Re: Hudson bay as an impact crater

On Mon, 23 Mar 2009 05:36:32 -0700 (PDT), Jack Linthicum
<jacklinthicum@xxxxxxxxxxxxx> wrote:

On Mar 23, 7:54 am, Richard Casady <richardcas...@xxxxxxxxxxxxx>
wrote:
On Sun, 22 Mar 2009 18:22:08 +0200, Eugene Griessel

<eug...@xxxxxxxxxxxxx> wrote:
Depends what you call "uncommon" - I think there are currently around
140 or so astroblemes that are accepted on the surface of the earth as
having an extraterrestrial impact origin, probably many more under the
sea.  Doubtless many more on land have been so eroded away that they
are no longer recognisable.

There is no reason to believe the earth has been hit either more or
less often than the moon. What with gravity the earth would be hit a
bit harder by any given rock, so the same bombardment would yield a
collection of slightly bigger craters.

Casady

I also have to ask if anyone else believes the effect of the Earth's
gravity on an incoming bolide is significant?

Not really - the more significant gravity field in the equation is
Jupiter. It has undoubtedly saved earth many times in the past from
incomings by perturbing the orbits. It has really been the big buddy.
By the time a large bolide's orbit is heading here it is hardly likely
that gravity plays a significant role in changing that orbital path.
Most of the large incoming stuff is tracked way beyond the orbit of
Mars and the minor alterations in course are very slight. If it is
going to get that close anyway we are probably doomed!

You can check the orbital elements for most life-threatening chunks on
the Harvard website - and these can be red into any number of astro
programs if you really want to know how doomed we are! I use Carte du
Ciel (which is a freebie) and it has an auto-updater link to the
Harvard site at:

http://cfa-www.harvard.edu/iau/Ephemerides/

Eugene L Griessel

Shotgun wedding - a case of Wife or Death.

- I post only from Sci.Military.Naval -
.

Relevant Pages

  • Re: How to Make Use of an Asteroid on Earth
    ... :>  SO, if you navigate the planetoid into a tight orbit say 1,000 km ... Earth or in space. ... Though the moon's gravity well is ... Getting resources from the asteroids - involve merely transporting ...
    (sci.space.policy)
  • Re: Gravity and the Sun
    ... > You have assumed that the Earth is free falling around the Sun ... > objects fall at the same rate in a gravity field. ... > orbit the Sun, but will either go away or fall straight to the Sun. ...
    (sci.physics)
  • Re: How to Make Use of an Asteroid on Earth
    ... :>  SO, if you navigate the planetoid into a tight orbit say 1,000 km ... Earth or in space. ... Getting resources from the Planets, and the Moon, involve transporting ... materials out of a gravity well. ...
    (sci.space.policy)
  • Re: airplanes and space flight
    ... The difficulty of getting to orbit is better ... > Only thing I can think is, that since earths gravity effects the craft ... the time you fall to the Earth, it's no longer there -- it's curved away ... > What if someone built a 30,000 ft high tube, similar to magnetic trains ...
    (sci.space.science)
  • Re: a new reward
    ... >> an object falls in a gravity field, it seems to be in accelerating motion. ... >> Earth, and we experience the acceleration as the surface of the Earth ... > C. - THE TIDAL FORCE ... both orbit the common center of mass of the pair. ...
    (sci.physics.relativity)