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[David McComas] ISIS, the Integrated Science Investigation of the Sun, is an experiment which looks at

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energetic particles over a broad range of
energies, from tens of thousands of electron

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volts up to about a hundred million electron volts.

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The ISIS instrument is based on solid state detectors.

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Those are detectors that when a particle passes
through them, energy’s deposited and you

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can measure that energy and you can measure
that the particle has actually passed through.

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So there’s the solar wind, which is this
continuous flow of lower-energy particles,

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and then there are much more sporadic and
episodic events like solar flares that spew

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out great numbers of these much more energetic
particles.

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in our higher-energy instrument, we have a
whole set of layers of these detectors so

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when a particle passes through those layers
it leaves energy in each and every one of

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those detectors.

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Those detectors are also segmented in pieces
like a pie and so when a particle comes through

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from a particular direction you can tell both
the direction the particle came through at

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and you can tell the energy and species of
that particle by looking at all the different

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energy depositions.

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In our lower-energy instrument, we also have
the same sort of solid state detectors, but

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in addition to that we use an extra trick,
which is when a particle passes through a

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very thin foil it ejects an electron, we’re
able to detect that, and that gives us the

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start timing for the particle.

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One of the big issues for ISIS is to understand
the difference between solar energetic particles

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that just come from the Sun with a certain
energy and those that are energized in interplanetary

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space as they move outward.

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By the time they get out to the Earth’s
orbit, that’s all so messed up, mangled

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up, that it’s kind of hard to tell the difference
between those, but as we get in closer and

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closer to the Sun, we’ll be able to differentiate
those two types of sources, which will be

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really important for understanding the fundamentals
of energetic particles in the solar system.

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By going in close and measuring the detailed
distributions of these energetic particles,

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their energies, directions, and their species,
we’re going to learn things that we couldn’t

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possibly learn by looking forever from a remote
distance.

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And by understanding our Sun in detail, we
can understand lots of other stars in much

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greater detail.