The Wall Street Journal recently asked me to review a new book called First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth. Astrobiology is a tricky subject to write about these days. It’s intensely exciting, despite the fact that its main object of study–life on other planets–has yet to be discovered.

I’ve given some thought to how we journalists should cover such a paradoxical science. We shouldn’t dismiss it outright, because astrobiologists have discovered fascinating things about life here on Earth, even if they have yet to find aliens. Yet we shouldn’t feel obligated to pump up every claim about the possibility of life elsewhere. We should be content to paint a portrait of the scientific process–including the intense debates–in all its gorey detail.

By this measure, I don’t think First Contact works. The author, Marc Kaufman, declares at the outset of the book that “before the end of this century, and perhaps much sooner than that, scientists will determine that life exists elsewhere in the universe.” Not whether life exists, mind you, but that it exists.

I don’t think he backed up that bold claim. Instead, he ...