbital period of Jupiter. Their result seems to be accurate enough， which partly justifies our method of determining the stepsize. However， since the eccentricity of Jupiter (∼0.05) is much smaller than that of Mercury (∼0.2)， we need some care when we compare these integrations simply in terms of stepsizes.
In the integration of the outer five planets (F±)， we fixed the stepsize at 400 d.
We adopt Gauss' f and g functions in the symplectic map together with the third-order Halley method (Danby 1992) as a solver for Kepler equations. The number of maximum iterations we set in Halley's method is 15， but they never reached the maximum in any of our integrations.
The interval of the data output is 200 000 d (∼547 yr) for the calculations of all nine planets (N±1，2，3)， and about 8000 000 d (∼21 903 yr) for the integration of the outer five planets (F±).
Although no output filtering was done when the numerical integrations were in process， we applied a low-pass filter to the raw orbital data after we had completed all the calculations. See Section 4.1 for more detail.
2.4 Error estimation
2.4.1 Relative errors in total energy and angular momentum
According to one of the basic properties of symplectic integrators， which conserve the physically conservative quantities well (total orbital energy and angular momentum)， our long-term numerical integrations seem to have been performed with very small errors. The averaged relative errors of total energy (∼10−9) and of total angular momentum (∼10−11) have remained nearly constant throughout the integration period (Fig. 1). The special startup procedure， warm start， would have reduced the averaged relative error in total energy by about one order of magnitude or more.
