How do you introduce yourself, scientifically?
I generally say that I’m an astronomer. More specifically, I’m an exoplanet astronomer, meaning I study planets that exist around other stars. In our solar system, all the planets orbit the Sun. I’m looking at planets in other stellar systems, orbiting stars much further away than the Sun.
What are the implications or broader impacts of your work?
This is really science for the sake of science. I think people have this idea that we’ll be able to go live on some of these exoplanets one day, but that’s not realistic, and that’s why it is so important to take care of Earth! In my work, we are trying to get an idea of what the general exoplanet population looks like to see what other types of planets are out there that we don’t find in our own solar system.
What do your data look like?
We take light from stars and split out all the different wavelengths (or colors) into something called a spectrum (Figure 2). There are features in the spectrum that we know should be there based on the chemical compositions of stars. Mutual gravity between planets and stars, the same gravity that causes the planets to orbit, also causes stars to wobble. When a star moves toward Earth as one of its exoplanets planet tugs it, spectral features shift to the blue side of the spectrum; alternatively, when the exoplanet tugs the star away from Earth, we see the features shift to the red side of the spectrum. We see these shifts over and over again as the planet and star orbit each other over and over – these shifts in the light spectrum can be converted directly to the speed (velocity) of the star’s movements toward or away from Earth. The phenomenon being measured is actually the Doppler Effect, which people are probably familiar with in their daily lives. If you think about a vehicle with a siren, the siren is high pitched as the car is coming towards you, but then as it passes the siren sound goes to a lower pitch. This is the same effect we are using to find exoplanets around stars far away, and we call it the Doppler method.
The really amazing thing is that we are looking at stars that are millions of miles away, but we are able to detect these effects that are equivalent to velocities as low as a meter-per-second – the speed of a slow walk or a baby crawling quickly.
Can you explain some of the steps that go into collecting your data?
I work as part of an international collaboration centering around an instrument called a spectrograph that we all use to collect data. That data is collected at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands, at a telescope called the Telescopio Nazionale Galileo (Figure 3). I’ve travelled to La Palma twice to collect data on the telescope. Before COVID, we all took turns going and collecting data for the whole team, but now there are observers based in La Palma who collect data for everyone. It’s fun to interact with people from all over the world, and see people coming together from so many places.
What happens after you collect your data?
We collect data as a team and we distribute data as a team. We have a group that meets every week to discuss the stars we have observed, and which should be our priority to study. Then we put out a call to all our members and ask who wants to ‘champion the target’, or analyze the data from that star (target). There is more than enough data to go around.
There is a processing pipeline the data goes through before I see it; a dataset is originally collected in the form of several spectra taken over a time span of several days. The analysis pipeline estimates the velocity of the star toward or away from Earth for each spectrum collected over time. When I start analyzing the data, it is a list of times and velocities. I then perform some statistical analyses to estimate the mass of the exoplanet causing the star’s motion.
In many cases, we’re following up on planets that we know exist. There is another way to detect exoplanets called the transit method – you can look for a bit of dimming in a star’s light that occurs when a planet moves in front of the star in our line of sight. From that dimming we can estimate the planet’s radius . As described above, using the Doppler method we can determine its mass. Using those two measures, the radius and mass, we can calculate the density of the star and then begin to make guesses about what it might be made of.
What makes an astronomer, or exoplanet astronomer, different from other scientists?
Astronomers like to interact with the public and share our science. A lot of the general public has a natural interest in astronomy. To me, that was part of its appeal. I really love outreach and I love sharing science with people, and so astronomy is a great field for that.
I think exoplanet astronomers are different from other astronomers because of how tangible exoplanets are. We know how big an exoplanet is, and how heavy it is, and we can start to imagine how it would compare to some of the planets in our own solar system. Things like gravitational waves or black holes are hard to visualize, but we can visualize what exoplanets might look like. There has even been a lot of art that has come out of this field because there are people who like to imagine what these exoplanets might look like, and they create their own visualizations.
Is there a common misconception about your field?
This idea that astronomers are looking through telescopes all the time. Most of our time is spent at a desk on a computer writing code and writing or reading papers. There is fun travel involved when you go to telescopes and collect data, but the majority of time is spent sitting at a desk and working on your computer.
Is there anything you would tell people interested in becoming an astronomer?
Even through most of college I had no idea that I was going to end up being an astronomer. I never considered it was possible for me to pursue this path. But if people are interested in astronomy, they should try it! You gain a very valuable skill set through studying astronomy, even if you don’t end up being an astronomer. I always say that when I got my undergraduate degree in astronomy and physics that I actually got a degree in problem solving. Astronomy is just about being able to break down these large problems into smaller pieces. A big part of that problem solving is the confidence to try.
Anything else you want to add?
Many of us who have ‘made it’ in the eyes of others (doing a PhD at Harvard, for example), still go through insecure moments. We question ourselves consistently over time. That’s part of the journey every step of the way. If anyone ever gets to a point where they are doubting if they are good enough or if they are smart enough, I hope they just remember that everybody comes to those moments. It’s important to take a second and recover from whatever is making you feel that way before making any big decisions. I easily could have dropped out of my PhD a few times, but I’m very glad I didn’t.
To learn more about Chani’s work:
- Follow them on Twitter: @SupahNava
- An interview with Chani: https://www.youtube.com/watch?v=emqXJWgJ5lM&t=2102s
This interview with Chani Nava, Graduate Student at the Center for Astrophysics | Harvard & Smithsonian, was conducted and edited for space and clarity by Malinda McPherson in September 2020.
Malinda J. McPherson is a PhD candidate in the Harvard University/MIT Program in Speech and Hearing Bioscience and Technology.
This piece is part of our special edition on the day-to-day lives of researchers working in many different fields of science. Are you interested in learning about a different type of scientist? Check out the rest of the special edition!