Tomás Alonso started in astronomy as an amateur, calculating orbits at age 12. Now this researcher at the Observatorio Astronómico Nacional is collaborating in the search for Planet 9
Tomás Alonso began calculating orbits of planets and asteroids at age 12, when he was still an amateur child saving his allowance to buy a telescope. Decades later, after four years at the European Space Agency and a career in radio astronomy, this astronomer has decided to return to his origins: optical astronomy and the passion for exploring the unknown. He now collaborates with Light Bridges on projects ranging from observing mutual events of Saturn’s satellites to searching for the elusive Planet 9 through the PLANETIX25 project, targeting that hypothetical ice giant that could be orbiting at more than 1000 times the Earth-Sun distance. In this interview, Alonso, currently employed at the Observatorio Astronómico Nacional in Madrid, tells us about his method for “cornering” Planet 9, the importance of taking risks in science, and why he decided to leave the laboratories to also dedicate himself to outreach.
How did your collaboration with Light Bridges come about?
I had just left the European Space Agency, where I had worked for 4 years, and was going to return to the observatory. I was in a transition period and I was interested in doing optical astronomy and working at Teide. I’d like to leave radio astronomy a bit behind and get into optical astronomy again.
At ESA I had a publication on numerical integration of orbits of asteroids and comets. I thought this type of work could be interesting for Light Bridges because they were making observations of near-Earth asteroids and searching for Planet 9.
What projects are you currently working on?
The idea is to start observing mutual events of Saturn’s satellites, which occur every 15 years. Since I have a lot of experience doing ephemeris and somewhat unusual calculations, the idea is to observe some of those events. We’re going to propose a series of observations with the TST that might help to define and improve the orbits of the satellites.
Tell us about your strategy for trying to find the whereabouts of Planet 9.
I had done some calculation attempts to try to define where that object or some other trans-Neptunian object of certain mass could be.
Basically the problem is that there are relatively few objects discovered that are sufficiently far away. If Planet 9 exists, it’s most likely at a tremendous distance, over 1000 astronomical units (AU), more than 1000 times the Earth-Sun distance. Some objects have been discovered at that distance, but most are around 100 AU or a bit more. Trying to derive the possible presence of such a distant object with what is already known is practically impossible because there’s no clue, it could be anywhere.
“Trying to derive the possible presence of such a distant object with what is already known is practically impossible because there’s no clue, it could be anywhere”
What I did was look at the most distant objects that have been discovered, around 500 astronomical units away. Within what constitutes a group, because there’s one at 1000 AU, but it’s isolated. I tried to study how they’re distributed, because normally when there’s a sufficiently massive object it tends to alter the orbits of other objects. The problem is that an object at 1000 AU is going to influence very little a group of objects at 500 because there’s so much distance in between.
So, how does your approach work exactly?
I took the most distant objects, beyond 500 AU, and looked at how they were distributed. The problem is that depending on whether an object is a bit closer or farther, there can be a very large difference in the time it takes to orbit around the Sun.
I looked for objects with quite eccentric orbits that had their aphelion, their maximum distance from the Sun, around 800 or 1000 AU, where this Planet 9 could be. Then I looked for objects that could have a more or less circular orbit, not so eccentric, which is what would be expected of a planet.
The idea is that this planet never gets close to these objects with such an eccentric orbit. That is, when one of these objects orbiting very elliptically is very far away, hypothetically close to that planet, the planet isn’t there, but is at another point in its orbit. This happens, for example, between Neptune and Pluto: when Pluto is at a distance similar to Neptune’s, Neptune isn’t there, so it doesn’t alter its orbit.
If I find enough objects that tell me that when an object was very far away 1000 or 5000 years ago, Planet 9 wasn’t there, I would conclude it’s not in that zone because it would have already altered that object’s orbit. So, if it’s not there, not here and not there, where can it be?
And what conclusions have you reached so far?
I got two or three promising zones in the sky. One of them is right in the Milky Way. Since practically the entire sky has already been observed with a fairly deep brightness limit, I thought that zone could be promising because if there’s a planet there it would be logical that it hasn’t been detected: there’s a lot of confusion from faint sources in the Milky Way, there are many background stars.
The problem is that many observations would need to be made, it’s looking for a needle in a haystack. It requires a lot of observation time and it’s really very difficult to find it. If an object that could be a planet were there, it might take centuries to leave that zone of the sky.
Have you already made observations in those zones?
We made some observations in one of those promising zones. There was some difficulty to define the coordinates in the image and I had to review that, but I did find moving objects in the image. Maybe some could be unknown asteroids, although they wouldn’t be trans-Neptunian objects because they moved quite a bit more fast. I would need some time to correct the astrometry of the images and see what can be detected.
It’s not so much about searching for Planet 9 as saying “well, if it exists it has to be…” The problem is that we narrow down the possibilities to two or three zones of the sky that are large. One is quite empty of stars, another is a zone somewhat in the Milky Way of the winter sky that’s not so populated, and the other is right in the Milky Way, a zone where there are already known trans-Neptunian objects but maybe there could be some surprises there.
Do you think telescopes in the Canary Islands can compete with the ones at Vera C. Rubin or Mauna Kea?
Now there are very efficient telescopes doing surveys like the LSST. If it’s not detected by us right away, that telescope will probably detect it. And if that telescope doesn’t detect it, surely we won’t either. It’s very complicated to think we can get ahead of people who have such resources and observation time, who are observing the entire visible sky every night with great resources.
“Light Bridges’ telescopes allow you to do somewhat riskier things that maybe in traditional observatories you couldn’t”
The main advantage is that Light Bridges’ telescopes allow you to do somewhat riskier things that maybe in traditional observatories you couldn’t. In a normal telescope they wouldn’t let you spend the whole night looking at something so speculative, but here this type of situation always allows you to get ahead of others.
Astronomy, as every other scientific discipline, is focused on specialization, but you still think that a more open approach is important.
Sometimes in science it happens that you’re very enclosed, very cornered, doing something very specific for many years and you become an expert who knows almost more than anyone about a small handful of objects in the sky, but only about that. Sometimes there are many astronomers who don’t even know where those particular objects are in the sky. They know everything about that object, but they wouldn’t know how to find it in the night sky.
I have a broader vision. I don’t like the idea of being enclosed, stabled, always studying the same thing with increasingly powerful telescopes, the same objects with increasing detail. From time to time you have to get out of there and do something different and maybe riskier, that you know almost certainly won’t work out. Surely in an entire astronomer’s career nothing will come out of that, but just the act of trying takes you out of being so enclosed. The universe is very vast and it’s worth exploring other things.
How did your passion for astronomy begin?
I started in astronomy as an amateur, I thought that was normal, and when you enter the professional field you see that most astronomers weren’t amateurs as children!
First I got into programming, at age 9. Then, at 12, I was already calculating orbits of planets, asteroids and such. I started reading a lot of books from then on, saving my allowance for a telescope. I thought that was normal for an astronomer, but you realize it’s the opposite: that an amateur becoming a professional doesn’t happen very often.
You also dedicate yourself a lot to outreach, right?
Yes, I’m quite active doing outreach. Years ago it was strange for a scientist to dedicate time and resources to outreach, but nowadays it is also given more importance.
Now, for example, I think that if I dedicated myself to doing papers, to really doing research, well, maybe each year I’d do one paper. Maybe it would be a paper that wouldn’t be especially outstanding in relation to the work done at the observatory, but in a year I can also do many individual things: every week I do either some graphics or videos related to the eclipses that will occur starting next year, or a celestial atlas, or an ephemeris server that I made myself that gives information and graphics of the night sky.
“I thought that was normal for an astronomer, but you realize it’s the opposite: that an amateur becoming a professional doesn’t happen very often”
These are works that I can finish in a year. At the same time I do one paper that would be one more of the many done at my research center, I could do quite a few works that maybe would be well received by many more people.
What other projects are you working on now?
There are collaborations, for example, with Astronomía magazine, where I do a section describing the sky each month. It’s a more open vision of dedicating resources and time to outreach materials, more possibilities to contribute to astronomy in different ways.
For next year, for example, I’m working on that with graphics and videos of the eclipses that will be published on the OAN website where I have published several things already, such as the celestial atlas. Now we want to review or improve the eclipse graphics for next year.
