| 1. |
- Davidsson, Björn J. R., et al.
(författare)
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Interpretation of thermal emission. I. The effect of roughness for spatially resolved atmosphereless bodies
- 2015
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 252, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Spacecraft observations of atmosphereless Solar System bodies, combined with thermophysical modeling, provide important information about the thermal inertia and degree of surface roughness of these bodies. The thermophysical models rely on various methods of generating topography, the most common being the concave spherical segment. We here compare the properties of thermal emission for a number of different topographies - concave spherical segments, random Gaussians, fractals and parallel sinusoidal trenches - for various illumination and viewing geometries, degrees of surface roughness and wavelengths. We find that the thermal emission is strongly dependent on roughness type, even when the degrees of roughness are identical, for certain illumination and viewing geometries. The systematic usage of any single topography model may therefore bias determinations of thermal inertia and level of roughness. We outline strategies that may be employed during spacecraft observations to disentangle thermal inertia, level of roughness and type of topography. We also compare the numerically complex and time consuming full-scale thermophysical models with a simplified statistical approach, which is fairly easy to implement and quick to run. We conclude that the simplified statistical approach is similar to thermophysical models for cases tested here, which enables the user to analyze huge amounts of spectral data at a low numerical cost.
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| 2. |
- Jenniskens, Peter, et al.
(författare)
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The impact and recovery of asteroid 2018 LA
- 2021
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Ingår i: Meteoritics and Planetary Science. - : John Wiley & Sons. - 1086-9379 .- 1945-5100. ; 56:4, s. 844-893
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Tidskriftsartikel (refereegranskat)abstract
- The June 2, 2018 impact of asteroid 2018 LA over Botswana is only the second asteroid detected in space prior to impacting over land. Here, we report on the successful recovery of meteorites. Additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. Video observations of the fireball constrain the asteroid's position in its orbit and were used to triangulate the location of the fireball's main flare over the Central Kalahari Game Reserve. Twenty‐three meteorites were recovered. A consortium study of eight of these classifies Motopi Pan as an HED polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. Before impact, 2018 LA was a solid rock of ~156 cm diameter with high bulk density ~2.85 g cm−3, a relatively low albedo pV ~ 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of ~0.2 kt. The orbit of 2018 LA is consistent with an origin at Vesta (or its Vestoids) and delivery into an Earth‐impacting orbit via the ν6 resonance. The impact that ejected 2018 LA in an orbit toward Earth occurred 22.8 ± 3.8 Ma ago. Zircons record a concordant U‐Pb age of 4563 ± 11 Ma and a consistent 207Pb/206Pb age of 4563 ± 6 Ma. A much younger Pb‐Pb phosphate resetting age of 4234 ± 41 Ma was found. From this impact chronology, we discuss what is the possible source crater of Motopi Pan and the age of Vesta's Veneneia impact basin.
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| 3. |
- Maturilli, Alessandro, et al.
(författare)
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Characterization of asteroid analogues by means of emission and reflectance spectroscopy in the 1-to 100-mu m spectral range
- 2016
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Ingår i: Earth Planets and Space. - : Springer Science and Business Media LLC. - 1343-8832 .- 1880-5981. ; 68
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Tidskriftsartikel (refereegranskat)abstract
- The last decades have seen a large number of missions targeting small bodies in the solar system. NASA, ESA and JAXA sent missions to different solar system small bodies (SSSB), and the Japan mission Hayabusa returned samples from the surface of the S-type asteroid Itokawa. JAXA launched in 2014 a follow-up mission (Hayabusa2) to collect a sample from carbonaceous (C-type) asteroid 1999 JU3 asteroid and bring it back to Earth. The NASA's OSIRIS-REx mission will launch in September 2016 to explore the carbonaceous asteroid Bennu. Despite an already existing rich collection of reflectance and emissivity spectral libraries for asteroid analogues, those are mostly based on measurements in air for a spectral range covering the visible to the medium infrared (approximately, from 0.4 to 25 mu m). To characterize minerals, rocks and meteorites suitable for being surface analogues for asteroids and SSSB in general, spectroscopic measurements are needed for a wider spectral range and in vacuum, conditions that more closely resemble those found on asteroid surfaces. To fill this gap we acquired spectral measurements over a large spectral range (1-100 mu m) for several meteorites and other analogues at the Planetary Emissivity Laboratory of the German Aerospace Center in Berlin. Those data provide more direct analogues for asteroid surfaces and expand our existing database of emissivity and reflectance measurements.
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