Interpretation of thermal emission. I. The effect of roughness for spatially resolved atmosphereless bodies

Davidsson, B.; Rickman, H.; Bandfield, J. L.; Groussin, O.; Gutiérrez, P. J.; Wilska, Magdalena; Capria, M. T.; Emery, Joshua P.; Helbert, J.; Jordá, L.; Maturilli, Alessandro; Mueller, Thomas

doi:10.1016/j.icarus.2014.12.029

Cited by 71 publications

(107 citation statements)

References 43 publications

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“…In particular on Eros, there is a marked deficiency of craters at spatial scales under 10 m such that the surface roughness is actually dominated by boulders (Chapman 2002). However, detailed thermophysical modelling of more realistic surface roughness topography has demonstrated that the hemispherical crater produces comparable degrees of beaming for the same degree of surface roughness present in the topography models investigated Davidsson et al 2015). Therefore, the slight elevation of surface roughness at small spatial scales implied here on Eros could be real.…”

Section: Geological Interpretation Of Surface Roughness Derived By Thmentioning

confidence: 80%

“…Beaming has been shown to be the result of two different processes: a rough surface will have elements orientated towards the Sun that become significantly hotter than a flat surface, and multiple scattering of radiation between rough surface elements increases the total amount of solar radiation absorbed by the surface (e.g. Davidsson et al 2015). Contrary to expectation, the flux enhancement caused by beaming is greatest for limb surfaces rather than surfaces located at the sub-solar region .…”

Section: Thermal Inertia and Surface Roughnessmentioning

confidence: 99%

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The surface roughness of (433) Eros as measured by thermal-infrared beaming

Rozitis

2016

Mon. Not. R. Astron. Soc.

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In planetary science, surface roughness is regarded to be a measure of surface irregularity at small spatial scales, and causes the thermal-infrared beaming effect (i.e. re-radiation of absorbed sunlight back towards to the Sun). Typically, surface roughness exhibits a degeneracy with thermal inertia when thermophysical models are fitted to disc-integrated thermal-infrared observations of asteroids because of this effect. In this work, it is demonstrated how surface roughness can be constrained for near-Earth asteroid (433) Eros (i.e. the target of NASA's NEAR Shoemaker mission) when using the Advanced Thermophysical Model with thermal-infrared observations taken during an "almost poleon" illumination and viewing geometry. It is found that the surface roughness of (433) Eros is characterised by an RMS slope of 38 ± 8° at the 0.5-cm spatial scale associated with its thermalinfrared beaming effect. This is slightly greater than the RMS slope of 25 ± 5° implied by the NEAR Shoemaker laser ranging results when extrapolated to this spatial scale, and indicates that other surface shaping processes might operate, in addition to collisions and gravity, at spatial scales under one metre in order to make asteroid surfaces rougher. For other high obliquity asteroids observed during "pole-on" illumination conditions, the thermal-infrared beaming effect allows surface roughness to be constrained when the sub-solar latitude is greater than 60°, and if the asteroids are observed at phase angles of less than 40°. They will likely exhibit NEATM beaming parameters that are lower than expected for a typical asteroid at all phase angles up to 100°.

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Section: Geological Interpretation Of Surface Roughness Derived By Thmentioning

confidence: 80%

Section: Thermal Inertia and Surface Roughnessmentioning

confidence: 99%

The surface roughness of (433) Eros as measured by thermal-infrared beaming

Rozitis

2016

Mon. Not. R. Astron. Soc.

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“…Thermophysical models of small bodies (cf. Davidsson et al 2015) should take into account our results for regions of high emergence angles (θ ≥ 40°).…”

Section: Discussionmentioning

confidence: 99%

On the effect of emergence angle on emissivity spectra: application to small bodies

et al. 2016

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Dependence of laboratory-measured emissivity spectra from the emergence angle is a subject that still needs a lot of investigations to be fully understood. Most of the previous work is based on reflectance measurements in the VIS-NIR spectral region and on emissivity measurements of flat, solid surfaces (mainly metals), which are not directly applicable to the analysis of remote sensing data. Small bodies in particular (c.f. asteroids Itokawa and 1999JU3, the respective targets of JAXA Hayabusa and Hayabusa 2 missions) have a very irregular surface; hence, the spectra from those rough surfaces are difficult to compare with laboratory spectra, where the observing geometry is always close to "nadir. " At the Planetary Emissivity Laboratory of the German Aerospace Center (DLR), we have set up a series of spectral measurements to investigate this problem in the 1-to 16-µm spectral region. We measured the emissivity for two asteroid analogue materials (meteorite Millbillillie and a synthetic enstatite) in vacuum and under purged air, at surface temperature of 100 °C, for emergence angles of 0°, 5°, 10°, 20°, 30°, 40°, 50°, and 60°. Emissivity of a serpentinite slab, already used as calibration target for the MARA instrument on Hayabusa 2 MASCOT lander and for the thermal infrared imager spectrometer on Hayabusa 2 orbiter, was measured under the same conditions. Additionally, a second basalt slab was measured. Both slabs were not measured at 5° inclination. Complementary reflectance measurements of the four samples were taken. For all the samples measured, we found that for calibrated emissivity, significant variations from values obtained at nadir (0° emergence angle) appear only for emergence angles ≥40°. Reflectance measurements confirmed this finding, showing the same trend of variations.

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“…The set of spectral measurements for asteroid analogues we are presenting can also help in the planning of future missions and provides important input for thermal models of small bodies (cf. Davidsson et al 2015). Specifically, such models solve the heat conduction equation in order to estimate the temperature in the regolith as function of time and depth below the surface.…”

Section: Resultsmentioning

confidence: 99%

“…It can also help to plan future missions and provides important input for thermal models of small bodies (cf. Davidsson et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Characterization of asteroid analogues by means of emission and reflectance spectroscopy in the 1- to 100-µm spectral range

et al. 2016

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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 µm). 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 µm) 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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Interpretation of thermal emission. I. The effect of roughness for spatially resolved atmosphereless bodies

Cited by 71 publications

References 43 publications

The surface roughness of (433) Eros as measured by thermal-infrared beaming

The surface roughness of (433) Eros as measured by thermal-infrared beaming

On the effect of emergence angle on emissivity spectra: application to small bodies

Characterization of asteroid analogues by means of emission and reflectance spectroscopy in the 1- to 100-µm spectral range

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