Skip navigation

Tag Archives: habitable zone

Is Earth the only known world that can support life? In an effort to find life-habitable worlds outside our Solar System, stars similar to our Sun are being monitored for slight light decreases that indicate eclipsing, or transiting, planets (see section 9.2d, pp. 240-243). Many previously-unknown planets are being found, including over 700 worlds recently uncovered by NASA’s Kepler satellite.

Credit: Planetary Habitability Laboratory (UPR Arecibo)

Depicted above in artist’s illustrations are twelve extrasolar planets that orbit in the habitable zones of their parent stars. These exoplanets have the right temperature for water to be a liquid on their surfaces, and so water-based life on Earth might be able to survive on them. Although technology cannot yet detect resident life, finding habitable exoplanets is a step that helps humanity to better understand its place in the cosmos.

Links: APOD for full-size image; Kepler mission website.


A space-based observatory to search for planets orbiting alien stars has been selected as ESA’s third medium-class science mission. It is planned for launch by 2024.

The PLATO – PLAnetary Transits and Oscillations of stars – mission was selected by ESA’s Science Program Committee for implementation as part of its Cosmic Vision 2015-25 Program. The mission will address two key themes: what are the conditions for planet formation and the emergence of life, and how does the Solar System work? (See Chapter 9, p. 233.)

Credit: ESA (Thales/EADS Astrium)

PLATO will monitor relatively nearby stars, searching for tiny, regular dips in brightness as their planets transit in front of them, temporarily blocking out a small fraction of the starlight. By using 34 separate small telescopes and cameras, PLATO will search for planets around up to a million stars spread over half of the sky. It will also investigate seismic activity in the stars, enabling a precise characterization of the host sun of each planet discovered, including its mass, radius and age.

When coupled with ground-based radial velocity observations, PLATO’s measurements will allow a planet’s mass and radius to be calculated, and therefore its density, providing an indication of its composition.

The mission will identify and study thousands of exoplanetary systems, with an emphasis on discovering and characterizing Earth-size planets and super-Earths in the habitable zone of their parent stars – the distance from the star where liquid water could exist on the surface.

Data from ESA’s recently launched Gaia mission will help PLATO to provide precise characteristics of thousands of exoplanet systems. These systems will provide natural targets for detailed follow-up observations by future large ground- and space-based observatories.

Links: ESA press release.