So called because of how you'd feel if you fell/landed on them.
Exploring Jupiter’s moon Europa will be a treacherous task, it seems: scientists reckon its surface is covered in sharp towering icy daggers. The menacing shards are known as penitentes, according to a paper published in Nature Geoscience this week. They normally form in dry cold climates, where sunlight melts snow and it …
It's more of a proposed explanation than an assumption, but I think there are better explanations.
Penitentes are formed by ablative erosion so the peak of the penitente is indicative of an older and higher surface level - the penitentes are not built up from the original surface but are what's left.after the surrounding material has been removed (by the aforesaid erosion). If we have 15m high penitentes then we need to know where that 15m of eroded material came from and where it subsequently went.
More likely, imo, is that the 'roughness' is due to either compression fractures, similar to what we see in the Arctic ice sheets, or the presence of cryovolcanic 'spines', similar in mechanism to those we see being erupted from lava domes. Neither of these explanations require the now missing eroded material.
That might be true with earth penitentes but on Europa the ground surface is all ice (with pink bits) so a source of ablative ice is not a problem. I also strongly suspect the physics is a mite different when the sublimating ice is in a vacuum.
But then I'm only a Stamp Collector so what do I know but I do suspect your assumptions are wanting.
Pen·i·ten·te | \ˌpenəˈtentā, -tē\
plural Penitentes\-ās, -ēz \
Definition of Penitente
: a member of a religious society of Flagellants in Spanish-American communities of the southwestern U.S. (as New Mexico) who practice self-whipping and other forms of penitential torture particularly during Holy Week
Not Clarke, more like a Hugh Walters book, "Journey to Jupiter".
Okay, so that one has the spiky bits set on a different moon and made of rock but he did have the "here be dragons" sentiment fairly well.
There's an entire series of these. Fun reads if you're not too fussy about what we now consider to be scientific accuracy.
Don't nukes fail to work very well in a vacuum? Also Europa is already bathed in very hard radiation whipped up to relativistic speeds by the local gas giant. Hardening the electronics of any lander so it survives long enough to take samples from the pink crevasses let alone drill through kilometres of likely very hard ice (cf the measurements of comet ice hardness) is very live issue.
The radiation pretty much precludes a manned presence on the surface any time soon barring some very sci-fi levels of technology advancement. But even so, think humans staying in shielded craft and sending the robots out into the radiation storm.
Actually they may well send a nuclear powered submarine probe there once all the bugs are worked out/etc.
In order to melt the ice it would need to get up to some 200C for several hours and the best way to do this would be something like a small plutonium source (238Pu) and a heat exchanger.
Or as we used to refer to it several years ago 'Arthur's Code'.
This came about because early versions of The Sphere by Michael Crichton spelt it that way.
One of several mistakes in the text, actually. Another was a transmission of a block of digits they receive (and it was only digits in the text) that one character identifies as a hex dump. Shortly after another character claims it can't coming from a 68000 processor "because the 68000 doesn't work in hex".
The film was better. Just.
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"They found that the regions near the equator reflect radar waves more readily than its poles, and the reflection patterns are best explained by the existence of these icy blades."
If the surface was smooth you would get more reflection at the equator than the poles.
If the surface is covered in penitentes to almost 15 metres or 50 feet in height, with a spacing of 7.5 metres there would be more reflections near the poles than the equator. All those surfaces perpendicular to the radar beam and all.
As I read it the penitentes are near the equator (warmer environment aiding sublimation, presumably). So, at the poles the radar signal just disappears into space unless it's pointing straight down. At the equator there are vertical and horizontal surfaces forming cavities which reflect the signal randomly creating a more or less omnidirectional return signal.
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