John Matese and Daniel Whitmire of the University of Southwestern Louisiana, Lafayette, in a recent paper say that tide-like variations in the pull exerted on the orbit of the solar system by the rest of the galaxy causes comets to pummel Earth once every 30 million years. Most comets orbit the sun in the Oort cloud, which lies 100,000 times farther out than the Earth. If the orbits are disturbed, some comets may fall into the inner solar system and crash onto Earth.
The team has calculated orbits into which comets from the Oort cloud could be tugged by the tides. There are two tidal forces, one which tugs matter in a direction perpendicular to the plane of the galaxy, and one -- the radial tide -- which pulls toward the centre of the Milky Way. Of the 84 comets studied, one-third are in orbits that had been influenced by the radial tide while in the Oort cloud. The probability that this could occur by chance is only two in a million (New Scientist , Vol 152, No 2062).
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
.png)
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.