Julia de León
A defender of the planet
Protecting our planet is in good hands, specifically in the hands of Julia de León. Asteroids threaten the Earth, but this astronomist and winner of the 2025 Mujeres a Seguir Award in the Science category dismisses scaremongering because she knows how hard the community works to identify these objects and develop defence techniques straight out of a science-fiction film.
The astronomist Julia de León (Santa Cruz de Tenerife, 1977) carries a great responsibility: protecting our planet. As the Spanish representative of the Planetary Defence Office at the European Space Agency, her work consists of studying and monitoring the asteroids that threaten the Earth. She does so from the Institute of Astrophysics of the Canary Islands (IAC) using the Gran Telescopio de Canarias, located in La Palma. “It’s a very important telescope and we should be proud,” she declares. Last year, she was asked to monitor the trajectory of asteroid 2024 YR4, described as “potentially dangerous”—something which happens when the likelihood of impact is over 1%—after the UN's planetary defence protocol was activated for the first time in history. “They literally pulled me out of bed,” remembers Julia who, despite everything, remains humble: “I make my small contribution, but this is the work of many researchers perfectly coordinated by NASA and ESA.” A recent winner of the Mujeres a Seguir (MAS) Award in the Science category—sponsored by Iberia—, with her commitment to sharing the facts, Julia also defends us against all those science naysayers. Listening to her—or reading her words—is a gift.
Where does your interest in science come from?
It comes from my passion for maths. It has always fascinated me. At school, I already thought solving problems of real life with numbers and formulas was magic. Even though I almost signed up to study Architecture because I was good at technical drawing, I ended up choosing Physics because it’s the ideal foundation if you want to work in science. I came to astronomy because it’s the best specialisation that can be studied in the Canary Islands, where we have two great observatories, the one in Teide (Tenerife) and in Roque de los Muchachos (La Palma).
Your work consists of monitoring asteroids. Is it as fascinating as it sounds?
I’d say yes, but my perspective is slightly biased (laughs). At the end of my studies, I worked for ESA in a different field, that of space debris. My job was observing the sky looking for those fragments, but I also started noticing the asteroids. I wrote my thesis on the composition of near-Earth asteroids. My research led me to the topic of spacecrafts and the exploration missions to characterise those objects. That’s how I specialised in potentially dangerous objects and planetary defence.
“Last year, after the UN planetary defence protocol was activated, I was asked to observe asteroid 2024 YR4, and it was very exhilarating”
When you receive a warning that an asteroid is heading towards the Earth and you are asked to study its trajectory, how do you feel?
The spark of research is ignited. It’s an adrenaline rush. You have to react quickly and it’s a bit nuts, but it’s worth it because it is pure science. Since I manage a research group, most of my time is also spent dealing with bureaucracy and that’s dull. When Last year, after the UN planetary defence protocol was activated, I was asked to observe asteroid 2024 YR4, and it was very exhilarating. We had to follow it minute by minute, incorporate our observations, redo the calculations and adjust the probabilities.
Is it important to raise awareness about the risks without resorting to scaremongering?
That’s right. Whether more or less catastrophic, it is an event that could happen. Fortunately, larger objects—those over a kilometre in size—are scarcer and that is why they impact Earth every so often. Their location is also perfectly defined. We have registered many observations of them and can precisely predict where they will be in the future. None have a high probability of impact. Smaller asteroids, those under 50 metres, are not a problem either because the atmosphere usually breaks them up or burns them. Those measuring between 50 metres and one kilometre are no laughing matter and we work on them more. The first step is identifying them because, according to our estimations, we are missing more than half. The second is developing defence techniques, methods that can allow us to avoid their collision with the Earth.
In fact, you took part in the DART mission, which managed to deflect an asteroid with a kinetic impactor. Are we ready?
Scientists need data to work with, and the idea is to perform tests to obtain them. The kinetic impactor technique consists of making a spacecraft collide with one of these objects to modify its trajectory slightly. Thanks to this mission, we start to have those data: how long it takes to build the spacecraft, how long the journey to the asteroid takes, how much we were able to modify its trajectory… The second phase of this project will be called Hera, and I will also take part. In fact, I’m responsible for one of the instruments onboard the unmanned spacecraft and what we are going to do is reach the asteroid—in October 2026—DART impacted against and observe it closely to collect more data.
Leaving aside the risks, why is it worth studying asteroids?
When I give talks, I always say that asteroids are like the leftovers from a construction site. That is, the planets are the houses, and the asteroids are the bricks left over from building them. They are rocks that did not manage to become part of the planets during the generation of our solar system, and, for this reason, they preserve many of their original properties. Analysing them provides information about the conditions that existed at that time. It is important to study the leftovers of our protoplanetary disc to understand how planets form in other stars.
“I always say that asteroids are like the leftovers from a construction site. That is, the planets are the houses, and the asteroids are the bricks left over from building them”
“Practicing and talking about science during these times, where critical thinking is an endangered species, is a challenge,” you assured us during the MAS Awards. Are you worried about the tendency to undervalue scientific knowledge?
It concerns me, but above all, it bothers me immensely. We are at a time when humans have access to massive amounts of information and, paradoxically, it is when we are becoming the most ignorant. I have a daughter, and I always tell her to check information, to question it constantly and learn how to identify reliable sources. Developing critical thinking is essential. I hate when fake news and theories with no scientific basis circulate in my field. Spending time and efforts disproving them is exhausting, but we have to do it, especially among young people. I give talks at high schools because that is where I can still influence their brains a little. I do what I can within my small field of action.
You have the largest infrared optical telescope in the world at your disposal: the Gran Telescopio Canarias. Is it a privilege?
As a researcher at IAC, I use that telescope often and I think it needs more publicity. It’s wonderful, and not just because of the data it provides. Building a telescope 10.4 metres in diameter was a major feat of engineering. Now they are building an even larger one in Chile—the ELT, measuring almost 40 metres in diameter—and their engineers came here to train and learn from our experience.
“I hate when fake news and theories with no scientific basis circulate in my field. Spending time and efforts disproving them is exhausting, but we have to do it”
How would you awaken the curiosity of young women and encourage them to join the female talent pool in science?
I’d tell them to believe in themselves, that they can do it. Being a female scientist is incredible and we’re the oddballs (laughs). I’m concerned that we give up the fight… From an early age, girls are given the subtle and perverse message that women are not brilliant, but hardworking. From that moment, they are conditioned to not choose careers in STEM. When I go to high schools, I can feel that self-perception among girls. As a society, we need to change this and soon because when they are in high school and have to choose what to specialise in, it’s already too late. Surprisingly, there are quite a few women in my field and that makes me really happy. We should perform a study to find out why this happens.
What is having an asteroid named after you like? We’re talking about (8324) Juliadeleon.
It’s absolutely geeky but so cool. Since there are so many asteroids, the International Astronomical Union (IAU) has a committee dedicated to naming them. When your colleagues consider that you have made a significant contribution to your field, they can nominate you and the committee has the final say. They named it after me quite a while ago and, even though it may seem silly, it made me really excited.
