Question on binary stars, Jovian planets, and comet impacts

[Junghalli]

This is something I've been wondering about. I know Jovian planets supposedly play an important role in shielding Earth from comet impacts. Now, in a relatively close binary system like Alpha Centauri there isn't room for such a planet, unless maybe it orbits both stars (orbits beyond the snow line are unstable because of the binary star), but would the binary star possibly serve an equivalent function? I would think that a binary star at, say, 20 or 40 AU out would be quite efficient at ejecting any comets with orbits that crossed into the inner solar system, and this would effectively protect inner terrestrial planets from comet impacts, hence complex life might have a good chance of being able to develop in such a solar system even without a Jovian planet present.

Is that reasonable, or am I wrong?

[Temujin]

It sounds rather reasonable, as while the distance from the planet is further, the star's mass is much greater. However, I believe there has been speculation that such a system could eject too many comets, and hence leave the planets short of water.

[Junghalli]

However, I believe there has been speculation that such a system could eject too many comets, and hence leave the planets short of water.

Deuterium ratios seem to indicate only ~10% of Earth's water at most came from comets (link) so that might not be a serious problem. A more serious problem might be where the stars are close enough that the inner icy regions would be swept clear.