My Favorite Moon

This is the text of  a speech I gave at a Westside Toastmasters meeting as a “Speech to Inform”. To build up some interest and suspense, I did not reveal right away which moon is my favorite. I showed the pictures, starting with Earth’s Moon, one by one during the speech. I wrote the speech assuming the audience was not familiar with planetary science research.

Do you have a favorite moon? Some of you may be thinking, “Now wait a minute, Karen. Isn’t there only one Moon?” Maybe you prefer that moon since it is the easiest to see and appreciate.

Earth's Moon

Super full Moon on March 19, 2011. Credit: Rolf Hempel.

Or maybe you are aware of some of the moons of other planets but don’t really have a favorite. I love looking up in the night sky at our moon, known as The Moon or Luna to planetary scientists. I get a little thrill whenever I see our bright moon in the sky. However, there are over 150 moons in our solar system with over 20 more to be confirmed. This picture below shows just the 19 moons that have enough gravity of their own to be nearly spherical. Our moon isn’t even the largest one – it’s only the fifth largest in this picture. After I read about some of its interesting characteristics around 2010, however, my favorite moon has been Enceladus, a moon of Saturn, the small white moon shown directly to the left of our Moon and the fourth smallest in the picture.

The major moons of the solar system

Credits: Montage by Emily Lakdawalla. The Moon: Gari Arrillaga. Other moons data: NASA/JPL. Processing by Ted Stryk, Gordan Ugarkovic, Emily Lakdawalla, and Jason Perry.

Enceladus, named after the giant Enceladus from Greek mythology, is a small moon of only 310 miles in diameter. It was discovered by the British astronomer William Herschel in 1789, but little was known about it until the Voyager spacecraft passed close enough to take some pictures. This picture was captured in 1981 when Voyager 2 passed near enough to photograph it.

Enceladus as seen by Voyager 2

Enceladus as seen by Voyager 2. Credit: NASA/JPL-Caltech.

Now, Enceladus is only 1/7th the diameter of our moon and 1/25th the diameter of Earth. Saturn is 1 billion miles away from the sun, or about 10 times farther away from the sun than Earth, so Enceladus is around 10 times farther away from the sun than Earth is as well. When the two Voyager spacecraft captured some images of Enceladus, planetary scientists discovered that the northern pole is marked with craters, but the southern pole is smooth with fissures. They noted large, smooth plains that indicated a geologically young terrain.

Diameter comparison of the Saturnian moon Enceladus, Moon, and Earth.

Diameter comparison of the Saturnian moon Enceladus, Moon, and Earth. Scale: Approximately 28.9 km per pixel. This picture was composed from File:Tethys Earth Moon Comparison.png, File:Full Moon Luc Viatour.jpg, and File:Enceladus (Mond) (15411804).jpg, by Tom.Reding

In a presentation I heard at a recent aerospace conference, Cassini Flight Director Michael Staab called Enceladus the Hoth Moon. When the Cassini spacecraft got close to Enceladus, scientists got significant new information about the surface of Enceladus, noting the fissures on the south pole resemble tiger stripes.

Enceladus image from Cassini mission

Cassini image of Enceladus. Credits: Cassini Imaging Team, SSI, JPL, ESA, NASA. Published: January 27, 2011

When Cassini took an image of plumes, planetary scientists collectively said, “Whaaaat?” and proceeded to plan more close flybys into Cassini’s mission. This tiny moon turns out to be cryogenically volcanic with southern geysers that some are calling “Cold Faithful”, while others call them plumes, or jets, or cryovolcanoes, and my husband wants to call them moon farts.

Two views of the plumes of Enceladus

Two views of the plumes of Enceladus. Left: Color-composite of Enceladus spraying into Saturn’s E ring. (Credit: NASA/JPL/SSI/Gordan Ugarkovic) Right: Dec. 25, 2009, view obtained at a distance of approximately 617,000 kilometers (383,000 miles) from Enceladus. (Credit: NASA/JPL/Space Science Institute)

NASA JPL was able to plan dives into the plumes and programmed Cassini to do so. These flights through the plumes by Cassini led to the discovery that the liquid spewing up through those geysers contains water, salt, hydrogen molecules, ammonia, and trace amounts of methane, propane, acetylene, and formaldehyde, which are all carbon-bearing molecules. This discovery indicates the possibility of hydrothermal activity to planetary scientists, and scientists have theorized that Enceladus has a global ocean under the icy surface which is heated by tides caused by Saturn’s gravity and by Enceladus’s core causing hydrothermal vents.

Possible explanation for plumes on Enceladus

Possible explanation for plumes on Enceladus. Credit: NASA/JPL-Caltech/Southwest Research Institute. Published: April 13, 2017

Planetary scientists are now excited to promote a new mission to Enceladus to determine if hydrothermal activity on the subsurface ocean floor could harbor microbes or other life. One mission proposed, called the Enceladus Life Finder, or ELF, mission, would orbit Saturn and fly through Encaladus’s plumes multiple times with more sensitive instruments to determine if the building blocks of life exist, and determine whether methane (CH4) found in the plumes could have been produced by living organisms. The biggest argument against such a mission is that Enceladus is too small a world to host much more life than microbes. The much larger moon, Europa, orbiting Jupiter is considered a better prospect for a more diverse ecosystem of life, if it has life at all. But I personally would love to see NASA or some other organization launch a mission to Enceladus to find out more about my favorite moon.

About Karen Grothe

Systems engineer, space enthusiast, lifelong learner, movie watcher, symphonic heavy metal music fan, Lego fan, reader, puzzler, wife, mom.

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