Around 251 million years ago, something happened to the Earth's climate that wiped out 90-95% of marine life and 70% of terrestrial life. Scientists at the National Center for Atmospheric Research (NCAR) have developed a computer model that demonstrates that rapid increases in carbon dioxide belched out of volcanoes did the trick. Temperatures were 10 to 30 degrees Celsius (18 to 54 degrees Fahrenheit) higher than they are today, which broke a cycle that pulled carbon dioxide out of the atmosphere.

On the night of August 4, 2005, legendary amateur astronomer Reverend Robert Evans discovered a supernova just north of galaxy NGC 1559. In the days that followed, astronomers classified it as a Type 1A supernova, the kind created when a white dwarf constantly pulls material from a larger stellar partner; eventually it can't hold any more and explodes as a supernova. These kinds of supernovae explode with a set amount of energy, so astronomers can use them to measure distance to galaxies.

Climate scientists are predicting that the Arctic Ocean could be completely free of ice during the summer within 100 years thanks to rising ocean temperatures. Several feedback mechanisms will also accelerate these changes. For example, the white ice reflects radiation from the Sun, and contributes to lower temperatures. As the ice melts, the region becomes darker and the melting should speed up.

Greetings, fellow SkyWatchers! I'd like to thank all of you who took the time to write to me about this year's Mars apparition and this week we'll look at both the "fact" and the "fiction". Now it's time to start our explorations as we check in on the planets, visit the "Lagoon", have a look at the M25, journey to the "Small Sagittarius Star Cloud", and track down the "Trifid". So, get your telescopes and binoculars ready, because...

Here's what's up!

As it passed through the ring plane, Cassini took this amazing photograph of Saturn's moon Pandora, hovering just above the rings. Saturn's F ring is thinly visible just above the main rings which are the dark line across the picture. You can also see some variation in the height of Saturn's cloud tops in this photograph, which look like ripples in an ocean. Pandora is only 84 km (52 miles across).

Researchers from the University of Michigan are predicting that when asteroid 99942 Apophis (2004 MN4) swings past the Earth in 2029, it will get so close that astronomers should learn a tremendous amount about how the Earth's gravity can shift asteroid orbits. The researchers are hoping that a space agency will put instruments on the surface of the asteroid to measure seismic data, similar to the way seismologists use earthquakes to probe the Earth's interior.

This is part 2 of an edited transcript of a presentation given by Pamela Conrad, a NASA astrobiologist who has been traveling to the ends of the Earth to study the extremes of life. In this second part, Conrad continues her explanation of how studying cold deserts here on Earth can aid the search for life in our Solar System. Part 1 is available here.

A researcher from the University of Toronto has found unexpectedly young material in meteorites, challenging theories about early events in the formation of the Solar System. A paper published in Nature reports that key minerals called chondrules have been found in meteorites that formed much later than the initial nebula that collapsed to form our Solar System. Instead, these chodrules were probably created when two newly forming planets smashed together.

The most successful comet hunter in history is actually the ESA/NASA SOHO spacecraft, which spends its time gazing at the Sun. Since many comets streak past the Sun all the time, they often get caught in SOHO's cameras. Toni Scarmato from Calabria, Italy discovered both SOHO's 999th comet, and then 5 minutes later he discovered its 1,000th as well. Almost all the discoveries have been made using SOHO's LASCO instrument, which images the Sun's large corona.

Even after all their safety improvements, NASA engineers weren't able to completely solve the problem of foam shedding off the space shuttle's external fuel tank. During Discovery's launch a large piece flew off; fortunately it completely missed the orbiter, but the risk remains. In order to give engineers time to come up with a solution, NASA is targeting March 2006 for Discovery to return to the launch pad and continue construction of the International Space Station.

NASA's Swift satellite has found brand new baby black holes, just seconds after birth. These newborn black holes are created at the heart of massive star explosions, called gamma ray bursts, and actually generate multiple blasts over the next few minutes. Nearly half of the gamma ray bursts seen by Swift follow a similar model, where there's an initial release of gamma rays, and then followed by several X-ray after-explosions as matter falling into the new black hole clogs up and releases more energy.

Pamela Conrad is an astrobiologist with NASA's Jet Propulsion Laboratory. She recently gave a lecture explaining how to searching cold deserts on Earth will help scientists understand environments that life could be hiding in the rest of the Solar System. The following article is the first part of an edited transcript of her presentation.

One of the most famous supernovae in recent memory is SN 1987A, which exploded in the Large Magellanic Cloud. Before its death, the star produced a ferocious stellar wind that carved out a large bubble in the surrounding, colder gas. When it went supernova, a shockwave traveled out in space, and astronomers have been waiting in anticipation for the shockwave to slam into the edge of this bubble. New images from NASA's Chandra X-Ray Observatory shows that this stage now appears to be underway.

Saturn's rings are separate from the planet they circle, and then even have an atmosphere of their own. During several flybys, Cassini has been able to detect very small amounts of molecular oxygen floating around the rings. Molecules of water are broken apart by ultraviolet light from the Sun; the hydrogen and some of the oxygen is lost into space, and some of the oxygen is frozen back into the rings. But there's enough of a cloud of these atoms around the rings that this process must be ongoing and kept in a continual balance.

John Bunyan took this picture of green aurora on the 5th August from Washington, USA. This image was taken with a Canon rebel.

Do you have photos you'd like to share? Post them to the Universe Today astrophotography forum or email them to me directly, and I might feature one in Universe Today.

When astronauts will be spending more time in space, it'll be helpful to know when there'll be clear "space weather", to minimize their exposure to dangerous amounts of radiation. NASA scientists have developed a better understanding of the underlying causes of solar flares, and think they can now predict times for "clear skies". Areas likely to explode as flares happen when magnetic fields of different alignments merge together on the Sun's surface. Electrical currents must then build up for several hours before a flare erupts.

NASA's Cassini spacecraft took this picture of Rhea, one of Saturn's moons. The reasonably close view is of the moon's southern polar region which has been extensively cratered during its long history. Cassini acquired this view on July 14, 2005 when it made a close flyby, passing only 239,000 km (149,000 miles) away from the moon. The large, well-defined oval-shaped crater on the upper right is approximately 115 km (71 miles) across.

A new NASA-funded study has discovered that sea ice in the Antarctic might actually be on the increase as global temperatures go up. There has been overwhelming evidence that sea ice is decreasing in the Arctic ocean, but scientists didn't realize there might be a difference between the two poles. As temperatures rise, it seems to create more precipitation around the southern pole, which falls as snow. The weight of the snow pushes sea ice below sea level, and causes the snow to melt and then freeze as additional ice.

Using NASA's Spitzer Space Telescope, astronomers have created a detailed survey of the structure of the Milky Way. Based on this evidence, they think the shape of the Milky Way is more complex than a plain old spiral. Our galaxy seems to have a long central bar, approximately 27,000 light-years in length. From our vantage point going around the Sun, we see this bar at a 45-degree angle.

David Moth took this picture of NGC 185 from Weymouth, England. David used 10" Newtonian and a Starlight Express MX5C.

Do you have photos you'd like to share? Post them to the Universe Today astrophotography forum or email them to me directly, and I might feature one in Universe Today.