Geoscience Reference
In-Depth Information
to those carried on the Mars Express and Rosetta spacecraft to a Sat-
urn Orbiter moving in the ring system (if it could be done). The corre-
sponding subsurface radar sounding would probe the interiors of different
ring particles. Could such parking orbits be achieved by the operation
of an electric propulsion system is an interesting engineering issue to be
investigated.
The Galileo mission was ended by plunging the Galileo Orbiter towards
Jupiter. Along this line of thinking, we should consider the option of keeping
the Cassini spacecraft in orbit until the arrival of the SAPPORO Orbiter
with enough fuel to crash into a chosen ring particle. Even though a little
cruel, such a Kamikaze mission now made famous by the Deep Impact on
comet 9P/Tempel 1 on July 4, 2005 could yield a lot of important informa-
tion on the meteoroid bombardment effect and the subsurface structure of
the ring particles.
2.5.
The cruise and magnetosphere science
In 1980's and 1990's when very few opportunities existed for the space
study of asteroids, space projects to the outer solar system like Galileo
had always been required to introduce into the mission plans one or two
flybys of asteroids in Earth-crossing orbits (i.e., the Near-Earth Aster-
oids) or in the major asteroidal belt. In future, our attention will likely
be shifted to the remote observations of asteroids in the outer asteroidal
belt like the Hilda asteroids and the Trojans in 1:1 orbital resonance with
Jupiter. In addition to their being the primitive bodies left over from the
formation of the solar system, the Hilda and Trojan asteroids have the
additional important property that they were formed in the vicinity of
the so-called snowline dividing the terrestrial rocky planets and jovian
gaseous planets. It might be fair to say that only when we have the first-
hand information on the chemical compositions of these outer-flying quasi-
snowball objects would we be able to understand the structure of the solar
nebula.
As for study of the Saturnian magnetosphere, we could envisage multi-
spacecraft observations combining the SAPPORO and Cassini Orbiters —
before the latter meets its demise by crashing into the rings. With the
advance in nanotechnology and miniaturization, it is expected that a new
generation of remote-sensing and plasma experiments will be onboard the
SAPPORO spacecraft. It can be imagined that an array of multi-wavelength
instruments ranging from infrared to X-ray wavelengths will be used to
