Meteors from rare long-period comets
Around the world, a network of low-light video security cameras are pointed at dark skies, capturing faint meteors and using triangulation to determine their trajectories and orbits. Peter Jenniskens of the SETI Institute leads this project, which is called CAMS. He said in May 2021 that he’s using the data to discover that some long-period comets, with orbits up to 4,000 years long, are the sources of some of the meteors captured by CAMS. The passes of these comets might sometimes create a meteor rain, he said, plus the potential for an impact by a comet. He said:
Until recently, we only knew five long-period comets to be parent bodies to one of our meteor showers, but now we identified nine more, and perhaps as many as 15.
CAMS stands for Cameras for Allsky Meteor Surveillance. The project now has networks of cameras in nine countries, including Australia, Chile and Namibia. The thin trail of debris left behind by long-period comets can be hard to detect, but the CAMS network has approximately doubled the number of meteor showers known to come from this type of comet.
Interactive map of CAMS data
The worldwide cameras have pinpointed the locations that meteors appear to come from – known as the radiant – and enabled scientists to create an interactive map of the data. The meteors appear as colored dots on the map. Red denotes the fastest meteors and blue the slowest. White dots represent sporadic meteors that do not come from any specific shower. The black dots on the map are stars. You can change the date on the map to find what meteors were detected on a certain date. Jenniskens described the interactive map:
These are the shooting stars you see with the unaided eye. By tracing their approach direction, these maps show the sky and the universe around us in a very different light.
Comets are not the main source of debris that impacts with Earth. However, historically they have caused some of the biggest impact events due to their large size and fast speed. The new survey results allow these faint, long-distant comets from as far back as 4,000 years to be spotted via the meteors left behind. Jenniskens said:
This creates a situational awareness for potentially hazardous comets that were last in near-Earth orbit as far back as 2,000 BC.
CAMS data reveal long-period comets
The team of scientists analyzed their data to find something unexpected: Long-period comet meteor showers can last for many days. Jenniskens said:
This was a surprise to me. It probably means that these comets returned to the solar system many times in the past, while their orbits gradually changed over time.
The team also discovered that the most dispersed meteor showers show the highest fraction of small meteoroids. Jenniskens explained why this might be:
The most dispersed showers are probably the oldest ones. So, this could mean that the larger meteoroids fall apart into smaller meteoroids over time.
The team hopes to go even farther into the past with help from CAMS. Jenniskens explained:
In the future, with more observations, we may be able to detect fainter showers and trace the orbit of parent comets on even longer orbits.
Long-period Comet Thatcher and the Lyrids
Comet Thatcher, shown in the above mapping examples, is a previously known long-period comet that’s responsible for the Lyrid meteor shower. Thatcher returns to the sun every 415 years, with its next arrival in our vicinity scheduled for approximately 2283 A.D. When not in the inner solar system, Comet Thatcher journeys as far out as 110 astronomical units (AU) from the sun.
In contrast, Pluto is about 40 AU from the sun.
Bottom line: Scientists using a worldwide network of cameras are tracking meteors from long-period comets – as long as 4,000 years – to better predict showers and dangerous meteors.