SCARI will be used to study the interaction of our
Solar System with the gas and dust that exists in between the stars, called
Interstellar Medium , or ISM. The ISM, and everything else in the
Galaxy, is rotating about the center of the Galaxy. This motion of the
ISM with respect to our own motion about the Galaxy causes an interstellar
wind. Our Solar System consists of the Sun, the planets and planetesimals,
as well as all the gas and dust streaming out from the Sun, called the
solar wind . The solar wind streams out radially from the sun, until
it is balanced by the interstellar wind. The point at which SCARI can detect
at the Lyman-alpha transition in the UV. This gas has passed from the ISM
into our solar system, through the heliopause and interface region. By
studying the temperature, density, and velocity of the hydrogen, and comparing
it to known values of the ISM well outside the solar system, we can learn
more about the interaction itself (Baranov and Malama, Journal of
The upper atmosphere of the Earth consists of mostly
Hydrogen. The same solar radiation which excites the hydrogen streaming
into the solar system from the ISM, also excites hydrogen within our own
atmosphere. SCARI will also see this hydrogen, which is called the Geocorona.
The top of this region is where hydrogen can escape completely from the
atmosphere, called the Exosphere, and starts above 500 km in altitude.
By looking at the Geocorona, SCARI will be studying hydrogen escape from
the Earth's atmosphere.
The hydrogen flux , or density and
speed at which hydrogen escapes Earth's atmosphere, is critical to understanding
the upper atmosphere. Predicted fluxes fall short of those observed, meaning
that the escape mechanisms known must be more effiecient, and/or there
must other escape mechanisms at work. SCARI will be able to measure the
speed and temperature of the escaping hydrogen, which will help narrow
this gap (Hodges & Brieg,Journal of Geophysical Research,96,769).