Gamma ray busts are the most powerful known explosions in the Universe, so if one went off in our galactic back yard, it could be bad for life on Earth. Researchers working with NASA think that a massive extinction hundreds of millions of years ago could have been started by such an explosion. If a GRB went off only 6,000 light-years away, it would strip away much of the Earth's ozone layer, and expose all surface life to deadly levels of ultraviolet radiation from the Sun.

When you look at a galaxy, you can only see a fraction of its total mass. The rest is made up of mysterious dark matter, which only interacts through its gravity. This dark matter usually extends as a giant halo around the galaxy, extending much further than the visible stars. But researchers in the UK have found ancient fossil galaxies concentrating dark matter at their centres. These fossil galaxies are the result of an entire galaxy cluster collapsing into a single enormous galaxy. Why the dark matter is concentrated is still a mystery.

In preparation for its return to flight, the space shuttle Discovery made the long slow journey atop its Crawler Transporter out to the launch pad yesterday. A small crack was discovered in the fuel tank insulation, but engineers didn't feel it was enough of a risk to delay Discovery from moving out to the launch pad. If everything goes well, Discovery will lift off on May 15, but a final report from the Columbia Accident Investigation Board could demand additional changes that would push the launch back.

The Chandra X-Ray Observatory has detected distant galaxies going through a period of tremendous star formation, at the same time the supermassive black holes at their centres are packing on material. These extremely luminous galaxies (and their black holes) went on this growth spurt more than 10 billion years ago, and they could be getting ready to turn into quasars - distant galaxies that contain the largest and most active black holes in the Universe.

NASA has given Spirit and Opportunity up to another 18 months to continue rolling around the surface of Mars in search of evidence of past water. The rovers have already completed their primary 3-month missions, and then an additional 11 months of extensions. Both rovers are still in surprisingly good shape, and are approaching targets that would have initially been considered out of reach. Opportunity set a new driving record on March 20, completing 220 meters (722 feet) in a single day's drive.

When the planetoid Sedna was discovered last year, astronomers noticed that it had a very slow rotation speed, only turning once every 20 days. One way to slow the rotation of a planet is through the interaction of a moon, but detailed observations of Sedna with Hubble failed to turn up any evidence of a satellite. New observations by astronomers with the Harvard-Smithsonian Center for Astrophysics have revised Sedna's rotation speed to once every 10 hours, which is what you'd expect for an object this size. No moon is necessary.

NASA's Cassini spacecraft made another close pass of Titan, Saturn's largest moon, on March 31, delivering new images and data from this mysterious moon. Although Titan's northern hemisphere had been imaged by Cassini's radar instrument on a previous flyby, this time it was able to take optical and infrared pictures that pierced through the moon's thick methane atmosphere. This composite image of four photographs was taken when Cassini was approximately 130,000 km (81,000 miles) away from Titan.

Astronomers have used the Spitzer and Hubble space telescopes to see some of the first stars that formed in the most distant galaxies ever seen. These stars, located in galaxies in the Fornax cluster, are about 13 billion light-years away - they emitted this light only a few hundred million years after the Big Bang. Even though they didn't have much time to form, these galaxies already look quite old, which means that star formation must have got going very early on.

Since its launch late last year, NASA's Swift space telescope has already spotted 24 gamma-ray bursts - the most powerful known explosions in the Universe. Now Swift has measured the distance to two of these explosions which occurred on March 18/19; both are more than 9 billion light-years away. Swift should become even more accurate in the next few months as more of its instruments are enabled.

When he developed his General Theory of Relativity, Einstein predicted that the motion of large masses should create ripples in spacetime called gravity waves. Now 100 years after his theory, a precise instrument is being prepared that should be able to find out if he was right or not. A joint ESA/NASA mission called LISA (Laser Interferometric Space Antenna) will launch in 2012. It will consist of three spacecraft flying 5 million km apart, which measure their distances from each other precisely. LISA should be able to detect black holes and neutron stars as well as echos from the Big Bang.

Starburst galaxies get their name from the enormous amount of star formation going on inside them; on average, they create 50 times as many stars as regular galaxies like our own Milky Way in vast regions of furious star formation. Astronomers from the UK think these regions could also be the home to black holes. The team looked at Hubble images of these star-forming regions, and compared them to X-ray images of the same locations and found the telltale signs for both star formation and black holes.

The chances of finding life somewhere else in the Universe depends on how many planets are capable of supporting life. Well, according to new calculations by astronomers at Open University, as many as half of all star systems could contain habitable planets. The team created mathematical models of known exoplanetary systems, and then added Earth-sized planets into the mix. They found that in half of all planetary systems they simulated, the gravity of the gas giants won't catastrophically affect the orbits of these smaller planets, giving life a chance to evolve.

Greetings, fellow SkyWatchers! This week's dark sky will give us the opportunity to wander into the galactic realm as we study the M81 and M82 and many other bright galaxy collections. April 8 provides an opportunity to witness a hybrid solar eclipse - with many portions of it viewable to the southern United States. We'll visit with the "Owl" and don the "Sombrero", so get out those binoculars and telescopes...

Because here's what's up!

NASA's Cassini spacecraft took this image of Pandora, orbiting just beyond Saturn's F ring. Pandora is only 84 km (52 miles) across. This image was taken on February 18, 2005, when the spacecraft was 1.2 million km (746,000 miles) away from Pandora. Cassini will make a much closer to approach to Pandora on September 5, when it comes within 31,600 km of the small moon.

A NASA-funded researcher has created an image of the Earth as it would look if you had gamma ray detectors for eyes. Gamma rays are the most energetic radiation known in the Universe - billions to trillions more energetic than visible light - and people usually associate it with extreme environments like black holes and supernovae. The radiation in this image was captured over the course of seven years by the Compton Observatory, which orbited the Earth from 1991 to 2000.

NASA's Cassini spacecraft took this picture of Mimas, Saturn's "Death Star" moon on February 18, 2005 at a distance of 938,000 km (583,000 miles). The image was taken using Cassini's ultraviolet filter, which helps to reveal better contrast of the moon's craters than would be possible in visible light. Mimas' large crater Herschel dominates the upper right of the picture.

Have you ever replaced the light bulb inside your fridge? Take a look next time. It draws about 25 watts of power. Now imagine this bulb on a spacecraft somewhere around Neptune and it's flashing madly away, trying to send a signal back to Earth. Somehow we need to see these flashes. Sound impossible? Well almost, but Douglas Mudgway in his book Big Dish describes the system, in particular the antenna sites, that was put into place to capture just this type of signal.

Launched from "Cape Kennedy" just 13 months of one another in 1972/73, Pioneer 10 and 11 are still up there though no longer kicking. But well before last phone home (in 2003 and 1995 respectively), the notes each pair played had changed pitch unexpectedly - they were slowly losing speed. Could the Pioneering Pair have been feeling a bit in the "dark" (as in "dark matter" or "dark energy")? Were they having a "Solar Quadrupole" moment? Could n-dimensional "branes" be behind it? Or has "back-gravity" from behind the Sun played a role? Before things get too exotic, maybe there's a simpler explanation.

A powerful Proton K rocket blasted off from the Baikonur Cosmodrome in Kazakhstan Tuesday night, carrying a Russian Express-AM2 communications satellite. It lifted off at 2231 GMT (5:31 pm EST), and placed its payload into a geosynchronous transfer orbit a few hours later. The Express-AM2 satellite will provide broadcast television and other communication services for Russia and Southeast Asia.