NASA's Cassini spacecraft took this image of Rhea, Saturn's second largest moon on June 2, 2004, when it was 990,000 km (615,000 miles) away. Rhea is 1528 km (950 miles) across, ancient, and cratered. More than 20 years ago, Voyager discovered that one of its hemispheres has bright, wispy streaks that might be deposits of water ice. Cassini is expected to fly only 500 km (311 miles) away from Rhea on November 26, 2005, so we've got a bit of a wait before getting the extreme close-up view.

NASA's Spitzer Space Telescope has uncovered a group of ancient galaxies that had eluded astronomers using other telescopes. The primordial galaxies were originally discovered using the UK's SCUBA instrument on the James Clerk Maxwell Telescope in Hawaii, but the instrument wasn't fine enough to determine which were galaxies in the background, and which were actually groups of galaxies, or objects in the foreground. Spitzer resolved the issue in only 10 minutes, giving the SCUBA team a new method of confirming their findings.

NASA has shortened its list of potential missions for its New Frontiers program down to two spacecraft. The first is called "Moonrise", and would send two identical landers to the Moon's south pole - which is believed to have water ice mixed in with the lunar soil - to return 2 kg (5 lbs) of material back to Earth. The second is called "Juno", and would send a spacecraft into a polar orbit around Jupiter to study the giant planet in great detail. Both missions will receive $1.2 million in funding to perform 7-month feasibility studies to see if they can launch by June 2010 at a cost of less than $700 million.

Astronomers have detected a small bright spot on a familiar neutron star, Geminga, located 500 light-years away. The hot spot was discovered using the XMM-Newton x-ray observatory, and it's the size of a football field. Geminga itself is only 20 km (12.4 miles) across, and spins 4 times a second, but it's got 1.5 times the mass of our own Sun. The hot spot is created because material ejected from the rapidly spinning object is being recaptured by its gravity, and then funneled by its magnetic field to strike a specific point, heating it up millions of degrees.

After several days of delays, NASA's Aura Earth observation satellite launched on Thursday atop a Boeing Delta II rocket. The liftoff was from Vandenberg Air Force Base at 1002 UTC (6:02 am EDT), and the spacecraft separated 64 minutes later. Once its science mission begins in the next few months, Aura will sample the Earth's atmosphere to help scientists answer several questions: is the ozone layer recovering? what processes affect air quality? and how is the Earth's climate changing?

Engineers with NASA have decided to get Spirit to drive up the Columbia Hills backwards because of an ongoing problem with one of its wheels. The problem cropped up a few months ago, when one of its front wheels started getting extra resistance; they've tried heating it, and giving it rest, but nothing's worked. Spirit is now keeping the wheel locked, and then driving backwards, dragging it along like an anchor. This has saved power, but slowed down its speed a bit. Spirit will still use the wheel when it's trying to cross difficult terrain.

Why does Iapetus have a dark side and bright side? That's a mystery scientists hope that the Cassini spacecraft will be able to solve as it spends the next few years orbiting the Saturnian system. The unusual light/dark nature of the moon was first revealed when the Voyager spacecraft swept past the moon more than 20 years ago. One theory is that the moon was coated by some other foreign material, but only on one side. Another idea is that it's being resurfaced from material inside the moon. This image was taken when Cassini was 3 million kilometres (1.8 million miles) away.

The world's largest commercial communications satellite, Telstar's Anik F2, was launched atop an Ariane 5G rocket today. The rocket lifted off from the European Spaceport in Kourou at 0044 UTC (8:44 pm EDT July 17), and carried the 5,950 kg (13,118 lb) satellite into a geostationary transfer orbit. Once it reaches its final orbit at 111.1 degrees West, the Anik F2 will provide data and broadcast services to all of North America.

It appears that Jupiter and Saturn formed in completely different ways, according to a new computer simulation sponsored by the Los Alamos National Laboratory. If the simulation is correct, heavy elements ended up concentrated at Saturn's heavy core, while they're spread pretty evenly around in Jupiter. This would indicate that a different process built up the two planets. The team ended up running 50,000 different scenarios based on every possible variation permitted by known astrophysics.

The European Space Agency is considering an ambitious new mission that will attempt to move an asteroid. Named Don Quijote, the mission would include two spacecraft: Sancho and Hidalgo, and launch as early as 2010-2015. The Sancho portion would rendezvous with an asteroid, study in in great detail for seven months, and then watch as Hidalgo smashes into it at tremendous speed. The impact would slightly shift the orbit of the asteroid, and give scientists an understanding of how much force would be required to move future space rocks. Five other missions were considered, including three observation, and two rendezvous missions.

Scientists from Columbia University and Rensselaer Polytechnic Institute have created a detailed map of Lake Vostok, which is buried 3,700 to 4,300 metres beneath the surface of Antarctic ice. They found that the lake is actually broken into two different regions; water probably doesn't flow between them. That means that scientists could find two completely different ecosystems, which have separately evolved to live in this hostile environment. By drilling down and sampling the water of Lake Vostok, scientists will learn important lessons about how to go about determining if there's life on Europa - one of Jupiter's moons which seems to have liquid oceans encased in ice.

Although Cassini has arrived at Saturn, NASA is still releasing photos it took of the Ringed Planet before it arrived. Here's a picture taken on May 22 when the spacecraft was 22 million km (13.7 million miles) away from Saturn. It was taken using a special filter which is sensitive to the emissions and absorption of methane gas, giving scientists a great view of the planet's cloud structures.

When astronomers first realized that the stars in the sky were like our Sun, only more distant, they wondered if those stars had planets too. And if they have planets, is there life? Intelligent life? There's an answer - yes or no - but we don't know it yet. NASA and the European Space Agency are working on a series of space and ground-based observatories that may help get an answer soon. In just a decade, you could gaze into the night sky, locate a star, and know that there's life there. Life could be everywhere.

When Robert Zubrin imagines the human colonization of Mars, he sees us eventually terraforming the planet to make it more earthlike. In this interview with Astrobiology Magazine, Zubrin details how terraforming the Red Planet might happen, and how long it could take before you can step outside your protective dome without being simultaneously flash frozen, irradiated, and asphyxiated.

The McDonald Observatory's Hobby-Eberly Telescope has found its first extrasolar planet. The planet is 2.84 times of the mass of Jupiter, and orbits star HD 37605 every 54.23 days. The discovering team used the "radial velocity" technique, where the star's velocity toward and away from the Earth is measured to determine the mass of the planet. The observatory is well-equipped to find planets because of its High Resolution Spectrograph instrument, which can measure the composition of objects with great precision.

A Blue Moon is a fairly rare event that happens when there are two full moons in a single month. Since the Moon's cycle lasts 29 days, and most months are 30 or 31 days long, it can happen - usually every 30 months or so. Since there was a full Moon on July 2, the next one will happen on July 31. Of course, the Moon won't actually turn blue - it's just a saying.

When Cassini swept past Saturn last week, it analyzed the planet's rings in many spectra to help scientists understand their composition. Here's a 1024x768 wallpaper of the rings in the ultraviolet spectrum, which shows that there is more water ice toward the outer part of the rings. The red in the rings indicates more "dirty" and smaller particles, while the turquoise is ice.

Astronomers with the Harvard Smithsonian Center for Astrophysics have discovered a pair of brown dwarfs circling one another, which should help answer some key questions about these objects. Are they large planets, failed stars, or something else entirely? One theory is that brown dwarfs form in clouds of interstellar gas, but they get ejected before becoming full stars. This pair of brown dwarfs, however, circle one another at 6 times the distance of the Sun and Pluto - their gravitational hold on one another is very tenuous. It's more likely they formed in a calm environment like regular stars.

The European Space Agency is working an ambitious new space observatory that will be capable of precisely mapping a billion stars in our galaxy. Called Gaia, the spacecraft will launch in 2010 and observe the sky for a period of five years. Astronomers will compile this detail into a 3D map of a billion stars, including their position, motion and even composition. With such a comprehensive map of the sky, Gaia will turn up all kinds of new objects, and give astronomers plenty of future targets to study with more sensitive instruments.

The Sea Launch team has begun looking into what caused a launch malfunction during last week's Telstar 18 mission, which placed the communications satellite 14,000 km short of its intended orbit. Based on preliminary data, the investigators know that the rocket's upper stage shut down 54 seconds prematurely, but the cause of this shutdown is unknown. The satellite is operating normally, and it still has enough fuel on board to maneuver itself to its final geosynchronous orbit position; however, it might have a shorter lifespan than originally designed.

NASA scientists have been busy in the last few days, downloading the mountains of data sent back from Cassini when it made its orbital insertion around Saturn last week. As part of the insertion maneuver, Cassini made the closest approach it'll make to Saturn's rings for its entire mission. One finding has been that the Cassini division - the large gap between the A and B rings - is mostly particles, and not entirely ice as originally believed. Scientists think it might be the remnants of a shattered moon. Cassini has also turned up excess amounts of oxygen at the edge of the rings.

Only days after arriving at Saturn, Cassini made its first flyby of Titan, the planet's largest moon. The spacecraft only got as close as 339,000 km (210,600 miles), but that was enough to reveal surprising new features about the moon's surface. Cassini is equipped with special camera filters that allow it to peer through the thick clouds that obscure most wavelengths of light. Darker regions seem to be made up of water ice, while the lighter regions are a mixture of ice and hydrocarbons. Cassini is scheduled to make 45 flybys of Titan, getting as close as 950 km (590 miles), so the view will only get better.

The concepts of Dark Matter (hidden mass that surrounds all galaxies) and Dark Energy (an accelerating force on the Universe) are still largely mysteries; astronomers have detected them, but they have no conclusive idea what they are. A new theory by Vanderbilt University researcher Robert Scherrer proposes that they are actually two aspects of a single, unknown force, called a K-essence field. Under some conditions, this field would have the repulsive force of dark energy, while in other conditions, it would appear to clump together and mimic the effect of invisible particles.

Astronomers have found that a nearby star, Tau Ceti, is surrounded by 10 times as many asteroids and comets as our own Solar System. Even if there are planets orbiting Tau Ceti, they would be unlikely to support life because of the frequent and devastating impacts by these objects. This discovery will help astronomers narrow down their search when looking for distant worlds that may support life; ones which have a small number of comets and asteroids.

As Cassini passed directly through a gap in Saturn's rings, it got the closest view any spacecraft has ever had of the Ringed Planet. This image was taken after the spacecraft had passed the ring plane, and was seeing it lit by the Sun. Cassini was only 195,000 kilometres (121,000 miles) above the rings when this picture was taken. One interesting feature is the wavy edge of the inner ring; this is caused by interactions with Saturn's moon Pan, which orbits in the middle of this gap.

New observations of Procyon from MOST, Canada's space telescope, have called long-held assumptions about the star into doubt. Launched a year ago, MOST watched Procyon 8-times a minute, making a total of 250,000 observations over the course of 32 days. It found that the star is completely stable, and doesn't pulsate or vibrate in any way. This challenges 20 years of speculation that Procyon does vibrate, and could reveal insights about its interior - astronomers will need to find a new candidate.

Another day, another wallpaper. Today it's a 1024x768 image of active star formation in the Large Magellanic Cloud (LMC), taken by the Hubble Space Telescope. This region is called N11B, and it contains new stars in all stages of early formation. The stars on the left of the image are among the most massive stars ever seen in the Universe. The region around them is clear of dust because of the strong stellar winds blowing from these powerful stars. As the dust is blown away, it collides with other clouds, which can collapse to form new stars.

Seven years after it set out from Earth, the Cassini spacecraft finally arrived safely at Saturn. Using its high-gain antenna to protect it from dust particles, the spacecraft crossed the ring plane early Thursday morning at 0203 UT (10:03pm EDT Wednesday). It fired one of its twin main engines for 96 minutes to slow down its velocity, and then pointed at Earth to transmit news of its successful arrival. The spacecraft then took detailed images of Saturn's rings, as Cassini isn't scheduled to ever get this close to them again. Cassini will now begin its 4 year mission to analyze Saturn and its moons.

A seven-year journey is nearly over as NASA's Cassini spacecraft is arriving at Saturn later today. The spacecraft will fire its main engine for 96 minutes beginning at 0236 UTC (10:36 pm EDT), which will put it into orbit around Saturn. Scientific data from the spacecraft will arrive on Earth about 4 hours later, and the first photographs will be returned 6 hours after that, at 1239 UTC (8:39 am EDT). As Cassini is performing these operations, the scientific equipment will be running, gathering as much data as possible on this extremely close pass.

NASA researcher Marc Cohen thinks that a permanent base on the Moon might not be the right way to get started - in the beginning, you've got to stay mobile. Cohen is proposing that NASA consider lunar bases that can move on wheels, or even legs. This would increase landing zone safety, provide equipment redundancy, and allow explorers to survey many sites of scientific interest. There are many challenges with this idea too, however, including constant repairs in the vacuum of the lunar surface, and carrying enough radiation protection to keep the astronauts safe.

Today is the day that Cassini is scheduled to make its arrival at Saturn, flying close to the planet and threading between two of its ring systems. Controllers have released this natural colour image of Titan, Saturn's largest moon. The moon is surrounded by a thick atmosphere rich in organic molecules, which give it this featureless orange glow. Cassini will get a much better view soon, though, as it will make its first close flyby in just a few days. It will release the Huygens probe in early 2005 which will actually land on its surface and give scientists a better idea of what's beneath those thick clouds.

Here's a simple question: how long is a day on Saturn? The answer, it turns out is very complex. Cassini recently measured its day at just over 10 hours and 45 minutes, but this is a full 6 minutes longer than the Voyager spacecraft measured. If this is correct, Saturn has slowed down 1% in only 23 years. Length of day is usually measured by a radio telescope, watching as the magnetic field sweeps around. With Saturn, however, it looks like the planet isn't locked to its magnetic field, which can slip around to different latitudes.

The Spitzer Space Telescope has taken a picture of a galaxy called NGC 7331; astronomers believe it's a virtual twin of our own Milky Way galaxy. Since we're inside our galaxy, many of its interesting features are shrouded by dust, so looking at NGC 7331 is like looking into a mirror 50 million light-years away. Spitzer's infrared spectrograph has revealed that our twin seems to have an unusually high concentration of massive stars at its centre, or a moderately active supermassive black hole, similar to the one at the heart of our own Milky Way.

A Zenit-3SL rocket lifted off from the Sea Launch platform today, carrying a Telstar 18 satellite into orbit. The rocket launched at 0359 UTC (11:59 pm EDT June 28), but a glitch put the satellite into a transfer orbit that was lower than expected. Engineers think that they should still be able the satellite into its final orbit using station-keeping thrusters, which will shorten its lifespan. Telstar 18 will provide broadcast satellite services to East Asia and the Pacific Ocean.

Engineers have nearly gotten to the bottom of the problem that forced spacewalkers to abort their trip outside the International Space Station last week. The primary oxygen bottle on Mike Fincke's Russian-built Orlan spacesuit lost pressure much more quickly than expected, so he and cosmonaut Gennady Padalka were ordered back in the station after only 14 minutes. Russian specialists are focusing on an injector switch that increases the flow of oxygen into the spacesuit. The crew should be able to repair the problem themselves, and use the suits when the spacewalk is rescheduled.

Astronomers have found a white dwarf star which has shut down its fusion reactor very recently - perhaps only 100 years ago. By probing this star with the Chandra X-Ray Observatory and the Far Ultraviolet Spectroscopic Explorer (FUSE), astronomers see that its heart is completely stripped of hydrogen and helium; the surface is largely carbon and oxygen, heated to 200,000 degrees. Nothing like this has ever been seen. Our own Sun will eventually become a star like this, after it has expended all of its hydrogen fuel.

NASA's Cassini spacecraft has turned its gaze on smog-covered Titan again, delivering its best picture yet of Saturn's largest moon. This image was taken on June 14, 2004 when the spacecraft was 10.4 million km (6.5 million miles) away; it's three times as much resolution as the previous image of Titan released a few weeks ago. Cassini took the picture using a special filter designed to see through Titan's atmospheric haze of methane to the surface below.

There's a classic scene in the movie Apollo 13 when scientists and engineers brainstorm solutions to "scrub" the spacecraft's air to remove toxic levels of carbon dioxide. All they've got to work with is what the imperiled astronauts have on board their capsule. They devise a clever solution using what the astronauts have available, and save their lives.

It's a fitting analogy, I think, to the challenge faced by the commissioners for the President's Commission on Implementation of U.S. Space Exploration Policy, a.k.a. the Aldridge report. How do you fundamentally change NASA to make it both safer and more willing to take risks? To re-energize the dream of human spaceflight? To stop battling free enterprise and embrace it? To get humans back to the Moon, and then on to Mars?

"You've got these resources at your disposal, now fix NASA."

NASA Administrator Sean O'Keefe announced a series of changes to the agency to better prepare it to fulfill President Bush's new vision for human space exploration; to "make it leaner and more focused on its goals." NASA will merge seven existing enterprises into four mission directorates, to create clearer lines of communication and authority: Exploration Systems, Space Operations, Aeronautics Research, and the Science Directorate. Further changes are on the way.

Here's the photo we've all been waiting for. This 1024x768 wallpaper image of Saturn's moon Phoebe was created by the Space Science Institute, who stitched together 5 separate images of the moon taken by Cassini. Phoebe's surface is pockmarked with large and small craters, indicating that the moon is extremely old. Scientists think that it might be part of an ancient family of icy objects which were pushed to the outer Solar System to form the Kuiper Belt. Phoebe was caught by Saturn's enormous gravity before it could escape.

The Supernova Integral Field Spectrograph (SNIFS), a new instrument designed to examine exploding stars, has observed its first target: supernova SN 2004cr. Mounted on board the University of Hawaii's 2.2 metre telescope on Mauna Kea, the instrument is designed to simultaneously observe a supernova, its home galaxy, and the surrounding sky. It should make very precise measurements of Type 1A supernovae, which are considered by astronomers to be "standard candles" - every explosion is the same brightness, so you can use them to measure the distance to galaxies.

Scientists working with NASA's Cassini spacecraft have stitched together photos taken by the spacecraft to build a complete picture of Phoebe, a moon of Saturn that the spacecraft passed on June 11. The tiny moon is likely an ancient collection of ice, rock and carbon-containing compounds similar to Pluto and Neptune's moon Triton. Planetesimals like this could be very common in the outer reaches of the Solar System, as they were ejected during the early formation of the planets. Phoebe was probably captured early on by Saturn, perhaps 4 billion years ago.