Yonatan Zeff

Yale researchers have designed a new tool to advance efforts to find Earth-sized planets in neighboring solar systems.

Led by astronomy professor Debra Fischer, the team has built the Extreme Precision Spectrometer — known as EXPRES — to improve precision in detecting rocky planets orbiting around stars in other systems, known as exoplanets. At the Lowell Observatory Discovery Channel Telescope in Arizona, Fischer began collecting data from the spectrometer last week.

“We will use EXPRES to discover new planets orbiting nearby stars and to measure their masses with greater precision than was possible before,” said Allen Davis GRD ’20, a member of the research group.

EXPRES uses a technique called the radial velocity method to detect planets and systems, explained Yonatan Zeff ’18, a researcher in the lab. Stars shoot wavelengths of light toward the Earth, and when a planet exerts a gravitational tug on its host star, a shift is visible in the light emitted by the star — a phenomenon known as the Doppler effect.

When the star moves away from the observer, the light is red-shifted, or slightly more red, and as it moves toward the observer, the light is blue-shifted. Spectrometers like EXPRES are able to detect this shift in frequency to identify the presence of a planet.

Moreover, radial velocity measurements can reveal other characteristics of an exoplanet, Davis said.

“A large but slow wobble might tell us that a Jupiter-sized planet is orbiting far away from its star, whereas a small and rapid wobble could indicate the presence of a rocky, Earth-like planet orbiting close-in to its star,” he explained.

While Fischer is in Arizona collecting data, several researchers in the group back at Yale are analyzing the results. Davis, for example, is translating the raw images into velocity measurements and leading one of EXPRES’ planet searches, he said.

Zeff explained that he is comparing the data to those of exoplanets that already have radial velocity measurements or other types of measurements to determine how much more accurate EXPRES is than other spectrometers.

The researchers said that EXPRES may facilitate the search for extrasolar life. The precision and accuracy of the radial velocity measurements could reveal the presence of Earth-like planets, Zeff said.

“The discovery of small, rocky worlds that reside in the ‘habitable zones’ of their stars — the region where liquid water could be present — is one of the most exciting objectives of EXPRES, since astronomers will one day search for biosignatures that would provide evidence of extrasolar life on these planets,” Davis added.

These results can have significant implications for the field of astronomy, Davis said. He suggested that each new world that the team finds has the potential to help answer questions about how planets form, how they interact with one another and how they migrate.

In the past, spectrometers had been limited to measuring velocity changes as small as one meter per second, but the researchers are now aiming for 20 centimeters per second — close to the shift that Earth itself has on star movement — Zeff said. As a result, EXPRES can help detect Earth-like planets orbiting at Earth-like distances, he said.

EXPRES also performs precise calibrations by producing bright and evenly spaced artificial lines to serve as a “ruler” and by correcting for the pixel-to-pixel sensitivity differences in the detector. Finally, it has a greater spectral resolving power than other spectrometer instruments, helping to distinguish actual radial velocity measurements from background noise.

Scientists first discovered an exoplanet orbiting a sunlike star in 1992.

Amy Xiong | amy.xiong@yale.edu