Violent Space Rock Smashups Caused a Dusty Wreck in a Nearby Planetary System
In a region of space not far from our solar system, two separate collisions between space rocks have scattered an incredible amount of debris. Dust clouds at the two 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 provided answers to a lingering mystery surrounding Fomalhaut b, long considered a candidate exoplanet due to its brightness. It turns out that this bright object that astronomers discovered in the sky in 2008 was not an exoplanet, but a huge cloud of dust left behind by a space collision. Now, a second similar collision has researchers intrigued to find out what’s going on in this bustling planetary system.
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A mysterious light in the sky
Sequence of a massive collision between two objects which created a cloud of dust near the star Fomalhaut.
(Image credit: NASA, ESA, STScI, Ralf Crawford (STScI))
Astronomers have always been uncertain about the true identity of the object initially known as Fomalhaut b, named after its nearby host star, Fomalhaut.
Researchers attempted to check the light source in 2023, but when they looked at images from NASA’s Hubble Space Telescope, it had mysteriously disappeared. However, they found a distinct light shining in a slightly different location, according to a press release about the new study,
By comparing this view with past images, the researchers confirmed that the missing object was a dissipating dust cloud, now called Fomalhaut cs1 instead of Fomalhaut b. This cloud has since disappeared, as the dust was pushed into interstellar space by radiation pressure from starlight.
Researchers are now closely monitoring the newest light source, a dust cloud called Fomalhaut cs2. CS1 and CS2 likely originated from rare collisions between planetesimals, which are rocky objects like asteroids.
Space rock wreck
The Fomalhaut cs1 and cs2 observations mark the first time planetesimal collisions have been observed outside the solar system, but with two collisions occurring just 20 years apart, the dusty Fomalhaut system could be a prime place to see planetesimals crashing into each other.
“The more dust there is in a system, the more planetesimals there are and the more likely they are to collide. Also, if you can concentrate the planetesimals into a ring, they will also be more likely to collide,” says study author Jason Wang, professor of physics and astronomy at Northwestern University. “Fomalhaut has one of the most important dust belts that we know of, and it’s concentrated in a ring, so in some ways it’s the ideal system for finding these collisions.”
Researchers hope to see more rare collisions between larger planetesimals in the future, because the dust grains produced could offer new insights into planet formation.
As for what will happen with Fomalhaut cs2, the researchers say it could disperse in the same way as cs1, but they are not yet ruling out a different outcome.
“It could be that CS2 involved a different type of collision than CS1, and that the time course is different. For example, a different scenario would be that a planetesimal collides with a dwarf planet and creates a giant dust cloud, except that the dust will remain bound to the dwarf planet and eventually settle on the surface,” says study author Paul Kalas, an astronomer at the University of California, Berkeley.
Distinguish between clouds and planets
Diagram from a Hubble Space Telescope image showing the ring of debris and dust clouds around the star Fomalhaut (marked with a white star). Dust clouds are marked with white dotted circles. The new study reclassifies CS1 – previously considered 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 as dust-covered exoplanets under the right conditions, as both are capable of producing similar brightness levels from reflected starlight. The researchers say that observing this brightness in different wavelengths will be a key practice to avoid misidentifications in the future.
The researchers plan to track Fomalhaut cs2 with the James Webb Space Telescope’s near-infrared camera, which can provide color data to discover details about the cloud’s composition, such as whether it contains water and ice. Through this, they hope to know where the planetesimals were born, how they evolved over time, and what happened in the moments before the chaotic crash.
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