When did we discover Pluto?

Pluto - a planet again?

The celestial body Pluto is smaller than our moon. And at least thirty times farther from the sun than the earth. That's why it's freezing out there, and pretty dark. It takes its name from Pluto, the Greek god of the underworld.

What was it like when Pluto was discovered?

The discoverer of Pluto, Clyde Tombaugh, was only 24 years old at the time and had only been working as an assistant at the observatory in Flagstaff / Arizona for a year. Before that he had lived on a farm and practiced astronomy as a hobby. But with his detailed drawings of celestial bodies he caught the eye of the astronomers and so they brought him to their observatory.

There he had the task of comparing photographs that had been taken just a few days from a certain region of the sky. He should look for a point of light that moved a little further from photo to photo - in contrast to the stars, which were always in the same spot in the photos. Tombaugh found that dot.

Pluto only a dwarf planet

It was the long-sought celestial body that, with its gravitational pull, was responsible for irregularities in the orbits of Neptune and Uranus. Today, however, Pluto is only referred to as a dwarf planet because it is so small that it did not manage to capture or knock all the other chunks that are still in its orbit around the sun with it. It's just one of many Pluto-like objects out there, but that was completely unknown 90 years ago.


Astronomers want to give Pluto back full planetary status

Thomas Kraupe is the head of the Hamburg planetarium and now wants to work with other astronomers with the project "Pluto for Planet" to ensure that Pluto gets its planetary status again.

With special demonstrations in the planetarium hall and a lot of background information on the Internet, the Hamburg astronomers want to contribute to the reversal of Pluto's degradation to a dwarf planet:

Solar system with very, very many planets?

That area out there is called the Kuiper Belt. A region on the edge of our solar system from which comets regularly travel towards Earth. And in which there are probably many more objects like Pluto buzzing around, which might even come into question as planets - if one is not too strict with the definition and it is sufficient as a planet to be plump and orbit the sun. So do we have a solar system with an abundance of planets?

Researchers suspected, according to Kraupe, dozens, hundreds, even thousands of objects beyond Neptune. Therefore, astronomers faced a difficult decision. On the one hand, one could have identified more than nine planets. But then there would have been a lot of planet names that should have been remembered. A challenge where many can just remember Mercury, Venus, Earth, Mars, Jupiter, etc. with simple donkey bridges.

Forgot Pluto for convenience?


Did the astronomers throw Pluto out of the equation out of sheer convenience? To prevent a possible flood of planets and to use mnemonics that would fill entire pages? The fact is that an additional criterion for planets was introduced in 2006:

Put simply, this killer criterion of the International Astronomical Union goes like this: If you want to be a planet, you must always have a free path on your journey around the sun. In contrast to Earth, Mars and Co., this is actually a problem for Pluto: On the one hand, a couple of Kuiper Belt colleagues could get in the way of its nearly 250-year orbit around the sun.

Pluto's orbit is determined by Neptune

And then its big neighbor Neptune is also causing stress: Pluto's orbit is not an independent orbit at all. Pluto's orbit is completely dominated by the orbit of the planet Neptune, the next inner large planet. Astronomers can calculate that and, according to astrophysicist Susanne Hüttemeister from the planetarium in Bochum, this orbit behavior will not change in 200 years or in 2000 or in two billion years.

Pluto fans find planetary criteria too strict

So Pluto does not determine its path alone. But Pluto fans like Thomas Kraupe find these international planetary criteria far too strict:

Scientific criteria for planets

Other scientists such as Susanne Hüttemeister leave such arguments cold: She does not mourn with:

Even if the discussion about when a planet is a planet may go on for light years, the astroscientists agree on one thing: The world of Pluto is extremely exciting and fascinating.

Ashes of the Pluto discoverer in space

This was shown by the successful mission of the “New Horizons” space probe, which incidentally also had a bit of ashes from Pluto discoverer Clyde Tombaugh on board when it flew by five years ago.

Planet as a world orbiting a star

That's why Hamburg's planetarium boss Thomas Kraupe doesn't want to give up his unusual space mission for Pluto's 90th birthday anytime soon. Even if it could still take light years until the distant dwarf on the dark edge of our solar system becomes a planet again ...: