NAIL: Junichi from Nihama City: The magnetosphere is invisible, isn't it?
How does ST5 mission map the magnetic field around Earth?
SLAVIN: I regret to say this but I have to agree with you.
It is invisible and as a magnetospheric physicist, I certainly wish that it weren't.
For example, if you could, if the human eye,
if there was enough visible light given off by the particles that are trapped in magnetospheres for us to be able to actually see them,
for example with the naked eye, then the largest object in the night, in the night sky would be the magnetosphere of Jupiter.
Jupiter is the largest planet in the solar system, but in terms of magnetic fields, it is truly a giant.
Now, if we can't see the magnetic fields though, exactly how do we know that a magnetic field is there?
Well, fortunately, there is a way to do this, and we use an instrument called a magnetometer.
A magnetometer has a special kind of material in its sensor head. It's a material that interacts with magnetic fields and actually amplifies them.
Once the magnetic field is amplified, if you, if you know how exactly to do the proper sort of electronics, it's actually quite easy to do the measurements.
The only unfortunate aspect is that you can only measure the magnetic field locally,
which once again brings us back to the need for simultaneous measurements of the magnetic field from a large number of points at the same time --
hence the constellations of micro-satellites.