Private mining companies and entrepreneurs will be licking their lips as they watch the skies this evening (19 July), as asteroid 2011 UW-158 – containing an estimated $5.4tn (£3.5tn) in platinum – hurtles past the Earth.

Asteroid 2011 UW-158, which is half a kilometre across, will come 30 times closer to the Earth than Mars – though still six times further away than the moon. This makes it too far away to be spotted with the human eye and observers are asked to use telescopes or watch live on the internet.

Slooh Community Observatory, which links telescopes to the internet so anyone with a link can watch, believes private companies may already be calculating how to exploit the natural resources of asteroids such as 2011 UW-158.

"It's always fun when an asteroid whooshes past our world so the Slooh telescopes will be watching live when asteroid 2011 UW-158 passes 30 times closer to us than the nearest planet, on July 19." says Slooh's Bob Berman.

Flat and jagged terrains make comet 67P/Churyumov-Gerasimenko look eerie in this image. ESA/Rosetta/NAVCAM

"What makes this unusual is the large amount of platinum believed to be lurking in the body of this space visitor. Can it be mined someday, perhaps not too far in the future?"

Under the 1967 space treaty, governments are forbidden from claiming ownership of any celestial body. However the treaty doesn't mention private companies, several of whom are already believed to be investigating the feasibility of mining asteroids.

One such company, Planetary Resources, recently launched a rocket called Arkyd 3 Reflight (A3R) from the International Space Station (ISS) as part of a 90-day mission to test the required components needed to mine asteroids.

Deep Space Industries have also expressed an interest in exploiting the resources of asteroids. The landing of the Rosetta drone on Comet 67P/Churyumov – Gerasimenko showed it is possible to meet and land on such objects despite their incredible speeds.

2011 UW-158 will zoom past the earth at around 11pm this evening but is expected to return in just three years' time – when it will be even closer, and possibly within reach for anyone with the resources and daring to snare it.