This NASA image of Pluto taken in 2015 is a blend of blue, red and infrared images. In 2006, the International Astronomical Union (IAU) declared Pluto one of dozens of dwarf planets. Source: NASA Johns Hopkins University Applied Physics Laboratory Southwest Research Institute
Words: Eric Alt
In 2006, the world lost many stars — American actor Shelley Winters, godfather of soul music James Brown, naturalist Steve Irwin — and there was only one real star – Pluto.
After the discovery of Pluto by American astronomer Clyde Tomaugh in 1930, the tiny marble-colored star was listed as the ninth planet in the solar system, and it quickly gained popularity because of its namesake with the pet dog in the Mickey Mouse animation (the character was originally named Rover, but changed to Pluto's name in 1931).
Then, in 2006, Mike Brown, a professor of astronomy at the California Institute of Technology and author of "How I Killed Pluto and Why It Had It Coming," interrupted the mood and removed Pluto's "planetary status." Since then, debates have begun in the scientific community and pop culture circles about Pluto's fate.
To celebrate the 94th anniversary of the discovery of Pluto, we asked Brown and Philip Metzger (retired astrophysicists at NASA Kennedy Space Center and current associate researcher at the University of Central Florida) to discuss and get their answers. Brown and others like her support a downplaying of Pluto's significance in favor of new discoveries such as the yet-to-be-identified Planet Nine, while Philip joins others in having a solid theory for Pluto's strong return.
On both sides of Pluto, how do you determine your personal position?
Mike Brown: Since I entered Caltech, one of my main areas of research has been the outer solar system and Kuiper Belt objects, such as Pluto. At the beginning of the 21st century, one of the big projects I was working on was the first real large-scale search for other objects the size of Pluto, other dwarf planets, ......At that time, they weren't called 'dwarf planets,' and I have to say, by the way, it was a stupid name.
Why?
Mike Brown: Because it creates unnecessary confusion. People think, "Well, there's a 'planet' here, so it's supposed to be a planet." And I'm going to say, "The seahorse will be happy to talk to you." "Before the International Astronomical Union coined the term, we used the term "planetoid" to describe these small, spherical objects, which was much better and less confusing. The only reason Pluto is called a dwarf planet is because some Pluto supporters slipped in in the hope of winning a vote to turn the dwarf planet into a planet. The vote was forcefully rejected, but the stupid argument remained. I blame those Pluto supporters for this.
Philip Metzger: We would say that there are a lot of dwarf planets, and these dwarf planets are actually Kuiper Belt planets. But in fact, we are not arguing for Pluto's "official reinstatement", because we don't think the vote to demote it is a trivial matter. IAU does not have the right to vote. They did so in violation of their own internal charter ......We argue that it has always been a planet because taxonomy is part of science, and valuable taxonomy is what scientists are using and find useful. The public astrology-based taxonomy has no effect on science, it does not fit any theory, but unfortunately this is the taxonomy adopted by the IAU.
All right. Perhaps we can start with the planetary standard.
Philip Metzger: In 2006, IAU decided: first, [a planet] must orbit a star directly. Judging from this, the Moon is not a planetary ......We call it a secondary planet, and Earth is a primary planetary ......The second criterion mentioned by IAU is that a planet should be large enough to pull itself into a spherical shape by its own gravity, which we call "gravitational circlery". The third condition – and the criterion used to kick out objects like Pluto – requires that planets must dominate their orbits from the gravitational plane, clearing them of other objects in their vicinity. IAU does not clarify what this article means, simply assuming that more specific definitions will be given in the future. You can argue that the Earth is not a planet because the Earth has not cleaned up its neighbors. What they're actually trying to say is that [a planet] must dominate gravity according to some unknown criterion that the IAU has not yet created.
Mike Brown: In the early 21st century, digital cameras started to get better and better, and finally, we were able to capture images all day. We use this technology to discover the largest, brightest, and most "short" planets in the solar system, including the one that really forced Pluto into strife. We found Eris, which is much larger than Pluto. And all of a sudden, we had to make certain trade-offs. Either some new planets have to be added, or some celestial bodies have to be excluded from the planets. If Pluto had been discovered today, no one would have said it was a planet.
Are we obsessed too much with symmetry (a physical property that doesn't change)? Is it because we all grew up with the idea of "nine planets" that the idea of "eight planets" or "infinite planets" is unsettling?
Mike Brown: No, there are no magic numbers. The point of the matter is not that Pluto must be ruled out, but that astronomers are forced to declare the fact that Pluto does not fit into our current understanding of planets. Those who support Pluto's retention are trying to redefine the planet because they are too eager to keep it as a planet, but their definition would add more than 200 planets to the solar system. Incidentally, the dominant Pluto supporters were involved in the NASA Pluto project. At the time of the launch, Pluto was still a planet; By the time the probe arrived, it had lost its planetary identity.
Philippe Metzger: It's culture, not science. What else is like this in nature? I mean, we're not going to say that there have to be nine mountains, nine rivers, or nine species of beetles. The funniest part is the whole word "astronomical". Ironically, astronomers are the ones who are reluctant to confront astronomical numbers. They want the number of planets to be eight.
Is this about changing the way science is taught in primary schools? We come up with a beautiful and easy-to-remember statement like eight or nine planets, and then we don't think too much about it. Should it be taught as an evolving concept?
Philip Metzger: Yes. Unfortunately, when we are taught that there are eight planets in the solar system and that these planets dominate their orbits, we return to the old concept of "geocentrism." It's simple, well-behaved, monocentric, and the planets are like God ruling their own orbits under this concept. What we advocate for schools should be that this is a changing universe. Things are constantly changing, evolving gradually. Planets also change their orbits.
So the search for "Planet Nine" is not about finding a replacement for Pluto?
Mike Brown: At the moment, [the existence of Planet Nine] is a great hypothesis that explains a lot of things that we find that we don't have other explanations. [But] until we look our telescope at Planet Nine and say, "Aha, it's there," this is still only the best hypothesis to explain many phenomena. I think we'll eventually find that star through a telescope and actually see it, but until then, the existence of Planet Nine is just a hypothesis.
At the end of the day, why do you think people have such feelings for Pluto and refuse to accept "Planet Nine" or any other possible "replacement"?
Philip Metzger: All I can say is that NASA's New Horizons flight over Pluto was truly inspiring. I was at Johns Hopkins University, where there was a control center at NASA. When astronauts first showed Pluto's **, it was so stunning......Geologically, it's so different – the mountains are as high as the Rocky Mountains, and they rise up actively; Glaciers flow on Pluto's surface; There is a layered atmosphere there; Most likely, there is also an underground ocean; Organic matter – the building blocks of life – is found all over the planet's surface. Pluto is not just a planet, but more like Earth than any other planet. It is the planet that most resembles a planet.
Mike Brown: I have feelings for Pluto. Growing up, it was a strange and mysterious presence at the edge of the solar system. Who hasn't thought it's weird, small, and cute? And now we see it. It's actually cool on the outside; That's a cool place.
Translator: Green Wine).
Related reading: Shocked! There are actually methane "dunes" on Pluto
Weird Pluto, I don't dare blow about such a big thing.