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Updated: Jun 17, 2026

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Scattering And Absorption of Light in Planetary Regoliths
Published on: July 1, 2019
E-type asteroid (2867) Steins as imaged by OSIRIS on board Rosetta.
H U Keller1, C Barbieri, D Koschny
1Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany. keller@linmpi.mpg.de
Summary
The Rosetta mission revealed asteroid Steins is a rubble pile, not solid rock. Images provide direct evidence of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect reshaping asteroids.
Area of Science:
- Planetary Science
- Asteroid Research
- Space Exploration
Background:
- The European Space Agency's Rosetta mission provided a unique opportunity to study small bodies in the solar system.
- Asteroid (2867) Steins was encountered en route to comet 67P/Churyumov-Gerasimenko.
Purpose of the Study:
- To characterize the physical properties and surface morphology of asteroid (2867) Steins.
- To investigate the potential influence of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect on asteroid shape.
Main Methods:
- High-resolution imaging using the OSIRIS (optical, spectroscopic, and infrared remote imaging system) cameras on board the Rosetta spacecraft.
- Analysis of surface features, including craters and linear faults.
- Crater counting to infer surface age and processes.
Main Results:
- Steins is an oblate body with an effective spherical diameter of 5.3 km.
- Surface exhibits linear faults and a prominent 2.1 km crater; no significant color variations were observed.
- A notable absence of small craters suggests a relatively young surface or ongoing resurfacing.
- Evidence indicates Steins is a rubble pile with a conical shape, likely modified by YORP spin-up.
Conclusions:
- The OSIRIS images provide direct observational evidence for the YORP effect acting on a main-belt asteroid.
- Steins' morphology and composition as a rubble pile are consistent with significant reshaping due to YORP-induced spin acceleration.
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