Munich

In focus: the picture on the left shows one of the first images taken by XMM-Newton, the Tarantula Nebula, part of the Large Magellanic Cloud. The one on the right shows the same region taken previously by ROSAT, a German X-ray satellite that went out of operation over a year ago. Credit: ESA

The jinx that destroyed or limited a string of X-ray-astronomy missions launched in the past nine months does not seem to have affected the European Space Agency's (ESA's) new XMM-Newton X-ray observatory. The first images, presented last week, show that the observatory's three X-ray cameras, its optical monitor and its two spectroscopes are operating well.

ESA also announced that it had added the name Newton to the observatory's working name of XMM (X-ray Multi-Mirror), in honour of Isaac Newton, who created the theory of gravity and discovered the Sun's spectrum.

X-ray astronomers are pleased that Newton, which was launched two months ago, has avoided the damage suffered by a similar mission, the US space agency NASA's Chandra. Low-energy protons partly damaged Chandra's cameras a few weeks after launch last July (see Nature 401 , 415; 1999).

The Newton observatory comprises three telescopes, each consisting of a nest of 58 mirrors, which are designed to detect X-ray photons from deep space. X-rays are emitted by very hot matter, so Newton can observe very hot and violent events in the cosmos, allowing studies of the evolution and death of stars, the structure and nature of the interstellar medium, and the physics of galaxies and quasars.

In addition to the damage to Chandra, X-ray astronomers had previously witnessed the loss of Abrixas, a small German-built X-ray satellite, immediately after its launch last May (see Nature 399, 93; 1999). Last week also saw the loss of Japan's major X-ray mission Astro-E, when its launcher failed to push it into the correct orbit (see right).

Newton scientists say they could have been affected by the problem that struck Chandra, because, like their US colleagues, they had not predicted the damaging effects of one type of cosmic radiation in the deep-space orbit chosen to avoid the influence of the Earth's atmosphere and used by both Chandra and Newton.

Damaging low-energy protons in the Van Allen belts through which both vehicles fly were funnelled by the telescope mirrors onto the cameras. Eight of the ten sensors in Chandra's cameras are ‘front-illuminated’, making them vulnerable to damage. “Normally these protons are stopped, but obviously they are reflected off the mirrors and we did not anticipate this,” says Richard Mushotzky, an astrophysicist at the Goddard Space Flight Center near Washington, and a member of Chandra's science working group.

The damage to Chandra's cameras does not affect the image resolution. But the spectral resolution, which allows the chemical composition of the observed objects to be analysed, has been reduced by up to a factor of five. In addition, the mission's ability to analyse X-ray sources that are greater over a field of view than one-fifth of the size of the full moon is also compromised, and these can now be observed, less efficiently, only with the undamaged ‘back-illuminated’ sensors.

Newton scientists say they have learnt from Chandra's misfortune. Having been more cautious with the original design of their EPIC X-ray cameras, which also include damage-sensitive front-illuminated sensors, they had incorporated a moving shield to allow the cameras to be shut off in the event of any unpredicted radiation damage while passing through the Van Allen belts or during a sunstorm, despite the extra resources this required.

Newton will make up for Chandra's partial loss, as the three big missions were originally complementary, so the weaknesses of one mission could be made up for by strengths in the others. Newton was optimized for sensitivity and for medium-to-high-resolution spectroscopy, Chandra for angular resolution — which has not been affected — and Astro-E for very-high-resolution spectroscopy.

“We are lucky that Newton is well suited to looking at large diffuse sources such as clusters of galaxies, just the capability we lost,” says Claude Canizares, an astrophysicist from the Massachusetts Institute of Technology and principal investigator of a Chandra instrument. “But we have completely lost the important piece of the scientific pie that Astro-E would have offered.”