The European Space Agency has administered the last rites to its Venus Express probe, saying that the spacecraft is now out of control and has gone "gently into the night."
"The available information provides evidence of the spacecraft losing attitude control most likely due to thrust problems during the raising maneuvers," said Patrick Martin, ESA's Venus Express mission manager. "It seems likely, therefore, that Venus Express exhausted its remaining propellant about half way through the planned maneuvers last month."
Venus Express was launched in 2005 and took station around its namesake four months later to map out the planet's weather systems. During the past eight years the craft has sent back images from one of the more bizarre atmospheres in the Solar System, and caused head-scratching with the discovery that Venus is slowing down.
Earlier Venus flybys and landing missions had taken measurements of the rotation rate of Venus to gauge its day-night cycle as the equivalent to 243.0185 Earth days. But the ESA probe's measurements showed Venus had slowed down 6.5 minutes in the past 16 years – which makes our leap year look like a very minor affair.
The probe's weather cameras have shown us the twin eyes of a constant 2,000 mile-wide storm that rages the South Pole of Venus, and its atmospheric testing equipment found evidence that the planet could once have had significant quantities of water and the materials for life as we know it.
That seems impossible now. The surface of the planet is a toasty 467°C (872°F), with light showers of sulfuric acid and clouds of sulfur dioxide floating in the lower atmosphere. Wind speeds are a brisk couple of hundred miles an hour, and Venus Express found that huge thunder and lightning storms also add to the hellishness.
The problem for the planet is its atmosphere, which is more than 96 per cent carbon dioxide. This keeps the planet very hot, even more so than its inner neighbor Mercury, but also makes it 93 times-denser than Earth's. It's that density that Venus Express has been testing – the hard way - in its last six months of operation.
When the Express started running out of fuel, ESA ordered it to try using Venus's thick atmosphere to aerobrake – using the atmosphere to slow down the spacecraft – to find out how much stress the design could take.
Aerobraking is key to space travel plans. Using planetary atmospheres to bring spaceships safely to ground saves huge amounts of costly and scarce fuel.
In 2010 the probe surfed across the very top of the dense atmosphere to gauge the beginnings of the braking effect caused by that much carbon dioxide. When the spacecraft's fuel supplies reached critical levels in May, ESA engineers decided to risk a deeper insertion.
The spacecraft controllers pushed the Express into a long elliptical orbit that dipped it as low as 130 kilometres (81 miles) from the surface of Venus. It survived a month-long acidic dunk, and on July 11 the ESA team boosted it back up to a safer orbit.
That last boost appears to have exhausted its fuel. As Venus Express drifted lower the team tried a second thruster maneuver on 23 November that would have seen the probe safe until next year, but the last dregs of fuel were insufficient.
Since then telemetry and command links with Venus Express have been growing steadily more garbled as the probe swoops deeper and deeper into the dense atmosphere. By now, the probe has most likely been torn apart by atmospheric resistance and spread across the rocky surface of Venus, but its discoveries will live on. ®