The Search for Exoplanets: What Astronomers Know

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.

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.

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.

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.

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.”

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.

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.

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.

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.

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.

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.

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.

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!

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.