When an asteroid approaches Earth, we have a rare opportunity to learn what it’s made of

Gravity calculations can provide abundant insight into a variety of phenomena. Everything from Einstein’s rings to the rocket equation depends at least in part on gravity. Now, a team of undergraduate students and faculty from MIT believe they have a new use for gravity calculations – understanding the internal density of asteroids.

The research came from a course offered at MIT known as “Essentials of Planetary Science,” which, like all good classes in a similar vein, focused at least in part on the formation of objects in the solar system. He also had a final project for the semester, which is so familiar to many students.

In this case, one of the undergraduate students in the class, Jack Dinsmore, who is now a graduate student at Stanford, wanted to answer a simple question with his final project—does an asteroid do anything when it just passes by Earth? After some preliminary modeling based on other equations taught in Planetary Science class, it turns out the answer is yes.

Details about the project caught the attention of Julien de Wit, the Planetary Science professor who taught the class. To complete his project, Dinsmore wrote code to model what happened to the orbital and rotational dynamics of an asteroid as it passed near Earth. According to his calculations, this was determined mainly by the shape, size and, most importantly, the density of the asteroid.

Density is critical in these calculations because it can help determine what asteroids are made of. In part this would be of interest to potential asteroid miners. But more importantly, it’s also useful to know if you want to divert one.

NASA recently did this successfully with the DART mission. However, many asteroids are “rubble piles” – essentially a bunch of rocks loosely held together by gravity. If you hit a probe on one of these, it certainly won’t make as much of an orbital change as it would if you hit a piece of solid metal.

So where you hit an asteroid and how dense it is above its surface can greatly affect the effectiveness of any potential redirect missions. There are some asteroids where this information could be incredibly useful – like Apophis, which, while not posing an immediate threat to Earth, is undoubtedly one in the medium to long term.

Apophis will also prove an excellent test of the theory of whether this modeling system will work to predict the shape and density of asteroids. It will have a close encounter with Earth in 2029, and Dinsmore and de Wit hope that interested astronomers, both amateur and professional, will collect enough data to compare with additional simulations they have developed for a wide variety of sizes. shapes and densities of asteroids.

This type of modeling is quite common in other fields – where scientists develop a series of models based on a variety of different quantities and determine which one is best for data collected on a real object. With this feedback, researchers should be able to work out what the interior of any asteroid would be like in a close encounter with Earth. All the more reason to keep an eye out for any near-Earth asteroids that might interest you.

Learn more:
MIT – Method for decoding asteroid interiors could help target asteroid diversion missions
Dinsmore & de Wit – Constraining asteroid interiors through close encounters
UT – Astronomers look ‘inside’ an asteroid for the first time
UT – An upcoming asteroid mission will be able to peer 100 meters below the surface

Lead Image:
Artist’s rendering of the recently completed DART mission to redirect an asteroid.
Credit – NASA / John Hopkins APL