On Tuesday, BBC4 broadcast two excellent Horizon documentaries from a few years back. An hour of “Mars: A Traveller’s Guide” from 2017 at 9pm followed by an hour of “Mission to Mars” from 2012/13at 10pm. Given that, fifty years ago, all we could see of the planet was a fuzzy reddish dot through a wobbly telescope, the scale and depth of visuals, quite apart from understanding in geology, geography, chemistry, atmospherics, etc. etc. was astonishing. It lifted the viewer literally into another world.

The opening commentary spoke enthusiastically about the first to land on Mars was alive today, and the programme would tell them “where to land and how to live”, with all the engaging conviction of the Disneyland tour guide. This was triggered by last month’s successful landing of NASA’s Perseverance rover, already adding to the billions of images we now have of the planet. Coming on top of the entertaining and scientifically plausible film The Martian and all our varied fixations with the Red Planet since Schiaparelli’s ‘canals’ triggered H.G. Wells “War of the Worlds” space amateur and scientific enthusiasts have seen colonisation as simply a matter of ingenuity and time.

In the cause of advancing science, expeditions to Mars make sense. But they are a dead-end. Mars is a dead world, closer to our Moon in its bleak inhospitability, with an atmosphere  0.6% as dense as our own, with polar ice caps that are not water but dry ice (CO2) because it gets as cold as -125degF there. As the planet has only 1/10^th the mass of Earth, it has lost almost all the atmosphere and water it once had. This makes the idea of “terraforming” into a habitable world a futile prospect, even if the necessary technology were developed.

If mankind were serious about colonising other worlds, we should ignore Mars and concentrate on Venus. The reason we don’t is, being shrouded in dense, acidic clouds, it provides few visuals and therefore doesn’t make good copy. But we ignore it at our peril. For, should another asteroid, such as the one that wiped out the dinosaurs, strike Earth, we will need a habitable alternative. We need our world to offer open air greenery to survive long-term. Given the cabin fever we are all suffering necause of Covid, livinf in cramped pressure domes and walking in space suits, Mars isn’t it.

Because of planetary alignment, a round trip to Mars will take three years, not least because it is 50 million miles further out from the sum. Venus, on the other hand,  orbits three times faster than Mars, giving many more alignments to work with. It is also only 25 million miles closer to the sun, halving the theoretical distance to travel.

But, quite apart from planetary logistics, we need to focus our best science on terraforming Venus into somewhere we could inhabit.

The basis and urgency for this longer-term and less media-savvy-approach lies in what we are doing to the planet we already inhabit: Earth. While Greta and a growing swathe of concerned people are urging everyone to ‘go green’ and some progress is being made by more enlightened governments, global warming has not been stopped, let alone reversed. Venus holds a lesson for us I n this, which we are yet to take seriously.

Ever since the Soviet Venyera probes started exploration in the 1960s, Venus may seem an even less hospitable world than Mars. Being Earth-sized, it has retained a substantial atmosphere. However, pressure on the surface is over 90 atmospheres (equivalent to 1,000-metre depth in the ocean) and a scorching 450 degC, whipped by gale force winds of 90% CO2. Lead would melt and life would seem impossible.

But, it was not always so. Some believe Venus had oceans and (possibly) life, as ‘recently’ as a billion years ago. But, as the sun grew warner, the oceans boiled away, water vapour creating a greenhouse effect, which released carbon from rocks . The resulting CO2 amplified the greenhouse effect, which ran away, giving the approximation to hell we find today.

Dealing with this may sound a daunting prospect, but the technology required to reverse developments on Venus towards making it habitable are close to those we need to develop a technical antidote for global warming on Earth: massive carbon capture on a planetary scale, releasing oxygen into the atmosphere as a by-product.

There will be no planting of trees or other living carbon sinks on Venus until the temperature is brought below 50 degC. There are organisms on Earth that tolerate massive pressure, such as the works that inhabit the Black Smoker hydrothermal vents on the ocean floor. Whether they could be bioengineered to withstand 450 degC to produce oxygen from CO2 seems a long shot. But if Venus’ clouds could be engineered to reflect much of the sunlight, if terraforming machines that  bound atmospheric carbon back into the rocks were built on the Moon and dropped onto the surface to work over centuries, Venus’ decline might be reversed.

This sounds—and is—fantastical, but so was powered flight to Julius Caesar, or space travel to Napoleon, or the iPhone to Alexander Graham Bell. The point is, the way we are going, we will need to pioneer such technology to deal with our self-made problems o Earth. And if we fail here, Mars will be no lifeboat for us. It will be several billion years before the Sun expands as a red giant and warms moons of the gas gieants, like Titan or Europa, into habitable worlds. Meantime, where else is there, but Venus?