article_snippet.sent: They are thought to have formed as Mercury has cooled and contracted .
article_snippet.sent: Among the features it has revealed to scientists in the past month are patterns of distinctive hollows - each around a couple of hundred metres wide - in the bottom of a huge impact basin.
article_snippet.sent: Data sent back by Mercury suggests these cliffs, or lobate scarps as they are called, have formed as Mercury has cooled and contracted over time, creating dramatic tectonic faults on the surface.
article_snippet.sent: Another image shows a meteorite crater that has almost completely filled with lava on Mercury's northern volcanic plains, leaving just the hint of a rim behind.
article_snippet.sent: Another image also shows how the contracting surface of the planet has also created strange formations where ridges and cliffs have hit other lava filled craters.
article_snippet.sent: This image by Messenger shows the distinctive hollows on the floor of the Zeami impact basin on Mercury .
article_snippet.sent: This ghostly crater filled with lava oozed from volcanic vents on Mercury leaving just the outline of a rim behind .
article_snippet.sent: This ghostly crater filled with lava oozed from volcanic vents on Mercury leaving just the outline of the rim has been deformed after This ghostly crater filled with lava oozed from volcanic vents on Mercury leaving just the outline of the rim filled with lava and then ridges formed as the surface cooled .
article_snippet.sent: Messenger has helped to reveal volcanic vents that measure up to 15 miles across that were once sources for the large volumes of lava that have covered the surface and carved out valleys.
article_snippet.sent: This image shows some of the mysterious irregularly shaped hollows on Mercury's surface in greater detail .
article_snippet.sent: This image shows fine-grained volcanic material that has blown across impact craters almost like snow .