By Dr David Whitehouse BBC News Online science editor

Hubble's new camera is expected to transform the so-called "discovery power" of the orbiting telescope.

Dr David Leckrone, of the American space agency's (Nasa) Goddard Space Flight Center, Hubble's chief scientist, says: "We're going after a lot of data we can't get now. We can't imagine what we will find."

The Advanced Camera System (ACS) is not only able to see finer detail but also has a much wider field of view than Hubble's current camera, the Wide Field Camera (WFC), which was itself state-of the-art when it was built.

"If you had two fireflies six feet apart in Tokyo, Hubble's vision with ACS will be so fine that it will be able to tell from Washington that they were two different flies instead of one," says Dr Holland Ford from Johns Hopkins University in the US.

Three detectors in one

The ACS will become Hubble's main instrument and, according to astronomers, will be 10 times more useful in probing the cosmos because of its faster, more efficient detectors and wider field of view.

ACS is a combination of three different detectors, each with their own specialised capabilities, detecting wavelengths of light ranging from visible to far ultraviolet.

How Hubble sees now...

With a field of view twice that of the WFC, ACS's wide field camera will conduct new surveys of the Universe. Astronomers will use it to study the nature and distribution of galaxies in order to understand how our Universe evolved.

ACS's high-resolution camera will take extremely detailed pictures of the inner regions of galaxies and search neighbouring stars for planets and planets in formation.

The solar blind camera on the ACS blocks visible light to enhance ultraviolet sensitivity. Among other things, it will be used to study weather on planets in our own Solar System.

In addition, the ACS has a system of filters to limit the wavelengths of light that enter its detectors. This will be useful to determine the physics of gas clouds, planetary atmospheres and distant galaxies.

What a difference

Just what a difference the new camera will make can be seen by comparing Hubble's current camera, the WFC, with a simulated ACS view.

The two views depict a distant massive cluster of galaxies. The first picture shows the cluster through the WFC. Its view depicts the galaxies in the cluster as faint smudges.

... and how it will see with the new camera

The ACS, however, will be able to see more galaxies in much more detail, including several faint arc-like features produced when the light from more distant galaxies is bent and magnified by the cluster, an effect called gravitational lensing.

In particular, the ACS will search for very young galaxies that existed less than a billion years after the Big Bang.

Hubble has already provided intriguing clues to how galaxies form and evolve.

The ACS's capabilities will allow astronomers to see objects and details that could never have been seen before, being able to spot galaxies that are several times fainter than those detected by the WFC.

But perhaps the most exciting prospect for astronomers is that Hubble will use the ACS to search for "direct evidence" of planets in nearby solar systems.

Although planets have been detected around many stars, all of them have been inferred through the gravitational "wobbles" they impart to their stars, rather than detected through a direct image of the planets themselves.