- 3246 - WATER - on the Moon and Jupiter? - Scientists are confident that water ice can be found at the Moon's poles inside permanently shadowed craters, craters that never receive sunlight. But observations show water ice is also present across much of the lunar surface, even during daytime. This is a puzzle: Any water ice that forms during the lunar night should quickly burn off as the Sun climbs overhead.
------------------ 3246 - WATER - on the Moon and Jupiter?
- Over a decade ago, spacecraft detected the possible presence of water on the dayside surface of the Moon, and this was confirmed by NASA's Stratospheric Observatory for Infrared Astronomy [SOFIA] in 2020.
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- Water shouldn't survive in that harsh environment on the surface of the Moon.. This challenges our understanding of the lunar surface and raises intriguing questions about how volatiles, like water ice, can survive on airless bodies.
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- Some scientists suggest that shadows created by the "roughness" of the lunar surface provide refuge for water ice, enabling it to form as surface frost far from the Moon's poles. They also explain how the Moon's exosphere may have a significant role to play.
The exosphere is the tenuous gases that act like a thin atmosphere above the surface.
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- Many computer models simplify the lunar surface, rendering it flat and featureless. As a result, it's often assumed that the surface far from the poles heats up uniformly during lunar daytime, which would make it impossible for water ice to remain on the sunlit surface for long.
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- How is it that water is being detected on the Moon beyond permanently shadowed regions? One explanation for the detection is that water molecules may be trapped inside rock or the impact glass created by the incredible heat and pressure of meteorite strikes. Fused within these materials the water can remain on the surface even when heated by the Sun while creating the signal that was detected by SOFIA.
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- One problem with this idea is that observations of the lunar surface show that the amount of water decreases before noon (when sunlight is at its peak) and increases in the afternoon. This indicates that the water may be moving from one location to another through the lunar day, which would be impossible if they are trapped inside lunar rock or impact glass.
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- Revised computer models factor in the surface roughness apparent in images from the Apollo missions from 1969 to 1972, which show a lunar surface strewn with boulders and pockmarked with craters, creating lots of shady areas even near noon.
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- Because there is no thick atmosphere to distribute heat around the surface, extremely cold, shaded areas, where temperatures may plummet to about minus 350 degrees Fahrenheit, can neighbor hot areas exposed to the Sun, where temperatures may reach as high as 240 Fahrenheit.
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- As the Sun tracks through the lunar day, the surface frost that may accumulate in these cold, shaded areas is slowly exposed to sunlight and cycled into the Moon's exosphere. The water molecules then refreeze onto the surface, reaccumulating as frost in other cold, shaded locations.
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- Understanding water as a resource is essential for NASA and commercial endeavors for future human lunar exploration. If water is available in the form of frost in sunlit regions of the Moon, future explorers may use it as a resource for fuel and drinking water.
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- Hydroxyl, which is a molecular cousin of water (a molecule with two hydrogen atoms and one oxygen atom), can serve as an indicator of how much water may be present in the exosphere. Both water and hydroxyl could be created by meteorite impacts and through solar wind particles hitting the lunar surface, so measuring the presence of these molecules in the Moon's exosphere can reveal how much water is being created while also showing how it moves from place to place.
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- This study could help us better understand the role shadows play in the accumulation of water ice and gas molecules beyond the Moon, such as on Mars or even on the particles in Saturn rings.
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- At more than five times the distance from the Sun as Earth, Jupiter is not expected to be particularly warm, and not have liquid water either. Based on the amount of sunlight received, the average temperature in the planet's upper atmosphere should be about minus 100 degrees Fahrenheit.
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- Instead, the measured value on the Jupiter surface is + 800 degrees Fahrenheit. The source of this extra heat has remained elusive for 50 years, causing scientists to refer to the discrepancy as an "energy crisis" for the planet.
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- What is a likely source of Jupiter's thermal heat? Astronomers have found that Jupiter's intense aurora, the most powerful in the solar system, is responsible for heating the entire planet's upper atmosphere to surprisingly high temperatures.
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- Auroras occur when electrically charged particles are caught in a planet's magnetic field. These particles spiral along invisible lines of force in the magnetic field towards the planet's magnetic poles, striking atoms and molecules in the atmosphere to release light and energy.
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- On Earth, this leads to the colorful light show that forms the aurora Borealis and Australis, also known as the northern and southern lights. At Jupiter, material erupting from its volcanic moon, Io, leads to the most powerful aurora in the Solar System and enormous heating in upper atmosphere over the polar regions of the planet.
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- Models of Jupiter's upper atmosphere suggested that winds heated by the aurora and headed to the equator would be overwhelmed and redirected by westward winds driven by the planet's rapid rotation. This would prevent the auroral energy from escaping the polar regions and heating the whole atmosphere.
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- High-resolution temperature maps from Keck II, combined with magnetic field data from Hisaki and Juno, allowed the team to catch the aurora in the act of sending what appears to be a pulse of heat toward Jupiter's equator.
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- The team observed Jupiter with the Keck II telescope for five hours on two separate nights in April 2016 and January 2017. Using the Near-Infrared Spectrometer (NIRSPEC) on Keck II, heat from electrically charged hydrogen molecules (H3+ ions) in Jupiter's atmosphere was traced from the planet's poles down to the equator.
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- Detailed maps show that the heat in the upper atmosphere was more widely distributed, with a gradual decrease in temperature closer to the equator.
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- Jupiter's magnetic field is strongly influenced by the solar wind; a stream of high-energy particles that emanates from the Sun. The solar wind carries its own magnetic field and when this meets Jupiter's planetary field, the latter is compressed.
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- Picture this like a beach: if the hot atmosphere is water, the magnetic field mapped by Juno is shoreline, and the aurora is ocean, these observations found that water left the ocean and flooded the land, and Juno revealed where that shoreline was to help us understand the degree of flooding. Analogy will do until we get more visits to Jupiter.
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- August 11, 2021 WATER - on the Moon and Jupiter? 3246
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