Shaping planetary systems early on: Experimental view on wind induced erosion of planetesimals

In the formation of a planetary system, the objects involved pass through a wide range of sizes starting with micrometre-sized particles and ending up as full-grown planets. An intermediate step in this evolution is represented by kilometre-sized planetesimals, which might consist of very loosely bound millimetre dust granules [1]. Their orbital velocity differs from that of the surrounding gas in the protoplanetary disk resulting in a headwind with relative velocities of the order of 50 m/s [2]. Since self gravity of such a planetesimal is very small, there is a possibility that it loses mass due to wind erosion. This raises the question at which wind speeds and ambient pressures the planetesimal is stable and at which it is not.

To recreate wind erosion on planetesimals in protoplanetary disks as realistically as possible, low pressures and a microgravity environment are needed. The latter can be achieved by placing an experiment in an aircraft that performs parabolic flights (A310 ZERO-G by Novespace). In a cylindrical vacuum chamber a second smaller cylinder is located in its center and can rotate at high frequencies up to 200 Hz to create a shear flow. With this setup, a laminar wind profile can be generated over a simulated planetesimal surface placed within at ambient pressures down to 10^-2 mbar.

We used this setup with millimetre dust aggregates consisting of SiO₂. The aggregates were produced in an analogous way as dust aggregates at the bouncing barrier in protoplanetary disks might form, i.e. by collisions of micrometre-sized particles, sticking and growing up to the bouncing size. This experimental setup has already been used in previous parabolic flight campaigns with glass spheres as sample [3]. This time, a more realistic approach was applied with these SiO₂ aggregates.

Wind erosion was observed at an ambient pressure that was an order of magnitude lower than before. Furthermore, by accurately measuring the residual gravity during the microgravity phases, it was possible to determine an angle of repose under the given conditions. Here we report the latest results of the parabolic flight campaigns.

Applied to planet formation, our results support and expand earlier findings that wind erosion might generate forbidden zones for pebble pile planetesimals, i.e. closer to the star [3,4] and wind erosion might filter out excentric orbits [5].

 

References

[1] Wahlberg Jansson K., Johansen A., Bukhari Syed M., Blum J., 2017, ApJ, 835, 109

[2] Weidenschilling S. J., 1977, MNRAS, 180, 57

[3] Demirci T., Schneider N., Steinpilz T., Bogdan T., Teiser J., Wurm G., 2020, MNRAS, 493, 5456-5463

[4] Rozner M., Grishin E., Perets H. B., 2020, MNRAS, 496. 4827-4835

[5] Cedenblad L., Schaffer N., Johansen A., Mehlig B., Mitra D., 2021, ApJ, 921, 123

 

Acknowledgements

This project is funded by DLR space administration with funds provided by the BMWK under grant 50 WM 2140. T. B. is funded by DLR space administration with funds from the BMWK under grant 50 WM 2049. K. J. is funded by DLR space administration with funds from the BMWK under grant 50 WM 1943. F. C. O., F. J. and M. K. are funded by DLR space administration with funds from the BMWK under grant 50 WM 2142. N. S. is funded by the DFG under grant WU 321/16-1. M. F. is funded by the DFG under grant TE 890/7-1. We also thank M. Aderholz who helped bringing the idea of this experiment to real life.