Call it moonception , if you ’d like . astronomer say that a moon - with - a - moon scenario could explain some of the strange feature of Iapetus , the third - enceinte of Saturn ’s 62 - experience moons .
Iapetus was first observe over three - hundred year ago by astronomer Giovanni Domenico Cassini , but it was n’t until 2004 , during NASA ’s Cassini mission to Giovanni ’s namesake , that astronomers detect a distinctive ridge , redolent of a walnut tree ’s seam , that runs almost absolutely along the moon ’s equator ( the ridge is clear visible in the figure of speech of Iapetus show up top ) .
How the ridge formed is just one of the lunation ’s many mystery . The overall shape of the lunar month , for illustration , hint that it once spin about its axis very cursorily , making a complete rotation once every sixteen time of day ; but current measurements show the moon to have a much longer 79 - day spin period .
What gave ascent to the lunation ’s typical ridgeline and its puzzling shape — and whether the two are somehow bear on — has been the content of some disputation in recent geezerhood . Now , Kevin Walsh and his fellow worker at Southwest Research Institute in Boulder , Colorado hypothesize that the two are , in fact , linked , and can actually be explained by the transient orbit of a sub - orbiter ( which we will refer to as a “ moonlet ” ) , get by a large wallop on Iapetus alike tothe one believed to have formed Earth ’s Moon .
https://gizmodo.com/the-moon-is-200-million-years-younger-than-expected-5832027
In a paperrecently posted on arXiv , Walsh and his colleagues explicate that such an impact could have bring forth both a disk of debris around Iapetus and a moonlet , the former orbit the planet at a smaller radius than the latter .
grant to the researchers , the gravitational interactions between the moonlet and the debris disk would have pushed the debris back onto Iapetus ’ surface , forming the typical ridge we see today . At the same time , Saturn would have take out Iapetus ’ moonlet further and further away from its surface , leading to the “ de - spinning ” of Iapetus itself . Eventually , say the researchers , the moonlet would have revolve far enough from Iapetus that Saturn would have strip it away all .
arXivviaScientific American
AstronomyAstrophysicsNASASaturnSpace
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