Understanding Planetary Defense: Insights from Professor Alan Fitzsimmons

By Ciarán Mallon

Just a month ago the HERA mission launched from Cape Canaveral, a mission years in the making which Queen’s own Professor Alan Fitzsimmons has been working on since the start. Professor Fitzsimmons was kind enough to sit down for an interview with The Gown to talk about the mission, as well as his career.

Professor Fitzsimmons is an expert in the field of asteroid and cometary physics, and a professor at QUB, working in the Astrophysics Research Centre. Like many who are interested in astronomy, he has had a passion for the topic from a young age. Fitzsimmons attributes part of his interest from a young age to simply looking through a friend’s telescope, “I looked at the moon…that was it. I went, this is cool… I want to learn more about this!” Having done an undergrad in physics and astronomy at the University of Sussex and then receiving a studentship for his PhD in cometary physics in Leicester, he went on to a post-doc position researching stars in the milky way and other galaxies. After some time Fitzsimmons moved to Belfast to work at Queen’s with the intent to ultimately go back to focusing on research “… I was gonna go back and be a full time planetary scientist… and that’s what I’ve been doing ever since.”

NASA’s DART (Double Asteroid Redirection Test) was a mission that was launched in November of 2021, and was the first practical step towards testing planetary defence by the redirection of an asteroid. This mission was aimed to change the orbit of an asteroid, called Dimorphos, around its parent asteroid Didymos.

The craft was a ‘kinetic impactor’, meaning its method of redirection was to crash into Dimorphos at a very high speed, imparting a large amount of kinetic energy onto the asteroid. On the 26th of September 2022 DART impacted Dimorphos, shortening its orbit around Didymos of 11 hours and 55 minutes by 32 minutes. [1]

The follow up mission to DART is ESA’s HERA mission, which launched on the 7th of October 2024. HERA is due to rendezvous with Dimorphos in December of 2026, and its primary job is to analyse the effect DART had on the asteroid; this includes measuring the crater made by DART and quantifying how much momentum was transferred [2].

Professor Fitzsimmons has been involved with planetary defence for 20 years, initially having written a couple papers on near earth asteroids and comets, and was invited by ESA to sit on a panel about the risk of asteroids and comets hitting the earth, “It was really those meetings from which eventually the NASA DART and ESA HERA missions grew out of.”

Kinetic impact, and therefore DART, was the most feasible way of testing asteroid redirection currently. The team hoped for a change in orbit of at least 7 minutes, this was exceeded by the actual 32 minute change in the orbit, “…it was within 24/48 hours of the impact we saw the evidence that: Wow! This thing really did move.” With regards to this success, Professor Fitzsimmons affirms that this experiment is not fully complete and is only half way through, “… we need to know exactly what happened to the moon [Dimorphos]. We need to know where the energy went… So we could apply that technique to other asteroids… that’s why we’re sending the HERA mission.” Fitzsimmons ensures that it is, however, certainly the beginning of an effective planetary defence program.

Now, Professor Fitzsimmons was at mission control for the launch of the HERA mission, and the crucial part of this launch, aside from everything going well on initial take-off, was establishing communication with HERA after it had separated from the rocket, “…we really needed that communication to happen, and that was the longest minute or two I’ve experienced in a long time. But it happened, so that was really good!”

One of the standout moments of the launch was the incredible image showing HERA separating from the Falcon 9 rocket it launched on with the crescent earth in the background. An unexpected shot that many of the team were really happy to see, “…I still don’t know if that was planned or not, but we were all pretty impressed by it.”

So far with HERA, everything is on track. The craft’s first deep space manoeuvre is to take place in November. The next big event for HERA will be next March, when it is due to use a gravitational assist about Mars to put it on a better orbit about the sun so it can rendezvous with the asteroid system. During this, the craft will make some measurements of Deimos, one of Mars’ two moons. Looking forward to HERA meeting up with the asteroid system, Fitzsimmons says that some of the exciting measurements that will be made include learning how these asteroids were formed. HERA will be the first mission to measure the interior structure of an asteroid, using the Juventas Cubesat. The majority of the evidence points to Dimorphos being a ‘rubble pile’ asteroid all the way through. However the exciting prospect of any experiment is the unexpected being the truth, “Science doesn’t go, ‘Oh no! We were wrong.’ Science says, ‘Oh! We were wrong, brilliant! We’ve found out something we didn’t know before about the universe’… You are trying to expand the sum knowledge of humanity.” This sums up exactly what many people find thrilling about science, and in particular astrophysics. That forefront of knowledge is always expanding, and with enough work anyone can be a part of it.

At the end of the interview, Professor Fitzsimmons offered some insightful comments for any students with a long career ahead of them. One major component of a great career is simply following what you’re interested in, and making it a work of passion, “If you are interested in it enough to work at it and study it, then you are giving yourself the best chance to get somewhere where you’ll be happy to be in future years!… You do the homeworks, you try and learn the stuff you are given, and you just try to know as much as possible. That’s how you end up flying around the solar system.”

[1] Bardan, Roxana. 2022. NASA Confirms DART Mission Impact Changed Asteroid’s Motion in Space. NASA. https://www.nasa.gov/news-release/nasa-confirms-dart-mission-impact-changed-asteroids-motion-in-space/

[2] Michel, Patrick, et al. 2022. “The ESA Hera Mission: Detailed Characterization of the DART Impact Outcome and of the Binary Asteroid (65803) Didymos”. The Planetary Science Journal. 3: 160