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| This artist's impression shows a grey, irregularly-shaped asteroid against a dark background. Credit: N. Bartmann (ESA/Webb), ESO/M. Kornmesser and S. Brunier, N. Risinger (skysurvey.org) |
A previously unknown 100-to-200-meter asteroid—roughly the size of Rome's
Colosseum—has been detected by an international team of European astronomers
using the NASA/ESA/CSA James Webb Space Telescope. Their project used data
from the calibration of the Mid-InfraRed Instrument (MIRI), in which the
team serendipitously detected an interloping asteroid.
The object is likely the smallest observed to date by Webb and may be an
example of an object measuring under 1 kilometer in length within the main
asteroid belt, located between Mars and Jupiter. More observations are
needed to better characterize this object's nature and properties.
The solar system is teeming with asteroids and small rocky
bodies—astronomers currently know of more than 1.1 million of these rocky
remnants of the early days of the solar system. The NASA/ESA/CSA James Webb
Space Telescope's ability to explore these objects at infrared wavelengths
is expected to lead to groundbreaking new science, but a team of scientists
have shown that Webb also has an unpredicted aptitude for serendipitously
detecting small and previously unknown objects.
"We—completely unexpectedly—detected a small asteroid in publicly available
MIRI calibration observations," explained Thomas Müller, an astronomer at
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."
The Webb observations which revealed this small asteroid were not originally
designed to hunt for new asteroids—in fact, they were calibration images of
the main-belt asteroid (10920) 1998 BC1, which astronomers discovered in
1998, but the calibration team considered them to have failed for technical
reasons due to the brightness of the target and an offset telescope
pointing. Despite this, the data on asteroid 10920 were used by the team to
establish and test a new technique to constrain an object's orbit and to
estimate its size. The validity of the method was demonstrated for asteroid
10920 using the MIRI observations combined with data from ground-based
telescopes and ESA's Gaia mission.
In the course of the analysis of the MIRI data, the team found the smaller
and previously unknown interloper in the same field of view. The team's
results suggest the object measures 100–200 meters, occupies a very
low-inclination orbit, and was located in the inner main-belt region at the
time of the Webb observations.
"Our results show that even 'failed' Webb observations can be scientifically
useful, if you have the right mindset and a little bit of luck," elaborated
Müller. "Our detection lies 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 detection of this asteroid—which the team suspects to be the smallest
observed to date by Webb and one of the smallest detected in the
main-belt—would, if confirmed as a new asteroid discovery, have important
implications for our understanding of the formation and evolution of the
solar system.
Current models predict the occurrence of asteroids down to very small sizes,
but small asteroids have been studied in less detail than their larger
counterparts owing to the difficulty of observing these objects. Future
dedicated Webb observations will allow astronomers to study asteroids
smaller than 1 kilometer in size, providing the necessary data to refine our
models of the solar system's formation.
What's more, this result suggests that Webb will also be able to
serendipitously contribute to the detection of new asteroids. The team
suspect that even short MIRI observations close to the plane of the solar
system will always include a few asteroids, most of which will be unknown
objects.
In order to confirm that the object detected is a newly discovered asteroid,
more position data relative to background stars is required from follow-up
studies to constrain the object's orbit.
"This is a fantastic result which highlights the capabilities of MIRI to
serendipitously detect a previously undetectable size of asteroid in the
main belt," concluded Bryan Holler, Webb support scientist at the Space
Telescope Science Institute in Baltimore, U.S.. "Repeats of these
observations are in the process of being scheduled, and we are fully
expecting new asteroid interlopers in those images!"
The study is published in the journal Astronomy & Astrophysics.
Reference:
T. G. Müller et al, Asteroids seen by JWST-MIRI: Radiometric size, distance,
and orbit constraints, Astronomy & Astrophysics (2022).
DOI: 10.1051/0004-6361/202245304
Tags:
Space & Astrophysics