Inferred winds and atmospheric circulation during the descent of Beagle 2 on Mars

Abstract

We present new global and mesoscale model results for the time of the Beagle 2 landing. We compare these results to inferred wind speed and direction profiles obtained from the analyisis of the Beagle 2 lander and its surrounding landing gear as seen in images of the landing site. On Mars, like on Earth, the lower layer of the atmosphere interacts thermally and mechanically with the surrounding terrain to produce, e.g. buoyancy driven slope winds and mountain waves. Understanding the role of the surrounding terrain on regional and local winds is important for understanding the transport of moisture and dust on Mars and interpretating lander meteorological observations. It is also important to understand and determine the resolution of an atmospheric model required to resolve the effects of topography on the atmosphere. Isidis Planitia, where Beagle 2 landed, is a plain in a giant impact structure on Mars spanning over 1000 km in diameter. It makes for a convenient region for study due to its enclosed nature and because it fits nicely within the typical domain sizes of mesoscale models.

Introduction

Beagle 2 landed in the Isidis basin back in 2003. Unfortunately, it did not transmit any data, but images from orbit show the apparently intact lander surrounded by its landing gear, such as parachutes and a heat shield (Bridges et al., 2017). The distribution of this equipment contains a valuable record of the winds that were blowing during its descent and landing. The reason this information is valuable is because the amount of data on Martian winds above the surface is almost non-existent, especially in terms of vertical profiles.  We decipher the images of Beagle 2 to infer wind speed and direction profiles and compare these with atmospheric models to advance our knowledge of the atmospheric circulations in the Isidis basin and the Martian atmosphere.

Method

A lander opens its parachute just before its descent through the most dynamic region of the atmosphere. Many of the early landers on Mars, from the 1990s onwards such as Pathfinder, Spirit, Opportunity and Beagle 2, did not measure the winds during their descent. However, images of their landing sites taken from orbit provide evidence of winds due to the deviation of jettisoned hardware, such as parachutes and heat shields, from the nominally straight line of the entry trajectory. To extract the wind speed and direction from these images we fit a trajectory model of Beagle 2 to the impact locations of its landing gear on the surface. The inferred wind speed and direction are then compared to the Laboratoire de Météorologie Dynamique (LMD) mesoscale and global atmospheric models.

Results

From the mesoscale atmospheric model the circulation at the Beagle 2 landing site appears to be a complex interplay of the Hadley circulation, topography and heating at the equator. The higher resolution of the mesoscale model modified the wind profile prediction from the GCM, especially in terms of wind direction. This is most likely due to the higher resolution of the topographic influenced circulations in the mesoscale model. A similar result was found with the Perseverance landing site (Paton et al., 2024), where increasing the resolution had dramatic effects on both wind speed and direction. The GCM and mesoscale results here also support the results from mesoscale modelling efforts made by Rafkin et al. (2004) and GCM modelling results made by Bingham et al. (2003) in preparation for the Beagle 2 mission. Differences in wind direction between the atmospheric model and inferred wind profile suggest convective cell activity in the afternoon planetery boundary layer.

Conclusions

We have inferred the wind speed and direction during the Beagle 2 landing and compared these to new mesoscale atmospheric model results. The inferred wind profile appears consistent with the mesoscale atmospheric model, although initial calculations did suggest high wind speeds above the planetary boundary layer. We found an improvement in the match between the inferred wind profile and the atmospheric model if the Beagle 2 airbags were deflected, after being released from the parachute, perhaps due to the aeolian landforms apparent in images of the landing site.

The results also demonstrate the need to carefully consider the grid size of the atmospheric model when the influence of topography is suspected. This is particularly important for Mars because of the dramatic variations in topography due to impact basins and other large geological features such as the north south dichotomy.

References

Bingham, S.J., Lewis, S.R., Newman, C.E., Read, P.L., Environmental predictions for the Beagle 2 lander, based on GCM climate simulations, Planetary and Space Science, 52, 259–269 (2004)

Bridges J. C., Clemmet J., Croon M., Sims M. R., Pullan D., Muller J.-P., Tao Y., Xiong S., Putri A. R., Parker T., Turner S. M. R. and Pillinger J. M., Identification of the Beagle 2 lander on Mars, Royal Society Open Science 4170785 (2017)

Paton, M. D., Savijärvi, H., Harri, A. -M., Leino, J., Bertrand, T., Viúdez-Moreiras, D., Lorenz, R. D. and Newman, C., Inferred wind speed and direction during the descent and landing of Perseverance on Mars, Icarus, 415, 116045 (2024)

Rafkin, S. C. R., Michaels, T. I. and Haberle, R. M., Meteorological predictions for the Beagle 2 mission to Mars, Geophysical Research Letters, 31, L01703 (2004)