Seen by an orbiting satellite, layers in a Martian trough reveal patterns of long-term climate change on the red planet.
Over the past couple million years, variations in Mars's orbit have changed the distribution of water ice around the planet. That means ice and dust have built up at the poles in varying amounts over time. (See Mars pictures.)
Looking at the walls of troughs in the polar deposit—like the one seen above in a picture from the Mars Reconnaissance Orbiter released yesterday—scientists can study changes in Martian climate the same way they use ice cores to track climate change on Earth.
Image courtesy NASA/JPL/University of Arizona
Moontrail Over Tehran
A time-lapse picture taken July 13 shows the waxing crescent moon setting behind the head of Milad Tower, the tallest tower in Iran.
The moon goes through eight distinct phases as it moves in relation to Earth and the sun. A waxing crescent follows the new moon, when the moon is totally dark as seen from Earth. As the moon orbits, its illuminated face grows, or waxes, until we see a full moon. Then the lunar orb fades, or wanes, back to the new moon phase. (Get more moon facts.)
A tumult of plasma, or charged gas, writhes on the sun's northern hemisphere on August 1, as seen in ultraviolet light by NASA's Solar Dynamics Observatory. The different colors show the temperatures on the sun, ranging from about 1 to 2 million Kelvin (1.8 million to 3.6 million degrees Fahrenheit).
The hourglass shape of the supernova remnant SN 1987A isn't as well balanced as thought, according to a new 3-D picture of the exploded star.
Using data from the European Southern Observatory's Very Large Telescope in Chile, astronomers have been able to confirm that, when massive stars explode, some of the ejected material gets shot into space faster than others, as predicted by recent computer models.
A snake-like pattern forms in the clouds due to airflow over the island of Tristan de Cunha, part of a British territory in the South Atlantic, as seen in a July 14 picture taken by NASA's MODIS satellite. The spiraling cloud patterns are known as von Karman vortices, or vortex streets.
Home to about 275 people, the tiny, volcanic island of Tristan de Cunha is considered the most remote inhabited island in the world, lying 1,750 miles (2,816 kilometers) west of South Africa and 1,510 miles (3,360 kilometers) east of South America (see map).