Surprise results from Earth's long-lost twin

29 November 2007

A mini space lab, Venus Express, has spotted speeding clouds of acid and a hurricane the size of Europe in the atmosphere of Earth's nearest neighbour, Venus. But can our twin planet teach us lessons closer to home? Antenna zooms in...

This research was published in the journal Nature on 29 November 2007.

Seen here as an artist's impression, Venus Express is beaming back data from seven different experiments all crammed into the space of a fridge-freezer.

Image: ESA - AOES Medialab

Two years ago scientists launched a spaceship packed with equipment to investigate the atmosphere of Venus, Earth's nearest neighbour. This week, the first results from Venus Express have been released - and the researchers have had quite a surprise.

Scientists call Venus Earth's 'evil twin' because even though the two planets started life together, they couldn't look more different today. But the new research suggests the planets are actually quite similar - and that Venus could even teach us a lesson about climate change here on Earth.

In contrast to Earth's oceans and balmy temperatures, Venus is a scorching dry mass surrounded by clouds of concentrated sulphuric acid.

Image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

Venus scientist Colin Wilson explains: 'Taken all together, results from the seven experiments suggest that Venus is much more like Earth than we'd initially thought. We found that gases move around Venus's atmosphere in a similar way to Earth's - and even saw some suggestions of lightning on the planet.'

Science coordinator Dmitri Titov agrees: 'Studying Venus we're always looking back at Earth and trying to understand what we can learn from this planet about our own home. We conclude that Venus and Earth are really twins that were just separated at birth... they have different conditions but the same processes are running on both planets.'

Scientists found this thousand-kilometre hurricane swirling at Venus's South Pole. It's similar to a more moderate effect at Earth's poles in winter. This picture is made up of many smaller images: on the right is night, and on the left, day.

Image:ESA/VIRTIS-VenusX/INAF-IASF/Obs. de Paris-LESIA

But why does it matter that Venus is like Earth?

Colin explains, 'Knowing that Venus shares some features with Earth helps us compare the two planets accurately. And it lets us read more into any differences we do find - like Venus's severe greenhouse effect, or the differences in the chemicals that make the two planets up.'

Colin Wilson (far right) is part of a team working on the VIRTIS camera - one of the seven experiments aboard Venus Express.

Image: Oxford University/EADS Astrium

Like Earth, Venus has a greenhouse effect produced mainly by carbon dioxide (CO2) in its atmosphere. But with over 200,000 times more CO2 than on Earth, temperatures there reach a sweltering 450 degrees Celsius. Scientists think that analysing Venus's extreme conditions could help us to understand climate change here too.

'On Earth, we know how gases like CO2 influence the greenhouse effect - but we don't fully understand what effect clouds have,' says Colin. 'Venus has loads of clouds, which Venus Express is busy studying, and we hope to use this information to better understand the effect of clouds on Earth's climate.'

This image from Venus Express shows CO2 in Venus's atmosphere. On Earth, the greenhouse effect is triggering further climate change with deadly consequences.

Image: ESA/VIRTIS-VenusX/INAF-IASF/Obs. de Paris-LESIA

Image: iStockphoto/Ooyoo

Clouds on Earth sometimes help to reduce the greenhouse effect by bouncing sunlight back into space. But the clouds can also make the greenhouse effect worse by helping to trap heat inside the atmosphere. Scientists hope that analysing Venus's clouds will help them work out how these two effects balance out.

So why aren't the twin planets identical?

The mission has also given researchers a clue into what saved the Earth from Venus's fiery fate until now. The two planets were formed around 4.4 billion years ago from the same cloud of gas swirling around the sun. Earth developed oceans and moderate temperatures, but Venus turned hot and dry. So what made the two worlds so different?

The planets are similar in size and distance from the Sun.

Image: ESA

Colin explains: 'We've long suspected that Venus's water was lost from the atmosphere into space. Now two separate results from Venus Express suggest we were right. First, we looked at hydrogen in the atmosphere, a basic part of water, and saw evidence that it had been lost to space over time.'

Using this method, researchers have worked out that Venus could have lost enough water to make an ocean four metres deep around the planet. A separate experiment confirmed that hydrogen and oxygen - the basic parts of water - are still being lost to the atmosphere now.

Scientists say Venus's oceans could have been even deeper - they're analysing data from Venus Express to find out.

Image: iStockphoto/Pederk

And Colin says Earth could be next: ' The planets might in fact be following a similar life story. Venus might well have been pleasantly Earth-like in the past, before its greenhouse warming took off. So it's quite possible that the Earth will end up looking like Venus. But don't worry, this wouldn't happen until a billion years or so from now.'

Space scientist Colin Wilson thinks Earth could one day go the way of Venus.

Image: University of Oxford

So what's next for scientists studying Venus?

Results are still beaming back from Venus Express and a Japanese spaceship is due to arrive in 2010. But thanks to Venus Express's analysis of the planet's blustery atmosphere, future scientists may be able to send balloons to ride the winds and send back data for years to come.

These images from Venus Express show how clouds are carried by the planet's wind, which could help scientists use balloons to get a long-term picture of the planet.

Image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

Not up to date with the Venus Express mission? Catch up with these Antenna stories.