Phase Reddening

Phase Reddening is the change in the color index and the absorption bands in atmospheric planetary bodies depending on the phase angle . In the case of asteroids , the effect of the phase reddening must be corrected, otherwise the classification derived from a single measurement may be incorrect.

In the case of asteroids as well as atmospheric moons and planets , a shift in the color index and the relative strength of absorption bands to the red is often measured. There is rarely a shift into the blue. The effect with (4) Vesta is around 0.002 mag / degree in the optical and increases in the near infrared. The effect is pronounced in near-earth asteroids with their phase angles of any size.

The phase reddening is the result of the scattering of electromagnetic radiation on the regolith , a fine dust on the surface of planetary bodies that are exposed to space erosion . In laboratory measurements it was found that the intensity of the phase reddening depends on the mean size of the regolith, the shape of the dust particles , the degree of compaction of the regolith and the shape of the surface. Since the regolith is continuously modified by space erosion, the observations of the Reddening phase can roughly be used to determine the age of the surface. However, the regolith can also be rejuvenated by rearrangement due to meteorite impacts and seismic tremors due to close encounters with planets.

literature

• SE Schröder, Y. Grynko, A. Pommerol, HU Keller, N. Thomas, TL Roush: Laboratory Observations and Simulations of Phase Reddening . In: Astrophysics. Solar and Stellar Astrophysics . 2017, arxiv : 1701.05822v1 .
• Juan A. Sanchez, Vishnu Reddy, Andreas Nathues, Edward A. Cloutis, Paul Mann, Harald Hiesinger: Phase reddening on near-Earth asteroids: Implications for mineralogical analysis, space weathering and taxonomic classification . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1205.0248v1 .