No one has made a hit album about spiders from Europa, which might be why a similar-looking shape there hasn\u2019t attracted the same attention, but it could be at least as scientifically significant. This shape, located in Manann\u00e1n Crater, lacks the numbers of the Martian counterparts, but makes up for that in longevity, surviving for decades where the Martian spiders appear each spring and vanish soon after.<\/p>\n
Professor Lauren Mc Keown of the University of Central Florida led the lab work explaining the Martian spiders, and has turned her attention to the one on Europa. She and co-authors called the shape Damh\u00e1n Alla (an Irish term for spider) and offer an explanation. Although they think Damh\u00e1n Alla has some commonalities with the Martian spiders, Mc Keown and co-authors think there is more to learn from \u201clake stars\u201d that form on Earth.<\/p>\n
The impact that created Manann\u00e1n crater left plenty of heat behind, Mc Keown and co-authors reason. Salty water melted by this heat formed a lens beneath the ice, and as this started to freeze it expanded, cracking the ice above. The crack exposed the remaining brine to the vacuum of space, the authors propose, causing an eruption, and depositing a new layer of ice in the spider shape. Salts and reduced porosity made this new deposit much darker than the surrounding ice.<\/p>\n
\u201cThe significance of our research is really exciting,\u201d Mc Keown said in a statement<\/a>. \u201cSurface features like these can tell us a lot about what\u2019s happening beneath the ice. If we see more of them with Europa Clipper<\/a>, they could point to local brine pools below the surface.\u201d<\/p>\n To test their thinking the team studied \u201clake stars\u201d or \u201cice octopi\u201d on frozen lakes, first described by Henry David Thoreau as part of the detailed weather observations which have since proven useful to climatologists<\/a> in setting a baseline.<\/p>\n In line with previous observations, lake stars near Breckenridge, Colorado form when a thin layer of ice on the lake is covered in enough snow for the weight to break the ice. Sometimes a solid object falling on the ice or warm water rising from below contribute to the puncture.\u00a0<\/p>\n Once the hole forms, warmer water rises from below the lake to reach the hole, sometimes creating brief fountains, and spreads to form the shape\u2019s arms. When the ice<\/a> refreezes, it forms a clear layer, allowing one to see the dark of the lake beneath the \u201cstar\u201d, while surrounding it, the thicker ice is opaque.<\/p>\n \u201cLake stars are really beautiful,\u201d Mc Keown said, \u201cand they are pretty common on snow or slush-covered frozen lakes and ponds. It is wonderful to think that they may give us a glimpse into processes occurring on Europa and maybe even other icy ocean worlds in our Solar System.\u201d<\/p>\n Professor Lauren Mc Keown beside an elongated lake star she thinks might be a model for Europa’s spider shape.<\/p>\n Image credit: Professor Lauren Mc Keown<\/p>\n Mc Keown and the team then sought to make Damh\u00e1n Alla replicas in the lab, using ice with grain sizes and salt concentrations matching those thought to exist on Europa. Their efforts were rewarded with what the team call \u201clab stars\u201d, which look like much smaller versions of the lake stars they studied or the Martian spiders. The extent to which the arms branch depends on the grain size of the ice.<\/p>\n We have yet to get images of Damh\u00e1n Alla at high enough resolution to confirm how similar the shape is, but Europa Clipper should change that.<\/p>\n This explanation conflicts with the initial hypothesis that Damh\u00e1n Alla was composed of fractures of Europa\u2019s icy crust.<\/p>\n If the authors are right, it could tell us a lot about how thick Europa\u2019s crust is, and therefore about how hard it would be for future missions to reach the internal ocean<\/a>. Then again, some might argue the presence of giant spiders is a non-verbal way of sending a message like that of the aliens in the book and film 2010<\/a>: \u201cAttempt no landing there.\u201d<\/p>\n<\/p>\n