Mike Brown always wanted to discover a planet. On August 25, 2006, Mike Brown killed Pluto.

Well, the truth is Pluto had been killed long before, but it wasn't until August 25 that the International Astronomical Union met, in Prague, to have the official vote. And it wasn't until August 25 that the press conference was held at Caltech, during which Mike Brown said, "Pluto is dead."

Xena was dead too, but the public didn't really care about Xena, briefly the "tenth planet." It wasn't actually Mike Brown that killed Pluto, it was Xena. But Mike Brown was the man who discovered Xena, so in a way, it was all his fault. You see, Xena is bigger than Pluto. Xena had its own moon, Gabrielle. And if Pluto was a planet, then Xena should be too. If if Xena was not a planet, Pluto should probably not be classified as a planet either. Now, Pluto, Xena, and a handful of other rocks orbiting our sun way out there are classified as "dwarf planets." Which aren't really planets at all.

Mike Brown is an astronomer at Caltech, and author of How I Killed Pluto and Why It Had It Coming. In his book, he writes about what the Pluto vote meant for him and his wife, Diane:

In the days that followed, I would hear from many people who were sad about Pluto. 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. Pluto seemed like the edge of existence. Ripping Pluto out of that landscape caused what felt like an inconceivably empty hole.

That first morning, Diane was having the same reaction, but for Xena instead of Pluto. For her, Xena was more than the thing that used to be called "the tenth planet." She had listened to me enough over the previous eighteen months that she had gotten to know all about the onetime tenth planet. She knew about its tiny moon, its incredibly shiny surface, and its atmosphere frozen in a thin layer all around the globe. Diane and I had discussed the excitement of the search, what to name the tenth planet, and how many more like it might be out there. Xena had become as much a part of our own mental landscapes as Pluto might have been for anyone else. And Xena would be forever linked in our minds to our daughter, Lilah, who was only three weeks old when Xena was announced to the world. All of those memories of the first months of Lilah's life -the lack of sleep, the dazed confusion, the questions about what life would be like after this sudden change - were tied up with all of our memories of what became tenth-planet mania - the rush to learn more, the push to discover others, the questions about what life would be like after this sudden change. And now, just a little after Lilah's first birthday, Xena was gone.

Are you confused about the names Xena and Gabrielle? Those are the code names used by Mike Brown and his colleagues before the objects were formally named. Xena is now known as Eris, the largest dwarf planet, and its moon is Dysnomia, who in Greek mythology is Eris' daughter and the demon spirit of lawlessness.

In this incredibly easy-to-read book, Brown tells the story of how he became a discoverer of planets, of long sleepless nights spent looking through telescopes and poring through data, and of scientific mysteries. Along the way - almost without the reader noticing - Brown explains quite a bit about how planetary science works. What constitutes a planet? How have those rules changed? If you're sitting there with your telescope, how do you know if you've spotted a planet anyway? How can you tell what that planet is made of without flying out to sample it? Is it possible to tell what the weather there is like?

To anybody who is mad that Pluto is no longer a proper planet, I'd recommend this book. Perhaps you'll come away with a bit less scorn for the planetary astronomers.

But more importantly, this book offers an important glimpse into the inner workings of a scientific field. It offers readers a chance to understand the human side of discovery, a rare peek at the edge of knowledge where objectivity and subjectivity sometimes overlap. Through the course of the book, Brown digs deep into important questions like: who gets the credit for new findings? What if two groups of scientists, working independent of each other, make the same discovery? And what if one of those groups, well, cheated? And what does it say about the state of scientific inquiry if a planet can be brought down by a majority vote?

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