Violent Space Rock Smashups Caused a Dusty Wreck in a Nearby Planetary System
In a region of space not far outside of our Solar System, two separate collisions between space rocks have scattered an incredible amount of debris. The dust clouds at both cosmic crash sites, giving off a radiant glow from reflected starlight, have now revealed that an unknown object theorized to be an exoplanet never actually existed.
A new study published in Science has delivered answers to an enduring mystery surrounding Fomalhaut b, long considered an exoplanet candidate because of its brightness. It turns out that this bright object that astronomers discovered in the sky in 2008 wasn’t an exoplanet, but a huge dust cloud left behind by a space rock collision. Now, a second, similar collision has researchers intrigued to find out what’s happening in this bustling planetary system.
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A Mysterious Light in the Sky
A sequence of a massive collision between two objects that created a dust cloud near the star Fomalhaut.
(Image Credit: NASA, ESA, STScI, Ralf Crawford (STScI))
Astronomers were always unsure about the true identity of the object first known as Fomalhaut b, named after its nearby host star Fomalhaut.
Researchers attempted to check on the light source in 2023, but when they looked through images from NASA’s Hubble Space Telescope, it had mysteriously disappeared. However, they found a separate light glowing in a slightly different location, according to a press release on the new study,
Comparing this sight with past images, the researchers confirmed that the departed object was a dissipating dust cloud, now referred to as Fomalhaut cs1 instead of Fomalhaut b. This cloud has since faded, as the dust has been pushed into interstellar space by radiation pressure from starlight.
The researchers are now keeping a close eye on the more recent light source, a dust cloud called Fomalhaut cs2. Both cs1 and cs2 likely emerged from rare collisions between planetesimals, which are rocky objects like asteroids.
Space Rock Wreckage
Observations of Fomalhaut cs1 and cs2 mark the first time planetesimal collisions have been seen outside of the Solar System, but with two collisions happening only around 20 years apart, the dusty Fomalhaut system may be a prime place to see planetesimals smash into each other.
“The more dust you have in a system, the more planetesimals you have and the more likely they will collide. Also, if you can concentrate the planetesimals into a ring, then they will also be more likely to collide,” says study author Jason Wang, a professor of physics and astronomy at Northwestern University. “Fomalhaut has one of the most prominent dust belts that we know of, and it is concentrated in a ring, so in some ways, it is the ideal system to find these collisions.”
Rare collisions between larger planetesimals are what the researchers hope to see more of in the future, since the dust grains produced could offer new insights into the formation of planets.
As for what will happen with Fomalhaut cs2, the researchers say it could disperse similarly to cs1, but they haven’t ruled out a different outcome quite yet.
“It could be that cs2 involved a different kind of collision than cs1, and the evolution over time will be different. For example, a different scenario is that a planetesimal impacted a dwarf planet and created a giant dust cloud, except the dust will remain bound to the dwarf planet and eventually settle back down on the surface,” says study author Paul Kalas, an astronomer at the University of California, Berkeley.
Telling Clouds and Planets Apart
Diagram from a Hubble Space Telescope image depicting the debris ring and dust clouds around star Fomalhaut (Marked with a white star). The dust clouds are marked with white dashed circles. The new study reclassifies cs1 — previously believed to be a planet — as a debris cloud.
(Image Credit: NASA, ESA, Paul Kalas (UC Berkeley))
The revelation that Fomalhaut cs1 was a dust cloud and not an exoplanet demonstrates the possibility of misidentifying light sources in space.
Dust clouds can appear just like dust-covered exoplanets in the right conditions, as both are capable of producing similar levels of brightness from reflected starlight. The researchers say that observing this brightness in different wavelengths will be a key practice to prevent misidentification in the future.
The researchers plan on tracking Fomalhaut cs2 with the James Webb Space Telescope Near-Infrared Camera, which can provide color data to uncover details about the cloud’s composition, such as whether it contains water and ice. With this, they hope to learn where the planetesimals were born, how they evolved over time, and what happened in the moments leading up to the chaotic crash.
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