An artist's illustration of the Voyager 1 probe heading towards the Oort Cloud. (Image credit: Science Photo Library/Alamy Stock Photo)
A new study suggests that the Oort cloud – a mysterious shell of icy objects at the edge of the solar system – may have a pair of spiral arms, making it look like a miniature galaxy.
The exact shape of the Oort cloud and the influence of external forces on it have remained a mystery until now. Now, researchers have developed a new model that suggests the Oort cloud's internal structure may look like a spiral disk. They published their results on February 16 on the preprint server arXiv, meaning the work has not yet been peer-reviewed.
The Oort Cloud arose as the unused remains of the giant planets of the Solar System (Jupiter, Neptune, Uranus, and Saturn) that formed 4.6 billion years ago. Some of these remnants are so large that they can be considered dwarf planets.
As these planets began orbiting the Sun, their motions ejected excess material well beyond Pluto's orbit, where they remain today. The inner edge of the Oort Cloud is approximately 2,000 to 5,000 astronomical units from the Sun, and its outer edge is between 10,000 and 100,000 AU. (One AU is about 93 million miles, or 150 million kilometers, the average distance from Earth to the Sun.)
This means that even at its current speed of about a million miles (1.6 million kilometers) per day, NASA's Voyager 1 spacecraft will not reach the Oort Cloud for 300 years and will not leave it for another 300,000 years.
This enormous distance means that the objects in the cloud are too small and faint — and moving too slowly — to be directly observed, even with the most powerful telescopes. Most of our evidence comes from long-period comets — “snowballs” of ice and dust flung out of the cloud into orbit around the Sun by gravitational perturbations.
Spirals within spirals?
The Oort Cloud and its spiral arms.
To better understand what the Oort cloud might look like, the scientists behind the new study used data on comet orbits and gravitational forces both inside and outside our solar system to build a model of the Oort cloud's structure.
A key aspect to understanding the shape of the Oort cloud is the “galactic tide” – the pull created by the stars
Sourse: www.livescience.com
