National Geographic Society

The Mars rovers are true survivors. Although Spirit and Opportunity were slated to work for just 90 Martian days, they've been putting in some serious overtime—they're now at just over 2,000 days on the job and counting.

For its part, Spirit has continued toiling away on Mars even after it broke a "foot," wore down one of its favorite tools, almost starved due to a strong dust storm blotting out sunlight, and suffered a series of memory glitches.

Then, this past May, the robust rover got stuck in the sand.

A screen shot from a computer simulation shows Spirit's current predicament.
—Picture courtesy NASA/JPL-Caltech

In the midst of a routine drive near Gusev crater, Spirit broke through a thin crust of soil over a filled-in crater. Its wheels became half buried in the soft sand, and the rover was struggling to gain traction on the slippery sulfates below.

So Spirit has stayed put for months while mission managers on Earth have raced to come up with an escape plan.

On Monday, NASA says, after working various tests, computer models, and presumably late nights, engineers will make the first attempt to free the venerable rover.

"This is going to be a lengthy process, and there's a high probability attempts to free Spirit will not be successful" Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters, said in a statement.

"Mobility on Mars is challenging, and whatever the outcome, lessons from the work to free Spirit will enhance our knowledge about how to analyze Martian terrain and drive future Mars rovers," McCuistion said.

The drive to freedom will start with a forward march up a mild slope, which mission managers hope will steer Spirit past a rock lying underneath. Data collected from the first drive attempt will help NASA figure out its next move, and it's anticipated that efforts to edge Spirit out of the crater will continue into early 2010.

But even if the rover can't be budged, Spirit has been learning a lot from its unexpected surroundings.

"The soft materials churned up by Spirit's wheels have the highest sulfur content measured on Mars," said Ray Arvidson, deputy principal investigator for the science payloads on Spirit and Opportunity.

"We're taking advantage of its fixed location to conduct detailed measurements of these interesting materials."

Your friendly neighborhood geologist will tell you that the age of the Earth is 4.54 billion years, give or take 45 million.

Since modern humans have been around for only about 60,000 years of that time, it's hard for us to even guess at how exactly the planet was born.

Luckily we have a variety of tools at our disposal to make sure we're making highly educated guesses, including orbiting observatories like the Spitzer Space Telescope.

Using its infrared vision to peer through dust and thick gases, Spitzer has seen plenty of evidence for young star systems taking shape since it was launched in 2003. But most of that evidence has been fairly static, considering that it takes planets millions of years to develop.

Now, in a rare catch, astronomers using Spitzer think they've witnessed an early stage of planet formation in real time.

—Image courtesy NASA/JPL-Caltech/R. Hurt (SSC)

The team watched one young star, LRLL 31, for five months, recording changes in its infrared light. The star had previously been called out for having a type of debris ring known as a transitional disk.

According to a popular theory of planet formation, some stars are surrounded by thick disks of dust and gases. Over time, larger grains within these disks start to collect material, and, like rolling snowballs, they grow larger as they pull more material unto themselves.

At some point, objects get so large that they carve gaps in the original disk, creating what's known as a transitional disk.

Spitzer showed that LRLL 31 has such a disk with both an inner and outer gap. What's more, the infrared light from the inner disk changes its brightness and wavelength every few weeks.

The team thinks the changes are due to a "companion"—some body circling the star inside the inner gap. As it orbits the star, this body pushes the disk's material around like a cornering boat pushes water, creating a "wave" that periodically changes the disk's height.

Higher waves facing Earth mean more and hotter material reflecting the host's starlight, so more infrared radiation and at shorter wavelengths. The wave also casts its shadow on the outer disk, blocking its longer-wavelength light.

The opposite scenario is true when the wave crests between Earth and the star.

Astronomers aren't 100 percent sure if the body creating the wave is really a developing planet or some other companion, maybe even another star.

But lead study author James Muzerolle, of the Space Telescope Science Institute in Baltimore, notes in a statement: "For astronomers, watching anything in real-time is exciting. It's like we're biologists getting to watch cells grow in a petri dish, only our specimen is light-years away."

After a successful four-year mission studying the ringed planet, the Cassini probe was still orbiting Saturn in near perfect health in June 2008. So NASA dug deep and found the funding to keep Cassini gainfully employed.

The extension, dubbed the Equinox Mission, is primarily focused on changes wrought on Saturn by the onset of equinox, when the sun shines directly on the gas giant's equator, which happens just once every 15 years.

In the past Saturn, its rings, and its moons were all illuminated from the south. But tomorrow the equinox comes, and afterward the sunlight will glide over to Saturn's northern face.

Over the long term, Cassini will be able to watch the planet's seasonal changes—at least until the currently funded mission ends in September 2010.

But the time immediately around the equinox is especially exciting, because changes in the planet's position combined with light coming in at different angles are exposing all sorts of 3-D effects in the normally "two-dimensional" rings.

Last week, for example, Cassini images revealed a new itteh bitteh moon hovering just outside Saturn's B ring.

—Image courtesy NASA/JPL/Space Science Institute, little white arrow courtesy moi

The small, light-colored object is so close to the dense rings—the scientists guess it's a mere 660 feet (200 meters) above—that it was effectively hidden until now.

The unique interplay of light brought on by the upcoming equinox caused the little moon to cast a long shadow on the rings. In general, Saturn's moons cast shadows on the rings only before and after an equinox, so pictures like this are incredibly rare.

That means it's a treat even when bigger, known moons decorate the rings with their own shadowy dances, since the shadows allow Cassini scientists to create unprecedented images with scientific punch.

Here, the moon Tethys casts its spiky shadow across the A and B rings in a mosaic of 17 pictures taken about 2 minutes, 17 seconds apart.

—Image courtesy NASA/JPL/Space Science Institute

The changing degrees of light and dark in the same parts of each shadow can tell scientists just how dense the planet's rings are in certain regions.

Saturn's moons also sometimes interact directly with the rings, as seen in this picture of the moon Prometheus creating dark "steamers" through the thin outer F ring.

—Image courtesy NASA/JPL/Space Science Institute

The 53-mile-wide (86-kilometer-wide) moon dips into the F ring when its orbit takes it farthest from the planet. The moon's gravity then pulls material out of the rings as it moves closer to Saturn. (Watch a movie of Prometheus "bouncing" off the F ring.)

So far we've only seen this phenomenon lit from the south, but it's due to happen again late this fall, after the equinox. Scientists hope light coming in from the north will, pardon the cliché, literally shed new light on the moon's effects on the F ring.

As for the equinox itself, Cassini will likely have its eye trained on Saturn to see the gas giant make its roughly 170,000-mile-wide (273,000-kilometer-wide) rings ... disappear!

As wide as the rings are, they're just 30 feet (9 meters) thick. As the planet turns on its axis during the equinox, the edge of the rings will line up with the light from the sun.

It's like turning a piece of white paper edge-on against a mostly white wall and then shining a light directly at it. For all you can see, the paper will seem to vanish.

—Image courtesy NASA/Hubble Heritage

Astronomer Galileo Galilei saw this happen in December 1612 (although through his low-power 'scope, he thought the rings were actually two moons on either side of the planet!).

He was appropriately baffled at the vanishing act, writing in a letter: "I do not know what to say in a case so surprising, so unlooked for and so novel."

Sadly the folks at home won't be able to witness the spectacle this year, as Saturn is also in solar conjunction—basically behind the sun as seen from Earth.

So let's all hope Cassini keeps working overtime and catches the equinox in action!