Constraining astronomical models with geological data

就像树木年轮可以用来计算过去的天文年，古老的珊瑚生长年轮可以用来估计过去每年的天数一样，未受干扰的沉积岩层可能会记录地球和其他行星轨道结构的周期性变化。这些天文变化影响大气顶部接收的太阳光的量，透过气候系统(例如冰期)，最终影响沉积在例如深海中的沉淀物的数量和类型。这些天文参数的变化：地球的偏心率、倾斜度(倾斜)和气候进动(自旋轴的摆动类似于旋转的顶部)，发生在数千到数十万年的时间尺度上。最近才通过国际大洋钻探方案获得了深海必要的地质记录，该方案在几公里深的海床下数百米处采集沉积物岩心。然而，尽管我们预计每年的季节都会有规律地变化，但以内行星为主的太阳系配置在数百万年的时间尺度上并不那么规则--它已经显示出它是“混乱的”。这意味着不可能无限期地计算地轴的变化倾斜度等方面。这阻碍了地质学家利用这些变化作为估计时间的“节拍器”或起步器的努力。这项研究的目的是利用沉积记录中的特征模式来提取天文参数，这些参数可以用来延长模型计算有效的时间尺度。这对于约束天文学家无法以其他方式获得的基本物理参数是很重要的。更具体地说，我们希望从过去3000万至5000万年的深海沉积物数据中发现几次明显的混沌行为，在极端情况下，这甚至可以让天文学家非常准确地测试爱因斯坦广义相对论的预测。这里提出的研究将通过天文学家和地球科学家之间的一种新的合作来完成。我们提出的研究的另一个目的是限制天文地球模型的演变：由于海洋、地球、月球和太阳固体部分的耗散潮汐，以及由于冰期和地幔对流等引起的地球上质量的重新分配，地球的自转正在变化，并且通常随着时间的推移而减慢。由于能量守恒，这一过程也导致了地球和月球之间的距离增加，目前每年只有几厘米。为了准确计算太阳系，特别是地球的轨道构型和变化，重要的是要限制过去地球自转的这种变化的强度。同样，正如树木年轮可以提供干旱和潮湿年份的信息一样，记录在沉积物中的气候指标的详细模式可以用来提取过去地球模型的参数。我们现在可以使用新获得的沉积物岩心和额外的测量结果，为天文学家获取重要信息。

Just as tree rings can be used to count astronomical years back into the past, and ancient coral growth rings can be used to estimate the number of days per year in the past, layers of undisturbed sedimentary rocks can potentially record cyclical variations in the orbital configuration of Earth and other planets. These astronomical variations affect the amount of sunshine received at the top of the atmosphere, filtered through the climate system (e.g. ice ages), which finally influences the amount and type of sediment deposited in, e.g., the deep sea. Changes of these astronomical parameters: the Earth's eccentricity, obliquity (tilt), and climatic precession (wobble of the spin axis similar to a spinning top), occur on time scales of thousands to hundreds of thousands of years. The necessary geological records from the deep sea have only recently become available through the international Ocean Drilling Program, which recovers sediment cores from hundreds of metres below the sea bed in waters several kilometers deep. However, although we expect seasons to change very regularly every year, the solar system configuration of predominantly the inner planets is less regular on time scales of millions of years - it has been shown that it is 'chaotic'. This means that it is not possible to calculate aspects such as the changing tilt of the Earth's axis back in time indefinitely. This hinders geologist's efforts to use these changes as 'metronome' or pace-maker to estimate time. The aim of this research is to use characteristic patterns in the sedimentary record to extract astronomical parameters that can be used to extend the time scale over which model calculations are valid. This is important in order to constrain basic physical parameters that cannot be obtained otherwise by astronomers. More specifically, we hope to find several distinct occurrences of chaotic behaviour from deep sea sediment data during the past 30-50 million years that, in the extreme case, would even allow astronomers to very accurately test the predictions of Einstein's general relativity. The research proposed here would be accomplished through a novel collaboration between astronomers and Earth scientists. One additional aim of our proposed research is to constrain the evolution of the astronomical Earth model: due to the dissipative tides in the oceans, the solid parts of the Earth, Moon and Sun, as well as redistribution of mass on Earth due to, e.g. ice-ages and mantle convection, the rotation of the Earth is changing, and generally slowing down with time. Due to conservation of energy, this process also results in an increasing distance between the Earth and Moon, currently a few centimetres per year. In order to accurately calculate the orbital configuration and variations of the solar system, and the Earth in particular, it is important to constrain how strong this change in the Earth's rotation has been in the past. Again, just as tree rings can give information about dry and humid years, the detailed pattern of climate indicators recorded in sediments can be used to extract parameters of the Earth model in the past. We can now use newly available sediment cores, and additional measurements, to obtain important information for astronomers.