A large number of bands of exocomets orbiting 74 nearby stars and their structure have been captured for the first time by astrophysicists, led by a team from Trinity College Dublin University.

The REASONS study, published in the journal Astronomy and Astrophysics, marks a major milestone in the study of exocluster belts, as their images and analyses reveal the location of the tiny stones inside them and thus the exocomets. Typically, they are located at a distance of tens to hundreds of astronomical au units (the distance from Earth to the Sun) from their central star.

In these regions, the temperature is so low (-250 to -150 degrees Celsius) that most compounds, including water, are frozen in these exocomets. So what astrophysicists are observing is where the ice reservoirs of planetary systems are located, and this project is the first to reveal the structure of these zones for a large sample of 74 exoplanetary systems.

The study used the Atacama Large Millimeter/submillimeter Array (ALMA) and Submillimeter Array (SMA) radio telescope arrays. Both observe electromagnetic radiation at millimeter and submillimeter wavelengths.

“Exocomets are rocks and ice at least 1 kilometer in size that collide within these bands to create the rocks we observe with the ALMA and SMA telescopes. Extracometric belts are found in at least 20 percent of planetary systems, including our own Solar System,” says Luca Matra, associate professor at Trinity’s School of Physics and lead author of the research.

He points out that “the power of a large study like REASONS is in revealing properties and trends on a broad scale. For example, it confirmed that the number of stones decreases for older planetary systems as belts are depleted by larger colliding exocomets, but showed for the first time that this decrease in stones is faster if the belt is closer to the central star. It also showed indirectly – through the vertical thickness of the belts – that there are probably invisible objects in these belts up to 140 km or the size of the Moon.”