据国外媒体报道，多年前世界末日预言者曾预言，称一颗未探测到的同伴恒星将周期性地向地球释放彗星，像宇宙时钟一样周期性地导致地球物种大灭绝。目前，一位天文学家已掌握确凿证据，并声称彗星或者小行星周期性变迁并不存在。
在最新一项研究中，研究人员指出叫做“涅墨西斯”或者死亡之星的一颗黑暗同伴星体将于2012年碰撞地球，带来毁灭性灾难。像其它神秘的2012灾难论，涅墨西斯假设论具有一定的科学研究支持：1984年，古生物学家提议每间隔2700万年天外星体将对地球构成毁灭性灾难。最初认为一颗褐矮星或者红矮星在太阳系边境破坏彗星轨道，并将彗星喷射释放至地球方向。
“涅墨西斯”具有X行星假设——它有一颗未探测到的行星潜在碰撞地球，同时，这种假设也与古代玛雅日历上的预言相符。但显然这种担忧性完全是臆造的，玛雅人“长期计算”的预言仅是一个日历而已，当时并没有任何科学工具进行计算分析。
2010年，研究人员报道称，如果邻近太阳系不远的“涅墨西斯”的确存在，那么它并不一定环绕一个2700万年的精密运行周期。这项研究发表在《皇家天文学会快报》上，并对涅墨西斯假设论描述为“最后的棺材钉”，但研究人员仍不能解释为什么地球物种灭绝周期为2700万年。美国堪萨斯大学物理学家艾德里安-米劳特称，对我而言，”这是一个非常棘手的问题“。
目前，德国马克思-普朗克天文学会研究员哥伦-巴勒-琼斯称，米劳特应当不必对此感到头疼。他发表在《皇家天文学会月刊》的分析文章指出，所谓“涅墨西斯”星体周期性释放彗星可能仅是一个模型，除非是经过统计学人工计算得出该结论。
琼斯在马克斯-普朗克学会的报道中指出，人们倾向于发现并不存在的自然现象，但不幸的是，一些确凿的统计分析数据显示出它的弱点。他观测了历史时期地球成坑比率，使用一种替代性方法评估了贝叶斯统计分析法的可能性。贝叶斯统计分析法提供了统计学的真实性检测，该分析排除了简单的周期性变化。相反，统计分析数据显示在过去2.5亿年以来地球陨坑成坑率逐渐增大。（生物谷 Bioon.com）
doi:10.1111/j.1365-2966.2011.19112.x
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Bayesian time series analysis of terrestrial impact cratering
Bailer‐Jones, C. A. L.
Keywords:methods: data analysis;methods: statistical;Earth;meteorites, meteors, meteoroids;planets and satellites: surfacesABSTRACTGiant impacts by comets and asteroids have probably had an important influence on terrestrial biological evolution. We know of around 180 high‐velocity impact craters on the Earth with ages up to 2400 Myr and diameters up to 300 km. Some studies have identified a periodicity in their age distribution, with periods ranging from 13 to 50 Myr. It has further been claimed that such periods may be causally linked to a periodic motion of the Solar system through the Galactic plane. However, many of these studies suffer from methodological problems, for example misinterpretation of p‐values, overestimation of significance in the periodogram or a failure to consider plausible alternative models. Here I develop a Bayesian method for this problem in which impacts are treated as a stochastic phenomenon. Models for the time variation of the impact probability are defined and the evidence for them in the geological record is compared using Bayes factors. This probabilistic approach obviates the need for ad hoc statistics, and also makes explicit use of the age uncertainties. I find strong evidence for a monotonic decrease in the recorded impact rate going back in time over the past 250 Myr for craters larger than 5 km. The same is found for the past 150 Myr when craters with upper age limits are included. This is consistent with a crater preservation/discovery bias modulating an otherwise constant impact rate. The set of craters larger than 35 km (so less affected by erosion and infilling) and younger than 400 Myr is best explained by a constant impact probability model. A periodic variation in the cratering rate is strongly disfavoured in all data sets. There is also no evidence for a periodicity superimposed on a constant rate or trend, although this more complex signal would be harder to distinguish.
