I was wondering what your readers thoughts might be on this subject.
How come the earth has not smashed into a larger object, like
all these dumb comets and meteors keep doing? Have we just been
very lucky, or are we well overdue? Sorry to bring such a grim subject up.
The earth was hit by comets and asteroids gazillions of times. Most of these, however, took place in the early days of the solar system. One really big one, maybe the size of Mars, hit the earth so hard that a chunk broke off and became the moon. Strikes were a major effect for hundreds of millions of years. Over billions of years the smaller debris were captured by the gravitational fields of the larger bodies and the number of objects flying randomly around the solar system decreased by an astounding percentage.
A few are still out there, and we are still hit by micro-meteors all the time, pebble-sized objects occasionally, and so on up the scale until a major mile-wide body hits maybe once every half a billion years. There is a band of snowballs called the Oort cloud that are perturbed by gravitational forces and become long-period comets. One of these will hit us eventually. (And maybe short-period comets out of another, closer, region called the Kuiper belt.) But that’s eventually in geologic time. It’s unlikely to happen in human scale time.
We have asteroids come as close as the moon on a regular basis, though. Nothing out there right now is known to have an orbit that will hit earth. It wouldn’t be very surprising for one to hit in the next thousand years or even the next hundred. But we’re not overdue. This is a completely random process. It might not happen for 100,000 years.
It’s not something that anybody is worried about. We have more immediate crises here on earth. But it’s a real risk, even if very long-term and low-probability. Such events are thought to have precipitated many of the major extinctions on the planet. Of course, the last one of those was 65,000,000 years ago. I’m not losing any sleep over it.
Is this what you’re actually asking? Why the earth hasn’t smashed into, say, the sun or one of the larger planets?
I accept that they are hitting us , BUT why are nt we hitting anything else .Dont forget we are travelling in an orbit too. And dont worry I am not losing any sleep over the matter, Im an insomniac anyway! 
YES!
Erm… NO! I think Im talkin about s*&t beyond our solar system!
Because orbits are stable. Unless something huge happens - like another sun coming through the system and perturbing everything - the planets (and even the asteroids) are locked in their orbits essentially forever.
WOW! Thats comforting. Cheers mate, i`m happy with that one!
Cite?
As an aside, you might also look up the subject of the long-term stability of the Solar System; something that’s interested astronomers and mathematicians for centuries. In general, the current arrangement- each planet’s orbit is about, but never exactly, twice as far from the Sun as the next nearest one- seems to be one that is very highly stable over billions of years. You might not be able to predict exactly where in it’s orbit the Earth will be one billion years and six days from now, but that it will still be in about the same orbit as it is now seems virtually guaranteed.
The shit beyond our solar system is so mind-blowingly far and sparse that I doubt anything large will ever hit us before the sun goes bye-bye. Unless the universe goes the way of the big crunch, which wouldn’t happen for billions of years anyway, we’re unlikely to ever encounter much of anything. Our galaxy might collide with another one, but the chances of our solar system actually physically smashing into some other object even when galaxies collide are pretty small.
We are specks of dirt in a huge and expanding universe. There is huge amounts of space between everything.
Ps Nobody is worried about getting hit? Wrong .we have telescopes all over trying to identify the final rock. It will happen again. We just do not know when. Check out
http://neo.jpl.nasa.gov/neo/ Identification and odds of getting hit .
Meteor Crater, AZ, looks like something smashed into us.
So do some sites off the Yucatan Peninsula, in Mexico / Guatemala.
And anything on a comparable scale as Earth in a position for Earth to collide with, under generally accepted models the collisions happened in the range of 4 to 5 billion years before present. Since then – there ain’t anything there large enough to be an issue.
Thanks to all of you for your answers, guys[and any gals].There was some interesting, informative stuff there. Again, Cheers.
from col.