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Harvard Horizons Podcast: The Search for Other Earths

Are there Earth-like worlds that could support life? PhD student Juliana García-Mejía tells a crowd at Harvard’s Sanders Theatre how, in search of an answer to that question, she created a new instrument to search the heavens.

This transcript has been edited for clarity and correctness.

As a kid growing up in Colombia, I remember running around the family's coffee farm surrounded by plantain palm trees in virgin forests. But what I remember most vividly were the evenings when my uncle would sit us cousins down to stare up at a sky teeming with stars. That is where I fell in love with the question that I intend to dedicate my life to researching: Is there life elsewhere in the universe?

I consider us all here extremely lucky to be alive during a time where we have the scientific framework and technology in hand to make significant leaps in answering this question. But what exactly does it mean to search for life in the universe from the perspective of an astronomer?

As it turns out, different astronomers will reply differently to this question. But to many of us, the first step in that quest consists of finding the nearest Earth-like planets to the solar system. That is, planets that have about the same size as our own, that orbit stars other than the sun. And the workhorse method by which we find those planets is known as the transit method.

So, I'm going to ask you all to put on your astronomer hats for a second and imagine that you're all observers trying to determine whether this star is orbited by a planet. If this star is indeed orbited by a planet and the orbit is oriented such that at some point the planet will pass precisely between all of you and the star, it'll generate a shadow. It will block some of that starlight.

Now, in detail, if we look at the amount of light that we're receiving from that star as a function of time. You'll notice that in the exact moment that a planet passes in front of that star, there will be a dip in that light curve. That dip is the measurable quantity that we are after. And as it turns out, the smaller the planet the harder it is to find.

So, finding an Earth-like planet around a star as large as the sun poses an immense challenge. Oh, we can help ourselves. We can see just a little bit by looking for those same Earth-sized planets around the smaller stars in the universe, so-called red dwarf stars. In that case, the dip in the light curve would be about a hundred times deeper, making our task just a little bit easier. And this is exactly the task that I set out to do for my Ph.D.

For my Ph.D. I set out to lead the construction of the Tierras Observatory, which is a new observatory located in Mount Hopkins, Arizona. And although it is a new observatory, we actually were using an old telescope that was built back in 1995, the year I was born. And this telescope is really old. So, the first few years we've spent a lot of time and effort building in that refurbishing, building, and rebuilding its control software. But at the end of the day, a telescope is a giant bucket. It's just that instead of collecting water like you usually do, you actually collect light. And in our case, our bucket of light is a 51-inch primary mirror that is the main part of the telescope. But at the end of the day, like I said, that's just helping us collect the light.

So, I also spent a lot of time building a new and innovative instrument that sits right underneath that primary mirror and addresses some of the main limitations of today's best ground-based and space-based observatories in our line of work. And to tell you what is so exciting and innovative about our instrument, I'm actually going to take you on a journey through the whole telescope.

So, let's imagine that there is light coming from a nearby red dwarf star. And by nearby, I mean that light is going to have to travel something like 100 trillion miles to make it to the earth and then make it to our primary mirror. And then after that light makes it through our primary mirror. It's going to bounce off to the secondary mirror. And then after bouncing off to that secondary mirror, it's going to make it down through the primary mirror hole. And after making it through the primary mirror hole, it's going to encounter the first element in the Tierras instrument, a custom filter.

This filter I designed and built, it's one of a kind and it's built to only allow the wavelengths, the colors of light that are not affected by the atmosphere to make it through the system. And this is important because it turns out the atmosphere is the greatest enemy to ground-based astronomy. After making it through the filter, this carefully filtered light is going to make it through a set of coded optics. And these optics allow us to increase the field of view of the telescope, thereby allowing us to monitor many more stars. This is not unlike how the second and third cameras in your iPhone in your pocket right now allow for wider images to be taken.

Finally, the arduous journey is going to be over at the CD Chip. That chip is going to convert all that light into a digital signal. Data that we can analyze in search of exciting discoveries.

My amazing team and I have already spent countless hours designing and building this instrument in the lab to then pop the whole thing up and take it over to Arizona. In Arizona, we carried out a careful and detailed installation effort, after which I spent entire days and nights aligning the telescope and overcoming all sorts of hardware and software problems.

It has already been an adventure of the most epic proportions. And we've even had some Eureka moments in the mix.

[Video of García-Mejía at Tierras Observatory playing] “Oh, look at your cluster! Oh my God!”

To that young Colombian girl that stared up at the sky from her Colombian from her family's farm. This first light image was a dream come true. But to the astronomer, this is only the beginning. And the data is coming in fast. We have the added advantage that every night of good weather is going to be dedicated to our experiments. And our telescope is led not by an observer that is a human, but, in fact, by a tireless robot that's observing night after night. I hope that all of you are as excited as I am about the future discoveries that our observatory will enable.

We could find Earth like planets that are small and temperate enough to sustain liquid water oceans and retain their atmospheres, but also moons and smaller bodies around those planets, which are crucial to understand their formation histories. All in all, these are all loose pieces, ciphers in a much larger puzzle, but one that's going to get us closer to answering the ultimate question of whether or not we are alone in this vast universe.

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