Ice beyond our Solar System

The Sun, like other stars, was formed from a cloud of hydrogen and helium molecules and dust. The solar nebula should had an initial temperature of 2000 Kelvin. As it cooled, different elements condensed into ices and grains. Some of the gas condensed out to form giant planets surrounded by a rotating disk of material from which many rings emerged.

The rings of Saturn are a spectacular sight but such rings have recently been found around a smaller object. This discovery was made within the EU-funded project ISANDAL (Ice: Small and near, distant and large. Understanding planet formation through observation of solar-system minor bodies and extra-solar planets).

Observations from the La Silla Observatory and other sites in South America helped ISANDAL scientists discover that the remote asteroid Chariklo is surrounded by two dense and narrow rings. This Centaur object is the smallest object found to have rings and only the fifth body in our Solar System.

Another highlight was the discovery of an asteroid that behaves like a comet through the cameras on the European Space Agency (ESA)'s Rosetta mission. Scientists saw a tail typically seen in comets coming out of this asteroid. The shape of the tail could only be explained as the trail of debris from the collision of two asteroids.

By combining different sets of images captured from the ground and by the Rosetta spacecraft, a 3D picture of the tail was created. This line of material did not resemble what ISANDAL scientists would have expected if there was ongoing comet-like activity.

As a result, ISANDAL scientists became the coordinator of the ground-based observation campaign for the Rosetta mission. This spacecraft orbits up to 100 km from the nucleus of 67P/Churyumov-Gerasimenko. To see the whole comet with its tail, it was necessary to observe it from the ground.

Therefore, the research work of ISANDAL scientists continued with the worldwide network of telescopes RoboNet on call to monitor microlensing alerts for evidence of extrasolar planets. These robotically controlled telescopes contributed a vast amount of data revealing that small and icy planets are common.

With its many discoveries, the ISANDAL project has opened a new chapter in the quest for alien worlds beyond our solar system.