A previously unknown asteroid 100 to 200 meters long — about the size of the Colosseum in Rome — has been discovered 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 happened to detect an intruding asteroid. The object is probably the smallest object yet seen by Webb and could be an example of an object less than 1 kilometer long within the main asteroid belt, located between Mars and Jupiter. More observations are needed to better characterize the nature and properties of this object.

The solar system is teeming with asteroids and small rocky bodies – astronomers currently know of more than 1.1 million of these rocky remnants from the early days of the solar system. The NASA/ESA/CSA James Webb Space Telescope’s ability to probe these objects at infrared wavelengths is expected to lead to groundbreaking new science, but a team of scientists has shown that Webb also has an unpredictable aptitude for detecting objects by chance. small and previously unknown objects.

“We have – quite 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 aimed at the ecliptic plane and our work suggests that many new objects will be detected with this instrument.”

The Webb observations that revealed this small asteroid were not originally designed to hunt for new asteroids. failed for technical reasons due to target brightness and an offset telescope. Despite this, the data on asteroid 10920 was used by the team to establish and test a new technique for constraining an object’s orbit and estimating its size. The validity of the method was demonstrated for asteroid 10920 using the MIRI observations in combination with data from ground-based telescopes and ESA’s Gaia mission.

While analyzing the MIRI data, the team found the smaller and previously unknown intruder in the same field of view. The team’s results suggest the object measures 100-200 meters, has a very low-inclination orbit, and was 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 bit of luck,” elaborated Muller. “Our detection is in the main asteroid belt, but Webb’s incredible sensitivity made it possible to see this object about 100 meters from more than 100 million kilometers away.”

The detection of this asteroid – which the team suspects is the smallest observed by Webb to date and one of the smallest detected in the main belt – if confirmed as a new asteroid discovery, would 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 due to the difficulty of observing these objects. Future Webb special observations will allow astronomers to study asteroids smaller than 1 kilometer, providing the necessary data to refine our models of the formation of the solar system.

In addition, this result suggests that Webb may also coincidentally contribute to the detection of new asteroids. The team suspects that even brief MIRI observations close to the plane of the solar system will always include a few asteroids, most of which will be unknown objects.

To confirm that the detected object is a newly discovered asteroid, more position data relative to background stars is needed from follow-up studies to constrain the object’s orbit.

“This is a fantastic result that highlights MIRI’s capabilities to coincidentally detect a previously undetectable size of a main belt asteroid,” concluded Bryan Holler, Webb’s support scientist at the Space Telescope Science Institute in Baltimore, USA. “Replays of these sightings are currently being planned and we expect completely new asteroid intrusions in those images!”

Magazine reference:

  1. TG Muller, M. Micheli et al. Asteroids Seen by JWST-MIRI: Radiometric Size, Distance, and Orbital Constraints★. Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202245304