Lead turns to liquid at 327 degrees Celsius. Drop a bar of it onto the surface of Venus and it would be a puddle before you got the toolbox open.

NASA puts the average surface temperature there at about 467 degrees Celsius, conditions the agency describes as hot enough to melt lead. Mercury orbits more than 50 million kilometres closer to the Sun and still cannot match that. Daytime highs on Mercury reach roughly 430 degrees, and the moment the Sun sets, the same ground plunges to about minus 180, per NASA’s Mercury fact page.

Proximity to the Sun turns out to be a poor guide to how hot a planet gets.

What Mercury is missing

Mercury has no atmosphere worth the name, just a wisp of stray atoms that scientists call an exosphere. Sunlight hammers the surface directly, and the ground gives that heat straight back to space with nothing there to catch it.

So Mercury swings. Its day-to-night temperature range is the widest of any planet in the solar system, something like 600 degrees between noon and midnight.

It even holds water ice, tucked into crater floors near its poles where sunlight has never landed. Permanent frost survives on the closest planet to the Sun, because nothing there can shift heat from place to place.

Venus has the opposite problem, which is that it cannot get rid of anything.

How the trap works

Ninety-six per cent of the Venusian atmosphere is carbon dioxide, and it presses down on the ground at about 93 times the pressure you feel at sea level on Earth, roughly what a submarine hull deals with 900 metres under the ocean. That crush is one problem. The heat is separate, and it comes down to what carbon dioxide does to sunlight, not how hard the air pushes. Caltech’s Cool Cosmos explains the mechanism in plain terms: sunlight filters through and warms the surface, and most of the heat the surface gives off cannot escape through all that gas.

Carbon dioxide is transparent to visible light and opaque to infrared. Energy walks in the front door and finds the back door bricked up.

Earth carries a comparable amount of carbon, mostly locked away in limestone, chalk and seawater, filed into the crust by rain and rock chemistry over billions of years. Venus keeps its entire budget in the air.

Venus is also the most reflective of the planets, bouncing roughly seven-tenths of the sunlight that reaches it back into space, as EarthSky explains. Sulfuric acid clouds do the work, and they are the reason Venus is such a bright evening star. By the numbers, that should leave Venus cooler than Mercury, which absorbs almost everything that hits it. But the sliver that does get through has nowhere to go once the carbon dioxide closes around it, so it builds up instead of draining away.

Then there is the pace of the place. Venus rotates once every 243 Earth days, so any patch of ground sits in darkness for months without cooling much. That dense, mobile atmosphere shifts heat around the globe like water circulating in a saucepan, keeping the night side nearly as hot as the noon side.

What the landers found

Soviet engineers tested all of this the hard way. Venera 7 reached the surface in 1970 and transmitted for 23 minutes before it died, long enough to report a surface temperature of 475 degrees and pressure 90 times Earth’s, according to the Planetary Society’s catalogue of every Venus mission. Venera 8 lasted 50 minutes two years later and confirmed there was enough light down there for a photograph. Venera 13 went on to send home the first colour images ever taken from Venus’s ground, catching a flat stretch of orange-tinted rock scattered with loose grit and thin angular slabs.

Every one of those landers cooked. The best of them managed about two hours.

That is what 467 degrees means in practice: a hard deadline for anything you build.

Whether Venus was ever any different

Was it always like this? The long-standing story says it wasn’t: Venus once held oceans, and a runaway greenhouse effect drove them off, as heat pushed water vapour into the sky until it trapped enough extra warmth to boil the seas dry.

A 2024 paper in Nature Astronomy pushed back on that. Tereza Constantinou and her colleagues at the University of Cambridge studied the chemistry of volcanic gases in the atmosphere and inferred that the planet’s interior is bone dry, which points to a Venus that formed hot and never hosted surface water at all. One paper is one paper, and other planetary scientists have flagged genuine uncertainties in the deep-atmosphere chemistry the argument rests on. The question is still open, and it matters well beyond Venus. Astronomers keep finding planets the size of Venus around other stars, and how they read those worlds depends on whether a scorched, dry rock like this one is a failed Earth or one that never had the chance.

It may not stay open for long. NASA’s DAVINCI mission, due to launch in the early 2030s, will drop a probe through the cloud deck, sampling gases the whole way down and photographing highland terrain that nobody has viewed from beneath the clouds since the 1980s. It will relay everything it gathers before it strikes the ground, since surviving the landing was never part of the plan.

Somewhere under all that carbon dioxide sits the answer to whether Earth got lucky or simply got the better address.