100 Extrasolar Planet Candidates...and Counting!

Episode Summary

Executive Summary: This episode focuses on the rapid rise of extrasolar planet discovery, especially the search for Earth-like worlds. Guest Steve Howell explains current detection methods, his PSI survey of distant stars, and future missions like Kepler, SIM, and Terrestrial Planet Finder. The show also answers whether planets can form in binary star systems and closes with Bruce Betts’ space trivia and skywatching update.

Main Topics: State of extrasolar planet discovery: How many planets were known at the time, how many were confirmed, and why the field was seen as a major scientific breakthrough. Methods for finding exoplanets: Discussion of radial velocity spectroscopy versus photometric transit searches, including strengths, limitations, and why smaller Earth-like planets were still elusive. PSI search for distant Jupiter-sized planets: Steve Howell describes a Planetary Science Institute project using a refurbished 1.3-meter Kitt Peak telescope to survey more distant stars and compare planet frequency across the galaxy. Future missions: Kepler, SIM, and Terrestrial Planet Finder: The conversation turns to upcoming NASA missions designed to improve precision and potentially detect or image Earth-like planets. Planets in binary star systems: Emily Lochtawala explains that binary systems can host planets in stable orbital zones around one star or around both stars together. Planetary Society update and trivia: Bruce Betts provides a skywatching note, space history item about Alan Shepard’s moon golf shot, and a new trivia contest.

Key Arguments: Most known extrasolar planets at the time were Jupiter-sized or larger; Earth-like planets had not yet been found because detection methods were not sensitive enough. Radial velocity spectroscopy detects planets by measuring tiny shifts in a star’s spectral lines, but it becomes difficult for fainter stars and lower-mass planets. Transit photometry can detect small dimmings when a planet crosses a star, but it requires very precise measurements and favorable alignments. The PSI project is unusual because it looks at more distant stars, out to nearly 1,000 parsecs, rather than focusing only on nearby bright stars. Kepler was presented as a major step forward because space-based photometry avoids atmospheric interference and can stare continuously at the same field for years. Terrestrial Planet Finder was described as a future interferometric mission intended to cancel out a star’s light and possibly image a planet directly. Binary star systems are likely capable of forming stable planets in two broad configurations: circumbinary orbits far from both stars, or planets orbiting one star closely enough that the companion star has little effect.

Data Points: Known planets outside the solar system: roughly 100 candidates - Steve Howell estimates the number of extrasolar planet candidates known at the time. Confirmed extrasolar planets: 10 to 15 - Howell says only a small subset were absolutely certain in the astronomical sense. Known planets a few years earlier: 9 - He notes that 15–20 years earlier, humanity knew only the nine planets in our own solar system. Binary star frequency near the Sun: about 50% - Emily says half of nearby stars are binary systems. Alpha Centauri separation: 23 astronomical units - Used as an example of a nearby binary star system. PSI survey reach: almost 1,000 parsecs - The project will search much farther out than the previously surveyed 40–50 parsecs. Previously known extrasolar planet region: within about 40 to 50 parsecs - Current detections had been limited to relatively nearby stars. Telescope aperture: 1.3 meters - The refurbished Kitt Peak telescope dedicated to the PSI search. Kepler observing duration: 4 years or longer - Kepler was planned to stare continuously at one field from space. Kepler target stars: 200,000 to 300,000 - Estimated number of stars Kepler could monitor. Terrestrial Planet Finder spacecraft: about 6 - Howell says the concept involved six connected telescopes. Space interferometry mission launch target: 2007 - Kepler was said to be launched in 2007; SIM is described as a nearer-term technology step. Moon golf shot date: February 6, 1971 - Alan Shepard’s famous golf shot on Apollo 14.

Pivotal Quotes: "It’s an incredible time to be alive" — Matt Kaplan: Reflecting on the rapidly growing field of extrasolar planet discovery. "Five years ago, we all knew how to make a solar system." — Steve Howell: He emphasizes that exoplanets have overturned assumptions based on our own solar system. "The real cornerstone there, the real jewel, will be if it can find planets that are the size of Earth." — Steve Howell: Discussing the science payoff expected from the Kepler mission.

Implications: The episode shows exoplanet science moving from discovery of giant planets to the search for Earth analogs, with new instruments and missions expected to transform what can be detected and eventually imaged.