After a 20-year search, astronomers have uncovered a grand total of 1,900 planets residing outside of the Solar System. According to a new Princeton study, the Gaia space observatory launched by the European Space Agency (ESA) could help that figure grow by a factor of ten by the end of the decade, eventually reaching 70,000 planets after 10 years of scouting.

The Gaia mission was launched late last year with the primary objective to accurately measure the position of up to a billion stars – one percent of the Milky Way’s population – via high-precision triangulation. In the process, the spacecraft is also expected to detect half a million quasars, tens of thousands of asteroids and comets within our solar system, and a large number of new, distant planets.

As planets orbit a star, gravitational effects cause the star to wobble in periodic and predictable patterns. By examining the star’s movement and breaking down the different wave components to the wobble, astronomers can identify both the number and the mass of orbiting planets in a given planetary system (the amplitude of the wobble relates to the planet’s mass, the period to the time it takes to complete a full orbit). According to a recent study, Gaia’s instruments are expected to be able to characterize the wobble of stars up to 1,000 parsecs (3,262 light-years) away.

The mission was first approved by the ESA in 2000, but our knowledge on the nature and distribution of exoplanets has greatly improved since then (for instance, one recent study claims that the Milky Way alone may be home to over 100 million planets capable of supporting complex life). Astronomers at Princeton have therefore revised their estimations and now believe that the probe may be able to detect an astonishing 20,000 planets during its five-year nominal mission, or up to 70,000 planets if the mission is extended to 10 years.

In Greek mythology, Gaia is the personification of Earth. There’s some irony in that name, given that the spacecraft won’t be able to detect distant Earths at all, but rather only planets that measure 1 to 15 times the mass of Jupiter and mostly have long orbital periods. But, despite this, the mission will still be able to provide a wealth of valuable information.

"It’s not just about the numbers," says Michael Perryman, who authored the study. "Each of these planets will be conveying some very specific details, and many will be highly interesting in their own way. If you look at the planets that have been discovered until now, they occupy very specific regions of discovery space. Gaia will not only discover a whole list of planets, but in an area that has not been thoroughly explored so far."

Most of the exoplanets discovered so far have been the work of Kepler in a small section of the sky (Image: Michael Perryman)

Out of the sheer number of planets they’ll discover, the researchers expect 25 to 50 of them to be very rare finds  –  "transiting planets" that were placed exactly between the spacecraft and the star at the time the observation took place. Another 1,000 to 1,500 planets will be orbiting M-class dwarf stars up to 100 parsecs (324 light-years) from Earth.

That should be enough to satisfy astronomers’ thirst for exoplanets at least until 2018, when the much more capable James Webb space telescope comes online.

A study describing the capabilities of the Gaia spacecraft was just accepted for publication in the Astrophysical Journal.

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