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.

A team of physicists from the University of California have built a cluster of nearly 300 computer processors capable of simulating some of the mysteries of the Universe. "The Space Simulator" has a theoretical performance of 1.5 teraflops, which places it at #344 on the list of the 500 fastest computers in the world. It was developed on a budget, though, at a cost of only $1,000 per processor; $500,000 for the whole cluster. It's been used to simulate the structure and evolution of the Universe, supernovae explosions, and X-ray emission from the centre of the galaxy.

Auditors with the US Government delivered a negative report this week about NASA's ability to properly estimate large projects, and manage them effectively. As part of this study, the General Accounting Office reviewed 27 programs, 10 of them in-depth, and came to the conclusion that "NASA lacks a clear understanding of how much programs will cost and how long they will take to achieve their objectives". In an appendix of the report, however, NASA acknowledged the flaws and detailed the steps it was taking to correct the situation.

Here's another picture for your Mars wallpaper collection. This time it's a 1024x768 image of a canyon on Mars called Valles Marineris, taken by the European Space Agency's Mars Express spacecraft. The full image was taken at a resolution of 16-metres per pixel. The image gives some clues about how such a dramatic surface feature developed, including some traces of volcanic activity and possible water-related activity. It's a heavily weathered part of Mars, however, so a lot has been obscured over hundreds of millions of years.

Cassini has turned to look at another of Saturn's moons; this time it's Iapetus. This image was taken on May 23, 2004, when Cassini was 20.2 million kilometres (12.5 million miles) from Iapetus. Although it's small and hazy in this picture, the moon is much larger than Phoebe, and measures 1436 km (892 miles) across. It was first photographed up close by the Voyager spacecraft, which found that it has a light and a dark side - this duality is just barely visible in this image.