Last September, NASA intentionally crashed a spacecraft into Dimorphos, a 160-meter-wide space rock orbiting a larger asteroid named Didymos. The goal of the mission, called DART (Double Asteroid Redirection Test), was to demonstrate humanity’s ability to move dangerous asteroids away from Earth. That part of the mission was successful beyond all expectations. But now scientists are also learning more about the origins of her two asteroids. the study Investigations conducted after the DART collision revealed that Dimorphos was made of the same material as Didymos, and that the pair of asteroids likely originated from a single object.
DART’s impact blew a large cloud of debris from Dimorphos. The initial cloud, consisting of particulate dust and gaseous material containing trace amounts of sodium and potassium, quickly expanded and moved away from the system. It dispersed within minutes. But a second cloud of heavier debris persisted for months. Using NASA’s 3-meter IRTF telescope in Hawaii, the researchers observed this secondary debris cloud for a week after the impact, watching it evolve and spread. What they discovered was that the spectroscopic signature of the Dimorphos debris matched that of Didymos before the collision.
That is, both asteroids were made of the same material: silicates (compounds of silicon and oxygen).
Before the DART collision, only 5% of the light from the system came from dimorphos. It has been significantly outperformed by its larger partner Didymos, making it incredibly difficult to obtain clear spectral observations of this small asteroid. But after the collision, the entire system became significantly brighter, with the largest piece of debris accounting for more than 64% of the light reaching Earth-based telescopes from the system. This bright glow has made it possible to study the composition of Dimorphos’ debris cloud.
The researchers found that the solar wind quickly dislodged the small particles, and the debris was mostly made up of heavier materials and larger rocks. This seems to be in contrast to the surface material of Didymus. Researchers predict that the material on Didymos’ surface is made up mostly of small particles. European Space Agency’s HERA mission You can check it out.
So if Didymos and Dimorphos are made of the same material, how did they become separate asteroids?
The leading theory is called the “rotating fracture” model.
“Asteroids smaller than a few tens of kilometers in diameter can be destroyed by high-speed rotation, which puts tension on their weak internal strength. As a result, ejected material enters orbit and eventually accumulates on the satellite. ”explain the researchers.
Didymos, a small, fast-spinning asteroid, is a good candidate for this model. It is almost certainly releasing particles into orbit around it. It also has a shape common to binary asteroids, that is, a spherical shape with a bulge around the equator. This geometry only strengthens the rationale for the rotating fracture model.
With new data collected after the DART impact, this case is largely closed. The fact that the spectral features are identical in Didymos and Dimorphos strongly suggests that they originated as a single object. Over time, this fast-spinning asteroid spewed material into orbit, which clumped together to form a small moon called Dimorphos. It remained there for centuries until DART interrupted its course and gave it a new trajectory (and gave us a unique opportunity to study it).
learn more:
Polihook et al. “Near-infrared spectral observations of the Didymos system — DART daily evolution before and after the collision shows that Dimorpho originates from Didymos” ArXiv preprint.
