2024-05-15 NASA
＜関連情報＞
- https://www.nasa.gov/missions/juno/nasas-juno-provides-high-definition-views-of-europas-icy-shell/
- https://iopscience.iop.org/article/10.3847/PSJ/ad24f4
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JE008105
ジュノーのジュノカムによるエウロパの画像 Juno’s JunoCam Images of Europa
C. J. Hansen, M. A. Ravine, P. M. Schenk, G. C. Collins, E. J. Leonard, C. B. Phillips, M. A. Caplinger, F. Tosi, S. J. Bolton and Björn Jónsson
The Planetary Science Journal Published:2024 March 21
DOI:10.3847/PSJ/ad24f4
Abstract
On 2022 September 29 the Juno spacecraft passed Europa at 355 km, the first close pass since the Galileo flyby in 2000. Juno’s visible-light imager, JunoCam, collected four images, enabling cartographic, topographic, and surface geology analysis. The topography along the terminator is consistent with previously reported features that may indicate true polar wander. A bright band was discovered, and indicates global symmetry in the stress field that forms bright bands on Europa. The named feature Gwern is shown not to be an impact crater. Surface change detection shows no changes in 22 yr, although this is a difficult task considering differences between the JunoCam and Galileo imagers and very different viewing geometries. No active eruptions were detected.
ジュノーの恒星参照ユニットが明らかにした、最近の活動を示唆するエウロパ表面の複雑な領域 A Complex Region of Europa’s Surface With Hints of Recent Activity Revealed by Juno’s Stellar Reference Unit
Heidi N. Becker, Jonathan I. Lunine, Paul M. Schenk, Meghan M. Florence, Martin J. Brennan, Candice J. Hansen, Yasmina M. Martos, Scott J. Bolton, James W. Alexander
Journal of Geophysical Research: Planets Published: 22 December 2023
DOI:https://doi.org/10.1029/2023JE008105
Abstract
On 29 September 2022 Juno’s low-light sensitive Stellar Reference Unit (SRU) captured a high-resolution (256–340 m/pixel) broadband (450–1,100 nm) visible image of Europa’s icy surface during the first close flyby of the Jovian moon since Galileo’s last encounter in 2000. Collected at a sub-spacecraft altitude of 412 km while the surface was illuminated only by Jupiter-shine (incidence angle: 48–51°), the SRU image reveals a 3 × 104 km2 region between ∼0°–6°N and 43.5°–51°W in remarkable detail at the highest resolution to date. Prior coverage by Galileo under high-sun conditions at 1 km resolution led to the characterization of the terrain as ridged plains with undifferentiated linea. The SRU image reveals a much richer and more complex picture. Intricate networks of cross-cutting ridges and lineated bands surround an intriguing 37 km (east-west) by 67 km (north-south) chaos feature with a concentric fracture system, depressed matrix margins, and low-albedo materials potentially associated with brine infiltration. The morphology and local relief of the chaos feature are consistent with formation in the collapse of ice overlying a salt-rich lens of subsurface water. Low-albedo deposits, similar to features previously associated with hypothesized cryovolcanic plume activity, flank nearby ridges. The SRU’s high-resolution view of many types of features in a single image allows us to explore their regional context and greatly improve the geologic mapping of this part of Europa’s surface. The image reveals several relatively youthful features in a potentially dynamic region, providing baselines for candidate locations that future missions can investigate for present day surface activity.
Key Points
- Juno’s Stellar Reference Unit imaged Europa’s surface at high resolution while it was illuminated by Jupiter-shine
- The image reveals a feature-rich region between 0°–6°N and 43.5°–51°W with hints of relatively recent activity
- A young 37 km by 67 km chaos feature and some low-albedo deposits adjacent to double ridges may be associated with subsurface liquid water
Plain Language Summary
On 29 September 2022, the Juno spacecraft performed the first close flyby of Jupiter’s icy moon Europa in generation. The low-light sensitive Juno SRU navigation camera was used to photograph a part of the surface that was lit only by sunlight scattered off Jupiter, from a spacecraft-to-surface distance of 412 km. This innovative use of a high-resolution star camera designed to detect dim stars produced Juno’s highest resolution image of Europa, and provides the highest resolution coverage of the targeted region to date. The imaged area is revealed to be incredibly complex and rich with many different types of terrains and features. Dark stains that may be associated with plumes, and an area of ice shell disruption nicknamed “the Platypus,” are compelling targets for future missions to investigate possible present day surface activity.
