IIn some ways, the last place you’d want to put the James Webb Space Telescope is, well, in space. If you owned a $10 billion car, you wouldn’t drop it in a hailstorm, and while there’s no hail in space, there are plenty of micrometeoroids – debris to high speed no bigger than a speck of dust but moving so fast they can pack a real destructive punch. Millions of these fragments rain down on Earth every day, but they incinerate in the atmosphere long before they reach the ground. The Webb, stationed in a location in space 1.6 million km (1 million miles) from Earth, has no such protection. And as NASA and others reported last week, its mirror — the heart of the space telescope — has already been hit five times by tiny space specks, the most recent of which caused real, but correctable, damage.
The Webb mirror is a piece of exquisite engineering. Measuring 6.5 m (21 ft, 4 in) in diameter, it is made up of 18 hexagonal segments, each of which can be moved along seven different axes to allow controllers to focus the entire instrument. Together, the segments, made of beryllium, have an area of 25 square meters (269 square feet). All are coated in reflective gold, but in a film so thin that if peeled off and packed into a sphere, it would measure no larger than a golf ball. Meanwhile, the beryllium is so well polished that if it were enlarged to US size, its greatest imperfection would be 7.6 cm (3 in). It’s a heck of a piece of gear to leave exposed to the space elements. But if you’re going to do your job where Webb does, it’s a risk you have to take.
What makes the recent micrometeoroid hit particularly troubling is that even though NASA scientists simulated such collisions on the ground, the impact that occurred is larger than those they modeled. “With the Webb Mirror exposed to space, we expected occasional micrometeoroid impacts to gracefully degrade the telescope’s performance over time,” Webb Telescope optics manager Lee Feinberg said in a statement. “This one…is larger than our degradation predictions assumed.”
This does not remotely mean that the telescope is seriously damaged before it can even begin its work. The position of mirror segments can be moved in increments measured in nanometers – or billionths of a meter – allowing a damaged segment to be refocused precisely to undo the effect of ding. Ground crews have already adjusted the damaged segment accordingly, keeping the telescope on track to release its first images to the public on July 12.
Webb has ways to defend himself. NASA can often predict approaching micrometeoroid showers, and the telescope can be moved to move its mirror away from the direction of incoming debris. But there’s no denying the certainty that in the decade the telescope is expected to operate, it will be tattooed again and again by dust and high-velocity squalls. Nor is it undeniable, however, that during this same decade the Webb should also render magnificent science. Space is a dangerous place to do business, but it’s also a very wealthy place.
This story originally appeared in TIME Space, our weekly newsletter covering all things space. You can register here.
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