Webb observations hint at giant asteroid collision in a nearby planetary system

HOUSTON  -   A collision between giant asteroids likely occurred in a neighboring star system called Beta Pictoris in recent years, and two different space observatories are helping to tell the tale.

The Beta Pictoris system, located just 63 light-years from Earth, has long intrigued astronomers because of its proximity and age. While our solar system is estimated to be about 4.5 billion years old, Beta Pictoris is considered a “teenage planetary system” at 20 million years old, said astronomer Christine Chen, a research scientist at Johns Hopkins University in Baltimore who has observed the system multiple times. “That means that it is still forming,” she said during a presentation at the 244th Meeting of the American Astronomical Society in Madison, Wisconsin, on June 10. “It’s a partially formed planetary system, but it’s not done yet.”  Chen observed Beta Pictoris, which has two known gas giant planets called Beta Pictoris b and c, using the now retired Spitzer Space Telescope in 2004 and 2005. At the time, Chen and her colleagues saw several different populations of dust within the system. “So I was super excited to reobserve this system in 2023 using the James Webb Space Telescope,” Chen said. “And I was really hoping to understand the planetary system in much greater detail, and we are definitely doing that.”  Since Webb opened its infrared eye on the universe in 2022, scientists have been utilizing the space observatory to peer through gas and dust to study supernovas, exoplanets and distant galaxies. By comparing the Spitzer and Webb observations, Chen and her colleagues realized that the data they captured 20 years earlier happened at a rather serendipitous time — and two of the major dust clouds had since disappeared. Chen is the lead author of a study comparing the observations that was presented Monday at the conference.  “Most discoveries by JWST come from things the telescope has detected directly,” said study coauthor Cicero Lu, a former Johns Hopkins doctoral student in astrophysics, in a statement. “In this case, the story is a little different because our results come from what JWST did not see.”

The team believes the Spitzer data hints that a pair of giant asteroids happened to collide just prior to the telescope’s observations of the system.  “Beta Pictoris is at an age when planet formation in the terrestrial planet zone is still ongoing through giant asteroid collisions, so what we could be seeing here is basically how rocky planets and other bodies are forming in real time,” Chen said.

 When Chen and her team observed Beta Pictoris between 2004 and 2005, they were likely glimpsing evidence of a “collisionally active planetary system,” but they just didn’t realize it yet, she said. In addition to the two known planets, previous research has detected evidence of comets and asteroids zipping around in the young system. As the comets and asteroids collide with one another, they create dusty debris and help form rocky planets.

The collision that occurred just before the Spitzer observations likely pulverized a massive asteroid into fine dust particles that were smaller than pollen or powdered sugar, Chen said.  She said the mass of dust created was about 100,000 times the size of the asteroid that killed the dinosaurs, which was estimated to be between 6.2 and 9.3 miles (10 and 15 kilometers) wide. The dust was then pushed out of the planetary system by radiation from the central star, which is slightly hotter than our sun. Initially, astronomers thought small bodies were colliding and replenishing the dust clouds seen in Beta Pictoris over time. But the powerful Webb telescope was unable to detect any dust. Although giant gas planets have formed in the system, rocky planets are likely still forming.

Astronomers anticipate making more observations of the system to see if more planets will appear. In the meantime, studying the system may help astronomers to better understand what the early days of our own solar system looked like. “The question we are trying to contextualize is whether this whole process of terrestrial and giant planet formation is common or rare, and the even more basic question: Are planetary systems like the solar system that rare?” said study coauthor Kadin Worthen, a doctoral student in astrophysics at Johns Hopkins, in a statement. “We’re basically trying to understand how weird or average we are.”

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