place Damaged by a micrometeoroid, should James Webb fear for his future?

Less than six months after its deployment, the James Webb Space Telescope was struck by a micrometeoroid that irreversibly damaged part of its primary mirror. More precisely segment C3, one of the 18 hexagonal mirrors responsible for returning the light rays to the secondary mirror, which will send them to the measuring instruments.

However, scientists want to be reassured: even with a chipping effect on the windshield, JWST continues to exceed all expectations. “Overall the impact at the telescope level is minimal, as long as a small portion of the mirror is concerned,” detailed a preliminary report released last week by NASA, ESA and the Canadian Space Agency. , project partner. A reorientation of 17 other mirrors also largely compensated for the C3 segment deformity without succeeding in correcting it completely.

For the first time, a report also shows the extent of the image damage: the effect on the mirror, bottom right, is clearly visible in the form of a white spot. In a single event, the C3 segment experienced ten times more degradation than scientists expected for the next six years. Released in early June, the impact would have occurred between May 22 and May 24.

Six hits were identified

Blame it on bad luck? This is one of the methods preferred by space agencies. But the latter also does not exclude the possibility of misjudgment of the threat. “The project team is also studying the micrometeoroid population, how impacts affect mirrors Berylliumand the effectiveness of certain risk mitigation measures,” the report said.

During the telescope’s six-month commissioning, five more collisions with mirrors were recorded, with negligible impact on image quality. These figures are consistent with the researchers’ predictions, which expected a micrometeoroid impact every month that could distort the mirror. No less than 19 other harmless collisions were also undetected in a span of three months.

known threats

Micrometeoroids have long been identified as one of the major threats to space exploration. Traces of planetary formation or comet debris, these tiny pieces of metal or rock, weighing less than a gram, are ubiquitous in the Solar System: every year, more than 30,000 tons are deposited on our planet incognito (we then talk about micrometeorites), which are sometimes buried in polar ice. is available But size isn’t everything. This tiny debris can reach velocities of several kilometers per second: at this speed, the slightest collision with a debris can generate energy comparable to a large caliber shot the size of a grain of wheat. And microscopic debris causes spacecraft friction over time.

While this has not been fully proven, some satellites have already been subjected to such effects. The habitable modules of the ISS have a Kevlar shield that is responsible for stopping or slowing micrometeoroids or other space debris that might cross its path. And for larger objects, the station is capable of performing evasive maneuvers.

A mirror open to space

Not so for the particularly weak James Webb Space Telescope. Unlike its cousin Hubble whose mirror is protected under a metal tube, JWST sits outside. A pebble passes by, and a collision with its 6.5 meter giant mirror is almost certain. But the risk was considered acceptable: according to the calculations of scientists, the deformation of the mirror after ten years should not exceed 0.1% of its total surface… Provided that the effects may not be multiplied like months. .

Over the next few months, the file should therefore be the focus of the JSWT team. And ways to limit the risk of collisions are already being considered, for example, by reconfiguring the telescope to reduce the mirror surface exposed when passing through a meteor shower. An event that may occur in May 2023 and May 2024, recalls the scientific journal Nature, when the telescope will pass by Halley’s comet.

A time machine

The culmination of a project that has spanned more than 25 years and seen costs climb into the tens of billions of dollars, the James Webb Space Telescope was launched on December 25 from the Kourou Space Center in French Guiana. Often touted as Hubble’s successor, it’s complementary after all: operating in the infrared, JWST can probe the distant universe and go back in time as it was just a few hundred million years after the Big Bang.

The size of a tennis court, JWST was sent to the Lagrange L2 point, 1.5 million kilometers from Earth, allowing it to accompany our planet in its orbit around the Sun.

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