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New AE professor predicts asteroid trajectories

5/5/2021

Debra Levey Larson

Siegfried Eggl
Siegfried Eggl

How to prevent collisions of asteroids with the Earth is just one of the research problems that fascinates Siegfried Eggl, who joined the faculty in the Department of Aerospace Engineering earlier this year.

Eggl is on NASA’s scientific investigation team for the Double Asteroid Redirection Test mission (DART), which, he says, plans to smash a spacecraft into asteroid. Its goal is to alter the asteroid’s orbit in a controlled manner so as to learn how to protect the Earth from potentially catastrophic impacts in the future. While Eggl was at the Jet Propulsion Laboratory, his team was asked to review whether DART would unintentionally create safety concerns for the planet. The good news is, according to the preliminary study, it won’t.  

“Most asteroids are like piles of rubble in space. They are held together by very little gravity and some electrostatic forces. In order to change its orbit by smashing a spacecraft into it, you have impart a powerful impact in a controlled way, but not destroy it. If it’s destroyed, all of the debris will form along the trajectory and that could cause some of it to impact the Earth,” Eggl said. “My role is to predict where the DART mission will push the asteroid with respect to the Earth.”

Schematic of the DART mission shows the impact on the moonlet of asteroid (65803) Didymos. Post-impact observations from Earth-based optical telescopes and planetary radar would, in turn, measure the change in the moonlet’s orbit about the parent body. Credits: NASA/Johns Hopkins Applied Physics Lab
Schematic of the DART mission shows the impact on the moonlet of asteroid (65803) Didymos. Post-impact observations from Earth-based optical telescopes and planetary radar would, in turn, measure the change in the moonlet's orbit about the parent body. Credits: NASA/Johns Hopkins Applied Physics Lab

Eggl said DART will launch in November of this year and is scheduled to smash into Dimorphos, a small satellite of the asteroid (65803) Didymos, in 2022, when it is fairly close to the Earth, a few times further away than our moon.

“We looked at the asteroid’s trajectory over the next hundred years,” he said. “It will come close to the Earth roughly every 20 years. NASA is very cautious and wants this kind of study for every perimeter of the mission. It’s a very nonlinear system with small changes, so you have to investigate case by case.”

Eggl said NASA keeps a database of all asteroid position measurements from the past, but for the vast majority of newly discovered asteroids, only their positions on the sky at a given date is known, without the distance, so there is some information lacking.

“It causes uncertainties in the position,” he said. “If we knew precisely where all the asteroids are, then it's not a big problem. We can just propagate the orbit and be done. But that uncertainty envelope makes it complicated. Additionally, we have to take into account not only general relativity but also how solar radiation influences the asteroid orbit. The fact that the Earth is a little deformed means the asteroid is deflected away from the Earth in a slightly different way every time it comes close. The work leads to very delicate equations and their solution requires a lot of computational power.”

In addition to his work predicting asteroid trajectories, Eggl is also part of a large effort to find asteroids.

“Right now, we only know a small fraction of all the asteroids that can actually cause harm to the Earth, the really big ones,” Eggl said. “We know very little about the smaller ones that are still large enough to devastate cities or even wipe out an entire state, so finding those is another research area of mine.”

Twilight photo of Rubin Observatory taken April 2021 in Cerro Pachón, Chile. Credit: Rubin Obs/NSF/AURA
Twilight photo of Rubin Observatory taken April 2021 in Cerro Pachón, Chile. Credit: Rubin Obs/NSF/AURA

This area of his research is with the Vera C. Rubin Observatory, which is currently being built in Chile. It will conduct a sky survey for 10 years, beginning in 2023.

“It will observe the entire available sky every three nights in a way that will be very conducive to finding asteroids,” Eggl said. “It is a wide-field reflecting telescope with an 8.4-meter primary mirror, so it’s really big. Creating a census of the Solar System is one of its main scientific objectives. My team is directly responsible for finding asteroids.”

Eggl admits that some of his work seems like astronomy. “It involves a lot of astronomy, but it's also planetary defense because you can't defend yourself against what you don't know is out there.”