Trillions of comets have been found in other star systems: why this discovery matters to us (photos included).

Astronomers have discovered comet rings orbiting stars in 74 star systems. This finding not only indicates the existence of trillions of icy exocomets, which are comets outside our Solar System, but also serves as a source of most of the water in these stellar systems. The study has been published in the journal Astronomy and Astrophysics, as reported by Space.

Astronomers identified objects known as planetesimal belts using the ALMA Submillimeter Array radio telescopes. These belts are located at great distances from their stars in 74 star systems within 500 light-years from us. The light detected by the radio telescopes comes from a vast number of pebbles measuring just a few millimeters, which were ejected by large comets, each about 1 km in size, during collisions over an extended period. Such planetesimal or exocomet belts have been found in at least 20% of the star systems in our galaxy.

In the Solar System, the equivalent of these objects is the Kuiper Belt, which contains millions of icy bodies, some of which pass through the inner Solar System as comets. The Kuiper Belt extends from 30 to 55 astronomical units from the Sun. One astronomical unit is approximately 150 million km or the average distance from Earth to our star.

Previously, astronomers had detected exocomets and planetesimal belts in other star systems, but they had never observed such a vast number of comets.

All 74 planetesimal belts vary in age; some formed relatively recently, while others are billions of years old. They are located at distances ranging from tens to hundreds of astronomical units from their stars. Despite the differences among them, the belts exhibit some patterns.

The study revealed that the number of pebbles decreases in older star systems, as the number of massive exocomets diminishes. Furthermore, it was found that the reduction in pebbles occurs more rapidly if the belt is closer to the star. Astronomers also obtained indirect evidence suggesting that these belts likely contain yet-invisible objects ranging from 140 kilometers to the size of the Moon.

Astronomers discovered that all 74 belts are significantly larger than expected and extend much farther from their stars. Some resemble the Kuiper Belt, but most are much wider.

This research provides astronomers with more data on how these icy belts form and evolve, as well as the role they play in planetary evolution. For instance, astronomers can determine whether comets deliver water to planets that are closer to their stars. Water is known to be essential for life, and it is possible that comets in the Solar System once delivered water to Earth.

Comparing planetesimal belts in other star systems with the Kuiper Belt will help unveil the secrets of this frozen region of space in the Solar System.