Saturn's second-largest moon Rhea, in front of the rings and a blurred Epimetheus (or Janus) whizzing behind. Acquired March 29, 2012.
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Over the past few days NASA’s Cassini spacecraft has performed flybys of several of Saturn’s moons. From the ostentatious Enceladus with its icy geysers to the rugged relief of Rhea, the sharp peaks of Dione’s frigid craters and even diminutive Janus, Cassini has once again returned a stack of stunning views from the Saturnian system, nearly 815 million miles from home.
Check out some of the images, and wish you were there!
110-mile (177-km) -wide Janus in front of Saturn's night side.A crescent-lit Enceladus shows off its jets. (South is up.)Enceladus' fractured surface is some of the most reflective terrain in the Solar System.Wide-angle view of Rhea, Saturn and MimasCrater peak on icy Dione
And here’s a color-composite of Janus I assembled from three raw images taken in ultraviolet, green and infrared color channels. The results were tweaked to make it a little more true-color as what we might see with our limited human vision:
Color composite of Janus in front of Saturn, made from raw images taken in UV, green and IR color filters. (NASA/JPL/SSI/J. Major)
“Though we’ve been in orbit around Saturn for nearly 8 years now, we still continue to image these moons for mapping purposes and, in the case of Enceladus, to learn as much as we can about its famous jets and the subterranean, organic-rich, salty, liquid water chamber from which we believe they erupt.”
– Carolyn Porco, Cassini Imaging Team leader
For more images from Cassini, check out JPL’s mission site and the CICLOPS imaging lab site here.
Color-composite image from Cassini raw data acquired on March 12, 2012. (NASA/JPL/SSI/J. Major)
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Little Enceladus and enormous Titan are seen on either side of Saturn’s rings in this image, a color-composite made from raw images acquired by Cassini on March 12, 2012. The original images were taken in red, green and blue color channels, and with a little Photoshop editing I combined them into a roughly true-color view of what Cassini saw as it passed within 1,045,591 km of Enceladus.
MESSENGER captured this high-resolution image of an elongated pit crater within the floor of the 355-km (220-mile) -wide crater Tolstoj on Mercury on Jan. 11, 2012. The low angle of sun illumination puts the interior of the pit crater into deep shadow, making it appear bottomless.
Pit craters are not caused by impacts, but rather by the collapse of the roof of an underground magma chamber. They are characterized by the lack of a rim or surrounding ejecta blankets, and are often not circular in shape.
Since the floor of Tolstoj crater is thought to have once been flooded by lava, a pit crater is not out of place here.
The presence of such craters on Mercury indicates past volcanic activity on Mercury contributing to the planet’s evolution.
Drown yourself in stunning images from NASA’s Goddard Space Flight Center set to awesome music from indie band One Ring Zero. Don’t hold back, just dive right in. You’ll love it, we promise.
The "surface" of Neptune, its uppermost layer, is one of the most turbulent and active places in the Solar System. Credit: NASA/JPL
How did Neptune get its name? Shortly after its discovery, Neptune was only referred to as “the planet exterior to Uranus” or as “Le Verrier’s planet”. The first suggestion for a name came from Johann Galle, who proposed the name Janus. Another proposal was Oceanus. Urbain Le Verrier, who discovered the planet, claimed the right to name his discovery: Neptune. Soon Neptune became the internationally accepted name.
In roman mythology, Neptune was the god of the sea. The demand for a mythological name seemed to be in keeping with the nomenclature of the other planets, all of which, except for Earth, were named for Greek and Roman mythology. Most languages today use some variant of the name “Neptune” for the planet.
Now that you know how the planet was named, how about some facts about the planet itself. Size wise, the planet has an equatorial radius 24,764 km, a polar radius of 24,341 km, and a surface area of 7.6408×10,sup>9km2. It has a volume of 6.254×1013km3, a mass of 1.0243×1026kg, and a mean density of 1.638 g/cm3.
Its atmosphere is composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen. It also contains a high proportion of ices like: water, ammonia, and methane. Astronomers occasionally categorize Neptune as an ice giant. The interior of Neptune is primarily composed of ices and rock. Traces of methane in the outermost regions account for the planet’s blue appearance. Neptune’s atmosphere is notable for its active and visible weather patterns. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching ?218°C. Temperatures at the planet’s center are approximately 5,000°C. Neptune is one of the most interesting planets in our solar system. There are plenty of other articles about the planet here on Universe Today.
We have written many articles about Neptune for Universe Today. Here’s an article about the size of Neptune, and here’s an article about the atmosphere of Neptune.
Cassini has detected molecular oxygen ions around Saturn's icy Dione
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There’s oxygen around Dione, a research team led by scientists at New Mexico’s Los Alamos National Laboratory announced on Friday. The presence of molecular oxygen around Dione creates an intriguing possibility for organic compounds — the building blocks of life — to exist on other outer planet moons.
Dione's signature "wispy lines" are actually the bright walls of long cliff faces. (NASA/JPL/SSI)
One of Saturn’s 62 known moons, Dione (pronounced DEE-oh-nee) is 698 miles (1,123 km) in diameter. It orbits Saturn at about the same distance that our Moon orbits Earth. Heavily cratered and crisscrossed by long, bright scarps, Dione is made mostly of water ice and rock. It makes a complete orbit of Saturn every 2.7 days.
Data acquired during a flyby of the moon by the Cassini spacecraft in 2010 have been found by the Los Alamos researchers to confirm the presence of molecular oxygen high in Dione’s extremely thin atmosphere — so thin, in fact, that scientists prefer the term exosphere.
While you couldn’t take a deep breath on Dione, the presence of O2 indicates a dynamic process in action.
“The concentration of oxygen in Dione’s atmosphere is roughly similar to what you would find in Earth’s atmosphere at an altitude of about 300 miles,” said Robert Tokar, researcher at Los Alamos National Laboratory and lead author of the paper published in Geophysical Research Letters. “It’s not enough to sustain life, but—together with similar observations of other moons around Saturn and Jupiter—these are definitive examples of a process by which a lot of oxygen can be produced in icy celestial bodies that are bombarded by charged particles or photons from the Sun or whatever light source happens to be nearby.”
On Dione the energy source is Saturn’s powerful magnetic field. As the moon orbits the giant planet, charged ions in Saturn’s magnetosphere slam into the surface of Dione, stripping oxygen from the ice on its surface and crust. This molecular oxygen (O2) flows into Dione’s exosphere, where it is then steadily blown into space by — once again — Saturn’s magnetic field.
Cassini’s instruments detected the oxygen in Dione’s wake during an April 2010 flyby.
Molecular oxygen, if present on other moons as well (say, Europa or Enceladus) could potentially bond with carbon in subsurface water to form the building blocks of life. Since there’s lots of water ice on moons in the outer solar system, as well as some very powerful magnetic fields emanating from planets like Jupiter and Saturn, there’s no reason to think there isn’t more oxygen to be found… in our solar system or elsewhere.
Read the news release from the Los Alamos National Laboratory here.
Image credits: NASA/JPL/Space Science Institute. Research citation: Tokar, R. L., R. E. Johnson, M. F. Thomsen, E. C. Sittler, A. J. Coates, R. J. Wilson, F. J. Crary, D. T. Young, and G. H. Jones (2012), Detection of exospheric O2+ at Saturn’s moon Dione, Geophys. Res. Lett., 39, L03105, doi:10.1029/2011GL050452.
Changing seasons in Mars’ northern hemisphere brings a change in the weather, and the clouds have rolled in to cover part of the polar surface in this intriguing image from the Mars Odyssey spacecraft.
Mars Odyssey’s THEMIS visual imager (VIS) captured this image on Jan. 24, 2012, as it passed over the Red Planet’s northern pole during one of its 2-hour-long orbits.
MESSENGER wide-angle camera image of Mercury's southern hemisphere.
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NASA’s MESSENGER spacecraft, about to wrap up its first full year in orbit around Mercury, captured this view of the planet’s heavily-cratered southern hemisphere on August 28, 2011. Because of its orbit, MESSENGER gets particularly good panoramic views of Mercury’s underside.
Here’s why…
MESSENGER’s orbit, established on March 18, 2011 at 00:45 UTC, is not a simple circling path around the first rock from the Sun. Instead it is highly elliptical, bringing it 124 miles (200 km) above Mercury’s north pole at its closest and more than 9,420 miles (15,193 km) from its south pole at its farthest! (See diagram below.)
The close approaches over the northern hemisphere allow MESSENGER to study the Caloris basin, Mercury’s largest surface feature and, at over 960 miles (1,550 km) across, one of the largest impact craters in the entire Solar System.
The view of Mercury’s southern hemisphere above features some notable craters as well: the relatively youthful 444-mile (715-km) -wide Rembrandt basin is seen at top right, while the smaller pit-floor crater Kipling can be discerned to its left, just below the planet’s limb.
When craters are larger than 300 km in diameter, they are referred to as basins.
During its 12 months in orbit MESSENGER will have experienced only two days on Mercury! This is because Mercury rotates very slowly on its axis, completing a full solar day (sunrise to sunrise) every 176 Earth days. (And you thought your work day seemed to last forever!)
This image, acquired by NASA’s MESSENGER spacecraft on December 12, 2011, reveals the blue coloration of the 32-mile (52-km) -wide Degas crater located in Mercury’s Sobkou Planitia region.
Degas’ bright central peaks are highly reflective in this view, and may be surrounded by hollows — patches of sunken, eroded ground first identified by MESSENGER last year.
Such blue-colored material within craters has been increasingly identified as more of Mercury’s surface is revealed in detail by MESSENGER images. It is likely due to an as-yet-unspecified type of dark subsurface rock, revealed by impact events.
The slightly larger, more eroded crater that Degas abuts is named Brontë.
The image was acquired with MESSENGER’s Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS), using filters 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue, respectively.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
The pale-orange coloration around the 39-mile (62-km) -wide Kuiper crater on Mercury is evident in this image, a color composition made from targeted images acquired by NASA’s MESSENGER spacecraft on September 2, 2011.
The color may be due to compositional differences in the material that was ejected during the impact that formed the crater.
Kuiper crater is named after Gerard Kuiper, a Dutch-American astronomer who was a member of the Mariner 10 team. He is regarded by many as the father of modern planetary science.
“Kuiper studied the planets… at a time when they were scarcely of interest to other astronomers. But with new telescopes and instrumentation, he showed that there were great things to discover, which is as true today as it was then.”
– Dr. Bill McKinnon, Professor of Planetary Sciences at Washington University in St. Louis
Airless worlds like Mercury are constantly bombarded with micrometeoroids and charged solar particles in an effect known as “space weathering”. Craters with bright rays — like Kuiper — are thought to be relatively young because they have had less exposure to space weathering than craters without such rays.
See the original image release on the MESSENGER site here.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
