I finished "Impact" by Douglas Preston last night. This is the third book in his "Wyman Ford" thriller series, and it's one to be avoided. Mr. Preston writes excellent "techno-thrillers", but this one is just silly. An alien space weapon, hundreds of millions of years old, buried in one of the moons of Mars, is awakened by a modern space probe, and threatens to destroy the Earth. Can Wyman Ford and a young girl (who just happens to be a genius) defeat it? I knew this was going to be a bad one when the aforementioned girl set up a telescope, looked at Orion, and saw... the Andromeda Galaxy! (The reason it's called "the Andromeda Galaxy", Mr Preston, is that it's in the constellation of Andromeda, which is nowhere near Orion.)
Mr Preston's written some excellent thrillers (including the two previous book in this series), but this one's just silly. Don't waste your time with it.
In case you're ever faced with the problem of having to stop an alien super-weapon from destroying the Earth, by the way...
Spoiler:
... you do so by sending it the message "WE SURRENDER" from your local TV station's satellite downlink dish. So now you know
.