The Search for 100 Earths

Episode Summary

Executive Summary: This Planetary Radio episode centers on Yale astronomer Deborah Fisher and Lowell Observatory’s Joe Lama describing the 100 Earths project and the Express spectrometer, an ultra-precise radial-velocity instrument designed to detect Earth-sized planets around nearby stars. They explain why current techniques struggle, how new engineering and statistics are pushing sensitivity toward a few cm/s, and how solar observations will help disentangle stellar noise from planetary signals.

Main Topics: The challenge of finding Earth analogs: Fisher and Lama explain why Earth-sized planets in Earth-like orbits remain rare in detections: both radial velocity and transit methods are biased toward larger or closer-in planets, making true habitable-zone analogs difficult to find. Express spectrometer and precision engineering: The conversation details the new spectrometer’s innovations—fiber scrambling, laser frequency combs, higher spectral resolution, improved flat-fielding, and better pipelines—designed to achieve unprecedented precision. Stellar noise as the remaining barrier: Beyond instrument errors, the surface activity of stars themselves (pulsations, spots, flows) creates signals that can mimic or obscure planets, requiring statistical modeling and multi-disciplinary collaboration. The 100 Earths project goals and timeline: The project aims to survey about 100 nearby stars, using Express to recover planets previously missed by older spectrographs and eventually identify habitable-zone Earth-like worlds. Lowell Discovery Telescope partnership: Lowell’s 4.3-meter Discovery Telescope provides the observing platform for Express, and both guests emphasize the observatory’s team, site quality, and historical-modern blend as central to the project’s success. Solar observations to calibrate planetary searches: A parallel effort will use a solar telescope with Express to measure the Sun as a known target, helping characterize stellar activity and validate methods for detecting tiny planetary signals like Venus. Future biosignature and large-telescope prospects: Fisher notes that the next step after finding candidate planets is future direct imaging and atmospheric spectroscopy with a much larger space telescope concept, aimed at searching for signs of life.

Key Arguments: Current exoplanet detection methods are systematically biased against Earth-like planets, so the apparent scarcity is largely observational rather than astrophysical. Radial-velocity precision has improved to the point that astronomers can measure stellar motion at the level of a few centimeters per second, but that is still not enough without controlling all other error sources. Finding exoplanets is now less competitive and more collaborative; former rivals now work together because the challenge has shifted from discovery race to precision problem-solving. The Sun can serve as a calibration benchmark: because it is a known planetary system and can be spatially resolved, it helps disentangle stellar activity from planetary signals. The 100 Earths project is designed to detect planets that earlier instruments likely missed, especially around nearby, well-studied stars that have been observed for decades. A planet’s magnetic field may be crucial for habitability because it helps retain atmosphere, making magnetic characterization an important future step beyond simple detection.

Data Points: Number of confirmed exoplanets: Thousands - Used to frame how common exoplanets are now, despite Earth-sized habitable-zone planets remaining elusive. Sun’s reflex velocity caused by Earth: 10 centimeters per second - Illustrates why Earth analogs are so hard to detect with radial-velocity measurements. Express precision: 4–5 centimeters per second - Target/achieved precision of the new spectrometer, enabling unprecedented sensitivity. Pixel shift sensitivity: About 1/1000th of a pixel - Express’s measurement precision expressed as detector-scale movement. Sample size for 100 Earths: 100 stars - Approximate target survey size for the Yale/Lowell radial-velocity program. Habitable-zone search window mentioned: Out to about 200 days - Approximate orbital periods for the Earth-sized planets the team hopes to recover first. Mass of candidate planet discussed: About 5 Earth masses - Example of a tentative planet signal being analyzed in the project. Mass of Neptune: Roughly 17 Earth masses - Used for classification comparison when discussing super-Earths versus Neptune-like planets. Lowell Discovery Telescope aperture: 4.3 meters - The telescope hosting Express. Commissioning of Lowell Discovery Telescope: 2013 - Year the telescope was commissioned. Instrument commissioning: February 2019 - Express was fully commissioned one year before the interview. Solar telescope aperture: 70 millimeters - The smaller telescope used for daily solar calibration observations. Photonic crystal fiber cost: $20,000 - Cost of the specialized fiber needed for the laser frequency comb feed. Spacecraft supplies delivered by Cygnus: More than 3.5 metric tons - From the Downlink segment summarizing cargo to the ISS. Breakthrough Listen data release: 2 petabytes - SETI data released for citizen-science analysis. Apollo 9 EVA test: First and only EVA of the EMU in space before Apollo 11 - Bruce Betts’ space history segment. Longest solo spaceflight: Valery Bykovsky in Vostok 5 - Trivia answer noted in the What’s Up segment.

Pivotal Quotes: "“It’s us against the star.”" — Deborah Fisher: Fisher explains the shift from human competition among exoplanet teams to the technical challenge of separating planetary signals from stellar noise. "“Everything has to be right.”" — Deborah Fisher: Her summary of the engineering and data-analysis discipline required for centimeter-per-second precision. "“You know, how can you not love your job when what you’re doing is traveling out to a telescope, observing other stars, looking for Earth planets?”" — Joe Lama: Lama describes why the work remains exciting and personally rewarding.

Implications: The episode shows exoplanet science entering a precision era: progress now depends on engineering, statistics, and collaboration. If successful, 100 Earths could identify nearby habitable-zone candidates for future atmospheric and life-search missions.