Heaven's Shadow - David S Goyer

Heaven's Shadow begins with the discovery of an object of unknown origin headed toward Earth. Speculation as to what it might be runs high, and leads to an international competition to be the first to land on it, to claim both the prestige and whatever other benefits there might be. Thus, two rival teams of astronauts begin a thrilling and dangerous race - but what they find when they reach their goal will turn out to be unlike anything they could have imagined . . .

What they have landed on is no asteroid but a spacecraft from a civilization that has travelled tens of thousands of years to reach earth. While the team try to work out what it is they are needed for, more sinister occurrences cause them to wonder if their involvement with this alien race will ead to anything but harm for humanity.