By Prashansa Srivastava
Have you ever considered why every planet we know about is shaped like a sphere? Why not an hourglass, or a cuboid? While those, and most other shapes, would break the laws of physics, there’s one unusual planet form that wouldn’t – a doughnut. This is exactly what planetary scientists Simon Lock at Harvard University and Sarah Stewart at the University of California are proposing.
According to them, a gigantic, rotating, doughnut-shaped mass of hot, vaporised rock known as a synestia is formed as planet-sized objects crash into each other. The knowledge of such structures can impact our understanding of the origin of the moon and the history of the shape of Earth itself.
Research behind the phenomenon
We know that violent galactic collisions in the earliest phase of the universe produced molten masses that eventually cooled to form what we call planets. Locke and Stewart are studying the results of such collisions but between two spinning objects.
Think of an ice skater – she slows her rate of spinning if she extends her arms and spins faster by tucking them in. Her angular momentum while rotating remains the same. When two spinning ice skaters catch hold of each other, their angular momenta add up and the total angular momentum remains unchanged. When these ice-skaters or Earth-sized rocky planets collide with other large objects, their immense angular momentum and high energy can lead to the creation of completely new structures.
Formation of a synestia
In a spinning, solid sphere, every point from the core to the surface of the sphere rotates at the same rate. Massive collisions, however, can cause the planet’s material to become molten or gaseous and expand in volume. If it gains enough momentum and reaches a large enough size, parts of the object overtake the velocity needed to keep a satellite in orbit, and that’s when it forms a synestia – a doughnut shaped planetary object.
Synestia comes from Greek with ‘syn’ meaning ‘together’ and ‘Estia,’ being a Greek goddess of architecture and structures. Colossal impacts between larger and hotter objects such as stars or gaseous planets could lead to longer lasting synestias.
How it impacts our understanding of the universe
Most planetary collisions formed synestia-like structures at some point in time. The Earth was probably a synestia itself, suggested Stewart, lasting for about a hundred years before losing enough heat and condensing into a solid object. This structure also provides a framework for lunar formation. The leading explanation for the moon’s origin suggests that the moon was formed from the debris of a collision between planetary objects. It is possible that such an impact could have instead formed a synestia from which the Earth and Moon both condensed.
Synestias have not yet been observed directly, but with our desire to explore and discover the cosmos, they might soon be found in the immensity of other solar systems alongside rocky planets and gas giants.
Featured image credits: Daily Mail