Question a-subj
A subject of much speculation, distinctive sets of parallel ridges mark the icy crust of Europa, Jupiter’s smallest moon. Researchers now claim that the ridges’ formation mechanism mirrors that of a strikingly similar pair on Greenland’s ice sheet. There, surface water seeped through fissures in the sheet and formed a water pocket that subsequently disrupted the overlying ice, forcing fragments of it upward and outward into peaks, as the pocket froze and expanded. Although Europa lacks liquid surface water, the same process could be driven by the moon’s subsurface ocean.
Which choice best states the main idea of the text?
The pair of ridges found on Greenland’s ice sheet appear to have formed long before the recently discovered sets of ridges on Europa formed.
Researchers don’t understand why Europa is marked by so many sets of ridges when the moon doesn’t have any liquid water on its surface that could have collected and expanded under the icy crust.
Researchers think that the ridges on Europa and the ridges in Greenland may have been formed by the same process even though Europa, unlike Greenland, doesn’t have liquid water on its surface.
The primary difference between the ridges on Europa and the ridges in Greenland is that unlike the Europa ridges, the Greenland ridges are parallel.