Overview
Throughout this course, you have concentrated on the contents of a single planetary system — our own — and on the method used by humans to logically and systematically explore it: science. In this module, you’ll go beyond our Solar System and explore the planets that have been found orbiting other stars.
Since the discovery of the first confirmed exoplanets in the 1990s, astronomers have identified more than 5,600 confirmed planets in over 4,000 planetary systems. These discoveries reveal extraordinary diversity — from giant worlds orbiting scorchingly close to their stars, to frozen super-Earths drifting between them — and they continue to reshape our understanding of how planetary systems form and evolve.
By examining just the first two planetary systems ever discovered, you’ll see how dramatically our expectations were overturned. You’ll also explore how insights from these discoveries have improved our understanding of our own Solar System’s structure and history.
Building on those early surprises, astronomers have developed an expanding toolkit for detecting and characterizing exoplanets. You’ll investigate techniques such as the radial velocity and transit methods — the workhorses of exoplanet detection — along with microlensing, astrometry, and direct imaging. You’ll also learn how modern instruments now allow atmospheric spectroscopy, revealing the chemical compositions and even possible cloud layers of distant worlds.
The module highlights the role of space missions that have transformed the field. The Kepler mission first demonstrated that planets are ubiquitous. Its successor, TESS (Transiting Exoplanet Survey Satellite), continues to find thousands of nearby worlds suitable for follow-up. The James Webb Space Telescope (JWST) is now probing exoplanet atmospheres in unprecedented detail, while upcoming observatories such as PLATO (ESA) and the Nancy Grace Roman Space Telescope (NASA) will expand these efforts even further. Together, these programs are revealing how planets form, migrate, and evolve — and what makes some potentially habitable.
Finally, the module invites you to step back and reflect on the broader meaning of these discoveries. How does the search for other worlds connect with our place in the Universe? What responsibilities come with expanding our reach beyond Earth? You’ll consider how astronomy’s pursuit of knowledge intersects with human values, cultural perspectives, and the rights of traditional knowledge keepers as we chart the future of exploration.
Learning Objectives
- Examine the current status of our search for extrasolar planets, including confirmed discoveries, key properties, and upcoming observatories.
- Explore and compare the major techniques used to detect planets orbiting other stars.
- Analyze what recent missions reveal about the diversity and evolution of planetary systems.
- Reflect on the development of knowledge in astronomy through the scientific method and its interaction with cultural and ethical values.
Key Terms and Concepts
- Extrasolar planets (exoplanets)
- Pulsar planets
- Hot Jupiters
- Kepler mission
- TESS mission
- James Webb Space Telescope (JWST)
- PLATO mission
- Nancy Grace Roman Space Telescope
- Radial velocity method
- Transit method
- Microlensing method
- Astrometry method
- Direct imaging method
- Atmospheric spectroscopy
- Super-Earths / Mini-Neptunes
- Rogue planets
- Habitable zone
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