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A key instrument of James Webb on short-time work following an anomaly

NASA wants to be reassuring, but it is to be hoped that this small malfunction does not hide a deeper problem.

NASA has announced that the Mid-Infrared Instrument (MIRI), one of the primary instruments of the James Webb Space Telescope, is currently down due to a technical issue. For the moment, there is not yet cause for alarm, and the agency considers that there is no risk for the device in the long term. But she still offered him a vacation time to get to the bottom of it.

The MIRI is one of the most important tools of the JWST. It is indeed the only instrument in the observatory that operates in the mid-infrared, ie it captures wavelengths between 5 and 28 micrometers. It offers four different observation modes. And one of them, labeled “medium resolution integral field spectroscopy”, or MRS, encounters some problems.

In this mode of observation, the telescope does not capture photos as such. Instead, it records light spectra. Very briefly, they make it possible to study the way in which different chemical species absorb light at certain very specific wavelengths; astronomers can then deduce lots of information about the objects that were in the path of the light rays.

The wheel of misfortune

To do this, the MIRI has a wheel equipped with different filters; simply rotate it to select the corresponding filter, and observe the targeted object at the desired wavelength. This makes the instrument extremely versatile and allows researchers to study the spectra of many diverse and varied astronomical curiosities…at least, when this all-important piece is working properly.


Because it is this element which is at the origin of the problem identified by NASA. At the end of August, the agency detected friction at the axis ; the structure did not rotate as well as expected. On Earth, a little bit of lube would certainly have sufficed. But the deal is very different when we talk about a machine parked in orbit about 1.5 million kilometers from our planet.

The rest of the instruments are doing well

As a precautionary principle, the space agency has therefore decided to do without medium-resolution spectroscopy in the near future. This mode of operation will therefore remain on the bench the time to identify the origin of this friction. “The Webb team has suspended observations that use this particular mode.”, announced the institution in a communicated. time to analyze his behavior. ”She is currently developing a strategy to relaunch MRS observations as soon as possible.”, she specifies.

However, she wants to be reassuring about the general condition of the telescope. “The observatory is healthy”, explains NASA. It also indicates that there is no need to worry about the other three MIRI observation modes. “Imaging, low-resolution spectroscopy, and coronagraphy are functioning normally and will remain available for scientific observation”, specifies the agency.

All that remains is to wait until NASA discovers the origin of the problem. The agency has not yet communicated on this subject, but it could be a consequence of the impact of a micrometeorite.

These objects are tiny pieces of rock, often smaller than grains of sand, which travel at very high speeds and can therefore cause considerable damage. This is one of the main threats the telescope has to deal with, and the engineers obviously took their precautions. But the instrument is not entirely immune to these collisions. Last June, for example, the machine was struck by a meteorite which left a mark, admittedly small, but visible and irreparable on one of the 18 hexagonal mirrors (see our article). It is therefore to be hoped that the MIRI has not been damaged beyond measure, even if the most sensitive components are of course carefully concealed behind protective armor.

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