"Bowl of Heaven" (Tor Books), by Gregory Benford and Larry Niven

About 100 pages into "Bowl of Heaven," I realized it isn't a stand-alone book. There's no mention of more volumes on the book jacket, but the world imagined here is too vast, the questions too many for 416 pages.

Once you come to terms with reading "to be continued" on the last page, it's easy to settle in and enjoy the sci-fi smorgasbord served up by Gregory Benford and Larry Niven.

There's a lot to savor. Fans of so-called "hard science fiction" will enjoy the descriptions of ionic scoop fusion drives and all the solar-powered gadgets put to practical use during deep space exploration.

The year is many centuries in the future. Earth is almost uninhabitable, and a brave band of intergalactic explorers is bound for Glory, a planet that tests show might provide a new start for humanity.

But sci-fi is never that simple.

Partway to their destination, the crew encounters a gigantic floating structure among the stars and veers off course to check it out.

"Bigger than the orbit of Mercury, huge beyond comprehension, the hemisphere was an artifact, a built thing, the first evidence of another intelligence in the galaxy," the authors write.

What Earth's refugees find on the surface poses some of the questions that science fiction has long enjoyed pondering: Are we alone? What does it mean to be human? And does evolution ever end?

First contact is oddly anticlimactic. The most evolved aliens are birds taller than 9 feet high that look somewhat like ostriches and are called Astronomers.

"The native ... strode forward on legs that articulated gracefully, taking great long strides. Mouth like a stubby beak. Spindly long arms ending in complicated hands."

Some of the best chapters are narrated by an astronomer named Memor. (Is it significant that the y is missing?) Reading them brings to mind how zoo animals must feel as we gawk at them in their manufactured habitats.

The human characters aren't very well developed by the end of book one. At times you find yourself cheering for the aliens to wipe out the hardy band of humans they call Late Invaders. Cliff, Beth, Irma and the rest spend a lot of time resorting to base animal instincts — arguing with each other and endlessly seeking food and water. But are they captives or free to continue on their way?

You'll only know if you read book two, "Shipstar," which the authors promise is "following soon."