Cosmic collisions can lead to some stupendous 'shows' as well as astronomical discoveries. Some 31 years ago Comet Shoemaker–Levy 9 (formally designated D/1993 F2) transfixed the astronomical world. SL-9 as it's abbreviated was a comet that broke apart in July 1992 and collided with Jupiter in July 1994, providing first direct observation of an extraterrestrial collision of Solar System objects.
Calculations showed that its unusual fragmented form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker–Levy 9 passed within Jupiter's Roche limit, and Jupiter's tidal forces had acted to pull the comet apart. The comet was later observed as a series of fragments ranging up to 2 km (1.2 mi) in diameter.
These fragments collided with Jupiter's southern hemisphere between July 16 and
22, 1994 at a speed of approximately 60 km/s (37 mi/s)
(Jupiter's escape velocity) or 216,000 km/h
(134,000 mph). The prominent scars from the impacts were more visible than
the Great Red Spot and persisted for many months.
Orbital studies of the new comet soon revealed that it was orbiting Jupiter rather than the Sun, unlike any other comet then known. Its orbit around Jupiter was very loosely bound, with a period of about 2 years and an apoapsis (the point in the orbit farthest from the planet) of 0.33 astronomical units (49 million kilometers; 31 million miles). Its orbit around the planet was highly eccentric (e = 0.9986)
I bring up this event because of its sheer uniqueness at the time, and the fact that now an even more distant asteroid impact appears to have been detected. And indeed we are talking about the collision of an asteroid with another asteroid. But not in our solar system like Comet Shoemaker-Levy with Jupiter (comet with a planet) but 25 light years away in the Fomalhaut system. In this case the impact generating a dusty debris cloud, which betrayed the specific dynamics.
Artist's rendition of colliding asteroids in Fomalhaut System
The star Fomalhaut, to be sure, is younger, brighter and more massive than our Sun. It is actually one of the brightest stars visible in the Northern Hemisphere, specifically within the constellation Piscis Austrinus.
Astronomers have observed Fomalhaut since discovering a dust belt around it in 2004 using NASA's Hubble Space Telescope which orbits Earth. In recent Hubble observations the asteroid collision resembled a luminous 'inkblot'. According to a professor of astrophysics at Cambridge University and the co-author of a paper describing the collision published recently in the journal Science:
"This is the first time we have seen a point of light appear out of nowhere in a planetary system." The point of light, in fact, revealed a collision between two asteroids, the first ever seen - according to Paul Kalas, an astronomer at the University of California, Berkeley and the lead author. The estimated size was about 37 miles across.
The two sources have been designated cs 1 and cs 2 for circumstellar source 1 and circumstellar source 2. Interestingly, Kalas first thought the curious bright spot near Fomalhaut in 2012 was a planet. But by 2014 it had disappeared so could not have been a planet given planets don't mysteriously vanish at the drop of a hat. That dust clouds - even if bright - can appear to be planets- then emerged as a warning to future observers. Kalas's group spotted the evidence for both collisions - in 2012 and 2023 - in the large belt of debris that encircles Fomalhaut in a circumstellar disk, e.g.
This dusty 'girdle' being the result of millions of impacts between rocky and icy bits that range in size from sand grains to far larger objects which astronomers refer to as planetesimals (which include both asteroids and comets). In this image we can see the planetesimals cs1 and cs2.
Researchers originally thought the collisions between planetesimals - whether asteroids or comets - were rare, maybe once ever 100,000 years. But spotting two in as many decades upended that view. The upshot is that Kalas and his team will continue to use Hubble as well as NASA’s James Webb Space Telescope to keep an eyes on Fomalhaut's environs for any more collisions.
Already, they note that a major insight is the recognition that dust clouds generated by colliding asteroids could be masquerading as planets in neighboring planetary systems. This is an incredible revelation as we will now have a solid basis to look for such collisions - which we've never seen in our own system- in other systems. This will open the door for future NASA efforts to coincide with other agency searches for other habitable worlds.
In addition, the techniques refined now will allow astronomers to estimate both the size of the colliding bodies and how many of them are in any given circumstellar disk, such as observed with Fomalhaut. This is information nearly impossible to obtain by any other means.
See Also:
Mini-Sampling Mission To Asteroid Bennu Unfolds Today As Millions Wait With Bated Breath
And:
Newly Discovered Asteroid Appears To Be A 2nd Earth "Trojan"
And:
NASA Predicts "No Risk" Of Apophis Collision In 2029: Why I'm Not Buying It
And:
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