Cassini produced large images of Saturn

Saturn looms large in the sharpest colour image yet taken of the planet by the approaching Cassini-Huygens spacecraft, due to arrive at the Ringed Planet on 1 July.

The image was taken when the bus-sized Cassini probe was over 56 million kilometres away from Saturn - a third of the distance between the Earth and the Sun. It is a composite of several exposures taken on 8 March and was released on Friday.

Even from this distance, some intriguing features can be seen. These include two small, grey, faint spots just visible at a latitude of about 40 degrees in Saturn's southern hemisphere. Saturn is about 10 times as wide as Earth, and the spots appear to be slightly smaller than our Moon.

However, unlike Hubble, Cassini will be able to follow the storms more or less continuously once in orbit, which will help understand the transient phenomena. "What we're after is meteorology on a completely different planet than Earth, but with all the same physics," says Fred Taylor, a planetary scientist at the University of Oxford, UK.

Two of Saturn's 31 moons, Mimas and Enceladus, also appear in the image as pinpoints of light, inform newscientist.com NASA's Cassini spacecraft is getting close enough to Saturn to photograph subtle features in the ringed planet's atmosphere. A new image shows two small, faint dark spots that the craft hadn't detected before.

The new image, released today, was taken March when the spacecraft was then 35 million miles (56.4 million kilometers) from Saturn, slightly more than one-third of the distance from Earth to the Sun. The planet is 23 percent larger in this image than it appeared in the preceding color image, taken four weeks earlier.

The image shows Saturn in natural color. Contrast and colors were slightly enhanced, however, to make features more prominent. The planet casts a stark shadow on its rings, which are made of icy particle ranging in size from dust to boulders and even small, embedded moons. Astronomers aren't sure how the rings were created. The two dark spots are visible in the planet's southern hemisphere.

Mission scientists expect them to become clearer in the coming months. Atmospheric spots on Jupiter and Saturn occur frequently and can last days, weeks or months. They are often akin to storms on Earth but, because the giant planets have no land to disrupt the flow of clouds, the storms or spots can endure for longer periods. The spots are located at 38 degrees South latitude, report msn.com

According to astronomy.com so when Saturn and its moons slipped across the Crab Nebula on January 5, 2003, astronomers monitored the event with the Chandra X-ray Observatory. The Saturn transit itself could not be observed because Chandra was passing through a zone of elevated radiation during the event, but a group led by Koji Mori of Pennsylvania State University did catch Titan’s passage. The moon cast a detectable shadow as it moved over the 2'-wide X-ray-bright portion of the Crab Nebula, the remnant of the A.D. 1054 supernova blast. Mori’s analysis found the shadow to be larger than Titan’s solid surface, yielding the first-ever measurement of the moon’s atmospheric extent in X rays: 880 km (547 miles).

The saturnian system has a conjunction with the Crab every thirty years, but transits are exceedingly rare. A conjunction similar to the 2003 event occurred in January 1296, but the remnant, which was only two-and-a-half centuries old then, was probably so small that a transit never happened. The next transit takes place in August 2267. The Huygens probe aboard the Cassini spacecraft will study Titan's atmosphere directly in 2005.