How soon we find a living exoplanet really depends on whether there's one relatively nearby, with the right orbit and size, and with biosignatures that we are able to recognize, Hu said. In other words, "There's always a factor of luck."

Scientists expect future space missions to detect hundreds of other exoplanets in coming decades.

A system of at least five exoplanets has been discovered by citizen scientists through a project called Exoplanet Explorers, part of the online platform Zooniverse, using data from NASA's Kepler space telescope.

The study of worlds outside our solar system will be continued by future spacecraft, such as NASA's Transiting Exoplanet Survey Satellite (TESS) and James Webb Space Telescope.

How do scientists detect exoplanets?

A new generation of space exploration instruments will be able to describe exoplanet atmospheres in much greater detail.

How do astronomers detect exoplanets?

The report from the National Academy of Sciences Committee on Exoplanet Science Strategy will be reviewed by Congress. Portions of it may be included in the final 2020-2030 Astronomy and Astrophysics Decadal Survey, which will fund the continuing search for exoplanets and the study of extraterrestrial life.

Exoplanets are planets that orbit other stars than the Sun.

Hu pioneered a method to detect surface minerals on bare-rock exoplanets and defined the atmospheric chemical signature of volcanic activity, which wouldn't occur on a gas planet.