When you look up at the night sky, planets seem calm and fixed. But a new study shows that nearby planetary systems can be violent and chaotic. Using NASA\u2019s Hubble Space Telescope, astronomers have watched the glowing aftermath of two massive collisions unfold around a nearby star.<\/p>\n
At first, astronomers thought they were watching an exoplanet. Instead, they realized they were seeing the dusty wreckage from two separate smashups between large rocky bodies. These events happened in real time, on astronomical scales, offering a rare window into how planets are built and destroyed.<\/p>\n
Optical images of the Fomalhaut system in 2012 and 2023. Both panels are white-light HST\/STIS images. The bright central star has been artificially eclipsed with a coronagraph, to reveal the fainter belt-like dust structure around the star, with intensity indicated by the color bar. (CREDIT: Science) A familiar star with a strange glow<\/p>\n
The system centers on Fomalhaut, a bright star about 25 light-years from Earth. It is younger and more massive than the sun and surrounded by one of the largest known debris belts. Jason Wang has helped monitor this system for two decades.<\/p>\n
\u201cThe system has one of the largest dust belts that we know of,\u201d Wang said. \u201cThat makes it an easy target to study.\u201d<\/p>\n
In 2008, Hubble images<\/a> revealed a faint point of light near the belt. Astronomers named it Fomalhaut b and proposed it was a planet reflecting starlight. The idea raised eyebrows because the object looked too bright and failed to appear in infrared data.<\/p>\n Years later, new observations deepened the mystery. The light source faded, grew larger, and then vanished. In 2023, when astronomers returned with Hubble, they found something unexpected. The original source was gone, but a new bright point appeared nearby.<\/p>\n \u201cWith these observations, our original intention was to monitor Fomalhaut b, which we initially thought was a planet,\u201d Wang said. \u201cWe assumed the bright light was Fomalhaut b because that\u2019s the known source in the system. But, upon carefully comparing our new images to past images, we realized it could not be the same source. That was both exciting and caused us to scratch our heads.\u201d<\/p>\n Composite image of the 2012, 2013, and 2023 observations. The white light STIS images from three epochs have been averaged (intensity indicated by the color bar) to show the relative positions of cs1 and cs2 (white labels), a decade apart. (CREDIT: Science) Not planets, but cosmic wreckage<\/p>\n The team renamed the original object Fomalhaut cs1 and the new one Fomalhaut cs2. Their conclusion was striking. Neither source was a planet. Both were clouds of debris created when large planetesimals collided at high speed.<\/p>\n \u201cThese were not planets at all,\u201d Kalas said. \u201cThis is certainly the first time I\u2019ve ever seen a point of light appear out of nowhere in an exoplanetary system<\/a>.\u201d<\/p>\n The brightness and location of cs2 closely match how cs1 looked when it first appeared two decades earlier. That similarity suggested the same cause. Two violent collisions, spaced only about 20 years apart, occurred in the same debris belt.<\/p>\n Theory predicts such events should be rare, perhaps once every 100,000 years in a system like this. Seeing two within a human lifetime stunned the researchers.<\/p>\n \u201cIf you had a movie of the last 3,000 years, and it was sped up so that every year was a fraction of a second, imagine how many flashes you\u2019d see,\u201d Kalas said. \u201cFomalhaut\u2019s planetary system would be sparkling with these collisions.\u201d<\/p>\n This artist\u2019s concept shows the sequence of events leading up to the creation of dust cloud cs2 around the star Fomalhaut. In Panel 1, the star Fomalhaut appears in the top left corner. Two white dots, located in the bottom right corner, represent the two massive objects in orbit around Fomalhaut. In Panel 2, the objects approach each other. Panel 3 shows the violent collision of these two objects. In Panel 4, the resulting dust cloud cs2 becomes visible and starlight pushes the dust grains away from the star. (CREDIT: NASA, ESA, STScI, Ralf Crawford (STScI)) Tracking motion and fading light<\/p>\n To be sure, the team carried out four independent analyses of the Hubble data. Wang led one of them, checking the measurements and motion of the new source.<\/p>\n \u201cThis is the first time we\u2019re seeing something like this,\u201d Wang said. \u201cSo, we had to make sure we can trust our images and that we are measuring the properties of the collision properly.\u201d<\/p>\n The data show cs1 moved outward at increasing speed before fading. That behavior matches what radiation pressure from the star would do to tiny dust grains. As the cloud expanded and thinned, sunlight pushed it apart faster, causing it to dim and spread until it disappeared.<\/p>\n Cs2 now sits near the inner edge of the debris belt<\/a>. It shines even brighter than cs1 did late in its life, suggesting a fresh collision. Earlier Hubble images were sensitive enough to see it, yet showed nothing, ruling out a background star.<\/p>\n What the debris tells you about planet building<\/p>\n The brightness of these clouds reveals their scale. Cs1 required an enormous amount of dust, far more than seen after asteroid breakups in our own solar system. The calculations point to parent bodies roughly 30 kilometers across, similar in size to large asteroids.<\/p>\n Jason Wang, an assistant professor of physics and astronomy at Northwestern. (CREDIT: Northwestern University) <\/p>\n Over hundreds of millions of years, repeated collisions like these help grind large bodies into dust. That process feeds debris belts and supplies the raw material that can clump together to form planets. Watching it happen elsewhere helps you understand how Earth and its neighbors once formed.<\/p>\n The clustering of the two collisions also raises questions. They occurred close together in space, not just in time. That pattern could be coincidence, but it might hint at unseen forces shaping where impacts happen, possibly from an undiscovered planet<\/a> or a tilted inner belt.<\/p>\n A warning for future planet hunters<\/p>\n The discovery carries an important lesson. Dust clouds from collisions can mimic planets for years. They reflect starlight and move with the star, just as a planet would.<\/p>\n \u201cFomalhaut cs2 looks exactly like an extrasolar planet reflecting starlight,\u201d Kalas said. \u201cWhat 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.”<\/p>\n As astronomers prepare to use powerful new telescopes, that warning matters. Misidentifying debris as a planet could skew estimates of how common Earth-like worlds really are.<\/p>\n Looking ahead with Webb<\/p>\n “Although Hubble can no longer collect the most precise data, our team is not done. We have secured time on NASA\u2019s James Webb Space Telescope<\/a>, using its Near-Infrared Camera to study cs2,” Wang shared with The Brighter Side of News.<\/p>\n \u201cDue to Hubble\u2019s age, it can no longer collect reliable data of the system,\u201d he continued. \u201cFortunately, we now have the JWST.\u201d<\/p>\n Webb\u2019s instruments can reveal the color, size, and makeup of the dust grains. That information may show whether the debris contains ice or water-rich material, clues that matter for understanding habitable worlds.<\/p>\n Practical Implications of the Research<\/p>\n This research reshapes how you interpret distant planetary systems. It shows that violent collisions can light up debris belts and fool even experienced observers. By learning how these dust clouds<\/a> behave, astronomers can avoid false planet detections and refine future surveys.<\/p>\n The findings also deepen knowledge of planet formation. Watching collisions in real time provides evidence of how rocky bodies grow, shatter, and recycle material. That insight helps scientists model the early history of our own solar system.<\/p>\n Beyond astronomy, the work informs planetary defense. Understanding how asteroids break apart, and how much debris they produce, supports efforts like NASA\u2019s asteroid redirection tests. In the long run, that knowledge can help protect Earth.<\/p>\n