Pluto. Poor little guy. He never wanted much. The others could be bigger, they could be better-looking or brag about themselves (“I’m burning hot!” or “I have rings!” or “I support life!”). He didn’t care. All he wanted was to be part of the planet club. And for about 75 years, that tiny frozen world billions of miles from the sun was a card-carrying member.

Then, in 2006, Pluto was kicked out — reclassified as a dwarf planet.

The credit — or, for the outraged nine-planet fans, the blame — goes to the International Astronomical Union. It also goes to Caltech astronomer Mike Brown, who just couldn’t help finding other tantalizing objects at the edges of the solar system that challenged Pluto’s planetary status.

“I would hear from many people who were sad about Pluto,” Brown writes in “How I Killed Pluto: And Why It Had It Coming.”

“And I understood. Pluto was part of their mental landscape, the one they had constructed to organize their thinking about the solar system and their own place within it.”

Brown’s book brims with humor and charm as he describes the thrill of the hunt that compensates for all the drudge work involved in astronomy.

Sure, he says, there’s certainly more ease today than in the 1930s when Clyde Tombaugh found Pluto. But hunting for distant objects is still a painstaking process of sifting images, either with computers or a magnifying glass, to find that faint dot that is more than just a scratch on the lens. There are also plenty of long, tedious nights and a frustrating application process to use the mightiest telescopes on the ground and the Hubble Space Telescope overhead to confirm calculations.

Brown’s a warm, generous guide, acknowledging the work of his colleagues — Chadwick Trujillo and David Rabinowitz — and also his readers’ limitations, using language that’s clear and simple. He includes touching glimpses of his marriage and the birth of his daughter that act as a nice counterpoint to the galactic story he’s telling (during his courtship of his wife, Brown says, the many “no’s” he experienced during the hunt were balanced by her “yes” to his proposal).

Don’t assume, however, that the astronomy business is pure romance. Hardly. There’s plenty of professional jealousy and dishonesty: Brown describes how a Spanish scientist might have stolen the claim to one of his team’s discoveries if there hadn’t been a computer trail showing that he was spying on the telescope positions of Brown’s team.

He also recounts the tortured collective decision-making of the IAU, during its 2006 meeting, when it first proposed revising the solar system to include 12 planets — adding, along with Brown’s discovery of Eris (a distant body slightly larger than Pluto), the asteroid Ceres and Pluto’s moon Charon — and then created a dwarf planet category instead.

Brown had much to gain by the former idea — how cool is it to have “planet discoverer” on your CV? — but he says he was pleased by the IAU’s decision because it “put a scientific foundation behind what most people think they mean when they say the word ‘planet.”‘

After Pluto’s demotion, one group wasn’t pleased: astrologers. They got over it, though, and Pluto’s still very important today in the making of horoscopes. And, for $12, you can still buy a glow-in-the-dark, hanging mobile of the solar system for your kids that features the sun and nine planets.

But scientists like Brown can’t go along with fortune-tellers or toymakers for a reason that’s unavoidable: the Kuiper belt. Out there, starting around the orbit of Neptune, are “vast numbers of small icy objects (that) circle the sun in cold storage” that are leftovers from the creation of the solar system. Pluto — along with Eris and other objects — are more rightly members of the Kuiper club, named for the astronomer who speculated about the belt’s existence, Gerard Kuiper.

Brown’s book is exhilarating for a simple reason: He directs our attention at something we never think about.