(Jasmine Li | Student Life)

Dr. Tansu Daylan, Assistant Professor of Physics, presented on exoplanets and their transits as part of the Saturday Science Lecture series leading up to the April 8 eclipse on Saturday, Mar. 2. 

In his talk, Daylan discussed how modern research and technology allow for better research and characterization of exoplanets — planets outside our solar system.

When planets get between us and a star, it is called a transit, and according to Daylan, these transits can tell us a lot about exoplanets. 

“If you actually measure the transit depth (the decrease in a star’s apparent brightness due to the exoplanet covering it) and [know] to some uncertainty the radius of the star, it will allow you to measure the radius of the planet, which is very important,” Daylan said. 

Measurements of transits using time-series photometry, aka measuring a star’s brightness over time, may also lead to calculations of orbital periods and inclinations, Daylan stated. 

“So, given this, people expected to be able to discover exoplanets using this method, and they tried for a long time, but it failed,” Daylan said, “And the reason why it failed so many times is because [they didn’t] have the photometric precision…you make too much of an error when you’re trying to measure the brightness.”

Daylan made the case that syzygies, when two objects align along our line of sight, are unlikely events due to the incredible vastness of space, only making the exoplanet search harder.

“The separation between typical stars is…about 200,000 times larger than the distance between the Earth and the Sun,” Daylan said. “These are points in a vast space, so [the chance] for them to actually align along any line of sight is very small.”

According to Daylan, the first transiting exoplanet was found in 1999 when its star’s brightness decreased by 1-2%. 

“You need your photometric measurements capability to be producing error bars that are much smaller than this,” Daylan said, “You have to do this search over many stars before you randomly hit one where the planet happens to have [the right characteristics] so that you can actually play the game.”

Daylan then moved to talking about the Transiting Exoplanet Survey Satellite (TESS), which he has personally worked with for years. It is a “full sky survey,” which allows TESS to search for transits over hundreds to thousands of stars at once, according to Daylan. 

Daylan stated that exoplanet discovery has slowed recently because of TESS’ focus on smaller planets which allow for mass and radius measurements, among others. This characterization has led to the discovery of a radius valley, about 1.5 to 2 times Earth’s radius, which few planets inhabit.

“It’s one of the most important findings of exoplanet research,” Daylan said, “Trying to make sense out of this radius valley, how and why it’s produced, is a very important scientific objective of the field at this point.”

However, TESS is not our only satellite looking at exoplanets, so Daylan moved to discussing the James Webb Space Telescope (JWST), which he has also worked with. JWST made a very important discovery in 2022. 

“You watch your star as the planet transits, and you collect photons in pockets of measurements (like transit depth), so you do that multiple times [using spectroscopy] and measure your transit [depth] across different wavelengths,” Daylan said. “This pointed to a major finding in the field: the very first detection of carbon dioxide in the atmosphere of an exoplanet.” 

Adheet Ganesh, a sophomore in attendance and contributor to the Masterminds science podcast, was not previously familiar with the amount of math behind this achievement.

“I was actually not familiar with how we measure the presence of exoplanets. Honestly, before this, I thought you could like take pictures [with a telescope],” Ganesh said, “The whole thing about atmospheric characterization [and how you can calculate all these values] was really cool.” 

Another member of the audience, who is a former physics graduate school student, was similarly impressed with the awesome mathematics behind these discoveries.

“It was really neat paying attention to his math equations because it seems like there’s so many variables…it’s kind of a neat little exercise in reversing the mathematics to figure out [these characterizations],” they said. “He gave me enough of a tease that I want to read up more on it.”

JWST achieved this “major accomplishment” because it is more sensitive (due to its larger aperture) and can observe longer wavelengths of light than the Hubble telescope, plunging deeper into the infrared, Daylan said. Yet, according to Daylan, an even greater telescope may be in the works.

“The survey from our astronomical research field in 2020 basically came out suggesting that we build a major telescope that [would] have roughly the aperture size (diameter of the lens/mirror) of JWST but also be able to do many other things,” Daylan said, “We call it the Habitable Worlds Observatory, and the idea is for it to fly in the early 2040s.”

Daylan concluded his talk by connecting back to the upcoming solar eclipse, an example of a syzygy, emphasizing its beauty.

“As a scientist, I feel like it’s a unique connection between our planets, our host star, and our natural satellite that we call the moon,” Daylan said. “As an Earthling, it’s just the fact that it gets cooler for three to four minutes and you suddenly see signs of [natural] nightlife. It’s a great experience.”

This Article was updated for accuracy on March 11th, 2024