An artist's impression shows Pluto with its largest moon, Charon, facing a distant sun.
Who killed Pluto? Who said it was dead? The dwarf planet is still kicking, thanks to a new book by its "killer" as well as new rounds of research that reference the icy world.
The Pluto-killer, of course, is Caltech astronomer Mike Brown -- who along with his colleagues found a world on the solar system's icy frontier that outweighed Pluto. The discovery of that bigger world, now known as Eris, set off an international debate that led to Pluto's removal from the International Astronomical Union's official list of planets in 2006.
Brown (whose Twitter handle is @plutokiller) tells the story of the planet quest and Pluto's setbacks in a book titled "How I Killed Pluto and Why It Had It Coming." But the book is as much about his own life as a scientist and a father. Brown's daughter, Lilah, was born during the very time that his biggest scientific discoveries were coming to light.
Brown told me it would have been "impossible" to tell the scientific story without including the story of Lilah's birth and babyhood. "They are so intertwined in my life that I can't help but mix them," he said. "Lilah's birth and the mere fact that she was a week earlier than I anticipated changed the way some of the astronomy happened. I couldn't tell either story without mixing the two together."
Even as the book was being written, Lilah was drawn into the Pluto drama.
"When she started being conscious of the book and the title of the book, she didn't really think much about whether Pluto should be a planet or not, but she was pretty sure that killing was bad," Brown said. "And so maybe six months ago, she became angry at me for having killed Pluto. She would tell me that killing is bad, and I shouldn't do it, and I should make Pluto come back. I should unkill Pluto."
Caltech astronomer Mike Brown is the author of "How I Killed Pluto and Why It Had It Coming."
Brown said Lilah eventually reconciled herself to her father's ways. She told him to keep looking for a new planet -- and if he ever found one, would he please name it Pluto? Now that the book has finally come out, she's positively proud of her planet-killing pop. "She's no longer mad at me," Brown said. "Now she goes around and tells everybody that her daddy killed Pluto."
The 45-year-old professor said his 5-year-old daughter has done a good job of winning over her peers. "The kindergartners all think it's great," Brown said. "The parents are a little less sure what to think."
I can't help but imagine Lilah as a rebellious teenager, wearing a "Save Pluto" T-shirt just to spite her father. That might liven things up at the Brown household: Mike Brown said he feels a continuing obligation to explain why it makes the most sense to think of the solar system as having eight planets, plus smaller non-planets that just happen to include Pluto and the half-dozen or so worlds he has had a hand in discovering. After all, that's why he wrote the book.
"I would be very glad to be done with it," he said of his Pluto-killing role. "I do actually think that these issues and these questions and these conversations are profound for our solar system, so I think they're worth having. I wouldn't argue, like some people, that they don't matter ... that they're just semantics. I do think they matter profoundly. So as long as the discussion is continuing, then I think I will feel the need to be part of it."
You might think Brown would be more interested in boosting the status of the worlds he found. In the book, he tells how his wife, Diane, tried to keep him from dissing his own discoveries. And in fact, for a while he was OK with seeing Eris as "the 10th planet." But as the debate continued, Brown came around to the opinion that the solar system's list of planets had to stop at eight.
Divisions in the solar system
It's not so much that Brown defends the IAU's controversial definition of planethood. Brown said the definition was "pretty crummily written" but nevertheless ended up expressing the right concept. For Brown, the bottom line is that the eight largest things that go around the sun are in a special category for which the name "planet" should be reserved.
"Right now in the solar system, we are perhaps lucky, or perhaps it's a matter of physics ... but we have a solar system that draws a very strong line between the eight largest objects, which are in circular orbits and dominate the solar system; and everything else, the next biggest thing being Pluto or Eris, flip a coin. That division is easy to see and to make," he said.
"The funny thing that will happen is if there is something out there that someone finds that breaks that very clear division," Brown continued. "Something bigger than Mercury that is in a non-circular orbit and kicked around by the giant planets. It seems almost inevitable that something like that is out there. ... And when that object is found, it won't be a question about Pluto at that point, it will be a question of, 'OK, what is this?' It is going to be a difficult argument to say that something that's bigger than Mercury shouldn't be a planet. I'll make it, but I'm not sure I'm going to win that one."
Brown said he's still on the hunt for just that type of planet, somewhere on the very fringe of the solar system, "because there's nothing more fun than making astronomers argue all over again." He's involved in the SkyMapper project to survey the Southern Hemisphere's skies from Australia -- a celestial frontier that's not been as thoroughly explored as northern skies.
Pluto in the press
Of course, Brown doesn't have to wait until something bigger than Mercury shows up to have an argument, or at least a discussion. For some reason, Pluto and its little pals just keep coming up as topics for astronomers to talk about:
- A month ago, astronomers reported that they took a fresh set of measurements for Eris' size, and came to the conclusion that it was about the same size as Pluto or perhaps even a bit smaller. Brown noted that the comparative size "doesn't matter at all" when it comes to the dwarf planets' status in the solar system. What's more, Eris is known to be about 25 percent more massive than Pluto -- which would suggest that the two worlds have different compositions.
- In contrast, the similarities between Pluto and Eris are highlighted in an article appearing in Nature this week. The article was written by Alan Stern, a planetary scientist at the Southwest Research Institute who heads up the science team for NASA's New Horizons mission to Pluto. Stern observes that the surface composition of the two dwarf planets are "surprisingly similiar," with the abundance of nitrogen at 90 percent or more, and methane at 10 percent or less. The similarities extend as well to Triton, a moon of Neptune that is thought to have originated in the same zone that gave rise to Pluto and Eris. Stern said recent reports suggest that New Horizons' findings "will be of relevance to a broader suite of small planets common to the outer solar system."
- Just today, researchers reported in the journal Science that some of Earth's precious metals must have been left behind by a collision with a Pluto-sized celestial body 4.5 billion years ago. The lead researcher, Bill Bottke, is a colleague of Stern's at the Southwest Research Institute. "The populations that were hitting Earth, the moon and Mars were pretty top-heavy," Bottke told Space.com. "Most of the mass was in the big guys." Big guys? He's talking about Pluto-sized objects, right?
Such references demonstrate that Pluto isn't dead yet. Lilah Brown needn't have worried so much about her father's murderous ways: Pluto is still out there, secure in its orbit. Scientists (including Brown) are still fascinated by dwarf planets and seeking to learn their secrets. Regular folks are fascinated by the story of Pluto's ups and downs -- which is why people keep writing about it. That goes for Brown's book as well as my own, "The Case for Pluto," which takes up the other side of the argument.
The interest in Pluto and its kin is likely to rise even higher in 2015 -- when New Horizons is due to fly by Pluto while NASA's Dawn probe settles into orbit around another dwarf planet, Ceres in the asteroid belt. (Dawn's rendezvous with the asteroid Vesta is likely to be one of next year's astronomical highlights.)
Brown's book provides yet another opportunity to read about, think about, and talk about how we see the cosmos around us -- and whether you think Pluto is dead or alive, that's a good thing.
More about 'How I Killed Pluto and Why It Had It Coming':
- Bad Astronomy: How to settle the 'What's a Planet' debate
- On Point: The man who killed Pluto (and other space odysseys)
- Universe Today: Q&A with Mike Brown, Pluto killer
- Daily Kos: How I killed Pluto
- New York Times: When a heavenly body got the boot
- The Atlantic: Read an excerpt from 'How I Killed Pluto'
More about 'The Case for Pluto: How a Little Planet Made a Big Difference':
- 80 years of Pluto
- A Pluto pilgrimage
- Pluto maps raise new questions
- Interactive: The new solar system
- More Cosmic Log coverage of Pluto
- Read an excerpt from 'The Case for Pluto'
Correction for 2 p.m. ET Dec. 10: I think of the Southwest Research Institute so much as SwRI that I mistakenly wrote Southwest "Regional" Institute. Thanks to Brent Markus for pointing out the error.