Accidental discovery of a dangerous asteroid by the James Webb Space Telescope.
Failed observations of a specific target using the James Webb Space Telescope (JWST) have resulted in something much more interesting. In the asteroid belt that stretches between Mars and Jupiter, the space telescope has detected a previously unknown and exceptionally small asteroid .
The as-yet-unnamed chunk of rock measures just 100 to
200 meters (328 to 656 feet) across and is most likely the smallest object yet
collected by JWST. It's not only a superb demonstration of JWST's capabilities,
but suggests that those capabilities can be harnessed to better categorize the
millions of pieces of debris lurking in the main belt.
“Completely unexpectedly, we detected a small asteroid in publicly available MIRI calibration observations,” says astronomer Thomas Müller of the Max Planck Institute for Extraterrestrial Physics in Germany. “The measurements are some of the first MIRI measurements targeting the ecliptic plane and our work suggests that many new objects will be detected with this instrument.”
Calibrating JWST's Golden Eye
When JWST opened its metaphorical honeycomb-shaped golden eye in July 2022, scientists began putting it through its paces, calibrating its instrumentation and making sure everything was working as it should. One of those instruments is the Mid-Infrared Instrument, or MIRI.
MIRI's calibration target was a much larger Main Belt
asteroid called (10920) 1998 BC1, discovered in 1998 and measuring 15.7
kilometers (9.75 miles) in diameter. Unfortunately, JWST's observations were
not particularly good: the telescope was not quite pointed correctly, and
images of the target were too bright and dull.
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| Surprise! The bright object at the bottom is 10920; the new asteroid candidate is the faint spot circled above. |
A Failure That Resulted in a Success
It wasn't a total failure as far as 10920 was
concerned; the images obtained by JWST allowed researchers to test some
techniques for constraining the asteroid's size and orbit, combined with data
from other ground-based and space-based telescopes.
But there was something else, too. Individual images showed a faint object moving relative to both 10920 and background light sources. The team did a careful analysis and found that the faint object was likely another, much smaller, previously unidentified asteroid.
An Important Discovery
The discovery has not yet been confirmed, but if it is, it will be one of the smallest asteroids ever discovered in the Main Belt. The detection of asteroids of this size is of vital importance for studies of the size and frequency distribution of objects in the belt.
You might think that finding asteroids in an asteroid belt is a no-brainer, but it’s a little more complicated than you might think . So far, astronomers have positively identified more than 600,000 Main Belt asteroids, and provisionally identified nearly 550,000 more… but there are estimated to be millions upon millions more of them, most of them in the small size range.
The Difficulty of Detecting Small Asteroids
And the smaller ones are much harder to spot than the larger ones. Which makes accidentally spotting one a big coup, really.
"Our results show that even Webb's 'failed' observations can be scientifically useful, if you have the right mindset and a bit of luck," says Müller.
The Incredible Sensitivity of JWST
"Our detection is in the main asteroid belt, but
Webb's incredible sensitivity made it possible to see this roughly 100-meter
object at a distance of more than 100 million kilometers."
The Asteroid Belt: A Vast and Sparsely Populated Place
The asteroid belt is a sparsely populated doughnut of rocks that lies in the plane of the Solar System and extends to a distance of between 2.2 and 3.2 astronomical units from the Sun: 329 million to 478.7 million kilometers, or 204.43 million to 297.45 million miles.
But the average distance between asteroids is estimated to be about 965,600 kilometres. Unless you're looking at the right patch of sky, you might not see anything at all.
A Window to the Asteroid Belt
JWST, in its calibration observations, was accidentally looking at the right patch of sky. And researchers believe that, in the future, it may have more such happy accidents when observing targets that align with the plane of the Solar System.
"We estimate," the researchers write in their paper, "that MIRI frames with near-ecliptic points and short integration times of only a few seconds will always include some asteroids; most of them will be unknown objects."
A Promising Future in the Exploration of the Asteroid Belt
This accidental discovery demonstrates the enormous potential of JWST to help unravel the mysteries of the asteroid belt. As the telescope continues its mission, many more unknown objects are likely to be discovered and new insights will be gained into the composition and distribution of this cosmic debris.
Excitement and excitement are palpable in the scientific community as new opportunities open up to explore and better understand our Solar System. JWST is proving to be an invaluable tool in this quest for knowledge, and its accidental discoveries could lead to significant advances in our understanding of the universe around us.
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