Man who 'killed Pluto' has no regrets

By Pallab Ghosh
Science correspondent, BBC News

image source, SPL
image caption, Pluto killer: Prof Mike Brown says he has no regrets about his role in Pluto's demotion

The New Horizons flyby has renewed calls for Pluto to be reinstated into the club of planets from which it was unceremoniously dumped in 2006.

But Dr Mike Brown of Caltech in Pasadena, who rejoices in the sobriquet of "the man who killed Pluto" told BBC News that those arguing for its reinstatement should stop living in the past.

"The people you hear most talking about reinstatement are those who are involved in the (New Horizons) mission. It is emotionally difficult for them," he said.

"They want Pluto to be a planet because they want to be flying to a planet. They would be far better off embracing the reality that it is not a planet and being excited about the fact that they are going to a new type of object in the outer Solar System."

Coup de grace

Calls for Pluto to be downgraded intensified after a candidate Kuiper Belt object was discovered in 1992. Some argued that Pluto was simply the first resident of this outer Solar System region to be discovered.

But the coup de grace was delivered by Prof Brown with his discovery of the dwarf planet Eris in January 2005. It was like Pluto but more massive.

This was one of the finds that eventually led the International Astronomical Union to set up a committee to examine how planets should be defined.

image caption, An artist's impression of Eris; its discovery did much to force the issue over Pluto's planet status

The IAU was forced to decide in 2006 whether it would admit Eris and other small worlds like Ceres, or boot out Pluto. It was a choice of one or the other - the status quo was not an option.

Prof Brown argues that had the IAU had decided to keep Pluto as a planet and enrol Eris, it would eventually find itself having to consider the candidacies of hundreds, possibly thousands of wannabe planets.

"There is no other way of categorising our Solar System than to describe it as having eight dominant objects in it which are the planets we know. It is really no good keeping Pluto and classifying it as one of the major objects because it is just not," he told BBC News.

So how did Prof Brown feel the day he heard that Pluto had been demoted? Was it a moment of joy, or was he wracked with guilt? He told me he felt it was more like a cold-blooded mercy killing necessary for the good of science.

"It had been clear to me for some years that Pluto had been wrongly classified. So I was quite happy with the idea (of demoting Pluto) that we could go back and fix those mistakes," Prof Brown explained.

No regrets

Pluto's demotion continues to be acrimonious. Many scientists say that it should remain a planet, arguing that it looks like a planet, behaves like a planet and has been thought of as a planet for three quarters of a century.

I asked Mike Brown whether he had any regrets.

"No, no regrets. But I am sad about the way the last decade has gone since Pluto's demotion. I wish that people had embraced Pluto's status as an interesting member of the Kuiper Belt rather than the discussion of whether Pluto was a planet or not," he explained.

When I met Mike Brown for the first time at a scientific meeting, there was a gleam in his eye - more mischievous than murderous - when I greeted him by saying: "You're the guy who killed Pluto."

When I spoke to him this week, I put it to him that he seems to relish in the title, indeed he uses it himself on his website, and his book is called "How I killed Pluto and why it had it coming".

He told me that it was intended as a clever joke but no one really understood it at the time.

image caption, And then there were eight. In 2006 Pluto was expelled from the solar system's exclusive club of planets

"I thought it was funny to talk about 'killing Pluto' because Pluto was god of the Underworld, but no one really picked up on that," he explained.

"It is a bold claim that grabs attention. And that is important educationally. I want people to understand what the Solar System is really like and if outrageously calling myself 'Pluto killer' helps then I'm happy with it."

Hate mail

Dr Brown still gets hate mail on Twitter, mostly - he says - from people who had learned that Pluto was a planet at school. But he says that children who have grown up with the idea of Pluto not being a planet are comfortable with the idea. He believes that the controversy will gradually die down.

"The Sun and the Moon used to be (thought of as) planets too but then we got over that a long time ago. I think it is far more interesting to be going to this new type of object rather than an odd ball planet on the edge of the Solar System.

"I'm hoping that after New Horizons, those discussions will die down and we can begin talking about Pluto and what we have learned about the rest of the Kuiper Belt."

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