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

Gravity calculations can provide many insights 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 MIT students and professors think they have a new use for gravitational calculations – understanding the internal density of asteroids.

The research stemmed from a class offered at MIT called Essentials of Planetary Science, which, like all good classes of a similar nature, focused at least in part on the formation of objects in the solar system. There was also a semester-limiting final project so familiar to many college students.

In this case, one of the students in the class, Jack Dinsmore, who is now a graduate student at Stanford, wanted his graduation project to answer a simple question – does an asteroid do anything just passing 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 professor of planetology who taught the class. To complete his project, Dinsmore wrote code to model what happened to an asteroid’s orbital and spin dynamics as it approached Earth. According to his calculations, this was mainly determined by the shape, size and above all the density of the asteroid.

Density is crucial in these calculations as it can help determine what asteroids are made of. Partly that would be interesting for potential asteroid miners. But more importantly, it’s also useful to know if you’re trying to distract one.

NASA successfully did this recently with the DART mission. Many asteroids, however, are “heaps of debris” — essentially a pile of rocks loosely held together by gravity. Slamming a probe into one of these certainly won’t cause as much of an orbital change as it would if you hit a section of solid metal.

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

Apophis will also prove to be an excellent test for the theory of whether this model 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 interested astronomers, both amateur and professional, will collect enough data on it to be able to compare it with additional simulations they run for a variety of sizes have developed. Asteroid shapes and densities.

This type of modeling is widespread in other fields – where scientists develop a range of models based on different sizes and determine which best fits the data collected on an actual object. With this feedback, researchers should be able to work out what the interior of an asteroid would look like in a close encounter with Earth. All the more reason to keep an eye on near-Earth asteroids that might be of interest.

Learn more:
MIT – Asteroid interior decoding method could help target asteroid deflection missions
Dinsmore & de Wit – Restricting the interior of asteroids through close encounters
UT – Astronomers look “inside” an asteroid for the first time
UT – An upcoming asteroid mission will be able to see 100 meters below the surface

main picture:
Artist’s rendering of the recently completed DART mission to divert an asteroid.
Credit – NASA/John Hopkins APL