An international team of astrophysicists have developed a new theory to explain the accelerating expansion of the Universe, known as "dark energy". Instead of a mysterious energy which is pushing matter apart at an accelerating rate, the team believes it could be the natural outcome of ripples in space and time created during the earliest moments of inflation after the Big Bang. These ripples could extend beyond what we can see with our telescopes, so we can only calculate their existence.

During its many months orbiting Saturn, Cassini has gotten a few good looks at Hyperion, one of the planets many moons. This irregularly shaped moon is reasonably large (266 km or 165 miles across) and chaotically tumbles in its orbit around Saturn. Cassini took these images in October 2004 and February 2005 at relatively similar distances. It will get a much better view in September, 2005, when the spacecraft is scheduled to make a flyby at an altitude of only 990 km (615 miles).

Researchers have discovered evidence of recent glacier movements and volcanic eruptions on Mars, overturning the long-held opinion that it's a cold, dead world. As recently as 350,000 years ago, glaciers moved from Mars' poles to its tropics, covering the planet in sheets of ice. And several of Mars' giant volcanoes were active as recently as 2 million years ago. The heat from these volcanoes could sustain microbial life in underground pools of liquid water.

An instrument on board the Mars Exploration rover Opportunity is malfunctioning, so mission controllers have decided to turn it off until they can figure out what's causing the problem. The problem is with its miniature thermal emission spectrometer (Mini-TES), which Opportunity uses to sense the mineral composition of distant rocks. The problem could be with a broken switch that helps position the mirror that directs infrared light into the Mini-TES. Even if engineers can't figure out a solution, Opportunity can still return some science with the instrument partially functioning.

Astronomers have known since 1998 that a mysterious force seems to be accelerating the expansion of the Universe. An international team of astronomers have observations from Hubble and a powerful computer simulation to find evidence of dark energy much closer to home. The team studied the motion of our local group of galaxies (40 galaxies within 5 million light years) and found that you could only explain their current positions if you include the influence of dark energy.

NASA's Cassini spacecraft has made a surprising discovery about Saturn's moon Enceladus: it has an atmosphere of water vapour. Cassini detected the atmosphere during both of its recent close flybys. Scientists are sure what's causing this cloud of water vapour, but it could be caused by volcanoes, geysers, or gasses escaping from the moon's interior. Enceladus' gravity is very small, so it wouldn't be able to hold onto an atmosphere for very long. This means there must be some continuous source replenishing it.

A hardy robot from Carnegie Mellon has found life in Chile's Atacama desert; one of the driest and most lifeless places on Earth. Life is barely detectable over most parts of Atacama, but the rover (named Zo?) was able to detect lichens and bacterial colonies in two regions that it explored. The solar-powered rover provides a good example of the kind of technology that will probably used to search for life on Mars. Next year Zo? will travel autonomously for two months, traveling 50 km in the search for life.

European astronomers have found a group of stars in the Omega Centauri globular cluster which seem to be some of the most rich in helium ever seen. These are bluer stars, and astronomers would expect that they contained lighter elements, but the team found exactly the opposite - they have more heavy elements than red stars. One theory to explain this is that previous generations of stars exploded as supernovae, and seeded the region with helium and heavier elements. These blue stars then formed from this material.

Greetings, fellow SkyWatchers! While the Moon will figure prominently in this week's scheme, there will be many occultations to view as well as lunar features. We'll return to visit both the M50 and M44, as well as learn about double star - Algieba There are two minor meteor showers and planets to explore. So grab your binoculars and telescopes, because...

Here's what's up!

NASA's Spirit rover has been fortunate enough this week to spot a tiny dust devil scurrying across the surface of Mars. The various orbiters have seen crisscrossing dust devil tracks, but this is the first time one has been captured on camera from the surface. It also appears that Spirit was recently dusted off by one of these mini-twisters, cleaning off accumulations of dust, and boosting its available power for operations. This also happened a few months ago to Spirit's twin, Opportunity.

A powerful Atlas V rocket lifted off from Cape Canavaral on Friday, carrying its heaviest cargo to date: the 5,959 kg (13,138 pound) Inmarsat 4-F1 satellite. The rocket had three additional solid boosters to help it carry this weight into orbit. The launch was delayed one day because of technical problems, but the launch itself went smoothly in good weather. The satellite will be used by Inmarsat to provide voice and data communication services.

Thanks to data collected by NASA's WMAP probe in 2001 and 2002, plus the hard work of astrophysicists, we now know that the Universe is 13.7 billion years of age - give or take a few hundred million years. And thanks to the way distant galaxy clusters interacted with the cosmic microwave background radiation (CMBR) some 7 billion years ago, we may soon be able to peel away layers of time and better understand irregularities in the shape of the universe as it is today.

Amateur photographer Bojan Stajcar took this picture of the lunar occulation of Jupiter on the 27th of February. This picture was taken 10 minutes after the Moon partially occulted Jupiter, at 11:04 pm local time, from Melbourne, Australia. The camera used was a mechanically modified Connectix Quickcam, with 320x240 pixel CCD sensor in the focus of the motorized ("Bartelized") homemade 10", f5.6 reflector. Note the difference in the surfaces brightness of the Moon and Jupiter. Despite the fact that the moon surface consists of very low reflective material (dominantly basalt), it is brighter, as Jupiter is 5 times further away from the Sun.

Scientists are in agreement that a rock from space smashed into the ground in Arizona 50,000 years ago, carving out a pit 1,250 metres (4,100 feet) across. But they're now starting to disagree on the speed the asteroid was going when it hit. One mystery that has been puzzling scientists: where is all the impact-melted rock? If it was going as much as 20 km/s (44,000 mph) as originally believed, it should have fractured into pieces which would have rained down over a larger area. But a new simulation calculates that it was going only half that speed, and probably came down as a swarm of material, not a single rock.

New observations from the Hubble Space Telescope are helping astronomers fine tune their models of star formation, including an estimate of just how massive a star can become. Hubble carefully observed the Arches cluster, a group of stars collectively weighing 10,000 solar masses. Standard theories predicted 20 to 30 stars in the cluster would have 150 solar masses, but none turned up; although, at least a dozen push 100 solar masses. What variables could limit the amount of mass a star can pack on?

It appears that galaxies in the early Universe didn't evolve at similar speeds or in the same ways. Almost right from the beginning, the Universe was filled with galaxies large and small, dusty and clear, active with star formation and relatively sedate. Researchers from the US used Infrared Array Camera (IRAC) aboard NASA's Spitzer Space Telescope to study galaxies 10-12 billion light-years away. Instead of finding a similar set of galaxies, they turned up tremendous varieties, as much as we see in the night sky today.

Cassini has made a few passes of Titan now, and the European Space Agency's Huygens probe has landed on its surface, so Saturn's largest moon is starting to reveal its secrets. Scientists involved with the mission have recently published some of their findings in the Journal Nature. Some of their insights include the discovery of a long river, 1,500 km (930 miles) long and evidence that winds on Titan blow faster than the moon rotates. The climate seems to revolve around liquid methane, which can flow in rivers, fall as rain, and collect in vast lakes.

NASA scientists have finally worked out why there's a safe zone in the Earth's radiation belts, thousands of km above the surface. It turns out that lightning in the lower atmosphere generates radio waves which interact with radiation around the Earth, removing some of its energy and changing the direction of charged particles. This safe zone could be used as a haven by satellites to reduce the damage they take while operating in these regions.