Counting down to the Transit of Venus - our nearest exoplanet test-lab

Mar 05, 2012
Image showing refracted sunlight observed during the 2004 egress with the DOT telescope in La Palma. Note the changes in brightness and latitude extension of the aureole. Credit: Tanga et al. 2012)

( -- Three months before the last transit of Venus this century, scientists are gathering at the Observatoire de Paris to finalise their observation plans in a workshop supported by the Europlanet Research Infrastructure and the EGIDE/PHC Sakura Program.

The of on 5-6 June 2012 will give scientists two important opportunities for science: firstly, to use Venus as an example of a transiting exoplanet.  Astronomers will use the transit to test the techniques they have developed to analyse the composition, structure and dynamics of exoplanetary atmospheres. Secondly, they will be able to make simultaneous Earth- and space-based of Venus's atmosphere.  These joint observations will give new insights into the complex middle layer of Venus's atmosphere, a key to understanding the climatology of our sister planet.

'This transit of Venus will be the last of our lifetime and will give a unique opportunity to closely observe an Earth-like planet passing in front of a Sun-like star,' said Dr Thomas Widemann of the Observatoire de Paris, who is co-organiser of the workshop. 

This video is not supported by your browser at this time.
Movie showing refracted sunlight observed during the 2004 egress with NASA's TRACE satellite. Credit: NASA/Pasachoff/Schneider/Widemann

'Corot, Kepler have confronted us with the discoveries of more and more super-earth sized planets. Venus and Earth are sister planets, yet Venus evolved in a dramatic, different way. If Venus were an extrasolar transiting planet, what would we learn about its physical characteristics? What would we miss or misinterpret? We will use Venus transit observations to characterize the spectral signature of Venus, and test the detection limits of gases in the atmosphere,' said Widemann.

The transit also gives a rare opportunity to study the atmosphere of Venus from Earth. As Venus appears to make contact with the edge of the Sun's disk, it becomes outlined by a thin arc of light, called the aureole. This aureole is caused by light refracted through Venus's atmosphere and is 10-100 times fainter than the visible surface of the Sun. The brightness and thickness of the aureole depends on the density and temperature of the atmosphere and the altitude of the atmospheric layers above Venus's cloud tops.

Counting down to the Transit of Venus - our nearest exoplanet test-lab
Image showing refracted sunlight observed during the 2004 egress with a ground-based coronograph using a 9-cm refractor. Credit: Tanga et al., 2012.

Although the aureole was first reported by observers in 1761, the transit in 2004 was the first time it could be photographed.  The results of these observations are  published the March issue of the journal Icarus.

'We didn’t know until 2004 that the aureole could be easily observed and had science value.' said Dr Paolo Tanga of Laboratoire Lagrange, Observatoire de la Côte d'Azur, who led the study. 'From three sets of observations in 2004 we have been able to build up a model of the aureole for the first time.' 

Spatially resolved observations along the curve of the aureole will allow the scientists to work out whether atmospheric phenomena observed by Venus Express, which has been orbiting Venus since 2006, are associated with variations in time or are dependent on latitude. 

Widemann explained, 'We need ground-based observations to understand the rapid variations we see in Venus Express data. At the time of the transit, we can simultaneously measure the temperature structure at all latitudes from pole to pole, along the terminator, and allow a detailed comparison with Venus Express measurements.'

Tanga, Widemann and colleagues are building a set of eight coronographs, each working in a different wavelength, to monitor the aureole during the June transit.  The coronographs, assembled in OCA, will be used in locations around the world where the transit will be most observable (Svalbard in Europe, The Far East, the US West Coast and Australia). The observations will be compared with data from other ground-based observatories, as well as Venus Express and the Hubble Space Telescope.

'The transits are an interesting marker of mankind's technological advances,' said Widemann. 'In the eighteenth century, pendulum clock allowed accurate timings during a Venus transit – to measure the Astronomical Unit. In the 19th century, we had a new tool in photography. In the 21st century, we are able to observe the phenomenon from space and from Earth at the same time.  It would be interesting to know what tools will be available in the 22nd century!'

Explore further: Student to live in simulated space habitat

add to favorites email to friend print save as pdf

Related Stories

Venus Express spacecraft fires main engine

Feb 20, 2006

One hundred days after its launch to Venus, the European Space Agency's Venus Express has successfully tested its main engine for the first time in space.

Spacecraft Tandem Provide New Views of Venus

Jul 19, 2007

NASA's Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft, known as Messenger, and the European Space Agency's Venus Express recently provided the most detailed multi-point images of ...

Venus has an ozone layer too: probe finds

Oct 06, 2011

( -- ESA's Venus Express spacecraft has discovered an ozone layer high in the atmosphere of Venus. Comparing its properties with those of the equivalent layers on Earth and Mars will help astronomers ...

Venus: Earth’s twin planet?

Nov 29, 2007

ESA’s Venus Express has revealed Venus as never before. For the first time, scientists are able to investigate from the top of its atmosphere, down nearly to the surface. They have shown it to be a planet ...

Venus Express equipment test successful

Nov 28, 2005

A recent check of the VIRTIS imaging spectrometer during the Venus Express commissioning phase has allowed its first remote-sensing data to be acquired, using Earth and the Moon as a reference.

Recommended for you

Student to live in simulated space habitat

1 hour ago

A Purdue University industrial engineering doctoral student is among six "crew members" spending the next eight months in a domed habitat on a volcanic landscape mimicking life on a Martian outpost.

The wake-up call that sent hearts racing

4 hours ago

"But as the minutes ticked by, the relaxed attitude of many of us began to dissolve into apprehension. Our levels of adrenaline and worry began to rise."

US-India to collaborate on Mars exploration

13 hours ago

The United States and India, fresh from sending their own respective spacecraft into Mars' orbit earlier this month, on Tuesday agreed to cooperate on future exploration of the Red Planet.

Swift mission observes mega flares from a mini star

14 hours ago

On April 23, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star. The initial blast from this record-setting series ...

Sandblasting winds shift Mars' landscape

18 hours ago

High winds are a near-daily force on the surface of Mars, carving out a landscape of shifting dunes and posing a challenge to exploration, scientists said Tuesday.

PanSTARRS K1, the comet that keeps going

21 hours ago

Thank you K1 PanSTARRS for hanging in there! Some comets crumble and fade away. Others linger a few months and move on. But after looping across the night sky for more than a year, this one is nowhere near ...

User comments : 0