Impact cratering and the Oort Cloud

Wickramasinghe, J. T.; Napier, W. M.

doi:10.1111/j.1365-2966.2008.13098.x

Cited by 30 publications

(20 citation statements)

References 30 publications

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“…For a quarter of a century, evidence that confirms the existence of real periodicity in these catastrophic events has been published, e.g. by Stothers (1998), Moon et al (2003), Yabushita (2004), Chang & Moon (2005), Stothers (2006) and Wickramasinghe & Napier (2008). Evidence against such periodicity has also been presented, e.g.…”

Section: Introductionmentioning

confidence: 74%

Detection of real periodicity in the terrestrial impact crater record: quantity and quality requirements

Lyytinen

Jetsu

Kajatkari

et al. 2009

A&A

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Aims. To determine the quantity and quality requirements for the terrestrial impact crater data which would allow reliable detection of real periodicity. Methods. Artificial impact crater data samples of different size and accuracy are simulated. Erosion is considered, as well as the effect of the unknown ratio between periodic and aperiodic impacts. The probabilities for detecting real and false periodicities are solved with the Rayleigh test from these simulated data.Results. Reliable detection of real periodicity is currently impossible -unless all impacts on Earth have been periodic.

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Section: Introductionmentioning

confidence: 74%

Detection of real periodicity in the terrestrial impact crater record: quantity and quality requirements

Lyytinen

Jetsu

Kajatkari

et al. 2009

A&A

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“…Since then, several authors have claimed that there is a significant periodic signal present, but the periods differ quite a lot from study to study. The signal is the most prominent for 40 large, well‐dated craters that are up to 250 Myr old (Napier 2006), but the period is difficult to measure, with estimates of between 24 and 26 Myr (Napier 2006), 30 Myr (Napier 2006; Stothers 2006), 36 Myr (Napier 2006; Stothers 2006), 38 Myr (Yabushita 2004; Wickramasinghe & Napier 2008) and 42 Myr (Napier 2006).…”

Section: Introductionmentioning

confidence: 99%

The effect of the solar motion on the flux of long-period comets

Gardner¹,

Nurmi²,

Flynn³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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The long‐term dynamics of Oort cloud comets are studied under the influence of both the radial and the vertical components of the Galactic tidal field. Sporadic dynamical perturbation processes, such as passing stars, are ignored since we aim to study the influence of just the axisymmetric Galactic tidal field on the cometary motion and how it changes in time. We use a model of the Galaxy with a disc, bulge and dark halo, and a local disc density and disc scalelength constrained to fit the best available observational constraints. By integrating a few million of cometary orbits over 1 Gyr, we calculate the time variable flux of Oort cloud comets that enter the inner Solar system for the cases of a constant Galactic tidal field and a realistically varying tidal field, which is a function of the Sun's orbit. The applied method calculates the evolution of the comets by using first‐order averaged mean elements. We find that the periodicity in the cometary flux is complicated and quasi‐periodic. The amplitude of the variations in the flux is of the order of 30 per cent. The radial motion of the Sun is the chief cause of this behaviour, and should be taken into account when the Galactic influence on the Oort cloud comets is studied.

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“…The multibody dynamics involved in putting these on a collision course with the Earth implies that cratering is a random phenomenon, but the rate of impacts is not necessarily constant in time. It has been suggested that gravitational perturbations of the Oort cloud due to the Galactic tide, passages of the Solar system near to molecular clouds, or an unseen solar companion, may send large numbers of comets into the inner Solar system as a comet shower, increasing the impact rate (Davis, Hut & Muller 1984; Rampino & Stothers 1984; Torbett & Smoluchowski 1984; Napier 1998; Wickramasinghe & Napier 2008; Gardner et al 2011). Simple dynamical calculations indicate that the Sun oscillates vertically about the Galactic mid‐plane with a period of 52–74 Myr, depending on the mass density assumed (Bahcall & Bahcall 1985; Shuter & Klatt 1986; Stothers 1998).…”

Section: Introductionmentioning

confidence: 99%

Bayesian time series analysis of terrestrial impact cratering

Bailer‐Jones¹

2011

Monthly Notices of the Royal Astronomical Society

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Giant 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 2400Myr and diameters up to 300km. Some studies have identified a periodicity in their age distribution, with periods ranging from 13 to 50Myr. 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 250Myr for craters larger than 5km. The same is found for the past 150Myr 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 35km (so less affected by erosion and infilling) and younger than 400Myr are 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.Comment: Minor typos corrected in arXiv v2. Erratum (minor notation corrections) corrected in arXiv v3. (Erratum available from http://www.mpia-hd.mpg.de/~calj/craterTS_erratum.pdf

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Impact cratering and the Oort Cloud

Cited by 30 publications

References 30 publications

Detection of real periodicity in the terrestrial impact crater record: quantity and quality requirements

Detection of real periodicity in the terrestrial impact crater record: quantity and quality requirements

The effect of the solar motion on the flux of long-period comets

Bayesian time series analysis of terrestrial impact cratering

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