2024-12-20 NASA
NASAのマーズ・リコネッサンス・オービター（MRO）は、火星の新年（第37太陽年）の開始に伴い、北極地域での季節的な変化を観測しています。春の到来により、二酸化炭素の霜が昇華し、氷の爆発や雪崩が発生し、砂丘の形状も変化しています。これらの現象は、火星の気候や地質活動を理解する上で重要な手がかりを提供します。
＜関連情報＞
- https://www.nasa.gov/missions/mars-reconnaissance-orbiter/avalanches-icy-explosions-and-dunes-nasa-is-tracking-new-year-on-mars/
- https://www.sciencedirect.com/science/article/pii/S0019103523004426
MRO/HiRISE長期観測による、火星で最も迅速な風食系からの砂丘の経年変化の解明 Revelations of interannual dune evolution from the swiftest aeolian system on Mars by MRO/HiRISE long-term monitoring
Matthew Chojnacki, David A. Vaz, Pruthviraj J. Acharya, Simone Silvestro, Isaac B. Smith
Icarus Available online: 11 November 2023
DOI:https://doi.org/10.1016/j.icarus.2023.115863
Highlights
- Annual polar dune sand fluxes were measured over 8 Mars years of the MRO HiRISE mission.
- Bedform dynamics vary depending on the year, topographic context, and seasonal ice coverage.
- Aeolian evolution was documented from sand patch to protodune to dune.
Abstract
The north polar region of Mars, with its greater atmospheric pressure and vast inventory of ever-changing volatiles (e.g., CO2, H2O), hosts arguably the most active and diverse aeolian bedform systems on the planet. Here, we explore how these dune fields evolve spatiotemporally using up to 8 Mars years (16 Earth years) of MRO HiRISE observations to test the impact of various boundary conditions on annual mobility. A high degree of sand flux heterogeneity was observed for some dunes, whereas other sites displayed steady-state migration relative to long-term rates. These large changes in annual migration are attributed to the variable length of the frost-free seasons, sediment availability in relation to the timing of peak katabatic winds, and the influence of global dust storms on seasonal ice thickness. Consistent with our previous work, we continue to observe extremely high transport rates at Olympia Cavi. All stages of aeolian system evolution are observable (sand patch > protodune > dune), along with additional phenomena not previously observed outside of terrestrial settings (e.g., dune calving and collisions, remote transfer). Transitory protodunes may evolve from modest sand mounds to prominent barchans with slipfaces several meters tall within 3–5 Mars years, while adjacent duneforms may suffer slipfaces collapse as they lose sand supply. These Martian protodunes, which appear to be larger than terrestrial equivalents, and mature dunes found downwind are among the swiftest yet reported on Mars. These rapidly evolving cryo-aeolian systems provide a window into longer-term landscape evolution of non-polar dune fields.
