Jag minnde äntligen det! Eternity artifact (2006) av L. E. Modesitt. Han är en av mina mest favoritförfattare!
Från Goodreads:
Five thousand years in the future, humankind has spread across the galaxy and more than a dozen different planetary and system governments exist in an uneasy truce. Human beings have found no signs of other life anywhere approaching human intelligence. Until scientists discover a sunless planet they name Danann.
Moving at unnaturally high speed, Danann travels the void just beyond the edge of the galaxy. Its continents and oceans have been sculpted and shaped and there is but a single, almost perfectly-preserved megaplex upon the surface--with tens of thousands of near-identical metallic-silver-blue towers set along curved canals. Yet, Danann has been abandoned for so long that even the atmosphere has frozen solid.
Orbital shuttle pilot Jiendra Chang, artist Chendor Barna, and history professor Liam Fitzhugh are recruited by the Comity government and its Deep Space Service as part of an unprecedented and unique expedition to unravel Danann's secrets. And there are forces that will stop at nothing to prevent them, even if it means interstellar war.