Over the next two years the James Webb Space Telescope (JWST) will fly through dust and debris left in the inner solar system by Hally’s comet.
Scientists are working on mitigation solutions right now to avoid a repeat of what happened in May 2022 when the $10 billion space telescope was damaged by a micrometeroid.
So don’t worry—Halley’s comet itself is not going to strike the Webb telescope.
Though it measures nine miles by five miles/15 km by 8 km wide it orbits the Sun every 75 years or so, Hally’s comet is not expected back in the inner solar system until 2061 when it will pass relatively close to Earth (and could thus be as bright as the brightest star Sirius).
Webb will probably be defunct by then, though it’s hoped humanity’s premier space observatory will last until the early 2040s.
Comets are made from dust, rocks and ice, so melt—and shed material—when they get close to the Sun. They leave streams of debris the size of sand grains on their way in and out of the solar system, both before and after they loop around the Sun.
Webb’s engineers anticipate about one meteoroid strike per month, but that could be hugely increased while the telescope travels through a meteor stream.
According to Nature NASA’s meteoroid environment office at the Marshall Space Flight Center in Huntsville, Alabama are now calculating meteor-shower forecasts for Webb’s engineers.
It could mean Webb being manoeuvred to point away from the incoming particles and so avoid them striking the mirrors. That means minimizing the time spent looking in the direction of orbital motion.
It’s a scenario that could become a live issue in both May 2023 and again in May 2024 when Webb travels through the Hally’s comet stream.
The Halley’s comet stream is the root cause of two famous meteor showers experienced on Earth—May’s Eta Aquarids and October’s Orionids. Both produce about 20 “shooting stars” per hour—which are tiny particles of dust that strike Earth’s atmosphere, then discharge energy as light.
Webb’s huge primary 6.5-meter mirror comprises 18 beryllium-gold hexagonal segments and is completely exposed to deep space. One of the mirror segments, called C3, was struck by micrometeorids between May 23 and 25, 2022. It caused permanent damage that can’t be corrected, though it’s hoped it won’t affect the observatory’s image quality.
Its primary mirror also was hit by four smaller measurable micrometeoroid strikes, though they were all in the predictable range.
Micrometeoroid strikes are an unavoidable aspect of operating in space, but Webb’s engineers are now reassessing how frequent its primary mirror will be struck—and what can be done about it.
Webb orbits the L2 point about a million miles/1.6 million kilometers from Earth.
Halley’s comet was last seen in the inner solar system in 1986 and next year marks its farthest point from Earth before it swings back towards the Sun. It’s currently about 35 au distant (35 times the Sun-Earth distance), which is roughly the distance from Earth to the dwarf planet Pluto. It’s currently in the constellation of Hydra, but close to bright star Procyon in the constellation of Canis Minor.
It’s the only known naked-eye comet that can appear twice in a human lifetime. It’s been observed every 75 years since 240 BC, though only in 1705 did English astronomer Edmund Hally work out that the same bright object kept returning to the night sky. He died 16 years before its 1758 appearance, which he had accurately predicted.
Wishing you clear skies and wide eyes.