Qfyilyi

This was a novel, in paperback, and I don't remember the title, author, or cover art.

What I remember about the story includes words such as:

• polity


• yellow energy


• needles (small attack spaceships)

and the story was about an expedition to a rogue planet, far out in the middle of nowhere, with one city, with extremely advanced technology, so advanced that almost none of it was understandable by the various people.

The expedition was several ships, including one huge ship, and they went through some type of gates that transferred the ships across many light years each time.

Two of the main characters were a historian who was previously a commando, and a pilot, and by the end of the story they decided to marry.

Another main character was an artist, who discovered an artifact in one of the buildings, which none of the scientists were able to discover.

I finally remembered it! The Eternity Artifact (2006) by L. E. Modesitt. He is one of my most favorite authors!

From 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.