After four years in orbit around Mercury, NASA's MESSENGER mission is sadly coming to an end. But before it plunges to its doom, mission controllers are taking full advantage of the spacecraft's close proximity to the surface. Here are some of the most detailed and vivid images ever taken of the Solar System's innermost planet.
These images were recently presented at a press conference at the Lunar and Planetary Science conference. All images: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
Hot and Cold
The top photo shows a series of craters at Mercury's north polar region. The large crater at top center is Prokofiev, which features a diameter of 70 miles (112 km). The colors are based on the maximum biannual surface temperature, which ranges from >400 K (126°C, 260°F) (shown in red) to 50 K (-223°C, -370°F) (shown in purple). Not surprisingly, as the planet closest to the Sun, it features some scorchingly hot surface temperatures, thus explaining the predominantly red coloration. That said, water ice deposits can be found within the cold and shaded craters, which feature surface temperatures less than 100 K (-173°C, -280°F).
The image above shows the wall of a volcanic vent located between the Rachmaninoff basin and Copland crater. The steep wall of the vent exhibits highly reflective layers and outcrops where the hollows are forming. The wall also features some spectacular fluting in the form of gullies sculpted by landslides.
The Young Ones
This is a hi-res view of Mercury's hollows — those weirdly shaped, flat-floored depressions — on the southwestern peak ring of the Scarlatti basin. The image also shows the abundance of small impact craters on the surface. Interestingly, there aren't many craters within the hollows themselves, which indicates how young they must be relative to the rest of the planet's surface.
Small Scarp Close-up
This is a good example of the kinds of photos MESSENGER is taking at its lower altitude. This image reveals a series of small fault scarps (indicated by the arrows). They're only 6.2 miles (10 km) in length, and quite shallow. These structures are quite young and may even be active today. Mercury's interior has cooled over billions of years, causing the planet to contract, forming a network of large landforms called lobate scarps.
The MESSENGER site explains:
The top left panel shows an image of Fuller, with the crater rim outlined in pink and the edge of a low-altitude broadband MDIS image in green. The large panel applies a different stretch to the same MDIS broadband image in the first panel, revealing details of the shadowed surface inside Fuller! In particular, as highlighted with yellow arrows in the bottom left panel, the image reveals a region inside Fuller that is lower in reflectance. The edge of the low-reflectance region has a sharp and well-defined boundary, even when imaged at 46 m/pixel, suggesting that the low-reflectance material is sufficiently young to have preserved a sharp boundary against lateral mixing by impact cratering. Models for surface and near-surface temperature within Fuller crater predict a region that is sufficiently cold to host long-lived water ice beneath the surface but too hot to support water ice at the surface. The low-reflectance region revealed in the images matches the thermal characteristics expected for a lag deposit of volatile, organic-rich material that overlies the water ice.
Those arrows are pointing to the largest lobate scarp on Mercury. Named Enterprise Rupes, it measures about 620 miles (1,000 km) long and features over 1.9 miles (3 km) of relief. Again, this feature is caused by the dramatic contraction experienced by Mercury over the course of billions of years.
Really amazing photos. MESSENGER is scheduled to plunge to its doom on April 30. Hopefully it'll have more to show us over the course of its final days.
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