The Search for Exoplanets: What Astronomers Know

Learning about the mission of exoplanetary science, which is the study of planets orbiting stars beyond the Sun; reviewing the planets in the solar system; a baseline for understanding the more than 1,000 worlds discovered in the Milky Way galaxy.

How astronomers can possibly find planets, given their faintness; direct and indirect methods of detection; discovering why a planet causes a star's position to change; a strategy for locating exoplanets without seeing them.

Exploring two indirect approaches for finding exoplanets; first, by measuring the Doppler shift in a star's color due to the pull of an orbiting planet; second, by measuring the drop in the brightness of a star as a planet transits in front of it.

Charting the history of exoplanet hunting; a false signal in the 1960s; ambiguous discoveries in the 1980s; the big breakthrough in the 1990s, when dozens of exoplanets turn up; astronomers find planets unlike anything in the solar system.

Investigating 51 Pegasi b, the first planet detected around a Sun-like star; it is roughly the size of Jupiter, but in an orbit much closer to its star than Mercury is to the Sun; probing the characteristics of these "hot Jupiters".

The standard theory of planet formation is based on the solar system; questioning whether this view requires revision based on the existence of misplaced giant planets; comparing competing theories that try to resolve this conflict.

A tiny percentage of exoplanets can be detected transiting their host stars; combined with Doppler shifts, transits provide information about a planet; how amateur astronomers can use this detection technique in their own backyards.

Surveying the history of spectroscopy; how a telescope and a diffraction grating can disclose the composition of a star and its planet; how transits and occultations are ideal for analyzing planetary atmospheres; the search for signatures of life.

Tracing Professor Winn's own search for the signs that tell whether a star has a tilted axis; why this is an important clue in the mystery of misplaced giant planets; how Professor Winn chances into the field of exoplanetary science.

How a new instrument leads the way in finding planets smaller than Jupiter-sized giants; halfway in size between Earth and Neptune, these worlds have uncertain properties; finding clues about their nature by considering the solar system's formation.

The planet search takes a leap forward in 2009 with the launch of the Kepler spacecraft; it uses the transit technique to observe nearly 200,000 stars; studying Kepler's goals and results; the persistence of the astronomer who champions it.

Digging deeper into the data from the Kepler mission, which discovers hundreds of compact multi-planet systems with closely packed planets; exploring the dynamics of these groupings, which have planets interacting through mutual gravitation.

How data from the Kepler spacecraft confirms the scenario of a planet with two suns; investigating the orbital mechanics of these systems; a double star complicates the heating and cooling cycle on a planet.

Exploring the theoretical limit of the smallest possible orbit for a planet, taking into consideration tidal stresses and other processes; focusing on Professor Winn's search for such objects, which find probable lava worlds.

The search for planets that may harbor life; the conditions that make Earth habitable, including its distance from the Sun, surface temperature, atmosphere and oceans; examining strategies for finding earthlike planets; the progress to date.

The most common stars are class M dwarf stars, which are smaller and less luminous than the Sun; Earth-sized planets are easier to detect around M-dwarf stars; exploring examples; the prospect for life on such worlds.

In billions of years, the Sun expands into a red giant, possibly engulfing Earth; how planet-finding techniques give astronomers insight into the processes inside giant stars; studying the planets around these stars for clues about Earth's fate.

Pinpointing the location of the nearest exoplanetary systems to Earth; the layout of the Milky Way galaxy; its size; the Sun's position; why the Kepler spacecraft focuses on exoplanets much more distant than those targeted by the Doppler technique.

Understanding 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.

Turning to direct imaging in the search for exoplanets; exploring the optics of telescopes to learn why spotting an exoplanet next to its parent star is difficult; seeing how this limitation is overcome in a handful of cases.

A wave of new projects to increase knowledge of worlds beyond the solar system; surveying ground- and space-based programs that are in the works; Professor Winn gives a preview of a space mission that he and his MIT colleagues are designing.

Peering into the future at projects that one day succeed in collecting light directly from an Earth-sized planet in the habitable zone of a nearby star; examining three different engineering approaches; the coronagraph, interferometer and starshade.

The quest for life on exoplanets; the search for extraterrestrial intelligence, a hunt for signals from alien civilizations inspired by a paper in 1959; how the Drake equation points to factors that determine how many such civilizations may exist.

The distinctive biosignatures that show the presence of life of any kind on an exoplanet; Professor Winn's tip sheet on exoplanetary discoveries likely in the near future; from the evidence of moons to planets being destroyed by giant stars.