Discovering other worlds

We call them exoplanets, or sometimes extrasolar planets. It is just a designation that they are planets around a different star; they are a different solar system. They are outside our own solar system.

We are measuring light from stars, very bright stars, and if they have planets around them, like our Earth around the Sun, then finding them is an enormous technological challenge. You can have an idea that says, I wonder if they are out there, but you need the technology to actually be able to see them. There have been these great advances in the ways in which you can find these tiny planets.

As the Earth orbits the Sun, they are actually orbiting their common center of mass, and that means that the Sun is wobbling around a bit as the Earth pulls it. If the Earth was a much heavier planet — Jupiter-sized or larger — it would make the Sun wobble a bit more. The earliest observations were able to show that stars were moving in a particular way; then the inference was that a planet must be going around it. Again, you are not seeing the planet in that method, but you are seeing how its gravity affects the star's motion. That was transformative and incredibly exciting, and still today, this method is used for detecting many new planets.

This tiny dimming of the planet is a very predictable thing, because every time the planet goes around that star, it will dim it a little bit. This new method has been used to find many, many new planets. Then there are multiple other methods, too. You can, for example, try to block out the light of the Sun to see the fainter planet next to it. You design your telescopes such that they inhibit the light from the star, and you can enhance the light that emerges from the planets. Now the field is transformed. Even though I do not work directly on that research myself, I see that in our community many people want to work in this area, because there are now thousands of planets and entire solar systems that have been discovered. They are incredibly weird, wonderful and exciting, and I really see that in the field of astronomy as this whole new, exciting area.

There are many powerful telescopes that people have in their own backyards, but the ability to measure many of them with high sensitivity generally requires the level of telescope used by the astronomical community.

We already have a sense of the variety of planets compared to our own solar system. There are different solar systems where the planets orbit their star in just hours, which none of our solar-system planets do, and there can be vastly different numbers of planets in the system. Some of them orbit two stars — you could imagine having two suns in the sky. Some of them may be purely covered in lava; some of them may be purely covered in water. The variety of sizes and composition must be immense. We are just starting to learn more about what they might be made of. Even though I do not study the details of these planets myself, because I study the universe — the whole thing — I do think a lot about the extent to which I feel sure there must be this huge variety of solar systems and planets. That is why I think it is very likely that there would be life elsewhere, just because of the sheer numbers, even though life itself is quite unlikely.

One of the great advances happening at the moment is to use telescopes to measure the atmospheres of these planets in greater detail and at the same time to use the largest, highest-resolution telescopes to image some of them. Because it is so hard, and these objects are so faint and so far away, we will need new telescopes as well. With our existing telescopes, we can make so much progress, but then we will need new, bigger, more advanced ones to look for these signatures in more detail.

Dark energy is there; it is going to keep growing. I would say now that I do not know, because until we have understood the nature of this dark energy, to me, all bets are off. All futures are possible. While we have these major components, this dark matter, this dark energy, that we do not fully understand, I would not like to rule out these different possible scenarios. Maybe it will change its behavior. Maybe we have not fully understood it. While I will say in the standard model right now the Big Crunch should not happen, I will also say, who knows? Other things are possible.

He also realized that he was not going to be alive to see the next one, and he charged, exhorted, younger astronomers to go and make the measurements. To me, there is something really magical about it, because he wrote this and basically said go and do this; I will not be able to, but you can. They did, and it happened. They measured the size of the solar system, and they measured the distance to the sun. I see astronomy full of these kinds of examples, when the technology just had not caught up with the ideas, or, in that case, the configuration of the solar system was not going to be right for these observations during that lifetime. I see that as being our role, too. We get to do a bit of the learning and discovery during our professional lives, but the most important thing is to train more junior researchers to become the next generation of scientists. To answer all the questions...well, there will always be more questions. Even to answer the questions we have now is a long journey.

Whether you look in different wavelengths or look in different ways, try to develop your observations not only to look for the thing you would like to find but to be open to things you were never expecting. Understand that it is a long journey — a journey that is going to take generations to keep doing — and keep up our scientific establishment while still trying to think outside the box.

Editor’s note: This article has been faithfully transcribed from the original interview filmed with the author, and carefully edited and proofread. Edit date: 2025