It is a rare occurrence indeed for a theory to be turned upside down by the cold accuracy of observation, until the Hubble Space Telescope has just dropped a bombshell in the young planetary system of Fomalhaut, because astronomers have been able to watch the effects of not one but two massive collisions between planetesimals in the solar system 25 light-years away in an occurrence expected only once every 100,000 years.
The rendezvous took place in 2004 and was believed to be with the exoplanet called Fomalhaut b, although it has since been realised that it was in fact a cloud of material in disintegration, named Fomalhaut cs1. The other rendezvous happened in 2023 in similar location. It was named as Fomalhaut cs2. Both rendezvous were described as being with a rock planet in disintegration, 30-60 kilometers in size, filled with water ice and methane as in a comet.
“This is certainly the first time I’ve ever seen a point of light appear out of nowhere in an exoplanetary system,” said Paul Kalas of the University of California at Berkeley. “It’s absent in all of our previous Hubble images, which means that we just witnessed a violent collision between two massive objects and a huge debris cloud, unlike anything in our own solar system today,” he added.
This becomes all the more interesting in light of the fact that cs1 and cs2 are comparatively very close to each other in the outer Debris disk of Fomalhaut. If Collisions between planetesimals are random in nature, the dust clouds formed should not lie so close to each other.
From the engineering and observation points of view, the observations show that one of the critical problems is that the dust clouds can read easily like planets in direct imaging observations. Analyzing the visible spectrum, the cs2 spectrum appears completely insignificant as an extra-solar planet illuminated by starlight. Kalas added, “What we learned from studying CS1 is that a large dust cloud can masquerade as a planet for many years. This is a cautionary note for future missions that aim to detect extrasolar planets in reflected light.”
Such types of collisions are related to young planetary systems. In the solar system, planetesimals were created through highly energetic collisions and the pebble accretion process, and there were also many other kind of collisions that resulted in the reduction of bodies to dust. It indicates that the results of catastrophic collisions might result in the formation of matter that exists in the system for many years, increased by the pressure of starlight, and affect different matter, creating secondary dust avalanches.
Systemic and other processes can also be explored under this system. Roughly 300 million planetesimals comparable in size to those that were destroyed under Cs1 and Cs2 remain in this system. The previous detection of gas emission of carbon monoxide within this system had already indicated a structure akin to that of the Kuiper Belt and comets of our solar system.
In the future, the observation follow-up would concentrate on the complementary capabilities of the Hubble Space Telescope and the James Webb Space Telescope. While the visible light images of the Hubble Space Telescope pick up well in the visible range, its ability would complement the Near-Infrared Camera of the James Web Space Telescope in the identification of the size and composition of the dust grains, as well as the detection of the presence of water ice. This would aid in distinguishing genuine planets from fragments of collisions and could offer physical characteristics of their parent bodies.
At this point, another group of people becomes relevant: the planetary defense experts. According to Jason Wang of Northwestern University: “Studying planetesimal collisions is important for understanding how planets form. It also can tell us about the structure of asteroids, which is important information for planetary defense programs like the Double Asteroid Redirection Test (DART).” Indeed, Fomalhaut system asteroid impacts pale in comparison to the actual impact of the Double Asteroid Redirection Test impact effort by a factor of a billion. But they carry so much more significance within the realm of people studying and loving space science—to have an actual opportunity to observe this phenomenon is, in fact, an unprecedented experience of something referred to as cosmic fireworks.
