Distance from sun saved earth from Venus' fate

Similar in size and often referred to as twin planets, the earth and Venus evolved from common origins into two contrasting worlds - one dry and inhospitable, the other wet and teeming with life.

The reason has had science stumped, until now. Writing in the journal Nature on Wednesday, a Japanese research team said the answer was to be found in the planets' respective proximity to the sun.

Though relatively close on a cosmic scale - the earth is 150 million kilometres from the sun, and Venus 108 million kilometres - the planets most likely orbit on either side of a "critical distance" from their central star.

This would explain, the researchers contended, why two similar-sized planets, almost identical in their molten state at the moment of creation about 4.5 billion years ago, can look so different once solidified.

At some 12,000 kilometres, Venus' diameter is about 95 per cent that of the earth, and its mass about 80 per cent. It orbits between the earth and Mercury, the closest planet to the sun.

As for their differences: Venus has no surface water and a heavy, toxic atmosphere comprising almost exclusively carbon dioxide.