Research has revealed the complexity of the inside of an asteroid for the first time.
The research has helped to shed light on what happens when collisions occur in the Solar System and has provided clues on how planets form.
Using telescope facilities around the world, it has also found first evidence that asteroids can have a highly varied internal structure.
By making extremely precise measurements the team of astronomers, led by Dr Stephen Lowry of the University’s Centre for Astrophysics and Planetary Sciences, found that different parts of a near-Earth asteroid – called Itokawa – have different densities.
The team obtained telescope images from 2001 to 2013 and after applying very detailed analysis, Dr Lowry and colleagues measured the speed Itokawa spins and how its spin rate is changing over time. They combined these delicate observations with new theoretical work on how asteroids radiate heat. Along with knowledge of the asteroid’s shape, this provided the space scientists with a unique opportunity to explore its interior, revealing the complexity within its core and secrets about its formation.
The spin of an asteroid and other small bodies in space can be affected by sunlight. This phenomenon, known as the YORP effect, occurs when absorbed photons from the Sun are re-emitted from the surface of the object in the form of heat. When the shape of the asteroid is very irregular the heat is not radiated evenly and this creates a tiny, but continuous, torque on the body and changes its spin rate.
Dr Lowry’s team measured that the YORP effect was slowly accelerating the speed at which it spins. The change in rotation speed is tiny – a mere 45 milliseconds per year – and was far from expected. It can only be explained if Itokawa’s ‘bi-lobed’ or ‘peanut-like’ appearance, as seen by the Hayabusa spacecraft in 2005, is actually the result of two bodies of very different densities, that came together at some point in its ancient history.
This research is the first time that astronomers have found evidence for the highly-varied internal structure of asteroids. Up until now, asteroid interiors could only be inferred using rough overall-density measurements. This rare glimpse into the diverse innards of asteroid Itokawa has led to much speculation regarding its formation. One possibility is that its origins lie within the catastrophic collapse of a double asteroid, also known as a binary asteroid system.
This new ability to probe the interior of an asteroid – without the need for a visiting spacecraft with penetrating radar – is a significant step forward, and may unlock many secrets of asteroids in the future.
The research, published online in the journal Astronomy & Astrophysics, is titled: “The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up”.