When astronomers first started taking ultraviolet images of Venus , they were somewhat baffled by a mysterious ‘ Y ’ shape that covered the entire planet . But now researchers say they have an answer - high intensity winds are distorting a ‘ wave ’ of clouds to produce a stretched effect . The discovery could also reveal how similar processes take place on other slow-rotating bodies in the solar system . Scroll down for a video animation showing the effect . Spanish astronomers have revealed a new theory for a ' Y ' shape on Venus ( annotated image from the Pioneer Venus Orbiter in 1979 shown ) . They say it is formed by winds pushing a 'wave ' of clouds on the planet . These winds move faster at higher altitudes , creating the odd shape . The latest theory was proposed by astronomers from the Institute of Astrophysics of Andalusia ( IAA-CSIC ) in Granada , Spain , in collaboration with the university of the Basque Country and the Institute of Astrophysics and Space Sciences of Portugal . Venus is slightly smaller than Earth but has a similar mass . It is the second closest planet to the sun at a distance of about 67 million miles ( 108 million kilometres ) , and takes about 225 days to orbit the sun . One day on Venus lasts as long as 243 Earth days . Its thick and toxic atmosphere is made up mostly of carbon dioxide and nitrogen , with clouds of sulphuric acid droplets . It 's believed that its atmosphere contributed to a runaway greenhouse effect that made the planet inhospitable . The planet 's extreme high temperatures of almost 480°C ( 900°F ) make it seem an unlikely place for for life as we know it . On Venus strong winds move the upper atmosphere 225 mph ( 360km/h ) , circling the planet every four to five Earth days . But the planet itself takes almost 243 Earth days to complete an orbit - meaning the winds are much faster than the rotation speed of the planet . The winds have a mostly constant speed at different latitude , but nearer the pole they circle the planet quicker as the circumference of the planet is smaller . This ultimately gives rise to this ‘ Y ’ shape , as the clouds at the top and bottom of the shape are moved more quickly . 'This [ atmospheric ] wave is dragged by the winds of Venus , so if they are constant the wave should round the planet without getting deformed , right ? ' Dr Javier Peralta , the IAA-CSIC researcher in charge of this study , told MailOnline . 'But we must consider that these waves propagate over a `` sphere '' , and `` circles '' completed both at the equator and at 40ºN have a different radius ( the higher latitude , the smaller the parallels or circles are ) . 'So , having the same velocity than that at the equator , anything moving horizontally at 40º will complete the longitude of the circle sooner that when doing the same at the equator . 'This is why the wave gets deformed . The area of the wave at higher latitudes complete circles quicker than at the equator . ' Winds on Venus can circle the planet in four to five Earth days . But the planet takes 243 Earth days to rotate , amplifying the Y shape . The effect is also amplified by the winds moving round the planet quicker nearer the poles ( Marine 10 image from 1974 shown left ) . An illustration of the surface of Venus is shown on the right . He added that the idea was not entirely new - but his theory was the first that explained a new type of atmospheric wave , different to anything seen on Earth . Using the new type of wave , he said they could predict the vertical structure of the Y feature , and show that it was trapped about the altitude where the winds are strongest . The shape is defined with dark regions , produced by an unknown compound that absorbs ultraviolet radiation . The wave seems to be 'pushing up ' this ultraviolet absorber from below on Venus - although what this substance is , which gives the feature its dark appearance , remains a mystery . 'It has been a mystery for decades . Nobody knows for sure , ' added Dr Peralta . 'Many candidates have been proposed : hydrobromic acid , amorphous sulfur , disulphur monoxide or even living sources such as bacteria . ' The strange shape on Venus was first spotted by Nasa 's Mariner 10 spacecraft when it arrived at Venus in 1974 . An illustration of the spacecraft is shown here . The new theory could have important implications for other slowly rotating bodies in the solar system . As the clouds are pushed through the atmosphere , those either side are dragged behind , giving the whole planet a ‘ stretched ’ appearance when viewed in ultraviolet wavelengths . When viewed in visible light , the planet simply appears bright yellow or white - as the high amounts of carbon dioxide in the atmosphere reflect a lot of sunlight . The astronomers have also , for the first time , created a simulation that reproduces the evolution of the shape over the course of a month . Understanding the shape will allow astronomers to study the ‘ super-rotating ’ nature of the Venusian atmosphere . ‘ A wave with the size of the Y must play a key role in explaining why the atmosphere rotates sixty times faster than the surface , so it was crucial to understand it , ’ said Dr Peralta in a release .
Spanish astronomers have revealed a new theory for a ' Y ' shape on Venus . They say it is formed by winds pushing a 'wave ' of clouds on the planet . These winds move faster at higher altitudes , creating the odd shape . Winds on Venus can circle the planet in four to five Earth days . But the planet takes 243 Earth days to rotate , amplifying the Y shape .