Cassini’s View of Saturn’s High North Saturn’s high north is a seething cauldron of activity filled with roiling cloud bands and swirling vortices. A corner of the north polar hexagon is seen at upper right. The image was taken on Aug. 25, 2008 at a distance of approximately 541,000 km (336,000 mi) from Saturn. Image scale is 29 km (18 mi) per pixel. Credit: NASA/JPL/SSI
Ganymede and Callisto are similar in size and are made of a similar mixture of ice and rock, but data from theGalileo and Voyager spacecraft show that they look different at the surface and on the inside. Just like Earth and Venus, Ganymede and Callisto are twins, and understanding how they were born the same and grew up to be so different is of tremendous interest to planetary scientists.
Ganymede and Callisto’s evolutionary paths diverged about 3.8 billion years ago during the Late Heavy Bombardment, the phase in lunar history dominated by large impact events. Impacts during this period melted Ganymede so thoroughly and deeply that the heat could not be quickly removed. All of Ganymede’s rock sank to its center the same way that all the chocolate chips sink to the bottom of a melted carton of ice cream. Callisto received fewer impacts at lower velocities and avoided complete melting. Ganymede is closer to Jupiter and therefore is hit by twice as many icy impactors as Callisto, and the impactors hitting Ganymede have a higher average velocity.
Itokawa is by far the smallest object featured on this blog, measuring only about 535 metres in length, and less than 300 metres in width and height. Its surface gravity is tiny (much less than a millimetre per second squared), so the spacecraft entered an orbit round the sun that was roughly parallel to the asteroid’s orbit, here about 7km away. So the rotation seen in the gif is Itokawa’s rotation, not the result of a camera orbiting around it.
Hayabusa later landed on the surface, collected some dust, and returned it to Earth for analysis. Google Images doesn’t seem to know of the photos near the surface, so I uploaded most of the good ones to an Imgur album here (edit: Google Images doesn’t recognise the photos I upload to it, but searching for ‘itokawa surface’ brings up some scattered results). I wouldn’t have guessed that a small asteroid would comprise lots of little rocks, just barely held together by their very weak gravity. But apparently such rubble piles are common.
Venus is the second closest planet to the Sun and has the highest surface temperature of any planet in our solar system, with an orbital period of about 225 Earth days. Because of its similar gravity and size, it is sometimes known as Earth’s “sister planet.” However, besides these two aspects, the two planets have almost nothing in common. With the densest atmosphere on any terrestrial planet in the solar system, the surface pressure on Venus is about 92 times that of Earth; the same pressure one kilometer beneath Earth’s oceans.
Even though Venus is comparatively much further away from the Sun than Mercury, it is the hotter planet with a surface temperature of around 462 °C; this is because of its dense atmosphere of greenhouse gases such as carbon dioxide and sulfur dioxide. One remarkable aspect of the atmosphere of Venus is the precipitation of liquid sulfuric acid. The surface geology of the planet has been observed by NASA for over twenty years now, and it is seen that there is extensive and violent volcanism at the surface.
Today marks the one-year anniversary of Curiosity’s epic arrivalon the surface of Mars. To celebrate, immerse yourself in every eye-popping detail of Curiosity’s harrowing plummet to the Martian surface in this ultra-high-definition video.
The original imagery, 297 frames, was compiled by NASA into a video that shows the rover’s final two-and-a-half minutes of a 14-minute, hair-raising descent that involved an abrupt 14,000-mile-per-hour to zero slowdown. The rover began capturing the imagery just before it ejected its heat shield, which can be seen in the first few seconds of the video.
Canning used a video processing technique known as motion-flow interpolation, which involves creating new frames to fit in between existing frames, increasing the overall frame rate from the original, which was just 4-frames-per-second, and making the video appear more fluid at 30 frames-per-second. He also enhanced the color and the detail of the imagery and re-rendered it at “enterprise-quality 1080p, 50,000 kbps (instead of the usual ~1000kbps).”
“I manually added thousands of motion-tracking and adjustment points,” Canning wrote of his process on Reddit, “I had to go the laborious manual route because the frame-rate is too low causing the footage to jerk around too quickly for automated motion tracking to handle it.”
On top of everything, Canning added something that other Mars descent videos have lacked: sound. Simulating the rover’s booming entry from space into the high atmosphere and then the quieter whooshing winds of Mars as it was lowered on its supersonic parachute really adds to the realism of the video.
Canning said he contacted NASA about the video, and that several people involved with the mission have gotten back to him, one who even requested to use it in NASA marketing material.
To get a nice behind-the-scenes look at Canning’s process, he has helpfully provided a “making of” video.
chorus: Clouds on Mars, photographed by Mars Express, 20th December 2005.
Around 70°S 192°E on the southern Terra Sirenum; this composite is about 50 by 75km. Charlier Crater is partially seen at top. The clouds might be dust picked from the dark region below, but I’m not sure.
Composite of 8 images: 3 (red, green, and blue light) for colour, and 5 monochromatic (ish) in sequence for motion. The colours are probably more suggestive than naturalistic.