Webb detects smallest main belt asteroid by chance: NASA

An asteroid roughly the size of Rome's Colosseum, between 300 and 650 feet in length, has been detected by scientists using NASA's James Webb Space Telescope.

The asteroid, detected by the international team of European astronomers, is likely the smallest object observed to date by Webb. (Bloomberg)

An asteroid roughly the size of Rome's Colosseum, between 300 and 650 feet, or 100 and 200 metres, in length, has been detected by scientists using NASA's James Webb Space Telescope, according to a new research.

The object, detected by the international team of European astronomers, is likely the smallest observed to date by Webb, the research said.

It may also be an example of an object measuring under 0.6 miles, or 1 kilometer, one of the smallest in length within the main asteroid belt located between Mars and Jupiter, the research said.

The team's project used data from the calibration of the Mid-InfraRed Instrument (MIRI), in which the team serendipitously detected an interloping asteroid, the research published in the journal Astronomy and Astrophysics said.

Calibration is the act of checking or adjusting the accuracy of a measuring instrument by comparison with a standard.

More observations are needed to better characterize this object's nature and properties, the research said.

"We - completely unexpectedly - detected a small asteroid in publicly available MIRI calibration observations," explained Thomas Mueller, 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," said Mueller.

According to the research, these Webb observations, were not 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.

The Webb observations were conducted to test the performance of some of MIRI's filters, 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 research said.

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 interloper in the same field of view, the research said.

The team's results suggested that the object measured 100-200 metres, occupied 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 Mueller.

"Our detection lies in the main asteroid belt, but Webb's incredible sensitivity made it possible to see this roughly 100-metre object at a distance of more than 100 million kilometers," said Mueller.

If confirmed as a new asteroid discovery, the detection of this asteroid would have important implications for our understanding of the formation and evolution of the solar system, the research said.

According to the research, 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, it said.

This result also suggested that Webb will also be able to serendipitously contribute to the detection of new asteroids. The team suspects 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, the research said.

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, the research said.

"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, Maryland.

"Repeats of these observations are in the process of being scheduled, and we are fully expecting new asteroid interlopers in those images," said Holler.