Astronomers are closing in on 1,000th alien planet to be discovered, just twenty years after spotting the first world beyond our solar system.

Four of the five main databases that catalogue the discoveries of exoplanets now list more than 900 confirmed alien worlds, and two of them puts the tally at 986.

Therefore, the 1,000th exoplanet may be announced in a matter of days or weeks, SPACE.com reported.

In 1992, researchers detected two planets orbiting a rotating neutron star, or pulsar, about 1,000 light-years from Earth, however, confirmation of the first alien world circling a “normal” star like our Sun did not come until 1995.

The largest number of discoveries of such planets in the near future could come from NASA’s Kepler space telescope, which racked up many finds before being hobbled in May this year, researchers say.

The telescope has already identified a staggering 3,588 planet candidates and scientists believe at least 90 per cent of them will end up being the real deal.

These numbers, however, represent just the tip of our Milky Way galaxy’s immense planetary iceberg.

Researchers have estimated that every Milky Way star hosts, on average, 1.6 planets — meaning that our galaxy perhaps harbours 160 billion such worlds.

Researchers, in 2011, calculated that “rogue planets” — which cruise through space unbound to a star — may outnumber “normal” exoplanets by 50 per cent or so, the report said.

For instance, scientists have found exoplanets as light and airy as Styrofoam and others as dense as iron.

They have also discovered a number of worlds that appear to orbit in their stars’ habitable zone — that just-right range of distances that could support the existence of liquid water and thus, perhaps, life.

More In: Science | Sci-Tech