interesting but there is one BIG flaw. for other heavenly objects to be moving in elliptical orbits that big there must exist a huge source of gravity pulling the planet along. there are no record of such massive "suns" existing.

not so.

no known object moves in a perfectly circular orbit -- a circle is a special case of an ellipse with zero eccentricity anyhow, so technically even a circular orbit is "elliptical"

pluto the (proto-) planet has a very eccentric orbit that crosses inside neptune's orbit periodically.

kuiper belt objects are pretty small in relation to planets.. only a few kilometers across. so to scale, a neptune, jupiter or a saturn is a sufficiently "sun-sized" mass.

an object doesn't have to be acted on by two very massive gravity wells in order to have a very eccentric orbit either -- the kuiper belt objects you're probably most familiar with are comets -- some of which are in hyperbolic orbits - meaning they swing around the sun only once in their lifetimes and then are flung out into the universe at some oblique angle. the missing force you expect to be due to another sun-sized mass is explained by their initial velocity and angle of approach. generally, any comet we see is in a very eccentric, elliptical orbit ( if they were more circular and stayed distant, or otherwise didn't pass close to the sun, they wouldn't have a tail and so wouldn't be visible )

now back to our story..

Velikovsky's scenario doesn't even require something to be in a closed orbit - like i mentioned about some comets, it's entirely possible that an object of any mass could pass through the solar system on a hyperbolic orbit, never to be seen again. AND the r^2 orbit is very stable, so even if a mass the size of all the other planets combined came as close to the earth as the moon's orbit, then zoomed on out of the solar system, in just a few years earth would be more or less back in it's regular orbital path and we would be none the wiser. kuiper belt objects? probably not - these are SMALL. the moon herself, only 3 days journey from here, is WAY more massive than any known proto-planet ( like 1.5 times bigger than pluto ), and only moves the tides a few inches by her gravity. for an object half the size of the moon to cause worldwide flooding, it would have to get close enough to splash down.. =\ hmm no record of THAT 3500 years ago.

for another interesting take on what could have caused the flood, read stephen baxter's new book "Flood"

there is good evidence that earth's mantle contains underground oceans containing perhaps as much as 4 times as much water than all the oceans on the surface holds. in the biblical account:

In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.

the water not only came from the clouds above but from underneath the ground!

we know less about what lies a few miles under our feet than we do about the kuiper belt -- we have no idea what unknown forces in the core could cause an upwelling of the underground oceans, or what possible extent such an event might have. now THAT is interesting.