Weather on Saturn's moon Titan: A methane drizzle

BERKELEY - Noted for its bizarre hydrocarbon lakes and frozen methane clouds, Saturn's largest moon, Titan, also appears to have widespread drizzles of methane, according to a team of astronomers at the University of California, Berkeley.

New near-infrared images from Hawaii's W. M. Keck Observatory and Chile's Very Large Telescope show for the first time a nearly global cloud cover at high elevations and, dreary as it may seem, a widespread and persistent morning drizzle of methane over the western foothills of Titan's major continent, Xanadu.

In most of the Keck and VLT images, liquid methane clouds and drizzle appear at the morning edge of Titan, the arc of the moon that has just rotated into the light of the sun.

"Titan's topography could be causing this drizzle," said Imke de Pater, UC Berkeley professor of astronomy. "The rain could be caused by processes similar to those on Earth: Moisture laden clouds pushed upslope by winds condense to form a coastal rain."

Lead author Mate Adamkovics, a UC Berkeley research astronomer, noted that only areas near Xanadu exhibited morning drizzle, and not always in the same spot. Depending on conditions, the drizzle could hit the ground or turn into a ground mist. The drizzle or mist seems to dissipate after about 10:30 a.m. local time, which, because Titan takes 16 Earth days to rotate once, is about three Earth days after sunrise.

"Maybe only Xanadu has misty mornings," he said.

Adamkovics, de Pater and their colleagues in UC Berkeley's Center for Integrative Planetary Studies report their observation in the Oct. 11 issue of Science Express, an online version of the journal Science. They also present their findings at the Division for Planetary Sciences meeting of the American Astronomical Society in Orlando, Fla.

Titan, larger than the planet Mercury, is the only moon in the solar system with a thick atmosphere, which is comprised mostly of nitrogen and resembles Earth's early atmosphere. Previous observations have shown that the entire moon is swathed in a hydrocarbon haze extending as high as 500 kilometers, becoming thinner with height. The south pole area exhibits more haze than elsewhere, with a hood of haze at an altitude between 30 and 50 kilometers.

Because of its extremely cold surface temperature - minus 183 degrees Celsius (-297 degrees Fahrenheit) - trace chemicals such as methane and ethane, which are explosive gases on Earth, exist as liquids or solids on Titan. Some level features on the surface near the poles are thought to be lakes of liquid hydrocarbon analogous to Earth's watery oceans, and presumably these lakes are filled by methane precipitation. Until now, however, no rain had been observed directly.

"Widespread and persistent drizzle may be the dominant mechanism for returning methane to the surface from the atmosphere and closing the methane cycle," analogous to Earth's water cycle, the authors wrote.

Actual clouds on Titan were first imaged in 2001 by de Pater's group and colleagues at Caltech using the Keck II telescope with adaptive optics and confirmed what had been inferred from spectra of Titan's atmosphere. These frozen methane clouds hovered at an elevation of about 30 kilometers around Titan's south pole.

Since then, isolated ethane clouds have been observed at the north pole by NASA's Cassini spacecraft, while both Cassini and Keck photographed methane clouds scattered at mid-southern latitudes. Also in 2005, the Huygens probe, build by the European Space Agency and released by Cassini, plummeted through Titan's atmosphere, collecting data on methane relative humidity. These data provided evidence for frozen methane clouds between 25 and 30 kilometers in elevation and liquid methane clouds - with possible drizzle - between 15 and 25 kilometers high. The extent of the clouds detected in the descent area was unclear, however, because "a single weather station like Huygens cannot characterize the meteorology on a planet-wide scale," said UC Berkeley research astronomer Michael H. Wong.

The new images show clearly a widespread cloud cover of frozen methane at a height of 25 to 35 kilometers - "a new type of cloud, a big global cloud of methane," Adamkovics said - that is consistent with Huygens' measurements, plus liquid methane clouds in the tropopause below 20 kilometers with rain at lower elevations.

Because earlier observers thought that the methane droplets in these clouds were too sparse to be seen, they referred to the frozen and liquid methane clouds as "sub-visible."

"The stratiform clouds we see are like cirrus clouds on Earth," Adamkovics said. "One difference is that the methane droplets are predicted to be at least millimeter-sized on Titan, as opposed to micron-sized in terrestrial clouds - a thousand times smaller. Since the clouds have about the same moisture content as Earth's clouds, this means the droplets on Titan are much more spread out and have a lower density in the atmosphere, which makes the clouds 'subvisible' and thus hard to detect."

If all the moisture were squeezed out of Titan's clouds, it would amount to about one and a half centimeters (six-tenths of an inch) of liquid methane spread around Titan's surface, Adamkovics said. This is about the same moisture content as some of Earth's clouds.

Since 1996, de Pater and colleagues have been using infrared detectors on the Keck telescopes to regularly monitor clouds and hazes on Titan. In past years, they have also used the VLT. The advantage of observing at infrared wavelengths is that Titan's haze is relatively transparent. At optical wavelengths, these haze layers form an impenetrable layer of photochemical smog.

By observing at different infrared wavelengths, scientists can probe different altitudes in Titan's atmosphere, depending on the strength of the methane absorption at that wavelength. Then, by using the methane absorption profile, they can pinpoint particular altitudes in Titan's atmosphere, allowing astronomers to see the surface and judge the altitude of methane clouds. Adamkovics first saw evidence of widespread, cirrus-like clouds and methane drizzle when analyzing Feb. 28, 2005, data from a new instrument on the European Southern Observatory's VLT - the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI).

Sharper images and spectra taken on April 17, 2006, by the OH-Suppressing Infra-Red Imaging Spectrograph (OSIRIS) on Keck II confirmed the clouds. Both instruments measure spectra of light at many points in an image rather than averaging across the entire image. By subtracting light reflected from the surface from the light reflected by the clouds, the researchers were able to obtain images of the clouds covering the entire moon.

"Once we saw this in both data sets, we altered our radiative transfer models for Titan and recognized that the only way to explain the data was if there was liquid or solid methane in the atmosphere," Adamkovics said. "This is a big step in helping us understand the extent to which solid clouds and liquids are spread throughout Titan's atmosphere."

UC Berkeley graduate student Conor Laver is the fourth author on the Science Express paper. The work was supported by the National Science Foundation and Technology Center for Adaptive Optics (CfAO), NASA and the Center for Integrative Planetary Science (CIPS) at UC Berkeley.

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Extreme star cluster bursts into life in new Hubble image

The Hubble Space Telescope has captured a spectacular image of NGC 3603, a giant nebula hosting one of the most prominent massive young clusters in the Milky Way, thus supplying a prime template for star formation studies.

NGC 3603 is a prominent star-forming region located in the Carina spiral arm of the Milky Way, about 20,000 light-years away from our Solar System. This latest image from the NASA/ESA Hubble Space Telescope shows a young star cluster surrounded by a vast region of dust and gas. Most of the bright stars in the image are hot blue stars whose ultraviolet radiation and violent winds have blown out an enormous cavity in the gas and dust enveloping the cluster.

The new Hubble image provides a snapshot in time of many stars with differing masses but similar ages inside the young cluster. This allows for detailed analysis of several types of stars at varying stages in their lives. Astronomers can then compare clusters of different ages with one another and determine which properties (such as temperature and brightness) change as the stars get older.

According to astronomer Dr. Jesus Maiz Apellaniz from Instituto de Astrofisica de Andalucia, Spain, who is leading the Hubble investigation, the massive star cluster in NGC 3603 appears to gather the most massive stars at its core. He and his team have discovered that the distribution of different types of stars at the centre of this very dense cluster is similar to that of other young star clusters in the Milky Way.

The team has also found that the three brightest stars in the centre are apparently misleading us into believing that they are more massive objects than theoretical limits allow. These heavyweight stars may actually consist of two or maybe more individual massive stars whose light has blended together. Even with the resolution of Hubble it is not possible to separate the individual stars in each of the three systems. This finding agrees with a recent discovery by Dr. Anthony Moffat from the Universite de Montreal, Canada, who used ESO's Very Large Telescope and Hubble's infrared NICMOS camera to measure the movements of the individual stars in two of the three systems. Dr. Moffat measured the largest individual mass to be roughly 115 solar masses, which is within the acceptable limits for conventional theory.

The swirling nebula of NGC 3603 contains around 400,000 solar masses of gas. Lurking within this vast cloud are a few Bok globules (seen at the top right corner of the image), named after Bart Bok who first observed them in the 1940s. These are dark clouds of dense dust and gas with masses of about ten to fifty times larger than that of the Sun. They resemble insect cocoons and are undergoing gravitational collapse on their way to form new stars. Bok globules appear to be some of the coldest objects in the Universe.

NGC 3603 was first discovered by Sir John Herschel in 1834. It is known to harbour a blue supergiant star called Sher 25 that can be spotted above and left of the densest part of the cluster. This star is believed to be near the point of exploding as a supernova and is often denoted as the Milky Way counterpart of the predecessor of the now famous supernova SN 1987A.

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Hubble shows 'baby' galaxy is not so young after all

The NASA/ESA Hubble Space Telescope has found out the true nature of a dwarf galaxy that astronomers had for a long time identified as one of the youngest galaxies in the Universe. Astronomers using the NASA/ESA Hubble Space Telescope have made observations of the galaxy I Zwicky 18 which seem to indicate that it is in fact much older and much farther away than previously thought.

Observations of I Zwicky 18 at the Palomar Observatory around 40 years ago seemed to show that it was one of the youngest galaxies in the nearby Universe. The studies suggested that the galaxy had erupted with star formation billions of years after its galactic neighbours, like our galaxy the Milky Way. Back then it was an important finding for astronomers, since this young galaxy was also nearby and could be studied in great detail; something that is not possible with observations made across great distances when the universe was much younger.

But these new Hubble data have quashed that possibility. The telescope found fainter older red stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as 10 billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.

"Although the galaxy is not as youthful as was once believed, it is certainly developmentally challenged and unique in the nearby Universe," said astronomer Alessandra Aloisi from the European Space Agency/Space Telescope Science Institute, who led the new study.

Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is mostly composed of hydrogen and helium, the main ingredients created in the Big Bang. In other words the stars within it have not created the same amounts of heavier elements as seen in other galaxies nearby. Thus the galaxy's primordial makeup suggests that its rate of star formation has been much lower than that of other galaxies of similar age. The galaxy has been studied with most of NASA's telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, and the Far Ultraviolet Spectroscopic Explorer (FUSE). However, it remains an outstanding mystery why I Zwicky 18 formed so few stars in the past, and why it is forming so many new stars right now.

The new Hubble data also suggest that I Zwicky 18 is 59 million light- years from Earth, almost 10 million light-years more distant than previously believed. On extragalactic standards this is still in our own backyard yet the galaxy's larger-than-expected distance may now explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint old stars in I Zwicky 18 are almost at the limit of Hubble's sensitivity and resolution.

Aloisi and her team discerned the new distance by observing blinking stellar distance-markers within I Zwicky 18. Massive stars, called Cepheid variables, pulse with a regular rhythm. The timing of their pulsations is directly related to their brightness. By comparing their actual brightness with their observed brightness, astronomers can precisely measure their distance. The team determined the observed brightness of three Cepheids and compared it to the actual brightness predicted by theoretical models specifically calculated for the low metal content of I Zwicky 18 in order to determine the galaxy's distance. The Cepheid distance was also validated through another distance indicator, specifically the observed brightness of the brightest red stars in a characteristic stellar evolutionary phase (the so-called "giant" phase).

Cepheid variable stars have been studied for decades (especially by Hubble) and have been instrumental in the determination of the scale of our universe. This is the first time, however, that variable stars with so few heavy elements were found. This may provide unique new insights into the properties of variable stars, which is now a topic of ongoing study.


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Cameras help astronomers find three exoplanets

The new planets were seen to pass in front or transit their host star. When astronomers see a transit, they can work out the size, mass and make up of the planet and they can use the planets to study how solar systems form. The UK led Super Wasp (wide angle search for planets) programme uses wide angle lenses with Ikon L large area CCD cameras (DW436N-BV), each housing a vacuum sealed, TE cooled E2V 42-40 sensor with 2kx2k pixels, supplied by Andor Technology in Belfast.

According to Don Pollacco who leads the Super wasp team at QUB: 'The system we have is extremely powerful - we are very happy with our cameras which enable us to find candidate planets.

'We are the only team to have found transiting planets in the northern and southern hemispheres; for the first time we have both Super Wasp cameras running, giving complete coverage of the whole sky'.

Two of the new planets, Wasp 4 and Wasp 5, have been the first to be discovered by the Wasp cameras in South Africa, the third planet, Wasp 3 was in the north, using cameras sited in the Canary Islands.

Said Mark Donaghy, Andor's head of marketing: ''We are delighted that our cameras are playing such an important role in the search for new planets particularly with this recent discovery.

'We have worked closely with Dr Pollacco and his team for many years to provide a powerful, reliable solution in the search for new planets'.

The three new planets are about the size of Jupiter and are orbiting their stars very closely, which means that their surface temperatures will be more than 2000C.

By finding Jupiter-mass planets around other stars, this suggests that there are many Earth-sized planets waiting to be discovered as technology advances.

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How to find in the sky the Orion Nebula?

The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of 1,270 light years away +/- 76 light years away (previous distance estimates of 1500 light years have been replaced with newer measurements), and is the closest region of star formation to Earth. The M42 nebula is estimated to be 30 light years across. Older texts frequently referred to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula. Yet older, astrological texts refer to it as Ensis, which is also the name of the star Eta Orionis.

The Orion Nebula is visible with the naked eye even from areas affected by some light pollution. However in that kind as the nebula is shown on many impressing photos, it not probably to see with the eye, even in a large telescope. Such photos turn out only at long time exposure.

To find the Orion Nebula, , you should find all over again Orion (see a map below). Constellation of Orion is well visible in the autumn and not visible in the spring.