Enceladus is the sixth-largest moon of Saturn, and was discovered in
1789 by William Herschel. Until the two Voyager spacecraft and Pioneer
11 passed near it in the early 1980s, very little was known about this
small moon besides the identification of water ice on its surface. The
Voyagers showed that Enceladus is only 500 kilometers in diameter and
reflects almost 100% of the sunlight that strikes it. The Cassini
orbiter performed several close flybys of Enceladus in 2005, revealing
the moon's surface and environment in greater detail. In particular,
the probe discovered a water-rich plume venting from the moon's south
polar region. This discovery, along with the presence of escaping
internal heat and very few (if any) impact craters in the south polar
region, shows that Enceladus is geologically active today. Enceladus
is one of only three outer solar system bodies where active eruptions
have been observed. Analysis of the outgassing suggests that it
originates from a body of sub-surface liquid water, which along with
the unique chemistry found in the plume, has fueled speculations that
Enceladus may be important in the study of astrobiology. (More...)
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Today's selected anniversaries:
Forces under Timur defeated the Ottomans in the Battle of Ankara and
captured Sultan Bayezid I.
The Austrian Navy led by Wilhelm von Tegetthoff defeated a much larger
Italian fleet in the Battle of Lissa.
Claus von Stauffenberg and others in the German Resistance attempted
to assassinate Adolf Hitler.
The Apollo 11 lunar module landed on the Sea of Tranquillity, where
Neil Armstrong and Buzz Aldrin (pictured) became the first men to walk
on the moon.
The Viking 1 spacecraft landed on Mars.
Wikiquote of the day:
"You don't have to be a fantastic hero to do certain things â€” to
compete. You can be just an ordinary chap, sufficiently motivated to
reach challenging goals. The intense effort, the giving of everything
you've got, is a very pleasant bonus." -- Sir Edmund Hillary