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Pages 9-25

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From page 9...
... Green symbols: numbered minor planets (asteroids) , red: NEOs, deep blue: Jupiter Trojans, light blue: comets.
From page 10...
... are asteroids at the outer part of the Main Belt (~3.7–4.2 AU) in 3:2 mean motion resonance with Jupiter; these objects are predicted to have originated in the same region as the Trojans and Kuiper Belt objects (KBOs)
From page 11...
... Ceres is now known to be the most water-rich body in the inner solar system after Earth. Ceres's visible-near infrared spectrum is similar to some C-complex asteroids, but its bulk density of 2,162 kg m–3,a intermediate between water ice and silicates, is more similar to icy moons of the outer solar system, and even early measurements showed the presence of hydrated minerals on the surface.1 Early thermal evolution models of Ceres indicate that it may have differentiated into a silicate core and a water-rich outer layer, which could suggest that Ceres harbored a global subsurface ocean for several hundred million years after its formation.b Measurements of hydrogen by Dawn indicate the presence of a global, subsurface water-ice table at depths less than a few decimeters at latitudes greater than 45°.c Water ice is also associated with some impact craters on Ceres.
From page 12...
... 9 These objects originate primarily in the main asteroid belt and are ejected into near-Earth space via dynamical "escape hatches," whereby asteroid fragments are constantly created by both collisions and mass shedding events. A fraction of this population of fragments, namely those of diameters ≲30 km, can escape the Main Belt via the gravitational resonances, thereby creating a quasi-steady-state population of near-Earth asteroids, 10 with a dynamical duration in the inner solar system of ~10 Myr.
From page 13...
... In this model, Jupiter's primordial Trojan population was lost and the Lagrange regions were repopulated with this scattered Kuiper Belt material. 15 The Jupiter Trojans thus may represent KBOs currently orbiting the Sun at 5.2 AU.
From page 14...
... Additional taxonomic types are discussed in the literature but are not included here. These various taxonomic types are distributed throughout the Main Belt, though important trends are observed (Figure 2-5)
From page 15...
... FIGURE 2-4 Representation of the visible-near infrared spectral shapes of the major taxonomic types of asteroids discussed in this report. The x axis represents wavelengths of 0.45–2.45 microns while the y axis represents normalized reflectance of values 1–1.5.
From page 16...
... The distribution shows significant overlap, but melted and metamorphosed asteroids tend to be concentrated in the inner belt, aqueously altered bodies in the middle, and bodies in which ice never melted in the outer belt.
From page 17...
... , which puts what we have learned about the composition of comets into the wider context of solar system evolution. In addition to the Rosetta mission, significant understanding of comets, particularly their organic matter, has been gained from samples returned by the Stardust mission and interplanetary dust particles (IDPs)
From page 18...
... Furthermore, interpretations of spectra are rendered difficult by effects such as space weathering, temperatures, and particle sizes. LINKS TO METEORITES In addition to spectroscopic surveys, comparisons between spectra of meteorites and asteroids can help illuminate the likely composition of parent body asteroids, particularly because space weathering processes (e.g., solar wind bombardment)
From page 19...
... Whereas "disrupted asteroids" are those active asteroids whose activity is driven by processes such as impacts and rotational disruption, the activity of another subset of active asteroids, "Main Belt comets (MBCs) ," is driven by sublimation of volatiles; these MBCs thus provide new clues regarding the abundance of asteroid ice, and the origin of terrestrial planet volatiles.
From page 20...
... 47 As described in Box 2-2 and in Figure 2-6, spectroscopic measurements of the D/H ratios in cometary comae indicate that water ice in comets is more D-rich than the water at the surface of Earth, constraining the amount of volatile material that could be delivered from cometary impacts. Furthermore, dynamical simulations of the formation of terrestrial planets suggest that the outer asteroid belt was the primary source of impactors on the early Earth.
From page 21...
... 2028 617 Patroclus and Jupiter Trojan Lucy (flyby) 2033 Menoetius NOTE: KBO, Kuiper Belt object; MBA, Main Belt asteroid; NEO, near-Earth object.
From page 22...
... Models such as the Grand Tack/Nice models suggest that planetary migration of Jupiter and Saturn produced sweeping resonance through the main asteroid belt and dislodged most of the asteroids. The resulting liberated asteroids could have been responsible for the impact cataclysms that occurred on all terrestrial planets and satellites around 4 billion years ago.
From page 23...
... Understanding the origin of organic compounds in early solar system materials is central to astrobiology. Individual asteroids are "astrobiological time capsules" 60 that preserve a record of the evolution of volatiles and organics starting in the interstellar medium, through the birth and early evolution of the solar system, to present-day space weathering at asteroid surfaces.
From page 24...
... CONDITIONS ON SMALL BODIES WITH RESPECT TO SURVIVAL AND PROLIFERATION In the framework of planetary protection for solar system small bodies, scientific understanding of life is based on our knowledge of life on Earth. Because of the incomplete current state of knowledge about small bodies as well as the survival-limits of life, all judgments regarding biological potential are qualitative, not quantitative.
From page 25...
... These findings are exemplified by recent small-body missions: Stardust captured organic matter samples from Comet 81P/Wild2. 70 Rosetta's close proximity to the coma of comet 67P/C-G allowed it to detect numerous organic species including aromatic hydrocarbons, oxygenated hydrocarbons, and a diverse population of sulfur-bearing molecules in addition to many inorganic species.


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