NATIONAL GEOGRAPHIC'S SPACE PICTURES THIS WEEK XLVI

Space Pictures This Week: Martian Gas, Cloud Trails
By Jane J. Lee, National Geographic News, 28 January 2013.

Mercury gets a close-up, ships leave cloud trails, and the sun shines in multiple colours in the latest space pictures.

1. Multi-coloured Sun

The sun is more than meets the eye, and researchers should know. They've equipped telescopes on Earth and in space with instruments that view the sun in at least ten different wavelengths of light, some of which are represented in this collage compiled by NASA and released January 22. (See more pictures of the sun.)

By viewing the different wavelengths of light given off by the sun, researchers can monitor its surface and atmosphere, picking up on activity that can create space weather.

If directed towards Earth, that weather can disrupt satellite communications and electronics - and result in spectacular auroras. (Read an article on solar storms in National Geographic magazine.)

The surface of the sun contains material at about 10,000°F (5,700°C), which gives off yellow-green light. Atoms at 11 million°F (6.3 million°C) gives off ultraviolet light, which scientists use to observe solar flares in the sun's corona. There are even instruments that image wavelengths of light highlighting the sun's magnetic field lines.

2. Martian Ice Fans

In a picture released January 24 by NASA and the Jet Propulsion Laboratory, black streaks of sand fan out over a seasonal ice cap at the Martian north pole.

Unlike on Earth, ice caps on on the Red Planet are made of frozen carbon dioxide - similar to the dry ice found in Halloween punch bowls.

When sunlight filters down through the Martian ice, it warms the sand - and the ice in contact with the dirt - turning solid ice directly into a gas in a process called sublimation. Once the trapped gas finds an outlet it erupts, dragging sand from Mars' surface along with it. (Related: "Mars Snow Falls Like Dry Ice Fog.")

3. Night-Shining Clouds

These luminous blue clouds at the edge of space are called polar mesospheric clouds, or noctilucent clouds. Formed between 47 to 53 miles (76 to 85 kilometres) up in the atmosphere, they're most visible during late spring and early summer in both the Northern and Southern Hemispheres.

They get their blue glow when the sun dips below the horizon, shrouding the ground in darkness but giving off enough illumination to light up the clouds. The yellow-orange band at the bottom of the blue layer is the stratosphere.

This picture, released January 21, was taken by the crew of the International Space Station as they passed over the Pacific Ocean south of French Polynesia (map).

4. Mercury’s Michelangelo

The Michelangelo basin, shown here in a close-up released January 24, resides in the Michelangelo quadrangle located in the southern polar regions of Mercury.

The image was taken as part of NASA's MESSENGER mission, whose satellite is the first spacecraft to orbit this innermost planet.

Since Mercury has no atmosphere, there is no wind to erode the many impact craters stamped onto its surface.

5. Snail Trails?

NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite snapped this image of clouds across the eastern Pacific, off the west coast of the U.S. and Canada, on January 15.

Scrawled across the fluffy clouds like drunken snail trails are ship tracks (centre). These human-made clouds form when atmospheric water vapour condenses on small particles lofted into the air from a ship's exhaust. (See pictures of a possible new cloud type.)

[Source: National Geographic News. Edited.]