Last week, while looking at some of the best images from the Cassini spacecraft, I commented on the fact that the smooth rings of Saturn are small, varied chunks of ice and rock when you get down to the smaller scales. Reflecting on that this morning, I was thinking about how observing objects in our universe at smaller scales gives new insight into the variety and complexity of natural phenomena. Not long after, I came across a story of a new interesting object in our own Solar System.
A new binary asteroid was discovered. This in itself isn’t too different or surprising, as astronomers have known about binary asteroids since 1993. What’s different about this one, named 288P, is that it’s the first binary asteroid that based on its behaviour can be classified as a comet.
Just over a year ago, 288P came close to Earth as it neared it’s closest approach to the Sun, allowing astronomers to take a close look at its structure as it flew by. They were surprised to find not one, but two asteroids about the same size, orbiting each other at a distance of about 100 Km. This is good news because it means the individual masses of the objects could be measured and calculated. But as the astronomers combed over their observations, they also found strong indications of sublimating ice, a comet-like behaviour that leads to comets having long icy tails.
This meant that 288P was also classified as a main belt comet, a comet that is part of the main asteroid belt between Mars and Jupiter. Main belt comets are important as they are relatively untouched in the billions of years since the solar system formed, and studying the few that exist give insights into how the solar system, and subsequently Earth, came to have water. This makes 288P an extremely important object to study.
After a bit of follow up study, it was found that 288P has likely only existed as a binary for about 5000 years, as a typical comet close to the Sun would lose all of it’s water over the billions of years between it’s formation and the present day. This means that it was likely a rocky body with its ice protected from the Sun a few meters below the surface, and then it broke apart into two pieces. The newly exposed ice could sublimate, creating the comet-like cloud around it. What a unique and fascinating history.
It’s the classic example of seeing an object from far away – like a comet – and classifying it based on comparisons to other comets that have been found. But once we look a bit closer, it was much different than a typical comet. It’s these stranger objects, the uncommon ones, that give the greatest test to our current scientific understanding. We know a current theory can explain a typical comet, but what about this strange new binary comet? If the theories can predict the most extreme and unique objects, they hold up. If they can’t, they need revision.
This is how science is done, and it’s why, as we develop the technology to more deeply observe, measure, and probe the world around us, we constantly test and revive scientific theories. This is also why our current theories are so good. They have been tested time and time again, and they’ve even been used to predict new observations that we haven’t made yet. It’s the reason that even though we call them ‘scientific theories,’ they are true facts. Bits and pieces may need revision as we discover new things, but the majority of core theories that explain the universe at the scale of human experience are accepted and unlikely to change.