the planeterrella: an outreach activity at the edge of science j. lilensten, c. simon, m....

The PlaneTerrella: an outreach activity at the edge

of science

J. Lilensten, C. Simon, M. BarthélémyLaboratoire de Planétologie de Grenoble

jean.lilensten@obs.ujf-grenoble.fr

Mid 19th century: localisation of the auroral oval

At the end of the 19th century, Thomson discovers the electrons, first called « cathode rays »

Kristian Birkeland (1876 – 1917)

Kristian Birkeland was already working on these cathode rays

Birkeland then had this extraordinary idea, while none was known from the space environment

Electron gun(cathode)

Magnetized sphere (+ anode)

Vacuum(about 1 Pascal)

His hat: he got really sick at the end of his life, due to the experiment

1895

Confirmed much later from space (here in 1985)

This is what he saw

Birkeland built 14 Terrellas, with increasing volumes and different magnetic / electric configurationsIn his enthusiasm, he pretended to have modeled the sun

By inverting anode and cathode and taking off the magnet.

What he saw (and he was the first one) was actually the ring current, which gave the Nobel Price to Van Allen.

He also thought having understood the rings of Saturn by inverting anode and cathode, but keeping the magnet in the sphere.

Kristian Birkeland was nominated 8 times to the Nobel price

In the 90’s, the Ingenior Terje Brundtland (Tromso University, Norway) rebuilt one of the Birkeland’s Terrella from the orgininal material. I had a chance to visit him.

The first one I built was for the Olympics of Physics in 1996 (with a physics professor near Lyon and his 16 years old pupils). We were ranked 2d. I made 2 more in high schools.

Mauro Messerotti gave me the opportunity to have one built (on my advises) in Trieste, for the COST 724 space weather school (ICTP- UNESCO). It was used for practical work

Several have been built in the world, always on Birkeland’s one model.I recently re-considered the experiment to build my own. I realized that Birkeland did something tricky:He hanged the sphere. It should have been screwed on a support.Then, he only used 1 sphere. I use now 2 of different sizes.

That way, I can of course still see the auroral ovals and the ring current. But I can even visualize the cusp and cleft

But also many more !!!.The interaction of a magnetized planet with a magnetized satellite

In many different magnetic configurations

I can simulate a magnetized exoplanet falling down on a star

This is why I call this experiment the « Planeterrella », and not the Terrella anymore. In order to do really science with it, I am now going through a rigorous calibration process

However, it is an easy experiment to build. After I publish it, I can provide anyone with the plans (ingenior time is expensive). My institute will only require to sign an aggreement to recognize CNRS (and I) as having provided them, and the idea of the Planeterrella.

Most of all, it is an amazing outreach activity

The actual cost is about 20 000 €. My next project is to lower the price with the help of ICTP – UNESCO and Mauro Messerotti. This will be made by transfering the making to developping countries.And then, distribute Planeterrellas to all the Physics Universities in developping countries.Because, it is also an amazing way to do plasma physics experiments.