Equinox on Saturn

About every 15 Earth years, Saturn’s experiences an equinox, much like Earth’s equinox. On Earth it occurs twice in Earth’s orbit—two times every Earth year—when the Sun lies in the Earth’s equatorial plane. As a result, the duration of day and night are approximately equal, which is also the origin of the term equinox.

Saturn also experiences this twice in its orbit, but its orbit lasts about 30 Earth years, meaning that the equinox takes place every 15 Earth years. Plus, this event is even more special on Saturn. Saturn has a very famous and widely recognized set of rings. These rings lie in Saturn’s equatorial plane, and therefore, when Saturn undergoes an equinox, the Sun also lies in the plane of the rings. Since the rings are very thin (at least compared to the size of Saturn), during the equinox the shadow from the rings disappears. The rings themselves also are barely visible because only the edges catch the light of the Sun.

The Cassini Spacecraft was present to capture photos from the most recent equinox last August. The below photograph was just recently released by the Jet Propulsion Laboratory, captured on July 18, 2009, just a few weeks before the equinox. The barely visible rings cast a thin shadow on the body of Saturn, creating a stunning view. In fact, the rings captured in the original images from Cassini were so dim that it was necessary to brighten them by a factor of 9.5 relative to the planet in order to produce the result (I’d be very interested to see the picture where the rings are not brightened).

The picture below is from just after equinox, when the shadow from the rings on Saturn is barely visible. Again, the brightness of the rings relative to the planet had to be increased in order to generate the image.

This equinox was also important in allowing Cassini to gather important data about the structure of the rings. When the rings are at a large angle to the Sun, small bumps and features are very hard to detect. However, when the Sun’s rays are parallel to the plain of the rings, the bumps and features create large shadows which are much easier to detect. And the results from this work were surprising. Some areas of Saturn’s rings ripple up and down, forming vertical formations about 800 km high. This phenomenon has not been explained yet. Meanwhile in some other areas, the particles in the ring are affected by the gravity of moons of Saturn, towering above the plain as high as 4 km. So while the rings may appear simple and peaceful in the images above, they have some very complex and strange features.

Tracing Saturn

Image: NASA/JPL/Space Science Institute

Looking at this picture just blew me away. It is so simple, yet is able to reveal Saturn's unique shape immediately.

The picture was taken by the Cassini spacecraft, currently orbiting Saturn, on February 13, 2010, with the sun located behind Saturn. Saturn's outline is created by scattered sunlight passing through Saturn's upper atmosphere. Some of this light is eventually captured by the cameras aboard Cassini. Near the bottom of the picture, the rings are visible since the picture is taken with Cassini located above the plane of the rings.

Water Molecules Discovered on the Moon

Distribution of water-rich minerals around a fresh crater.

Image: ISRO/NASA

The data from three separate spacecrafts have found signs of water molecules on the Moon, more than what has been predicted in the past. In addition hydroxyl (OH, in contrast with H₂O, water) has also been found in the lunar soil.

This finding is very surprising because the Moon has long been thought to be a parched and waterless place. Although the moon reaches frigid temperatures in the dark (reaching down to 100K or -173°C), the extreme temperatures in the sunlight were thought to have made the water evaporate completely. The only places immune to this were thought to have been the permanently dark craters at higher latitudes, near the poles of the Moon. However, the new finding suggests that water is much more widespread throughout the Moon.

"Mission Accomplished, but New Questions Await!"

That's what NASA is announcing about their Cassini mission. Today, on June 30, Cassini is ending its primary mission, lasting for four years. But Cassini is not done with Saturn and its moons. There is still much too left to learn about Saturn, and the primary mission was just the start.

Now, Cassini starts a new journey, with a new two-year mission. This extended mission, called the Cassini Equinox Mission, was approved in April. After Cassini unleashed new information about Saturn's moons Titan and Enceladus, these two moons became the prime targets for te extended mission. The mission will also focus on the seasonal effects on Titan and Saturn, and looking and analyzing the geometry of the rings of Saturn during the Saturn equinox in August 2009, when sunlight will pass directly through the plane of the the rings.

Find out more about Cassini at NASA and JPL.

Image from NASA/JPL.

Cassini Meets The Jets of Enceladus

NASA's Cassini spacecraft made a close flyby on Wednesday March 12 of Enceladus, one of Saturn's numerous moons. Cassini flew by the moon at 15 kilometers per second (32,000 mph), through icy water jets, that are similar to geysers. With the information from the flyby, the tiny ice moon Enceladus is revealed to be active and hot. It also has a lot of water vapor and organic material.

There are many fractures running along the moon's south pole, from which the geysers shoot out water vapor at 400 meters per second (800 mph). The geysers added evidence that there may be liquid water under the icy crust of Enceladus.

Also, new heat maps of Enceladus taken by Cassini show higher temperatures in the south pole region, and hot tracks running along the fractures (see image at right). The strips of warmth, also called "tiger stripes," are giant fissures that are the source of the geysers.

The surprising thing about all this news was that the material coming from the inside of Enceladus resembles that of a comet. The Ion and Neutral Mass Spectrometer aboard the Cassini spacecraft saw a combination of volatile gases, water vapor, carbon dioxide, carbon monoxide, and organic materials. It seems that all of these materials are pointing ton one thing: life. However, the final ingredient, liquid water, has not been confirmed yet.

All of these developments may lead to more information about the formation and composition of Saturn and its moons.

For more information:

• An animation of the jets on Enceladus (requires Quicktime).
• NASA Mission News (1, 2).
• Wikipedia (Cassini, Enceladus).

The Seas of Titan

The Cassini Spacecraft has been orbiting Saturn for some time now, but recently, it has found seas on one of Saturn's moon, Titan, the second largest moon in the solar system. The dark features, caught by Cassini's radar instrument are found near Titan's north pole and are thought to be filled with liquid methane or ethane. Scientists think that these lakes must be continuously re-supplying methane to Titan's atmosphere, finding an answer to the mystery.

Find out more at:

• NASA
• Wikipedia (Cassini-Huygens, Titan)