Dione and Enceladus


Nice job Cassini and team!

The original caption from Cassini site:

Although Dione (near) and Enceladus (far) are composed of nearly the same materials, Enceladus has a considerably higher reflectivity than Dione. As a result, it appears brighter against the dark night sky.

The surface of Enceladus (313 miles or 504 kilometers across) endures a constant rain of ice grains from its south polar jets. As a result, its surface is more like fresh, bright, snow than Dione’s (698 miles or 1123 kilometers across) older, weathered surface. As clean, fresh surfaces are left exposed in space, they slowly gather dust and radiation damage and darken in a process known as “space weathering.”

This view looks toward the leading hemisphere of Enceladus. North on Enceladus is up and rotated 1 degree to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 8, 2015.

The view was acquired at a distance of approximately 52,000 miles (83,000 kilometers) from Dione. Image scale is 1,600 feet (500 meters) per pixel. The distance from Enceladus was 228,000 miles (364,000 kilometers) for an image scale of 1.4 miles (2.2 kilometers) per pixel.



Tomorrow, 17 November, the Leonids meteor shower peaks.   You will see probably 20 meteors an hour from this storm.  Not huge numbers but good to see just the same.

I will add that I am biased a little.  Many years ago, on 16 November my dog got wrapped around something outside.  It was cold and naturally I had to go get her.  I saw the most amazing fireball I have ever seen and the reason I can remember the details.  I got to see it come in from the east and break apart — it was spectacular!

For quite a while I was calling it a Leonid fireball, because it happened after all at the Leonid peak.  I have since decided it was more likely a Taurid.  Firstly because the Taurids are known for fireballs and they are still around, and secondly, the Leonids have the constellation Leo as a radiant.  Leo does’t rise that early, closer to midnight in fact.  The best viewing time is between midnight and sunrise, nice dark skies and the moon won’t be much of an issue this year.

If you look towards morning you will be treated to a beautiful line up of Venus, Mars, and Jupiter. They will point the way to the Leonids radiant just follow the line up.

The image above (made with Stellarium) shows the location the planets and the Leonid radiant at around  04:50 your local time on 17 November, but I’m also going out right now.

Polar Vortex


The polar vortex of Venus – south pole.

ESA has a nice video version located here.

Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. Oxford

ESA’s caption:

This ghostly puff of smoke is actually a mass of swirling gas and cloud at Venus’ south pole, as seen by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express spacecraft.

Venus has a very choppy and fast-moving atmosphere – although wind speeds are sluggish at the surface, they reach dizzying speeds of around 400 km/h at the altitude of the cloud tops, some 70 km above the surface. At this altitude, Venus’ atmosphere spins round some 60 times faster than the planet itself. This is very rapid; even Earth’s fastest winds move at most about 30% of our planet’s rotation speed. Quick-moving Venusian winds can complete a full lap of the planet in just four Earth days.

Polar vortices form because heated air from equatorial latitudes rises and spirals towards the poles, carried by the fast winds. As the air converges on the pole and then sinks, it creates a vortex much like that found above the plughole of a bath. In 1979, the Pioneer Venus orbiter spotted a huge hourglass-shaped depression in the clouds, some 2000 km across, at the centre of the north polar vortex. However, other than brief glimpses from the Pioneer Venus and Mariner 10 missions in the 1970s, Venus’ south pole had not been seen in detail until ESA’s Venus Express first entered orbit in April 2006.

One of Venus Express’ first discoveries, made during its very first orbit, was confirming the existence of a huge atmospheric vortex circulation at the south pole with a shape matching the one glimpsed at the north pole.

This south polar vortex is a turbulent mix of warming and cooling gases, all surrounded by a ‘collar’ of cool air. Follow-up Venus Express observations in 2007, including this image, showed that the core of the vortex changes shape on a daily basis. Just four hours after this image the vortex looked very different and a day later it had morphed into a squashed shape unrecognisable from the eye-like structure here.

A video of the vortex, made from 10 images taken over a period of five hours, can be seen here. The vortex rotates with a period of around 44 hours.

The swirling region shown in this VIRTIS image is about 60 km above the planet’s surface. Venus’ south pole is located just up and to the left of the image centre, slightly above the wispy ‘eye’ itself.

This image was obtained on 7 April 2007 at a wavelength of 5.02 micrometres. It shows thermal-infrared emission from the cloud tops; brighter regions like the ‘eye’ of the vortex are at lower altitude and therefore hotter.


Curiosity’s Look at Mount Sharp


Click the image for a larger version.  In case you don’t read the press release below, this image is adjusted to “Earth light”, or how this would appear if it were on Earth.

The press release:

This view from the Mast Camera (Mastcam) on NASA’s Curiosity Mars rover shows a site with a network of prominent mineral veins below a cap rock ridge on lower Mount Sharp.

Researchers used the rover in March 2015 to examine the structure and composition of the crisscrossing veins at the “Garden City” site in the center of this scene. For geologists, the vein complex offers a three-dimensional exposure of mineralized fractures in a geological setting called the Pahrump section of the Lower Murray Formation. Curiosity spent several months examining sites in the Pahrump section below this site, before arriving at Garden City.

Mineral veins such as these form where fluids move through fractured rocks, depositing minerals in the fractures and affecting chemistry of the surrounding rock. In this case, the veins have been more resistant to erosion than the surrounding host rock.

The component images of this mosaic view were taken by the left-eye camera of Mastcam on March 27, 2015, during the 938th Martian day, or sol, of Curiosity’s work on Mars. The scene is presented with a color adjustment that approximates white balancing, to resemble how the rocks would appear under daytime lighting conditions on Earth.

For scale, the cap rock scarp is about 3 feet (1 meter) tall.

Polar Vortex


The Cassini spacecraft took this image of the polar vortex on Saturn’s moon Titan in 2012.

Now scientists have detected a monstrous new cloud of frozen compounds in the moon’s low- to mid-stratosphere – a stable atmospheric region above the troposphere, or active weather layer.

Read on for the Cassini press release:

Continue reading

Pluto’s Twin Ice Volcanoes?

plutovolcanoThis is simply amazing!  Imagine, nitrogen lava.

Scientists using New Horizons images of Pluto’s surface to make 3-D topographic maps have discovered that two of Pluto’s mountains, informally named Wright Mons and Piccard Mons, could possibly be ice volcanoes. The color is shown to depict changes in elevation, with blue indicating lower terrain and brown showing higher elevation; green terrains are at intermediate heights.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
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