Post by Quadibloc
True dat. In David Weber's "The Armageddon Inheritance", the Achuultani
use many large space ships to move the entire moon of Iapetus into
position to crash into Earth.
Of course, in the real world, if somebody wanted to crash something into
the Earth, they would have much better places to find it in than the deep
gravity well of Saturn.
To be fair, they've already tried crashing probably thousands? of
smaller (but not small!) rocks into Earth and a number has gone
through to hit the planetary shield (most were redirected or blown
IE, they've already thrown everything from small Tunguska sized ones
up to rocks larger than the Chicxulub impactor at Earth.
So the Achuultani finally decided to go BIG *and* far out from Earth
to avoid the defenders even being able to see it before they started
moving it (they IIRC failed but it did delay detection). They don't
stop grinding Earth defences using smaller rocks just because of this
I assume Jupiter has moons in a similar mass range but in setting it
can easily be argued that Iapetus made sense for them to use.
Being far out actually helps them considering their (effectively
magical) drive systems, it gives them more time to build up speed,
lots and lots of speed.
Starting from an orbit further out means a greater starting speed
differential and they also went the "long" way and accelerated all the
way, instead of just changing the speed enough for a transfer orbit
Make no mistake, even on an transfer orbit from Saturn with "minimum"
impact energy Iapetus would make Chicxlub look like a firecracker but
it does give the defenders a lot of time to try to do something about.
Coming in at a high multiple of this speed makes deflecting it a LOT
harder and in-story the humans still ALMOST managed to do this, at the
cost of almost all their remaining spacecraft. Then <SPOILER>
Post by Quadibloc
But I suppose it's a good way to demoralize the people of Earth, by showing
them just how powerful Achuultani technology is.
They already know they WILL loose unless Colin comes back with a
miracle, it's just a question of how long it will take them to be
Throwing something that large and fast limit the options for the
defenders and force the specific response the Achuultani want - the
defenders HAS to come far outside the range of the Earths orbital
defences with every mobile platform they still have available to try
to deflect it or it's "game over".
Just because the Achuultani know they will win eventually doesn't mean
they don't want to reduce their losses, even if it's just a small
scouting force of many.
Iapetus weighs more than 100,000 times as much as the best guess of
the Chicxlub impactor AND it's coming in at IIRC 100+ km/s vs the ~20
km/s Chicxlub came in on. So the impact would have millions of times
the energy of that one...
Even calling it "Extinction level event" is grossly underselling what
this would do to Earth. I strongly doubt it would punch through but
"X% of the Earth is melted" is NOT a good thing when it shows in an
Asteroid Impact Calculator.