But the direct impact on a mirror took NASA by surprise and is still being analyzed. The details of the micrometeoroid attack were revealed by NASA in a blog post dedicated to Webb.
“Between May 23 and May 25, NASA’s James Webb Space Telescope had an impact on one of its key mirror segments,” the NASA Webb blog stated. “After initial assessments, the team found that the telescope is still operating at a level that exceeds all mission requirements, despite a marginally detectable effect on the data.”
The 18 mirror segments can be individually adjusted in response to meteoroid impacts like this one, NASA said.
“By adjusting the position of the affected segment, engineers can cancel out some of the distortion…although not all of the degradation can be canceled out in this way,” the NASA blog stated. “Engineers have already performed a first such adjustment for the newly affected segment … and additional planned mirror adjustments will continue to adjust this correction.”
The exact size of the micrometeoroid is not known. It might not have been bigger than a grain of sand, said Heidi Hammel, a planetary astronomer who has long been involved with the telescope. and will use it to study our solar system. Even something so small can cause damage because of the tremendous speed with which the telescope orbits the sun and periodically bumps into a random particle.
This was a known danger, because although it is lonely in space, it is not as empty as it seems.
“There is no loss of science in this event. … This telescope is out there in space – we knew there would be small impacts on it. We were surprised at the success so early on,” Hammel said.
She said scientists predicted this impact every five years on average.
This extraordinarily complex observatory, billed as the long-awaited successor to the still functioning Hubble Space Telescope, is orbiting the Sun in a position that keeps it about 1 million miles from Earth. It is too far away for astronauts to visit and not designed to be repaired or instruments changed.
Webb has been going through a “commissioning” phase for months, as its instruments are calibrated and the 18 gold-plated hexagonal mirrors are aligned to function as a single massive mirror about 6 meters in diameter.
So far, NASA has reported nothing but success.
“Astronomers are giddy at how well things are going (but also nervous not to jinx it, yes we can be superstitious too) and eager to start doing science!” University of Chicago astrophysicist Michael Turner in an email.
The telescope, folded in on itself at launch last year, flourished over the course of many days as its broad solar shield opened and mirrors unfolded. The telescope traveled for 29 days to reach its outpost, an orbital position known as L2, where other telescopes operated safely and provided scientists with data on the frequency of micrometeoroids.
“While the telescope was being built, engineers used a mix of simulations and real-life test impacts on mirror samples to get a clearer idea of how to strengthen the observatory for in-orbit operation. This most recent impact was larger than modeled and beyond what the team could have tested in the field,” stated NASA’s Webb blog.
The Webb is unlike most telescopes: it’s wide open, with the mirrors exposed rather than stuffed into a tube. The telescope is designed to observe the universe at infrared wavelengths that are beyond Hubble’s detection range.
This requires extremely cold mirrors and instruments, That’s why mirrors are always facing away from the Earth and the Sun. NASA has announced that the “first light” images will be released on July 12, but did not say what they will show.
However, it has already produced an image of a star, used to focus the mirrors. In the background of this image are numerous galaxies whose light was emitted billions of years ago, and this has excited astronomers who expect Webb to see deeper into space (and into the past) than Hubble, launched in 1990.
Webb has several goals, including studying the oldest light in the universe, emitted a few hundred million years after the big bang. It will also analyze the evolution of galaxies and study objects in our own solar system, including small icy bodies that orbit the sun far beyond Neptune’s orbit.