Astronomers have discovered alien planet number 700 and the number are expected to pile up as scientists improve their planet-hunting techniques.

As of recent count, the Extrasolar Planets Encyclopedia, a database complied by astrobiologist Jean Schneider of the Paris-Meudon Observatory, has placed the total number of exoplanets stand at 702.

However, astronomers are expecting that the total tally of new planets will increase by hundreds or thousands in the near future.

In November 2010, the count topped 500. This increased to more than 600 in October 2011 when the European Southern Observatory announced 50 newfound planets including one "super-Earth" which scientists found to be a candidate for hosting life.

And the pace of discovery is only going to keep accelerating, as scientists continue to hone their planet-hunting techniques and the data continue to pour in.

In fact, one instrument, the NASA's Kepler space telescope, could more than double the number of known exoplanets. Since its launch in 2009, it has identified 1,235 planet candidates. Although only 25 of them have been confirmed, Kepler scientists said that an estimated 80 percent will end up as new finds.

The first discovery of an alien world was in 1992 when astronomers detected two planets orbiting a rotating neutron star, or pulsar, about 1,000 light-years from Earth. However, confirmation of a planet circling a "normal" main-sequence star other than our sun did not come until 1995.

Astronomers say that the search for alien planets is more than increasing the tally but rather it is about understanding the nature and diversity of alien worlds in our galaxy and beyond.

Indeed, the diversity is astounding. Astronomers have found one planet as light and airy as Styrofoam while another as dense as iron. Another one was found to orbit two suns. And most important, researchers have confirmed a number of planets which have qualities where life could exist.