ESA Venus Express snaps swirling vortex

Credit: ESA /VIRTIS/INAF-IASF /Obs. de Paris-LESIA /Univ. Oxford

This ghostly puff of smoke is actually a mass of swirling gas and cloud at Venus' south pole, as seen by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard ESA's Venus Express spacecraft.

Venus has a very choppy and fast-moving atmosphere, although wind speeds are sluggish at the surface, they reach dizzying speeds of around 400 km/h at the altitude of the cloud tops, some 70 km above the surface.

At this altitude, Venus' atmosphere spins round some 60 times faster than the planet itself.

This is very rapid; even Earth's fastest winds move at most about 30% of our planet's rotation speed.

Quick-moving Venusian winds can complete a full lap of the planet in just four Earth days.

Polar vortices form because heated air from equatorial latitudes rises and spirals towards the poles, carried by the fast winds.

As the air converges on the pole and then sinks, it creates a vortex much like that found above the plughole of a bath.

Artist view of ESA Venus Express in orbit.

Credit: ESA

In 1979, the Pioneer Venus orbiter spotted a huge hourglass-shaped depression in the clouds, some 2000 km across, at the centre of the north polar vortex.

However, other than brief glimpses from the Pioneer Venus and Mariner 10 missions in the 1970s, Venus' south pole had not been seen in detail until ESA's Venus Express first entered orbit in April 2006.

One of Venus Express' first discoveries, made during its very first orbit, was confirming the existence of a huge atmospheric vortex circulation at the south pole with a shape matching the one glimpsed at the north pole.

This south polar vortex is a turbulent mix of warming and cooling gases, all surrounded by a 'collar' of cool air.

Follow-up Venus Express observations in 2007, including this image, showed that the core of the vortex changes shape on a daily basis.

Just four hours after this image the vortex looked very different and a day later it had morphed into a squashed shape unrecognisable from the eye-like structure here.

A video of the vortex, made from 10 images taken over a period of five hours, can be seen below. The vortex rotates with a period of around 44 hours.

The dynamic nature of the South polar vortex can be seen in this video sequence, composed of images obtained on 7 April 2007. 

The video is composed of a series of ten images taken over a period of five hours at half-hourly intervals, at a wavelength of 3.9 micrometres. 

The vortex is rotating with a period of about 44 hours. In video, the point of view of the observer has been rotated at the same rate so that the vortex appears stationary in the centre of the image. 

These images were obtained as part of the ‘VIRTIS movie’ sequence, previously reported on 7 May 2007. 

This movie shows that the vortex is very complex, with atmospheric gases flowing in different directions at different altitudes. 

The bright region at the top-centre appears to be the most active region and its brightness suggests that it is where atmospheric gases are flowing downward. 

Extending leftward from this point is an ‘S’-shaped feature which is seen frequently in the polar vortex. 

A very similar feature was observed at the northern polar vortex in 1979 by Pioneer Venus. 

Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. of Oxford

The swirling region shown in this VIRTIS image is about 60 km above the planet's surface. Venus' south pole is located just up and to the left of the image centre, slightly above the wispy 'eye' itself.

This image was obtained on 7 April 2007 at a wavelength of 5.02 micrometres. It shows thermal-infrared emission from the cloud tops; brighter regions like the 'eye' of the vortex are at lower altitude and therefore hotter.

ESA Rosetta: Amazing new photo of comet 67/P

OSIRIS narrow angle camera view of 67P/C-G from a distance of 1000 km on 1 August 2014. 

Credits: ESA/Rosetta/MPS for OSIRIS Team MPS /UPD /LAM /IAA /SSO /INTA /UPM /DASP /IDA

As the ESA's Rosetta spacecraft closes to within 1000 km of comet 67P/Churyumov-Gerasimenko, the Rosetta science team has released a new image and made the first temperature measurements of the comet's core.

The temperature data show that 67P is too hot to be covered in ice and must instead have a dark, dusty crust.

The new image was acquired on August 1st at 02:48 UTC by the OSIRIS Narrow Angle Camera onboard Rosetta at a distance of approximately 1000 km. It shows the rough surface of the double-lobed core in amazing detail.

Thermal observations of comet 67P/Churyumov-Gerasimenko were made by Rosetta's visible, infrared and thermal imaging spectrometer, VIRTIS, between 13 and 21 July, when Rosetta closed in from 14 000 km to the comet to just over 5000 km.

At these distances, the comet covered only a few pixels in the field of view and so it was not possible to determine the temperatures of individual features.

But, using the sensor to collect infrared light emitted by the whole comet, scientists determined that its average surface temperature is about -70°C.

Although -70°C may seem rather cold, importantly, it is some 20–30°C warmer than predicted for a comet at that distance covered exclusively in ice.

"This result gives us the first clues on the composition and physical properties of the comet's surface," says VIRTIS principal investigator Fabrizio Capaccioni from INAF-IAPS, Rome, Italy.

Other comets such as 1P/Halley are known to have very dark surfaces owing to a covering of dust, and Rosetta's comet was already known to have a low reflectance from ground-based observations, excluding an entirely 'clean' icy surface.

The temperature measurements provide direct confirmation that much of 67P's surface must be dusty, because darker material heats up and emits heat more readily than ice when it is exposed to sunlight.

"This doesn't exclude the presence of patches of relatively clean ice, however, and very soon, VIRTIS will be able to start generating maps showing the temperature of individual features," adds Dr Capaccioni.

As Rosetta approachs and later orbits the comet, the sensor will study the variation of daily surface temperatures in order to understand how quickly the surface reacts to solar illumination.

In turn, this will provide insight into the thermal conductivity, density and porosity of the top tens of centimetres of the surface—important data to help select a target site for Rosetta's lander, Philae.

ESA's Rosetta: Measuring the temperature of Comet 67P /Churyumov–Gerasimenko

The first temperature measurements of comet 67P/Churyumov–Gerasimenko were made between 13 and 21 July, when Rosetta closed in from 14 000 km to the comet to just over 5000 km. 

The observations were made by the spacecraft’s visible, infrared and thermal imaging spectrometer, VIRTIS, and revealed an average surface temperature of –70ºC. 

This implies the surface is predominantly covered in dust rather than ice, which would yield a lower temperature. 

The finding does not exclude localised patches of ice. The observations were made when the comet was roughly 555 million kilometres from the Sun. 

Credit: ESA

ESA's Rosetta spacecraft has made its first temperature measurements of its target comet, finding that it is too hot to be covered in ice and must instead have a dark, dusty crust.

The observations of comet 67P/Churyumov–Gerasimenko were made by Rosetta's visible, infrared and thermal imaging spectrometer, VIRTIS, between 13 and 21 July, when Rosetta closed in from 14 000 km to the comet to just over 5000 km.

At these distances, the comet covered only a few pixels in the field of view and so it was not possible to determine the temperatures of individual features but, using the sensor to collect infrared light emitted by the whole comet, scientists determined that its average surface temperature is about –70ºC.

The comet was roughly 555 million kilometres from the Sun at the time, more than three times further away than Earth, meaning that sunlight is only about a tenth as bright.

Although –70ºC may seem rather cold, importantly, it is some 20–30ºC warmer than predicted for a comet at that distance covered exclusively in ice.

"This result is very interesting, since it gives us the first clues on the composition and physical properties of the comet's surface," says VIRTIS principal investigator Fabrizio Capaccioni from INAF-IAPS, Rome, Italy.

1P/Halley comet

Indeed, other comets such as 1P/Halley are known to have very dark surfaces owing to a covering of dust, and Rosetta's comet was already known to have a low reflectance from ground-based observations, excluding an entirely 'clean' icy surface.

The temperature measurements provide direct confirmation that much of the surface must be dusty, because darker material heats up and emits heat more readily than ice when it is exposed to sunlight.

"This doesn't exclude the presence of patches of relatively clean ice, however, and very soon, VIRTIS will be able to start generating maps showing the temperature of individual features," adds Dr Capaccioni.

In addition to global measurements, the sensor will study the variation of the daily surface temperature of specific areas of the comet, in order to understand how quickly the surface reacts to solar illumination.

In turn, this will provide insight into the thermal conductivity, density and porosity of the top tens of centimetres of the surface. This information will be important in selecting a target site for Rosetta's lander, Philae.

It will also measure the changes in temperature as the comet flies closer to the Sun along its orbit, providing substantially more heating of the surface.

"Combined with observations from the other 10 science experiments on Rosetta and those on the lander, VIRTIS will provide a thorough description of the surface physical properties and the gases in the comet's coma, watching as conditions change on a daily basis and as the comet loops around the Sun over the course of the next year," says Matt Taylor, ESA's Rosetta project scientist.

"With only a few days until we arrive at just 100 km distance from the comet, we are excited to start analysing this fascinating little world in more and more detail."

Rosetta is an ESA mission with contributions from its member states and NASA.

Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI.

Rosetta will be the first mission in history to rendezvous with a comet, escort it as it orbits the Sun, and deploy a lander.

Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed.

By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in-situ observations, the Rosetta mission should become the key to unlocking the history and evolution of our Solar System, as well as answering questions regarding the origin of Earth's water and perhaps even life.

ESA Venus Express VITRIS: Ready to aerobrake through planet's atmosphere

This global view of the southern hemisphere of Venus is a mosaic of images obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express on 16 May 2006. 

The night-side hemisphere (in red at the top) is made of infrared images taken at 1.74 micrometres, showing the lower layers of the cloud deck surrounding the planet at about 45-km altitude. 

The day-side hemisphere (in blue at the bottom) is made of ultraviolet images taken at 480 nanometres. 

It shows the cloud top layer at about 65-km altitude. 

The red part of the central panel was taken at 3.8 micrometres, and shows the double vortex at the south pole, at an altitude of about 60 km, surrounded by a collar of ‘cold’ air. 

Credit: ESA /VIRTIS-VenusX IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)