Paris, France - Impatient astronomers at the European Space Agency (ESA) have taken some sneak pics with the Herschel telescope, snapping a first set of images weeks before engineers have even finished commissioning the device.

The Photoconductor Array Camera and Spectrometer has obtained images of M51 - known as the whirlpool galaxy - for a first test observation. ESA scientists now have pictures in three colours which, they say, clearly demonstrate the superiority of Herschel, the largest infrared space telescope ever.

The image above shows Messier 51 (M51), the famous ‘whirlpool galaxy’ first observed by Charles Messier in 1773. This spiral galaxy lies relatively nearby, about 35 million light-years away, in the constellation Canes Venatici. M51 was the first galaxy discovered with a spiral structure.

The image is a composite of three observations taken at 70, 100 and 160 microns, taken by Herschel’s Photoconductor Array Camera and Spectrometer (PACS) on 14 and 15 June, immediately after the satellite’s cryocover was opened on 14 June.

Herschel, launched only a month ago, is still being commissioned and the first images from its instruments weren't actually due to arrive for a few weeks. But engineers and scientists couldn't wait, and decided to try to plan and execute test observations immediately after the cryocover was opened. The objective was to produce a very early image that gives a glimpse of things to come.

Above left is the best previous image of M51, taken by NASA’s Spitzer Space Telescope, with the Multiband Imaging Photometer for Spitzer (MIPS), with the Herschel observation on 14 and 15 June at 160 microns on the right. The obvious advantage of the larger size of the telescope is clearly reflected in the much higher resolution of the image: Herschel reveals structures that cannot be discerned in the Spitzer image.

These images of M51 at 70, 100 and 160 microns clearly demonstrate that the shorter the wavelength, the sharper the image — this is a very important message about the quality of Herschel’s optics, since PACS observes at Herschel’s shortest wavelengths.