New studies of ripples and dunes shaped by the winds on Mars testify to variability on that planet, identifying at least one place where ripples are actively migrating and another where the ripples have been stationary for 100,000 years or more.

Odysseus Crater, with a size of epic proportions, stretches across a large northern expanse on Saturn's moon Tethys.

Odysseus Crater, with a size of epic proportions, stretches across a large northern expanse on Saturn's moon Tethys. This view looks toward the leading hemisphere of Tethys. Odysseus Crater is 450 kilometers, or 280 miles, across. North on Tethys is up and rotated 3 degrees to the right.

Subtle gravitational tugs suggest the interior has been too cold and sluggish to split completely into separate layers of ice and rock.

Scientists studying Titan have found analogies to a type of spectacular terrain on Earth known as karst topography.

A day after a targeted flyby of the moon Rhea, the Cassini spacecraft made its closest approach of the mission to Helene at about 1,800 kilometers (1,131 miles). The small moon is referred to as a trojan moon because it is gravitationally tied to the much larger moon Dione.

On March 2, 2010, Cassini swooped down to within about 100 kilometers of Rhea to ?sniff? the moon. Particle and fields instruments will use the data collected to try to determine what is coming off Rhea.

A massive "current of fire" on the sun has started running at high speed, surprising researchers and challenging some models of the solar cycle.

Last month's 8.8 magnitude earthquake in Chile was so strong it might have shifted the axis of the entire Earth.

NASA's venerable Mars rover Spirit is starting a second career as an explorer of the Martian core--but first it must survive the deadly Martian winter.

NASA's Solar Dynamics Observatory amazed onlookers last week when it flew past a sundog and destroyed it. Must-see videos of the event captured shock waves from the rocket billowing through the sundog, eliciting cries of delight and amazement from the crowd below.

Imagine holding the entire sun in the palm of your hand. Now you can. A new iPhone app developed by NASA-supported programmers delivers a live global view of the sun directly to your cell phone.

Who are these masked men?

Fixed to a tripod, a camera can record graceful trails

What's happening on the surface of Saturn's moon Helene?

The two galaxies on the far left were unknown until 1968.

What's that bright object in the sky?

Is it art?

Only 11 million light-years away,

Terrestrial gamma-ray flashes (TGFs) surge through thunderstorms at about the same altitude where commercial airliners fly. Do these blasts of gamma-radiation pose a hazard to air travelers?