"We knew it was a long-term vortex; we also knew that it changes shape every day. But we thought that the centres of the vortex at different altitudes formed only a single tube, but that is not so. Each centre goes its own way, yet the global structure of the atmospheric vortex does not disintegrate," explains Itziar Garate-Lopez, head researcher and member of the UPV/EHU's Planetary Science Group.

In fact, the centres of rotation of the upper and lower vortex rarely coincide in their position with respect to the vertical, and as the researchers have published in their paper, "they form a constantly evolving permanent structure" on the surface of Venus.

Long-term vortices are a frequent phenomenon in the atmospheres of fast rotating planets, like Jupiter and Saturn, for example. Venus rotates slowly, yet it has permanent vortices in its atmosphere at both poles. What is more, the rotation speed of the atmosphere is much greater than that of the planet.

"We've known for a long time that the atmosphere of Venus rotates 60 times faster than the planet itself, but we didn't know why. The difference is huge; that is why it's called super-rotation. And we've no idea how it started or how it keeps going."

The permanence of the Venus vortices contrasts with the case of the Earth. "On the Earth there are seasonal effects and temperature differences between the continental zones and the oceans that create suitable conditions for the formation and dispersal of polar vortices. On Venus there are no oceans or seasons, and so the polar atmosphere behaves very differently," says Garate-Lopez.

Looking at the poles of Venus
The UPV/EHU group has been able to monitor the evolution of the south pole vortex thanks to one of the instruments on board the European Space Agency's Venus Express spacecraft, which has been orbiting our neighbouring planet since April 2006.

"The orbit of this craft is very elliptical: it gets very close to the North pole and South pole, yet the planet is observed from a greater distance, which allows a more global vision to be obtained.

This is what we needed for our study, a more complete view of the vortex and at a lower speed, so that the instrument we used could capture the images we needed." Also needed was a more extended view offering a detailed view of the planet's south pole, whereas the north pole is observed from much shorter distances, which prevents it from being observed globally," explains Garate-Lopez.

The UPV/EHU astronomers have been using the VIRTIS-M infrared camera on the Venus Express probe and have been analysing data obtained in the course of 169 earth days, and in particular, they have been studying in great detail the data on the 25 most representative orbits.

Garate-Lopez explains that this is no straightforward task: "This camera doesn't take individual photos like an ordinary camera, it divides the light into different wave lengths that enable various vertical layers of the planet's atmosphere to be observed simultaneously. Besides, we have compared images separated by one-hour intervals and this has enabled us to monitor the speed at which the clouds move," says Garate-Lopez.

The UPV/EHU astronomers Agustin Sanchez-Lavega, director the Planetary Science Group, Ricardo Hueso and Itziar Garate-Lopez have been working in collaboration with experts from the Astrophysics Institute of Andalusia (CSIC-Spanish Scientific Research Council), the Astronomical Observatory of Lisbon (CAAUL), the Paris Observatory and the Institute of Space Astrophysics and Cosmic Physics in Rome. Garate-Lopez, I., R. Hueso, A. Sanchez-Lavega, J. Peralta, G. Piccioni, P. Drossart. A chaotic long-lived vortex at the southern pole of Venus. Nature Geoscience, 24 March 2013, DOI: 10.1038/NGEO1764.

]]> Wed, 12 JUN 2013 00:36:16 AEST Pasadena CA (JPL) Mar 07, 2013 - A distant world gleaming in sunlight, Earth's twin planet, Venus, shines like a bright beacon in images taken by NASA's Cassini spacecraft in orbit around Saturn.

One special image of Venus and Saturn was taken last November when Cassini was placed in the shadow of Saturn. This allowed Cassini to look in the direction of the sun and Venus, and take a backlit image of Saturn and its rings in a particular viewing geometry called "high solar phase." This observing position reveals details about the rings and Saturn's atmosphere that cannot be seen in lower solar phase.

One of the Venus and Saturn images being released is a combination of separate red, green and blue images covering the planet and main rings and processed to produce true color. Last December, a false-color version of the mosaic was released.

Another image, taken in January, captures Venus just beyond the limb of Saturn and in close proximity to Saturn's G ring, a thin ring just beyond the main Saturnian rings. The diffuse E ring, which is outside the G ring and created by the spray of the moon Enceladus, also is visible.

Venus is, along with Mercury, Earth and Mars, one of the rocky "terrestrial" planets in the solar system that orbit relatively close to the sun. Though Venus has an atmosphere of carbon dioxide that reaches nearly 900 degrees Fahrenheit (500 degrees Celsius) and a surface pressure 100 times that of Earth's, it is considered a twin to our planet because of their similar sizes, masses, rocky compositions and close orbits. It is covered in thick sulfuric acid clouds, making it very bright.

]]> Wed, 12 JUN 2013 00:36:16 AEST Paris (ESA) Feb 01, 2013 - Measurements obtained with ESA's Venus Express spacecraft have shed new light on the interaction between the solar wind and the second planet from the Sun. During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet.

Scientists have long known about the existence of the solar wind, a continuous outflow of electrons and protons which flows at high speed across interplanetary space. However, this stream of charged particles is highly variable, both in speed and density.

Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999. Although such unusual episodes have been studied near Earth, which is surrounded by a strong magnetic field, there have been very few opportunities to study what happens near planets with negligible magnetic fields, such as Venus.

A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun. NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day.

Meanwhile, Venus Express, which is in an extremely elliptical, near-polar orbit, was able to study the interaction between this sparse solar wind and the planet's ionosphere - the electrically charged region of its upper atmosphere.

The ionosphere is created by incoming extreme ultraviolet light and X-rays from the Sun which splits the atoms in the upper atmosphere of Venus and creates a layer of electrons and ions.

The key data for the ionosphere came from two instruments on board Venus Express: the magnetometer, which continuously measures the local magnetic fields, and the Analyser of Space Plasmas and Energetic Atoms (ASPERA-4), which measures the energy and masses of ions when the spacecraft is closest to Venus. The instruments showed that the solar wind density at Venus decreased to 0.2 particles per cubic cm, while the dynamic pressure dropped to 0.1 nPa - about 50 times lower than normal.

Detailed analysis of the data from Venus Express has been published recently in the journal Planetary and Space Science by an international team of scientists. The measurements showed that the typical features of the ionosphere's tail region, on the night side of Venus, were no longer present during the period of sparse solar wind.

Previous spacecraft measurements have established that most of the ionospheric plasma (ionised gas) on the night side of Venus is supplied by plasma moving across the terminator, from the day side to the night side, driven by plasma pressure gradients. This nightward flow, which mainly involves oxygen ions (O+), takes place about 150-300 km above the surface of Venus, with a flow speed reaching several kilometres per second.

On 4 August, this flow pattern was clearly disrupted. As Venus Express flew behind the terminator, between 300 km and 15 000 km above the planet, its instruments revealed that the O+ plasma was moving much more slowly than usual for this location.

"The data indicate that the O+ flow across the terminator was still taking place, but it was observed to be travelling more slowly, and over a much wider region, than it does under normal solar wind conditions," said Yong Wei, a researcher at the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany, who was the lead author of the paper.

"We believe that the low solar wind pressure, which results in weaker magnetic fields, makes it easier for ions to flow from the day side to the night side of the planet."

The data also provide new insights into the processes which shape the ionosphere around Venus and the rate of loss of atoms from the upper atmosphere.

It has been known for a long time that tenuous solar wind has two competing effects on the night-side ionosphere. The ionosphere above the terminator becomes higher, enabling plasma to pass more easily from the day side to the night side, and the lack of magnetic fields tends to enlarge the size of the night-side ionosphere.

On the other hand, the weaker pressure may cause lower flow speeds of this plasma. The new Venus Express data show conclusively that the first effect outweighs the second, enabling the ionosphere to expand in the planet's wake.

"The observations show that the night side ionosphere moved outward to at least 15 000 km from Venus' centre over a period of only a few hours," said Markus Fraenz, also from the Max Planck Institute for Solar System Research, who was the team leader and a co-author of the paper. "It may possibly have extended for millions of kilometres, like an enormous tail."

"Although we cannot determine the full length of the night-side ionosphere, since the orbit of Venus Express provides limited coverage, our results suggest that Venus' ionosphere resembled the teardrop-shaped ionosphere found around comets, rather than the more symmetrical, spherical shape which usually exists."

The results also show that erosion of the planet's upper atmosphere by the solar wind ceases when the wind nearly disappears, but may be enhanced in the aftermath of such a period. A large "bubble" of slow-moving ions is formed behind the planet and when pressure increases again this bubble will partly be lost into space, temporarily accelerating the rate of erosion again.

"This is another example showing that use of similar techniques at Venus, Earth and Mars is a powerful tool for comparative planetology," said Hakan Svedhem, ESA's Venus Express Project Scientist. "We are now able to compare what happens when an extremely weak solar wind regime impacts the inner planets.

"It also shows the importance of having access to data from an international fleet of spacecraft, in which NASA's STEREO can act as a solar wind monitor whilst ESA's Venus Express and Mars Express are inside planetary ionospheres and observing their interaction with the solar wind."

Y. Wei, et al., "A teardrop-shaped ionosphere at Venus in tenuous solar wind", 2012, Planetary and Space Science, 73, 1, 254-261, DOI:10.1016/j.pss.2012.08.024

]]> Wed, 12 JUN 2013 00:36:16 AEST Williamstown, MA (SPX) Jan 14, 2013 - Many people around the world were thrilled to see a transit of Venus in June (June 5 in the United States and June 6 in Asia, on the other side of the International Dateline), the dark silhouette of Venus passing in front of the Sun. Jay Pasachoff of Williams College (Williamstown, MA) and the California Institute of Technology (Pasadena, CA) and Glenn Schneider (Steward Observatory, University of Arizona) organized extensive observations of the transit.

With support from the Committee for Research and Exploration of the National Geographic Society, they observed the six-hours of the transit from the 10,000-foot mountaintop of Haleakala on Maui, Hawaii.

The event was a rare opportunity to see close up, in our own solar system, the type of transit that is being studied by many scientists around the world using NASA's Kepler spacecraft and ground-based telescopes. Some thousands of these exoplanet transits have been seen.

Though it was widely and correctly said that the 2012 transit of Venus was the last to be seen before the year 2117, that restriction applies only if you are limited to observing from Earth.

The Pasachoff-Schneider team subsequently organized observations of a transit of Venus that was occurring if you were on Jupiter on September 20, using NASA's and ESA's Hubble Space Telescope to observe the reflection of sunlight off Jupiter's clouds.

Subsequently, they used NASA's Cassini mission, in orbit around Saturn, to try to observe the December 21, 2012, transit of Venus that was occurring if you were on Saturn.

The data are still under study for the Jupiter and Saturn events, and it cannot yet be said whether the attempts to detect the transit succeeded.

Pasachoff, with his colleagues as co-authors, is presenting his team's observations of transits of Venus as an analog to exoplanet transits at the 221st meeting of the American Astronomical Society being held on Sunday, January 6th, through Thursday, January 10th, in Long Beach, California.

The scientific paper is scheduled for Wednesday morning, and Pasachoff will participate in a press conference related to exoplanets on Tuesday morning.

The observations using 14 orbits of the Hubble Space Telescope to study Jupiter, at both ultraviolet and infrared wavelengths, in September were joint with David Ehrenreich of the Observatory of Geneva, Switzerland, and Alfred Vidal-Madjar, of the Institut d'Astrophysique in Paris, France. The observations will be studied with the help of a grant from NASA through the Space Telescope Science Institute.

The observations using the Cassini spacecraft in December were headed by Philip Nicholson of Cornell, who is on the Cassini team. Each of those transits, at Jupiter and Saturn, lasted about 10 hours, with a drop in the solar intensity of only a hundredth of a percent.

Based on their study of the previous transit of Venus visible from Earth, in 2004, using a NASA spacecraft as well as their own ground-based observations, Pasachoff and Schneider concentrated their efforts on studying Venus's atmosphere. It becomes visible as a bright whisker or arc on the edge of Venus for several minutes before Venus entirely enters the solar disk and after Venus entirely leaves the Sun.

As part of the team, Kevin Reardon of the National Solar Observatory, then also at the Arcetri Observatory, Florence, Italy, used the Dunn Solar Telescope on Sacramento Peak, New Mexico, to observe Venus's atmosphere at high resolution as Venus entered the Sun.

From sites in the continental United States, Venus and the Sun set partway through the transit, so only the opening phases were observable. These observations were also supported by Pasachoff's grant from the Committee for Research and Exploration of the National Geographic Society.

Because of the predicted visibility of Venus's atmosphere, Paolo Tanga of the Observatory in Nice, France, and Thomas Widemann of the Observatory of Paris in Meudon, France, prepared nine identical telescopes especially to observe Venus's atmosphere at the June 2012 transit.

These telescopes are called coronagraphs, since they block out the everyday solar surface, as do specialized telescopes for studying the solar corona. One of them was with Pasachoff and Schneider at Haleakala, where it was operated by Bryce Babcock and undergraduate Muzhou Lu '13 of Williams College.

It had a blue filter, and its results will be compared with those from the 7 other coronagraphs used photographically, with two each having blue, yellow, red, and infrared filters, respectively.

The ninth coronagraph was used visually by Minnesota historian of science William Sheehan to detect Venus's atmosphere; Pasachoff and Sheehan have written articles showing that the scientist long credited with discovering Venus's atmosphere, at the 1761 transit, in all likelihood did not actually see it.

Determining just what could be seen visually of Venus's atmosphere, with both modern and ancient telescopes, helps researchers today to interpret the old situation.

On Haleakala, Schneider had brought a small telescope; he and Pasachoff were able to see Venus's atmosphere with their own eyes looking through it, with a suitable safe solar filter, of course, always necessary for looking at the Sun except during totality of a total solar eclipse (of which Pasachoff and Schneider have each seen 30, most recently in Queensland, Australia, on November 13/14).

Also at the site with telescopes and electronic cameras as part of the Pasachoff-Schneider team was Ronald Dantowitz of the Clay Center Observatory (Brookline, MA). His equipment took hundreds of thousands of short exposures, the rapidity of the images helping counteract the 40 mph winds at the Haleakala site. The images clearly show the transit and Venus's atmosphere.

During the summer of 2012, undergraduate student Eric Edelman of Wesleyan University, sponsored by the NSF's student research support for the Keck Northeast Astronomy Consortium, worked at Williams College with Pasachoff on these and other transit-of-Venus images.

Another major US site for observation was the New Jersey Institute of Technology's Big Bear Solar Observatory in California. Vasyl Yurchyshyn of their staff led the observations; Joseph Gangestad, a Williams College alumnus now at The Aerospace Corporation, represented the Pasachoff-Schneider group there.

The observations with Big Bear's New Solar Telescope showed not only the atmosphere of Venus very well but also the so-called black-drop effect that delayed scientists' discovery of the size and scale of the universe for centuries. Pasachoff, Schneider, and Leon Golub of the Harvard-Smithsonian Center for Astrophysics explained the cause of the black-drop effect fully for the first time based on a previous spacecraft observation of a transit of Mercury, and then observed it at the 2004 transit of Venus. The extensive observations of the black drop in 2012 will lead to further analysis and confirmation.

The observations of the details of the transit, and the visibility of Venus's atmosphere, showed the moving parts that go into any transit observation, for planets in our solar system or outside it.

Only about 90% of the dips in stellar brightness observed with the Kepler spacecraft are actually from exoplanet transits, so it is especially important to understand all the workings of transits.

The closest analog in our own solar system to exoplanet transit observations are made by two NASA spacecraft that study the Total Solar Irradiance, the total amount of energy received from the Sun each second on a unit of area at the Earth's average distance from the Sun.

Collaborating scientists who run their respective spacecraft that measure TSI are Richard Willson of ACRIMsat for his Active Cavity Radiometer Irradiance Monitor 3 instrument, and Greg Kopp of the University of Colorado for SORCE/TIM (Solar Radiation and Climate Experiment/Total Irradiance Monitor).

They have provided graphs, which are being shown by Pasachoff in his talk, that show the 0.1% dip in solar intensity that occurred because of Venus's blocking that tiny bit of the Sun from being visible from Earth's vantage point.

Coordinated observations during all three transits were made from all possible spacecraft aloft to study the Sun, so that variations on the Sun itself could be monitored and separated from the effect of the transit as seen from Earth, Jupiter, and Saturn, respectively.

The spacecraft-related scientists who collaborated, coauthors on the paper, include Alphonse Sterling of NASA's Marshall Space Flight Center and Murray Silverstone of the University of Alabama at Tuscaloosa for the Japanese-American Hinode spacecraft's Solar Optical Telescope; Philip Scherrer and Jesper Schou of Stanford University for their Helioseismic Imager on NASA's Solar Dynamics Observatory; and Leon Golub, Patrick McCauley, and Kathy Reeves for data processed from their XRT x-ray telescope on Hinode.

The Atmospheric Imaging Assembly on Solar Dynamics Observatory also observed the transit. The European Space Agency's Solar and Heliospheric Observatory was so far toward the Sun from the Earth that no transit of Venus was visible for its instruments.

Much work remains to be done on the data from the three transits of Venus. But there won't be another transit of Venus visible from Earth until 2117, another transit of Venus visible from Jupiter until 2024, or another transit of Venus visible from Saturn until 2028.

The collaborating scientists will soon apply for observing time with the Hubble Space Telescope for the 2014 transit of Earth that would be visible from Jupiter, since it would be exciting to detect Earth's atmosphere in an analogous way to the current observations of exoplanet atmospheres, and to provide therefore a test of current methods of observation and analysis.

Paper to be delivered, Wednesday morning, January 9, 2013: Pasachoff, Jay M., Glenn Schneider, Bryce A. Babcock, Muzhou Lu, Eric Edelman, Kevin Reardon, Thomas Widemann, Paolo Tanga, Ronald Dantowitz, Murray D. Silverstone, David Ehrenreich, Alfred Vidal-Madjar, Philip D. Nicholson, Richard C. Willson, Greg A. Kopp, Vasyl B. Yurchyhyn, Alphonse C. Sterling, Philip H. Scherrer, Jesper Schou, Leon Golub, Patrick McCauley, and Kathy Reeves, "Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn," 221st AAS Meeting, Long Beach, CA, January 9, 315.06.

Also: Edelman, Eric, Jay M. Pasachoff, Glenn Schneider, Bryce A. Babcock, Muzhou Lu, Kevin Reardon, Thomas Widemann, Paolo Tanga, and Ronald Dantowitz, 2013, "The 2012 Transit of Venus: A Closer Look at the Cytherean Aureole," 221st AAS Meeting, Long Beach, 353.04.

]]> Wed, 12 JUN 2013 00:36:16 AEST Paris (ESA) Dec 27, 2012 - Observations from NASA's Pioneer Venus orbiter, which reached Venus in 1978, suggested that Venus's ionosphere had two states: a magnetized state with a large- scale horizontal magnetic field and an unmagnetized state with no large-scale magnetic field but with numerous small-scale thin magnetic structures known as flux ropes.

Venus's ionosphere was observed to be in the unmagnetized state most of the time, but strong solar wind pressure shifted it to the magnetized state.

Now, using magnetic field observations made in 2008 and 2009 from the European Space Agency's Venus Express, Zhang et al. report a third state: a magnetized state with giant flux ropes.

The giant flux ropes, which form quite often, have strong magnetic fields and diameters of hundreds of kilometers.

They are considerably larger and have stronger magnetic fields than the flux ropes that were seen during the unmagnetized state.

lthough giant flux ropes have previously been seen in Venus's magnetotail, the authors believe this is the first observation of the phenomenon in Venus's ionosphere.

It is not yet known how the giant flux ropes form.

"Giant Flux Ropes Observed in the Magnetized Ionosphere at Venus" - Geophysical Research Letters, doi:10.1029/2012GL054236, 2012.

]]> Wed, 12 JUN 2013 00:36:16 AEST Huntsville AL (SPX) Dec 21, 2012 - Last June, astronomers urged sky watchers to observe the transit of Venus. It was a once in a lifetime opportunity, they said. The black disk of the second planet wouldn't crawl across the face of the sun again for more than 100 years. In fact, it's happening again this week--not on Earth, but Saturn.

"On Friday, Dec. 21st, there will be a transit of Venus visible from Saturn, and we will be watching it using the Cassini spacecraft," says Phil Nicholson, a Cassini science team member from Cornell University. "This will be the first time a transit of Venus has been observed from deep space."

Because Saturn is 10 times farther from the sun than Earth, this transit of Venus won't be so easy to see.

The silhouette of the second planet will be just a tiny black speck on the shrunken disk of a sun 10 times farther from Saturn than Earth. Cassini won't be beaming back any "beauty shots." Nevertheless, the spacecraft will be conducting potentially ground-breaking science.

"As Venus crosses the face of the sun, we will see if we can detect chemical compounds in the planet's atmosphere by looking at the spectrum of sunlight filtered by Venus," explains Nicholson.

This is, essentially, an experiment in exoplanet studies. NASA's Kepler spacecraft routinely discovers new planets around distant stars by looking for the minuscule reduction in starlight that occurs during a planetary transit. Watching Venus transit the sun from the faraway orbit of Saturn is a good analog.

"We already know what Venus's atmosphere is made of," says Nicholson. "But this will give us a chance to see if we can pull this information out of a faint, distant planetary transit."

The research team will be using Cassini's VIMS instrument. VIMS is an infrared spectrometer designed to tease out the chemical composition of Saturn and its moons. It isn't designed for planetary transits, but with a little ingenuity Nicholson and colleagues have figured out how to gather useful data.

"VIMS has a heavily-filtered 'solar port' 20 degrees off the main axis of the spectrometer. We use it to occasionally observe the sun for calibration purposes--or to watch the sun set in the atmosphere of Saturn's moon's Titan," says Nicholson.

"On Dec. 21st we'll be using the solar port to monitor the transit of Venus."

The images won't be very impressive. Only a few pixels will fit across the entire solar disk. But the researchers aren't looking for images. "We want spectra," says Nicholson. "Carbon dioxide, the main constituent of Venus's atmosphere, has several absorption bands squarely inside our 1 to 5 micron observing window."

VIMS will gather data for the entire 9 hours of the transit--as well as many hours before and after for comparison. "Even with so much observing time, we still might not detect any chemical signatures," cautions Nicholson. "The signals are going to be faint--only a few parts in a million--so this is an extremely difficult observation."

Nevertheless, Nicholson is looking forward to Friday. "While most people have to wait a hundred years for the next transit of Venus, we get to experience one right away. And if we make any discoveries at the same time... so much the better."

]]> Wed, 12 JUN 2013 00:36:16 AEST Rome, Italy (SPX) Dec 17, 2012 - A team of Italian astronomers performed a very difficult measurement for which it was necessary to use the most advanced instrumentation in combination with an unusual technique, so as to involve even the Moon as a natural astronomical mirror. The challenge was the observation of effect occurred during the transit of Venus across the Sun on June 6th, dubbed "Rossiter-McLaughlin effect".

This is a phenomenon that occurs when a celestial body passes in front of a star, hiding a part of its rotating surface and that produces a temporary distortion in the profiles of the spectral lines of light coming from the eclipsed star.

Astronomers led by Paolo Molaro, from INAF Astronomical Observatory of Trieste succeeded in this ambitious task, observing and measurirng the magnitude of this tiny effect. Their findings are published online in a paper of the journal Monthly Notices of the Royal Astronomical Society Letters, published by Oxford University Press.

The Rossiter-McLaughlin effect has already been observed in systems composed of two stars that eclipse each other, but it becomes more and more difficult to observe when the celestial body is the size of a planet, and moreover not so great as Jupiter but rather similar in size to the Earth, just as it is during the transit of Venus.

Measuring the extent of this weak effect on the light from other planetary systems through telescopes of the next generation such as E-ELT (the European Extremely Large Telescope) will be a useful tool for the search and study of exoplanets. Astronomers will be able to learn important orbital parameters in these systems and thus improve our understanding of the history of their formation.

"Critical to the success of this mission was the use of the HARPS spectrograph at ESO that now, along with his 'twin brother' installed at the Telescopio Nazionale Galileo (TNG) operated by INAF on Canary Islands, represents the state of the art for measuring radial velocities of celestial objects and the best hunter of planetary systems around other stars.

The measured magnitude of the effect is comparable to being able to track the speed of a person walking at a slow pace at a distance of 150 million kilometers, the space that separates us from the Sun.

Nowadays there is no other instrument capable of recording so tiny changes, especially if you only have a few hours to measure them" said Lorenzo Monaco, an Italian astronomer working at ESO.

But the mere use of HARPS would not be sufficient to achieve this result. The observations of the integrated light of the sun at high resolution are in fact extremely difficult to conduct and to overcome this problem, astronomers pointed their instruments to the Moon to capture the sunlight reflected from it.

For this reason, the transit was observed by astronomers in Chile when in fact it would be impossible to do so, since in that region of the world it was night. This unusual strategy has imposed special calculations to achieve the desired results.

"The transit of Venus seen from the Moon has a slightly different schedule than what has been observed on Earth," said Simone Zaggia from INAF Astronomical Observatory of Padua, who participated in the mission.

"The Moon was in fact 8 degrees ahead of the Earth and Venus reaches alignment with the Sun and the Moon about two hours later. The transit was also slightly longer than that observed on Earth because the Moon was above the plane of rotation of the Earth around the Sun".

Observations show that the partial eclipse on the solar disc produced by the transit of Venus has generated a modulation in the radial velocity of the Sun of less than one meter per second, which is just 3 km/h.

"The agreement with the theoretical models is around a few centimetres per second and is an amazing result ever reached before" says Mauro Barbieri, from University of Padua, who is also a member of the team. "Among other things, this change in velocity is comparable with that due to the natural expansion and contraction of our star. However, our observations have allowed us to clearly see the Rossiter-McLaughlin effect during transit".

The results obtained from these observations - the only ones with purely scientific purposes that have been carried out on the Earth during the last transit of Venus - will be of great help to astronomers, who in the next decade will be able measure this phenomenon in extrasolar systems, unleashing the full potential of new generation of telescopes such as the E-ELT.

"This measurement - says Paolo Molaro - foretells the sensational results that in a few years will be able to get thanks to the advent of the 40-meter class telescopes equipped with high-resolution spectrographs. This mammoth astronomical instruments will open for sure a new horizon in the study of orbital properties of other Earth-like planets that are found around other stars in our galaxy".

]]> Wed, 12 JUN 2013 00:36:16 AEST Paris (ESA) Dec 04, 2012 - For decades, planetary scientists have debated whether Venus possesses active volcanoes. The latest twist to the tale is provided by data sent back from ESA's Venus Express orbiter, revealing unexplained major changes in the amount of sulphur dioxide gas above the planet's dense cloud layer.

Since Earth and Venus are similar in size and mass, and both planets formed around the same time and in the same region of the Solar System, one might expect them to virtual twins.

However, Venus is enveloped by a thick blanket of clouds, composed mainly of sulphuric acid droplets. Hurricane force winds at the cloud tops sweep around the planet in only four days - a phenomenon known as super-rotation.

Beneath the clouds, the carbon-dioxide-rich atmosphere has a density 90 times greater than on Earth. This suffocating atmosphere acts like a greenhouse, trapping solar heat and causing the surface temperature to soar to around 460 degrees Celsius.

Although it is the closest planet to Earth and it has been visited by numerous spacecraft, Venus retains many mysteries. One enduring question is whether there are any active volcanoes.

Radar imagery has revealed more than 1000 volcanic structures and evidence of possible periodic resurfacing of the planet by floods of lava.

By studying emission of infrared radiation from lava flows around a volcanic mountain, Venus Express has also found indirect evidence that volcanism has taken place within the last 2.5 million years. However, no definitive proof of current volcanic eruptions has yet been found, and the debate continues to rage.

The latest contribution to the investigation into active Venusian volcanism comes from the SPICAV-UV spectrometer on board Venus Express, which has been in orbit around the planet since 2006.

By studying the SPICAV data, a team of scientists from France and Russia has discovered an unusual change in the amount of sulphur dioxide (SO2) gas in the upper atmosphere.

Rise and fall of sulphur dioxide.
The SPICAV data show that the concentration of SO2 above the main cloud deck increased slightly to about 1000 parts per billion by volume (ppbv) between 2006 and 2007, but then steadily decreased over the next five years, reaching only 100 ppbv by 2012. This is very reminiscent of a pattern observed by Pioneer Venus during the 1980s, the only other multi-year dataset of SO2 measurements.

Since Venus does not experience any seasons, the authors of the paper in Nature Geoscience suggest two possible explanations: periods of active volcanism, or long-term variability in the general circulation of the atmosphere.

"Sulphur dioxide is a key indicator of the processes taking place in the upper atmosphere of Venus," said Emmanuel Marcq, of LATMOS, Universite de Versailles-Saint-Quentin, France, the lead author of the paper.

"SO2 is known to be an important, and constant, constituent of the lower atmosphere of Venus. A steady supply of SO2 to high levels is provided by air rising from the hot, lower atmosphere. When it gets above the clouds, SO2 is rapidly destroyed by solar UV light, so it has a very short life, less than half a day, in the upper atmosphere of Venus."

"This means that the only explanation for a marked rise and fall in SO2 concentration at an altitude of 70 km is an enhanced injection of enriched gas from lower levels, beneath the clouds."

Although SO2 is an important constituent of volcanic outgassing, the authors of the paper suggest that the increase observed by Venus Express may be the result of a plume of heated gases rising to high altitudes, rather than a direct injection of SO2.

"An explosive volcanic eruption, rather like a more powerful version of the 1991 Mt. Pinatubo eruption on Earth, could act like a piston, blasting a column of gas up to these levels," said co-author Jean-Loup Bertaux, Principal Investigator for Venus Express SPICAV instrument that made the detections. "This extra convection could carry SO2 above the clouds and temporarily increase its concentration."

On the other hand, the amount of SO2 in the lower atmosphere has remained remarkably stable at very high levels over more than a decade, and there has been no evidence of an increase in thermal emission from the planet's surface to coincide with the changes observed by SPICAV.

This opens up the possibility that the increased levels of SO2 above the clouds could have been caused by a change in the global atmospheric circulation which increased the movement of gases from the lower to upper atmosphere.

"During periods of scarce SO2, there is usually a greater amount above the poles of Venus than near the equator," said Emmanuel Marcq. "However, this distribution pattern was reversed in our 2006-2007 data when SO2 was abundant.

This suggests that there may have been stronger advection (upwelling) near the equator of air from the lower, SO2 -enriched regions of the atmosphere until 2007. Over the same period of time, the mean UV brightness of the cloud tops also declined.

"It is possible that long-term variations occur in the atmospheric circulation, resulting in injections of SO2 from lower levels and changes in cloud chemistry, revealed by observations of UV absorption."

"The atmospheric circulation of the planet is not yet fully understood," said Jean-Loup Bertaux, "but we believe there may be two simple Hadley cells in which air rises at the equator, spreads out at cloud level towards the poles, then sinks toward the surface, before flowing back to the equator.

"Whichever explanation is correct, it seems that the shift in SO2 concentrations between the poles and equator, as well as the periodic rise and fall at high altitudes, are consistent with fluctuations in the SO2 supply from the lower atmosphere at low latitudes."

"There are very few opportunities to search for evidence of active volcanism on Venus," said Hakan Svedhem, ESA's project scientist for Venus Express.

"Since there are no other spacecraft studying Venus at the present time, Venus Express is the only means to find evidence for such activity. Although it is not yet possible to explain the results, the SPICAV data are very intriguing and show once again the similarities in the physical processes that occur on the terrestrial planets."

The results presented in this article are reported in "Variations of sulphur dioxide at the cloud top of Venus's dynamic atmosphere" by Emmanuel Marcq, Jean-Loup Bertaux, Franck Montmessin and Denis Belyaev, published in the 3 December issue of Nature Geoscience.

]]> Wed, 12 JUN 2013 00:36:16 AEST Los Angeles CA (SPX) Oct 18, 2012 - The very rare astronomical event of Venus, the nearest planet to Earth, passing in front of the solar disk on June 5th and 6th, 2012, was captured by an international team headed by Jay Pasachoff (Williams College and Caltech) and Glenn Schneider (University of Arizona) in the US, and Thomas Widemann (Paris Observatory in Meudon) and Paolo Tanga (Observatoire de la Cote d'Azur in Nice) in France.

A major observing site - from which Pasachoff, Schneider, and their team observed the June 5th event with a variety of instruments - was the 10,000-foot-high volcano Haleakala on Maui, Hawaii. (Some locations saw the transit on June 6th in their local time zones.)

No transit of Venus across the face of the Sun will be visible from Earth until the year 2117, 105 years in the future, so the Pasachoff/Schneider team felt an obligation to amass the fullest possible set of data not only to study in 2012 but also for the background of the astronomers of the 22nd century.

The first major goal was to study the atmosphere of Venus as it bent sunlight toward Earth. A second major goal was to provide an analog in our own solar system to the now-observed transits of thousands of exoplanet candidates discovered in recent years by the Kepler spacecraft and other telescopes on the ground and in space, presumably as exoplanets passed in front of their host stars. (Some 80 or 90 percent of those exoplanet candidates are real exoplanets; our detailed observations of a transiting planet in our own solar system, with our sunspotted Sun seen in two dimensions, may help scientists determine methods to tell which faraway events are real exoplanet transits.)

At Haleakala, Pasachoff and Schneider had one of nine coronagraphs, specialized telescopes to block out bright objects to reveal faint ones beside them (a type of telescope originally designed for viewing the solar corona without an eclipse). These coronagraphs were designed by Tanga and Widemann; the other eight coronagraphs were spread out at sites around the world.

The coronagraph at Haleakala was operated by Bryce Babcock of Williams College and Williams College undergraduate Muzhou Lu, using a blue filter. Tanga was at Flagstaff, Arizona, with a coronagraph using a yellow (visual) filter, while Widemann was at Svalbard in the Arctic with a coronagraph using an infrared filter.

This Venus Twilight Experiment was readied to study Venus's atmosphere as sunlight passed through the region of twilight there, and was bent by the atmosphere toward Earth.

The observations will be interpreted together with simultaneous observations made with the European Space Agency's Venus Express spacecraft, which is in orbit around that planet.

Other observations made by the Williams College Expedition on Haleakala were made with a series of advanced electronic cameras operated through telescopes by Ronald Dantowitz of the Clay Center Observatory, Dexter-Southfield Schools, Brookline, Massachusetts. Assisting on site were Robert Lucas of the University of Sydney and videographer Aram Friedman, Ansible Technologies.

Coordinated observations were made from the Sacramento Peak Observatory in Sunspot, New Mexico, by Williams College alumnus Kevin Reardon of the National Solar Observatory staff. He used the giant Dunn Solar Tower, which provided large-scale images of the Sun and is equivalent to a 55 thousand millimeter telephoto lens, giving a magnification about a thousand times greater than a "normal" camera lens.

Additional coordinated observations were made from the Big Bear Solar Observatory in California by Vasyl Yurchyshyn and by a bevy of NASA telescopes in space, including the Solar Dynamics Observatory's Atmospheric Imaging Assembly and Helioseismic Magnetic Imager; the Solar Optical Telescope and X-ray Telescope aboard the Japanese Hinode spacecraft; and two telescopes that continually monitor the total amount of light coming from the Sun: ACRIMsat operated by Richard Willson and SORCE/TIM operated by Greg Kopp.

Though it has been widely and correctly quoted that the 2004 and 2012 transits of Venus are the last such to be seen from Earth until 2117, the Pasachoff/Schneider group didn't give up their planet-transit quest in June.

They teamed up with French scientists David Ehrenreich of the Observatoire de Geneve, Switzerland, and Alfred Vidal-Madjar of l'Institut d'Astrophysique in Paris to use the Hubble Space Telescope to try to detect the transit of Venus that was visible from Jupiter on September 20.

They did so by using 14 orbits of Hubble to stare at Jupiter, taking 124 images total divided between an ultraviolet filter and a near-infrared filter. For 10 hours in the midst of the observations, the sunlight reaching Jupiter and reflecting off Jupiter's clouds dimmed by a hundredth of a percent since Venus obscured that tiny fraction of the solar disk, and Venus's atmosphere made an even slighter differential effect.

It will take many months of data analysis before the scientists know if the effect can be detected. The same scientists will join with Cornell University astronomer Philip Nicholson on December 21 to use the Cassini spacecraft in orbit around Saturn to look directly at the Sun and to try to detect the transit of Venus that will be visible from there. These observations from Jupiter and Saturn are particularly appropriate analogs to the exoplanet transits that are now the center of so much astronomical attention.

Pasachoff, Jay M., Glenn Schneider, Bryce A. Babcock, Muzhou Lu, Kevin P. Reardon, Thomas Widemann, Paolo Tanga, Ronald Dantowitz, Richard Willson, Greg Kopp, Vasyl Yurchyshyn, Alphonse Sterling, Philip Scherrer, Jesper Schou, Leon Golub, and Kathy Reeves, 2012, "The 2012 Transit of Venus for Cytherean Atmospheric Studies and as an Exoplanet Analogue," DPS, Reno, 508.06.

Tanga, P., Th. Widemann, A. Ambastha, B. A. Babcock, J. Berhier, S. Bouley, F. Braga-Ribas, K. Brasch, W. Burke, F. Colas, T. Fukuhara, L. Fulham, M. Imai, M. Lu, P. Machado, L. Maqueet, J. M. Pasachoff, J. Roberts, G. Schneider, W. Sheehan, C. Sigismondi, N. Thouvenin, F. Vachier, and Ch. Veillet, 2012, "The Venus Twillight Experiment: probing the mesosphere in 2004 and 2012," DPS, Reno, 508.07.

Widemann, Th., P. Tanga, K. P. Reardon, S. Limaye, C. Wilson, A. C. Vandaele, V. Wilqueet, A. Mahieux, S. Robert, J. M. Pasachoff, and G. Schneider, 2012, "Asymmetry in the polar mesosphere revealed by the 2012 Venus aureole," DPS, Reno, 508.08.

Pasachoff, Jay M., 2012, "Print, Web, and Podcast ToV Outreach," DPS, Reno, 411.10.

Pasachoff gave a preliminary report of the transit of Venus observations as "A Glorious Transit of Venus: Last in Our Lifetime," in Sky and Telescope magazine for October 2012, pp. 20-27.

He reported on preliminary results in June at the American Astronomical Society meeting in Anchorage, Alaska. His hour-long lecture on "Transits of Venus and Mercury: Exoplanet Analogs in Our Solar System," is available online.

]]> Wed, 12 JUN 2013 00:36:16 AEST Paris (ESA) Oct 05, 2012 - Venus Express has spied a surprisingly cold region high in the planet's atmosphere that may be frigid enough for carbon dioxide to freeze out as ice or snow. The planet Venus is well known for its thick, carbon dioxide atmosphere and oven-hot surface, and as a result is often portrayed as Earth's inhospitable evil twin.

But in a new analysis based on five years of observations using ESA's Venus Express, scientists have uncovered a very chilly layer at temperatures of around -175 degrees C in the atmosphere 125 km above the planet's surface.

The curious cold layer is far frostier than any part of Earth's atmosphere, for example, despite Venus being much closer to the Sun.

The discovery was made by watching as light from the Sun filtered through the atmosphere to reveal the concentration of carbon dioxide gas molecules at various altitudes along the terminator - the dividing line between the day and night sides of the planet.

Armed with information about the concentration of carbon dioxide and combined with data on atmospheric pressure at each height, scientists could then calculate the corresponding temperatures.

"Since the temperature at some heights dips below the freezing temperature of carbon dioxide, we suspect that carbon dioxide ice might form there," says Arnaud Mahieux of the Belgian Institute for Space Aeronomy and lead author of the paper reporting the results in the Journal of Geophysical Research.

Clouds of small carbon dioxide ice or snow particles should be very reflective, perhaps leading to brighter than normal sunlight layers in the atmosphere.

"However, although Venus Express indeed occasionally observes very bright regions in the Venusian atmosphere that could be explained by ice, they could also be caused by other atmospheric disturbances, so we need to be cautious," says Dr Mahieux.

The study also found that the cold layer at the terminator is sandwiched between two comparatively warmer layers.

"The temperature profiles on the hot dayside and cool night side at altitudes above 120 km are extremely different, so at the terminator we are in a regime of transition with effects coming from both sides.

"The night side may be playing a greater role at one given altitude and the dayside might be playing a larger role at other altitudes."

Similar temperature profiles along the terminator have been derived from other Venus Express datasets, including measurements taken during the transit of Venus earlier this year.

Models are able to predict the observed profiles, but further confirmation will be provided by examining the role played by other atmospheric species, such as carbon monoxide, nitrogen and oxygen, which are more dominant than carbon dioxide at high altitudes.

"The finding is very new and we still need to think about and understand what the implications will be," says Hakan Svedhem, ESA's Venus Express project scientist.

"But it is special, as we do not see a similar temperature profile along the terminator in the atmospheres of Earth or Mars, which have different chemical compositions and temperature conditions."

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