photo: national geographic
A rare and spectacular ice formation called penitent ice, which can be observed in a scaled down form on Earth, could pose some problems in the logistics behind landing a probe on Jupiter's moon Europa.
Jupiter's icy moon is probably covered with vertical blades of ice in some areas that can be 30 feet tall. Although the presence of the icy formation has not been confirmed yet, scientists suspect that the climate conditions on the moon probably could favor the existance of the ice in this kind of formation.
One of the aims of scientists working on the project would be to send a lander to sample different regions of the moon where the water springs up through the icy crusts.
"These areas could allow a robotic probe to sample a proxy for ocean water that lies several km deep"
On Earth penitent ice can be found at extreme altitudes in areas where the air is both cold and very dry, so that the ice can turn from solid to vapor, or sublimate.
On earth, these formations occur when the ice forms over a terrain that is itself 'spiked' and where the furrows entrap the sun's energy, and become deeper, the tall spikes are left behind.
During the 44th Lunar and Planetary Science Conference in Texas held just yesterday, scientists related that the formation of ice on the jovial moon would also require a specific amount of overhead sun exposure.
The exposure must be at a definite angle, so that the blades of ice retreat and acquire their peculiar shape. On Earth this angle is 30 degrees from the Equator.
Europa is tidally locked to Jupiter, which in turn, is tidally locked to the Sun. Because of the rarified atmosphere on Jupiter, there is little risk that warm, cloudy days could interfere with the penitent ice formation, and the Sun would then sculpt these formation on the moon's surface.
Using the angle of the Sun, the team of researchers was able to estimate the temperature of the moon's surface. And in their estimation, these formations are relegated to a zone that is between 15 and 10 degrees of the equator. The blades could be between 3 and 30 feet in depth.
The upper crust of Europa is relatively 'young'. Its surface has been reconfigured by unknown processes more than 50 million years ago. Regions in the icy crust of Europa may also wander from their original location, so that the penitents could be transported further than their optimal latitude band.
A glaciologist at the conference however, highlighted the fact that because the blades are so deep, their depth could shield most of the shaft from the wind, which could make them even deeper.
The glaciologist also noted that the icy formation are almost never in the coldest spots of the snowpack. He also offered a theory about the moon's surface. 'Since the temperature and atmospheric pressure are very low, sublimation rates are very low. The vapour simply migrates from areas of high pressure to lower ones, causing a very slow growth of snow crystals."
His theory could be proven by measuring the polarization of the surface, since the blades are oriented east to west. Also, the area around the equator is anomalously cold, which means that it holds heat better than other areas, which could also be an indicator of the existence of the ice formations.
The probe scientists want to send, would sample the ocean water that rises from the crust. There is already evidence that the salty water makes its way to the exterior of the moon. Sampling the icy formation would then give researchers a picture of what the composition of the underlying oceans is.
Nasa had planned an orbiter mission in conjuction with Europe's space agency, called the Europa-Jupiter System mIssion (ESJM), to be launched in 2020. Unfortunately the plan was abandoned due to budget constraints. However the agency is still hoping to salvage some of the ESJM program and send it to Europa in a mission that would be called "juice".
Source : BBC news 3.20.13
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