Pre-solar nebulae, circumstellar dust shells and dust rings are the building blocks of solar systems and it is believed, are closely related to the origin of life. Our solar system is the obvious place to study the conditions and processes which lead to the formation of planets and the evolution of their surfaces and atmospheres, and to search for traces of pre-biological chemistry. It is therefore essential to study primordial bodies like comets and asteroids as well as the evolved planets and their satellites.

Comets and Asteroids

Comets are composites of ice and dust with diameters up to several 10s of km, which orbit in the Kuiper Belt and Oort cloud. If they are somehow deflected towards the inner solar system, their surfaces are exposed to intense solar radiation and the ices start to vaporize. Since this interaction with solar radiation is very probably the first chemical processing in billions of years, comets provides us with information about the composition of matter at the time of their formation. Their different compositions seem to represent different regions of the pre-solar nebula. Some are rich in silicates, others in reduced carbon or hydrocarbons; others show various proportions of minerals like olivine. Most of them seem to be rich in water. Spectroscopic information of the most important volatile components of comets like H₂O and CO₂ or organic C-X stretch bands cannot be obtained from the ground since the absorption from water and carbon dioxide in the lower atmosphere blends out those bands. SOFIA is therefore ideally suited to address those questions.

Most asteroids orbit in the main belt between the orbits of Mars and Jupiter. Asteroids are thought to be remnant material from the processes of formation and initial development of planets and therefore an important source of information on conditions in the early solar system. Apart from the scientific question of their origin and composition, the so-called near-Earth asteroids (NEAs) are also interesting as potential sources of raw materials for future generations and as targets for current space missions such as NEAR and DS1. Observations of asteroids in the MIR and FIR with SOFIA will provide crucial information on their physical characteristics, such as sizes, albedos and the thermal properties of their surfaces (see, e.g. Harris et al.1998). Well-studied asteroids with accurately known characteristics will serve as important photometric standards for SOFIA in the MIR and FIR, as in the case of ISO (Mueller and Lagerros 1998).

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Planets and their satellites

The composition of the planets is directly linked to the distribution of matter and volatiles during the formation of our solar system. The radial partitioning of matter during the formation of planets should reflect itself in the different compositions of the planets. For the big outer planets, which are difficult to investigate, models range between two extremes: outer planets and their satellites consist of (1) water, methane, and ammonia or (2) carbon monoxide, water, and molecular nitrogen. In the currently accepted model, the giant planets consist of (2), while their satellite's compositions are dominated by (1). The satellites of the outer planets may retain surface spectral signatures of the primordial partitioning of these constituents. It is therefore important to determine the composition of the volatile-rich outer planet satellites and Pluto, the composition of their atmospheres (if any) and the nature of the surface-atmosphere interactions.

The spatial-seeing-limited NIR resolution of SOFIA is about 2 arcsec, high enough to spatially resolve several of the planetary disks and study their zonal atmospheres. The following table lists SOFIA's spatial NIR resolution on planets and satellites.

On Mars, SOFIA will be able to study the transport of the volatiles CO₂ and perhaps H₂O between the polar caps and the equator region due to seasonal cycles. On Jupiter, SOFIA can spectroscopically map the cloud band system and its variations in NIR and MIR lines. SOFIA will be able to resolve the Great Red Spot, which color is still unexplained.

Stellar occultations of planets and satellites have been a very valuable source of information on planetary atmospheres and rings during the KAO flights. SOFIA's mobility is ideally suited for observations of these occultations, which provide a spatial resolution of only a few kilometers. In 1997, the rings of Uranus were discovered with the KAO during a stellar occultation. SOFIA not only will provide a much-improved sensitivity but also long term monitoring of changes within these atmospheres and rings.

The content of this page was excerpted from a PDF document "SOFIA Astronomy and Technology in the 21st Century" by Alfred Krabbe and Hans-Peter Roeser.

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