The Search for Exoplanets: What Astronomers Know

Course No. 1802
Professor Joshua Winn, Ph.D.
Princeton University
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Course No. 1802
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Course Overview

Half a century ago, television viewers thrilled to the exploits of the original Star Trek series with its mission “to explore strange new worlds.” Today, astronomers are doing exactly that, analyzing the data from advanced telescopes and discovering strange worlds orbiting other stars in our galaxy.

Most of the countless stars they are monitoring are invisible to the unaided eye, and the thousands of confirmed and candidate planets they’ve detected can’t be imaged directly, except in a few rare cases. Yet researchers are able to use subtle clues obtained in ingenious ways in order to assemble an astonishing picture of planetary systems far different from our own:

  • Systems containing “hot Jupiters,” giant planets orbiting so close to their host stars that it takes days—not Jupiter’s 12 years—to make one orbit.
  • Earth-sized planets orbiting even closer—in one case careening around its sun every 8 hours, completing three of its “years” in one of our days.
  • Planets circling two different suns, recalling the famous scene in Star Wars, where Luke Skywalker watches a double sunset from his home planet.

These results are much more than science fiction brought to life. They are an astronomical revolution, comparable to the Copernican revolution that established our current view of the solar system. As recently as 1990, it seemed possible that the solar system was an unusual or even unique phenomenon in our galaxy. Now we know that planets are everywhere, and we are living during a new golden age of discovery, with the prospect of finding many planets like our own.

The Search for Exoplanets: What Astronomers Know immerses you in this incomparable adventure in 24 beautifully illustrated half-hour lectures conducted by veteran planet hunter Joshua N. Winn, Associate Professor of Physics at the Massachusetts Institute of Technology.

An award-winning teacher, Professor Winn is also a pioneer in the field of exoplanetary science—the study of planets beyond the solar system. He served on the science team of NASA’s Kepler mission, the most productive planet-finding effort to date, and he is taking part in a new space telescope project that will focus on finding rocky planets in the habitable zones of their parent stars, laying the groundwork for the ultimate objective: detecting earthlike planets with the chemical signatures of life. This goal may still be many years away, but meanwhile Dr. Winn and his colleagues are helping to rewrite the book on planet formation and the evolution of planetary systems.

A Scientific Detective Story

Designed for everyone from armchair explorers to serious skywatchers, The Search for Exoplanets follows the numerous twists and turns in the hunt for exoplanets—the false starts, the sudden breakthroughs, and the extraordinary discoveries. Dr. Winn covers all the necessary background, reviewing the simple mathematics of planetary orbits and the scientific principles behind the techniques that eventually found planets at mind-boggling distances from our home base.

Considering that a star is millions to billions of times brighter than even its largest planet, this is a scientific detective story like no other, involving methods such as these:

  • Astrometry: A star and its planet both orbit their common center of mass, typically a point slightly off-center from the center of the star. In principle, this effect can be observed as a tiny wobble in the star’s position in the sky.
  • Doppler shift: The slight wobble of a star due to orbiting planets can also be detected as a fluctuating color shift (known as the Doppler shift) in the star’s spectrum, as the star alternately moves toward the observer and then away.
  • Transit: When a planet crosses in front of a star (known as a transit), it blocks a small percentage of the starlight. Sensitive instruments can measure this minor drop in light level. The greater the dimming, the larger the planet.
  • Gravitational lensing: A foreground star acts like a lens when it passes in front of a more distant star, bending the light of the background star. If the star in front has a planet in the right position, the light temporarily bends a bit more.
  • Direct imaging: Most difficult of all is recording an actual image of an exoplanet, which has been compared to spotting a firefly buzzing around a searchlight, with a telescope thousands of miles away. Even so, it has been done!

These techniques not only signal the presence of planetary systems, but also allow astronomers to analyze the data to determine how many planets there are, how large, how far from their parent star, their likely compositions, and the characteristics of their atmospheres. Viewers of The Search for Exoplanets will feel like Dr. Watson in the presence of Sherlock Holmes, as Professor Winn extracts a wealth of information from a spectrum, a light graph, a diffraction pattern, and other subtle clues.

Explore Unknown Worlds

To help you grasp the vastness of the universe, Professor Winn demonstrates a virtual scale-model solar system, centered on Times Square in New York City, that serves as a yardstick for comparisons throughout the course. For example, if the Sun is reduced to the size of an adult human, then at the same scale Earth is the size of a grape, two and a half blocks away, and the closest star with a known planet is 32,000 miles away—a distance 30% greater than the circumference of the entire Earth. Imagine trying to detect a grape at that distance!

The lectures are lavishly illustrated with astronomical photographs, graphics, computer animations, and special effects that help you appreciate the extraordinary variety of planetary systems. And Professor Winn’s personal anecdotes add a human dimension, showing the challenge and excitement of science. Since exoplanetary science is unusually interdisciplinary, you are introduced to a wide range of fundamental ideas, including these:

  • Astronomy: Among the topics you cover are planetary science, stellar evolution, telescopes, cosmology, and asteroseismology (the science of star “quakes”).
  • Physics: You investigate orbits, tides, the electromagnetic spectrum, spectroscopy, optics, quantum mechanics, and special and general relativity.

  • Life sciences: You learn about the quest for life, which combines the search for signals from extraterrestrial intelligence with the hunt for biosignatures of microbial life.

After completing this fascinating course, you will be well equipped to understand one of the most momentous developments of our time. Exoplanets will be making big news for years to come, and at the end of the course Professor Winn describes ambitious projects that are on the drawing board as well as discoveries that he predicts for the near future. Perhaps the only reason exoplanets haven’t attracted more attention is that science fiction long ago prepared us for these wonders. But unlike the adventures on Star Trek, these projects are real. We invite you to join a scientist who is on a mission that can only be compared to the exploits of Columbus, Magellan, and Lewis and Clark.

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24 lectures
 |  Average 30 minutes each
  • 1
    Why Study Exoplanets?
    Learn about the exciting mission of exoplanetary science - the study of planets orbiting stars beyond the Sun. Review the eight planets in our solar system, which provide a baseline for understanding the more than 1,000 worlds recently discovered in our region of the Milky Way galaxy. x
  • 2
    How to Find an Exoplanet
    Given the extreme faintness of a planet relative to the star it orbits, how can astronomers possibly find it? Learn about direct and indirect methods of detection. As an example of the indirect method, discover why a planet causes a star's position to change, providing a strategy for locating exoplanets without seeing them. x
  • 3
    Doppler and Transit Planet-Finding Methods
    Explore two other indirect approaches for finding exoplanets: first, by measuring the Doppler shift in the color of a star due to the pull of an unseen orbiting planet; and second, by measuring the tiny drop in the brightness of a star as a planet transits in front of it. x
  • 4
    Pioneers of Planet Searching
    Chart the history of exoplanet hunting - from a famous false signal in the 1960s, through ambiguous discoveries in the 1980s, to the big breakthrough in the 1990s, when dozens of exoplanets turned up. Astronomers were stunned to find planets unlike anything in the solar system. x
  • 5
    The Misplaced Giant Planets
    Investigate 51 Pegasi b, the first planet detected around a Sun-like star, which shocked astronomers by being roughly the size of Jupiter but in an orbit much closer to its star than Mercury is to the Sun. Probe the strange characteristics of these hot Jupiters," which have turned up around many stars." x
  • 6
    Explaining the Misplaced Giant Planets
    The standard theory of planet formation is based on our solar system. But does this view require revision based on the existence of misplaced giant planets - hot Jupiters circling close to their parent stars? Compare competing theories that try to resolve this conflict. x
  • 7
    The Transits of Exoplanets
    A tiny percentage of exoplanets can be detected transiting - or passing in front of - their host stars. Combined with Doppler shifts, transits provide information about a planet's size, mass, density, and likely composition. Learn how ambitious amateur astronomers can use this detection technique in their own backyards. x
  • 8
    Sniffing Planetary Atmospheres
    Survey the history of spectroscopy to understand how a telescope and a diffraction grating can disclose the composition of a star and its planet. Then learn how transits and occultations are ideal for analyzing planetary atmospheres, paving the way for the search for signatures of life. x
  • 9
    Stellar Rotation and Planetary Revolution
    Trace Professor Winn's own search for the subtle signs that tell whether a star has a tilted axis. Discover why this is an important clue in the mystery of misplaced giant planets. Also hear how he chanced into the field of exoplanetary science. x
  • 10
    Super-Earths or Mini-Neptunes?
    Learn how a sensitive new instrument led the way in finding planets smaller than the Jupiter-sized giants that dominated the earliest exoplanetary discoveries. Halfway in size between Earth and Neptune, these worlds have uncertain properties. For clues about their nature, consider how our solar system formed. x
  • 11
    Transiting Planets and the Kepler Mission
    The planet search took a giant leap forward in 2009 with the launch of the Kepler spacecraft, which used the transit technique to observe nearly 200,000 stars over a four-year period. Study Kepler's goals, results, and the persistence of the astronomer who championed it. x
  • 12
    Compact Multiplanet Systems
    Dig deeper into the treasure trove of data from the Kepler mission, which discovered hundreds of compact multiplanet systems, with planets much more closely packed than in our solar system. Explore the dynamics of these groupings, which have planets interacting strongly through mutual gravitation. x
  • 13
    Planets Circling Two Stars
    See how data from the Kepler spacecraft confirms a scenario straight out of the movie Star Wars: a planet with two suns. Investigate the tricky orbital mechanics of these systems. A double star also complicates the heating and cooling cycle on a planet. However, the view is spectacular! x
  • 14
    Lava Worlds
    Explore the theoretical limit of the smallest possible orbit for a planet, taking into consideration tidal stresses and other destructive processes. Then focus on Professor Winn's search for such objects, which found probable lava worlds - planets heated to rock-melting temperatures by their extreme closeness to their host stars. x
  • 15
    Earthlike Planets
    Begin your search for planets that may harbor life by studying the conditions that make Earth habitable, including its distance from the Sun, surface temperature, atmosphere, and oceans. Then examine strategies for finding earthlike planets and the progress to date. x
  • 16
    Living with a Dwarf Star
    The most common stars are class M dwarf stars, which are smaller and less luminous than the Sun (class G). Earth-sized planets are much easier to detect around M-dwarf stars, especially if the planets are within the relatively close-in habitable zone. Explore examples and the prospect for life on such worlds. x
  • 17
    Living with a Giant Star
    In billions of years, the Sun will expand into a red giant, possibly engulfing Earth. Learn how planet-finding techniques give astronomers insight into the processes inside giant stars. Then study the planets around these behemoths for clues about Earth's ultimate fate. x
  • 18
    Our Nearest Exoplanetary Neighbors
    Pinpoint the location of the nearest exoplanetary systems to Earth. First, get the big picture on the layout of our Milky Way galaxy, its size, and the Sun's position. Also learn why the Kepler spacecraft focused on exoplanets much more distant than those targeted by the Doppler technique. x
  • 19
    Finding Planets with Gravitational Lensing
    Get a lesson in Einstein's general theory of relativity to understand an effect called gravitational microlensing, which allows astronomers to deduce a planet's existence without recording any light from the planet or its host star. This technique reveals exoplanets that would otherwise go undetected. x
  • 20
    Finding Planets with Direct Imaging
    Turn to the most obvious way to find exoplanets: direct imaging. Explore the optics of telescopes to learn why spotting an exoplanet next to its parent star is so difficult. Then see how this limitation has been overcome in a handful of cases. x
  • 21
    Near-Term Future Planet-Finding Projects
    The success of exoplanetary science has spurred a wave of new projects to increase our knowledge of worlds beyond our solar system. Survey ground- and space-based programs that are now in the works. Professor Winn gives a preview of a space mission that he and his MIT colleagues are designing. x
  • 22
    Long-Term Future Planet-Finding Projects
    Peer into the future at ambitious projects that may one day succeed in collecting light directly from an Earth-sized planet in the habitable zone of a nearby star. Examine three different engineering approaches: the coronagraph, interferometer, and starshade. x
  • 23
    The Search for Life on Exoplanets
    Join the quest for life on exoplanets, focusing on the search for extraterrestrial intelligence (SETI) - a hunt for signals from alien civilizations inspired by a landmark paper in 1959. See how the famous Drake equation points to factors that determine how many such civilizations may exist. x
  • 24
    Coming Soon: Biosignatures, Moons, and More!
    Explore the distinctive biosignatures that show the presence of life of any kind on an exoplanet. Then close with Professor Winn's tip sheet on exoplanetary discoveries likely in the near future - from evidence of moons to planets being destroyed by giant stars. x

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Your professor

Joshua Winn

About Your Professor

Joshua Winn, Ph.D.
Princeton University
Dr. Joshua N. Winn is the Professor of Astrophysical Sciences at Princeton University. After earning his Ph.D. in Physics from MIT, he held fellowships from the National Science Foundation and NASA at the Harvard-Smithsonian Center for Astrophysics. Dr. Winn’s research goals are to explore the properties of planets around other stars, understand how planets form and evolve, and make progress on the age-old question of...
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Reviews

The Search for Exoplanets: What Astronomers Know is rated 4.4 out of 5 by 36.
Rated 5 out of 5 by from Good Class Dr. Winn is an exceptionally brilliant person, who's boyishly passionate about his work. His enthusiasm is infectious - particularly to those of us who have been fascinated with science fiction since we were kids, and who will always be thrilled by the search for extraterrestrial life, and discovery of other worlds. Few will disagree with Dr. Winn that the notion that thousands of other planets are at this time orbiting distant stars, which may harbor other forms of life, forces us to put our own puny problems in perspective.
Date published: 2019-06-05
Rated 5 out of 5 by from Enjoyable, well presented, lavishly illustrated Having some science background from college, this material was well presented in a way a lay person or someone with some scientific background can enjoy. The professor has an excellent, deliberative, and relaxed presenation style. Many nice illusrations and graphics. A little bit of math, but nothing that would keep it from being enjoyable to the lay person. I really enjoyed this course, and learned quite a lot. It gets a high recommendation from me.
Date published: 2019-03-31
Rated 5 out of 5 by from Learn About Exo-Planets - No Math Required These lectures are very informative in understanding the advances made in discovering exo-planets. The methods used to locate these planets is very interesting and explained in easy to understand language by the excellent lecturer. These lectures are appropriate for non-science students, and almost no math is needed to enjoy the lectures. I think it is very important to get these lectures via DVD, because the graphs and art work are important in understanding the content. These lectures appear to have been recorded in 2014 or 2015 so are a bit dated due to the rapid changes in this field, but the course is very valuable anyway.
Date published: 2019-03-01
Rated 5 out of 5 by from Liked the course The professor speaks clearly and explains well. The quality of the recording is good. I have no science background beyond high school physics and chemistry and found the course very engaging.
Date published: 2019-01-21
Rated 3 out of 5 by from More than I wanted to know This course is interesting, but goes into greater detail than I wanted, especially when covering all the math. I found the history of the searching the most interesting.
Date published: 2018-09-11
Rated 4 out of 5 by from The search for Exoplanets: what astronomers know. An interesting, relevant and current subject. The subject was well presented and one did not have to be an astronomer/scientist to follow and understand the material .
Date published: 2018-04-06
Rated 5 out of 5 by from Great introduction to the field I thoroughly enjoyed this course. I learned a great deal. As a retired scientist I am impressed by the achievements in the search for exoplanets. I wish Professor Winn had spent some more time in discussing the difficulty of these observations--the sensitivity, the precision and the accuracy of the measurements required in exoplanet work. He discussed using the Doppler shift to detect star rotation and the perturbations caused by the planets of this rotation. I wish he had discussed the parts-per-billion (or even greater) precision required, the spatial (angular) resolution required, and the ability to detect these perturbations amid a sea of noise. I once heard a good explanation of difficulty in such parts-per-billion measurements to the lay public. It is similar to searching and correctly identifying a few persons from the entire population of the world! Not only that, the exoplanet researchers were trying to determine how much faster or slower these few people are walking than the rest of the people in the whole world! My comments here can also be applied to the Course Radio Astronomy, a course I thoroughly enjoyed as well.
Date published: 2018-03-27
Rated 4 out of 5 by from Very informative Except for a little math this course explains extremely well exoplanets and their history.
Date published: 2018-03-27
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