Europe on Wednesday unveiled plans to launch a major space observatory in 2024 aimed at finding planets orbiting other stars, one of the new frontiers of astronomy.

An unmanned probe named PLATO -- for PLAnetary Transits and Oscillations -- will look for telltale wobbles in starlight that point to an "exoplanet" moving in front of its host star, the European Space Agency (ESA) said.

The six-year mission has a budget of 600 million euros ($821 million), ESA said.

Equipped with 34 small telescopes and cameras, PLATO will scrutinise thousands of star systems.

Its will seek out Earth-sized planets and "super-Earths" that orbit stars in the so-called habitable zone, the agency said in a press release.

This is the distance at which surface water can exist in liquid form and thus nurture life, as opposed to existing permanently as ice or a vapour.

A total of 775 confirmed extrasolar planets have been found since the first was spotted in 1995, according to a tally kept by the website http://exoplanets.org.

Nearly 3,500 sightings by the specialist Kepler orbital telescope await confirmation.

So far, astronomers have only discerned uninhabitable planets made of gas, or rocky planets that are so close to the Sun that any atmosphere will have probably been stripped away by scorching heat.

Launched by a Soyuz rocket from ESA's base in Kourou, French Guiana, PLATO will take up position at the so-called L2 point, located 1.5 million kilometres (937,000 miles) from Earth.

L2 gives it year-round observation of the cosmos without the view being disturbed by the Sun, Earth or Moon.

It is the go-to place for space observatories. L2 has been used by Europe's Herschel, Planck and Gaia telescopes and is designated for NASA's eagerly-awaited James Webb Space Telescope (JWST).

PLATO will build on experience with France's 2006-2012 CoRot probe and with Cheops, a 30-centimetre (12-inch) planet-hunting telescope that will be launched in 2017 in partnership with Switzerland, said Alvaro Gimenez, ESA's director of science and robotic exploration.

"Its discoveries will help to place our own Solar System's architecture in the context of other planetary systems," said Gimenez.

PLATO was selected by ESA's Science Programme Committee in a beauty contest for projects in the agency's 2015-2025 "Cosmic Vision" initiative.

It saw off four rival bids: EChO (the Exoplanet CHaracterisation Observatory); LOFT (Large Observatory For x-ray Timing); MarcoPolo-R (to collect and return a sample from a near-Earth asteroid); and STE-Quest (Space-Time Explorer and QUantum Equivalence principle Space Test).