Shulou(Shulou.com)11/24 Report--

CTOnews.com, February 9 (Xinhua)-- although the large telescope James Webb is not designed to track fast-moving objects, it can still do so, and successfully broke the limit to observe the collision between the DART probe and the asteroid Dimorphos last September, NASA revealed.

On September 26, 2022, after 10 months of space travel, a 570kg double asteroid redirection test (DART) probe crashed into the 190m wide asteroid / small moon Dimorphos to change its orbit (around a large rock called Didymos).

The experiment, the first real project in a planetary collision experiment, aims to prove that humans can save themselves by changing their orbits if an innocent asteroid threatens Earth. The impact and its results were observed by countless telescopes from Earth and space at that time, and Weber certainly couldn't miss it.

Stefanie Milam, a scientist from NASA's James Webb Space Telescope sub-program and of the Goddard Space Flight Center in Maryland, said scientists had to do everything they could to move the telescope to see the historic space wonder.

Milam wrote in a blog post that Webb is mainly built to observe the most distant objects in the universe, and it can only follow slow-moving objects in pre-launch tests.

The fastest moving object that astronomers expect to track with Weber is Mars, which currently roams the universe at a speed of about 30 milliseconds per second (CTOnews.com Science Popularization: one arc second is one stroke 60 arc minutes, or one stroke 60 degrees). This means that it takes us about 17 hours to observe Mars passing through the full moon on Earth.

But in fact, during the DART impact, the near-Earth asteroid Didymos / Dimorphos was only 11 million kilometers away from Earth, or even less than one-fourth of the average distance between Mars and Earth. As a result, it is much faster, at least more than 100 milliseconds per second, but that is more than three times the speed of Weber's design, which is undoubtedly a challenge.

It is worth mentioning that Weber does not have the usual lens, which relies on fine guidance sensors (FGS) to track and image specific moving objects. The FGS is a special camera that locks the reference star, also known as the guide star, to keep its focus on the target all the time. However, when an object moves too fast for Weber, its guidance sensor must jump from one guide star to another to stay focused, which is technically demanding.

In fact, before the collision, Weber's team had practiced such high-speed tracking operations on several other near-Earth asteroids, such as 2010 DF1 of space rock moving through the sky at a speed of 90 milliseconds per second, with an angular velocity almost as fast as Dimorphos.

"if we can successfully track the asteroid, we will know that we can track the DART impact," Milam wrote. "We have completed the test two weeks before the date on which DART affected Dimorphos!"

Thanks to good preparation, Weber's near-infrared camera (NIRCam) finally succeeded in capturing a series of images, including, of course, the DART impact and its results, revealing how the asteroid was scattered into the surrounding space.

Of course, the Weber Telescope is not the only space telescope to observe this image, even the old Hubble Telescope was successfully involved. In addition, the Italian-built LICIACube also captured images of the star impact from a short distance of 600 miles (1000 kilometers) in the universe.

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