Anne Minard, Author at Universe Today

August 6, 2009December 24, 2015 by Anne Minard

Titan Shaping Up to Look a Lot Like Pre-Life Earth

An artist's imagination of hydrocarbon pools, icy and rocky terrain on the surface of Saturn's largest moon Titan. Image credit: Steven Hobbs (Brisbane, Queensland, Australia)

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It’s more than a billion kilometers (759 million miles) away, but the more astronomers learn about Titan, the more it looks like Earth.

That’s the theme of two talks happening this week at the International Astronomical Union meeting in Rio de Janeiro, Brazil. Two NASA researchers, Rosaly Lopes and Robert M. Nelson of the Jet Propulsion Laboratory in Pasadena, California, are reporting that weather and geology have very similar actions on Earth and Titan — even though Saturn’s moon is, on average, 100 degrees C (212 degrees F) colder than Antarctica (and certainly much more frigid than either California or Brazil; lucky astronomers).

The researchers are also reporting a tantalizing clue in the search for life: Titan hosts chemistry much like pre-biotic conditions on Earth.

Wind, rain, volcanoes, tectonics and other Earth-like processes all sculpt features on Titan’s complex and varied surface — except, according to additional research being presented at the meeting, scientists think the “cryovolcanoes” on Titan eject cold slurries of water-ice and ammonia instead of scorching hot magma.

“It is really surprising how closely Titan’s surface resembles Earth’s,” Lopes said. “In fact, Titan looks more like the Earth than any other body in the Solar System, despite the huge differences in temperature and other environmental conditions.”

The joint NASA/ESA/ASI Cassini-Huygens mission has revealed details of Titan’s geologically young surface, showing few impact craters, and featuring mountain chains, dunes and even “lakes.” The RADAR instrument on the Cassini orbiter has now allowed scientists to image a third of Titan’s surface using radar beams that pierce the giant moon’s thick, smoggy atmosphere. There is still much terrain to cover, as the aptly named Titan is one of the biggest moons in the Solar System, larger than the planet Mercury and approaching Mars in size.

New Cassini mosaic showing a dried-out lake at Titan's south pole.

Titan has long fascinated astronomers as the only moon known to possess a thick atmosphere, and as the only celestial body other than Earth to have stable pools of liquid on its surface. The many lakes that pepper the northern polar latitudes, with a scattering appearing in the south as well, are thought to be filled with liquid hydrocarbons, such as methane and ethane.

On Titan, methane takes water’s place in the hydrological cycle of evaporation and precipitation (rain or snow) and can appear as a gas, a liquid and a solid. Methane rain cuts channels and forms lakes on the surface and causes erosion, helping to erase the meteorite impact craters that pockmark most other rocky worlds, such as our own Moon and the planet Mercury.

Another Cassini instrument called the Visual and Infrared Mapping Spectrometer (VIMS) had previously detected an area, called Hotei Regio, with a varying infrared signature, suggesting the temporary presence of ammonia frosts that subsequently dissipated or were covered over. Although the ammonia does not stay exposed for long, models show that it exists in Titan’s interior, indicating that a process is at work delivering ammonia to the surface. RADAR imaging has indeed found structures that resemble terrestrial volcanoes near the site of suspected ammonia deposition.

Nelson said new infrared images of the region, also presented at the IAU, “provide further evidence suggesting that cryovolcanism has deposited ammonia onto Titan’s surface. It has not escaped our attention that ammonia, in association with methane and nitrogen, the principal species of Titan’s atmosphere, closely replicates the environment at the time that life first emerged on Earth. One exciting question is whether Titan’s chemical processes today support a prebiotic chemistry similar to that under which life evolved on Earth?”

Many Titan researchers hope to observe Titan with Cassini for long enough to follow a change in seasons. Lopes thinks that the hydrocarbons there likely evaporated because this hemisphere is experiencing summer. When the seasons change in several years and summer returns to the northern latitudes, the lakes so common there may evaporate and end up pooling in the south.

Lead image caption: Artist’s impression of hydrocarbon pools, icy and rocky terrain on the surface of Saturn’s largest moon Titan. Image credit: Steven Hobbs (Brisbane, Queensland, Australia)

Source: International Astronomical Union (IAU)

August 5, 2009December 24, 2015 by Anne Minard

Spitzer Changes Its Glasses, Sees Cotton Candy

Infrared picture of a cloud, known as DR22, bursting with new stars in the Cygnus region of the sky.

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The Spitzer Space Telescope has run out of the liquid helium that kept its optics cool — but the scope has already returned compelling new images as if to say:

I don’t need no stinkin’ helium.

At five and a half years, Spitzer’s prime mission more than doubled initial expectations. It finally ran out of liquid helium in May and was retooled for a new “warm mission” that began July 27. With its two remaining infrared channels, the telescope promises to observe with roughly the same sensitivity as a 30-meter ground-based telescope.

The lead infrared image shows the dying star NGC 4361, which was once hot like our Sun before it puffed out.

This next one shows dusty gas in blue and hot clouds in orange in DR22, a cloud bursting with new stars in the Cygnus region of the sky.

Spitzer's infrared eyes can both see dust and see through dust. The blue areas are dusty clouds, and the orange is mainly hot gas.

The new images were snapped with the two infrared channels that still work at Spitzer’s still-quite-chilly temperature of 30 Kelvin (about minus 406 degrees F). The two infrared channels are part of Spitzer’s infrared array camera: 3.6-micron light is blue and 4.5-micron light is orange.

This last picture shows a relatively calm galaxy called NGC 4145, 68 million light-years away in the constellation Canes Venatici.

Barred Spiral Galaxy NGC 4145, 68 million light-years away in the constellation Canes Venatici.

All of The new pictures were taken while the telescope was being re-commissioned, on July 18 (NGC 4145, NGC 4361) and July 21 (Cygnus), 2009.

Since its launch from Cape Canaveral, Florida on Aug. 25, 2003, Spitzer has made many discoveries. They include planet-forming disks around stars, the composition of the material making up comets, hidden black holes, galaxies billions of light-years away and more.

Perhaps the most revolutionary and surprising Spitzer finds involve planets around other stars, called exoplanets. In 2005, Spitzer detected the first photons of light from an exoplanet.

Warm Spitzer will address many of the same science questions as before. It also will tackle new projects, such as refining estimates of Hubble’s constant, or the rate at which our universe is stretching apart; searching for galaxies at the edge of the universe; characterizing more than 700 near-Earth objects, or asteroids and comets with orbits that pass close to our planet; and studying the atmospheres of giant gas planets expected to be discovered soon by NASA’s Kepler mission.

“The performance of the two short wavelength channels of Spitzer’s infrared array camera is essentially unchanged from what it was before the observatory’s liquid helium was exhausted,” said Doug Hudgins, the Spitzer program scientist at NASA Headquarters in Washington.

Credit for all images: NASA/JPL-Caltech

Source: NASA’s Spitzer site and a press release through the American Astronomical Society (AAS).

August 5, 2009April 26, 2016 by Anne Minard

Hubble, Gemini Spot ‘Hyperactive’ Stars in Small, Young Galaxies

We all know youngsters are a handful, but this really takes the cake: astronomers have clocked the speeds of stars in infant galaxies at about a million miles an hour, about twice the pace of our Sun’s cruise through the Milky Way.

The small galaxies date to 11 billion years ago, when the universe was just a couple billion years old. Their stars, astronomers say, are buzzing and whirling at head-spinning rates.

Continue reading “Hubble, Gemini Spot ‘Hyperactive’ Stars in Small, Young Galaxies”

August 5, 2009December 24, 2015 by Anne Minard

New View Toward Carina Reveals Star Fest, Exploding “Engine”

A remarkable new view of the Milky Way toward the constellation Carina is alive with a flurry of stars — and the pièce de résistance is a binary star that’s all dressed up in a nebula of its own making.

The European Southern Observatory (ESO) released the new images this week.

The unusual star, HD 87643, has been extensively studied with several ESO telescopes, including the Very Large Telescope Interferometer (VLTI). Surrounded by a complex, extended nebula that is the result of previous violent ejections, the star has been shown to have a companion. Interactions in this double system, surrounded by a dusty disc, may be the engine fueling the star’s remarkable nebula.

HD 87643 is at the center of the extended nebula of dust and gas on the first image, obtained with the Wide Field Imager on the ESO/MPG 2.2-meter (7.2-foot) telescope at La Silla Observatory in Chile. The central panel is a zoom on the star obtained with NACO on ESO’s VLT on Paranal. The last panel zooms further , showing an image obtained with the AMBER instrument making use of three telescopes of the VLTI. The field of view of this last panel is less than one pixel of the first image.

HD 87643 is a member of the exotic class of B[e] stars — luminous, powerful blue stars with strong spectral evidence of hydrogen. The new image is part of a set of observations that provide astronomers with the best ever picture of a B[e] star.

The central star’s wind appears to have shaped the surrounding nebula, leaving bright, ragged tendrils of gas and dust. A careful investigation of these features seems to indicate that there are regular ejections of matter from the star every 15 to 50 years.

A team of astronomers, led by Florentin Millour of the Max-Planck Institute for Radio Astronomy in Bonn, Germany, has studied the star HD 87643 in great detail.

The sheer range of the observations, from the panoramic WFI image to the fine detail of the VLTI observations, corresponds to a zoom-in factor of 60,000 between the two extremes. The astronomers found that HD 87643 has a companion located at about 50 times the Earth–Sun distance and is embedded in a compact dust shell. The two stars probably orbit each other in a period between 20 and 50 years. A dusty disc may also be surrounding the two stars.

The presence of the companion could be an explanation for the regular ejection of matter from the star and the formation of the nebula: as the companion moves on a highly elliptical orbit, it would regularly come very close to HD 87643, triggering an ejection.

Source: European Southern Observatory (ESO). Check the site for more images and a video. A paper about the results is here.

July 30, 2009December 24, 2015 by Anne Minard

Newly Discovered Cometary Route Sneaks Past Jupiter, but Decreases Risk of Earth Impacts

Astronomers have used the comet record — including 2001 RX14 (Linear) at left, captured in 2002 by the Sloan Digital Sky Survey — to model a new route for incoming comets that sneaks past Jupiter’s gravity.

The pathway might even be the dominant one that delivers Oort Could comets on an Earth-bound trajectory, say the authors of a new study in Science this week — but if that’s true, comets only rarely cause extinctions on Earth.

(Image credit: Mike Solontoi/University of Washington)

Scientists have debated how many mass extinction events in Earth’s history were triggered by a space body crashing into the planet’s surface. Most agree that an asteroid collision 65 million years ago brought an end to the age of dinosaurs, but there is uncertainty about how many other extinctions might have resulted from asteroid or comet collisions with Earth.

In fact, astronomers know the inner solar system has been protected at least to some degree by Saturn and Jupiter, whose gravitational fields can eject comets into interstellar space or sometimes send them crashing into the giant planets. That point was reinforced last week (July 20) when a huge scar appeared on Jupiter’s surface, likely evidence of a comet impact.

There are about 3,200 known long-period comets, which can take anywhere from 200 to tens of millions of years to orbit the Sun. Among the best-remembered is Hale-Bopp, which was easily visible to the naked eye for much of 1996 and 1997 and was one of the brightest comets of the 20th century.

It has been believed that nearly all long-period comets that move inside Jupiter to Earth-crossing trajectories originated in the outer Oort Cloud, a remnant of the nebula from which the solar system formed 4.5 billion years ago. It begins about 93 billion miles from the sun (1,000 times Earth’s distance from the sun) and stretches to about three light years away (a light year is about 5.9 trillion miles). The Oort Cloud could contain billions of comets, most so small and distant as to never be observed.

The orbits of long-period comets can change when they are nudged by the gravity of a neighboring star as it passes close to the solar system, and it was thought such encounters only affect very distant outer Oort Cloud bodies.

It also was believed that inner Oort Cloud bodies could reach Earth-crossing orbits only during the rare close passage of a star, which would cause a comet shower. But it turns out that even without a star encounter, long-period comets from the inner Oort Cloud can slip past the protective barrier posed by the presence of Jupiter and Saturn and travel a path that crosses Earth’s orbit.

In the new research, University of Washington astronomers Nathan Kaib and Thomas Quinn used computer models to simulate the evolution of comet clouds in the solar system for 1.2 billion years. They found that even outside the periods of comet showers, the inner Oort Cloud was a major source of long-period comets that eventually cross Earth’s path.

By assuming the inner Oort Cloud as the only source of long-period comets, they were able to estimate the highest possible number of comets in the inner Oort Cloud. The actual number is not known. But by using the maximum number possible, they determined that no more than two or three comets could have struck Earth during what is believed to be the most powerful comet shower of the last 500 million years.

“For the past 25 years, the inner Oort Cloud has been considered a mysterious, unobserved region of the solar system capable of providing bursts of bodies that occasionally wipe out life on Earth,” Quinn said. “We have shown that comets already discovered can actually be used to estimate an upper limit on the number of bodies in this reservoir.”

With three major impacts taking place nearly simultaneously, it had been proposed that the minor extinction event about 40 million years ago resulted from a comet shower. Kaib and Quinn’s research implies that if that relatively minor extinction event was caused by a comet shower, then that was probably the most-intense comet shower since the fossil record began.

“That tells you that the most powerful comet showers caused minor extinctions and other showers should have been less severe, so comet showers are probably not likely causes of mass extinction events,” Kaib said.

He noted that the work assumes the area surrounding the solar system has remained relatively unchanged for the last 500 million years, but it is unclear whether that is really the case. It is clear, though, that Earth has benefited from having Jupiter and Saturn standing guard like giant catchers mitts, deflecting or absorbing comets that might otherwise strike Earth.

“We show that Jupiter and Saturn are not perfect and some of the comets from the inner Oort Cloud are able to leak through. But most don’t,” Kaib said.

Source: Science and Eurekalert. The paper appears online today at the Science Express website.

July 30, 2009December 24, 2015 by Anne Minard

Saturn Sees Days Shorter Than Thought, Winds Like Jupiter — Sort of

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A new estimate of Saturn’s rotation rate reveals days on the gas giant are five minutes shorter than previously believed — and that Saturn’s atmosphere has much in common with that of its planetary neighbor, Jupiter.

The new results appear today in the journal Nature.

(Image caption: Saturn as photographed by Cassini-Huygens. Credit: NASA)

An image of Saturn from NASA's Cassini spacecraft, clearly showing the 'geographic' South Pole of the planet (at the center of the circle of clouds, lower left). The bulk rotation of the planet is around an axis passing through the South Pole and Saturn's clouds (of ammonia ice) are organised into dark 'belts' and light 'zones' that are generally aligned with lines of latitude, indicating the influence of the planet's rotation on its meteorology.

For planets with solid surfaces, the spin rate can simply be determined by tracking the motion of landforms as they rotate across the surface.

Like the rocky planets, gas giant planets such as Jupiter and Saturn spin on their axes with well defined rotation periods. But, with no solid surface features to track, measuring the rotation period of a gas giant is a challenge. The approach that has worked for Jupiter, Uranus and Neptune — using the rotation of the planet’s magnetic field to infer its bulk rotation — gives results for Saturn that change with time, and implies a pattern of atmospheric winds that is very different from that seen on Jupiter.

Peter Read, of the University of Oxford in the UK, and his colleagues used atmospheric dynamics on Saturn to derive a rotation rate that is slightly faster than those inferred from magnetic measurements. When Saturn’s atmospheric winds are viewed relative to this new interior reference frame, they show a pattern of alternating eastward and westward jets similar to the pattern seen on Jupiter.

“This shifted reference frame is consistent with a pattern of alternating jets on Saturn that is more symmetrical between eastward and westward flow,”Read and his co-authors write. “This suggests that Saturn’s winds are much more like those of Jupiter than hitherto believed.”

The authors propose a new rotation rate of 10 hours and 34 minutes, as opposed to the previous estimate of 10 hours 39 minutes. The new rate also sheds light on Saturn’s interior structure, including its density and the mass of a possible rocky core. And it bears on the latitudinal gradient of temperatures below the clouds.

In a related editorial, Adam Showman of the University of Arizona in Tucson writes that there remain key differences between the atmospheres of Saturn and Jupiter: “Saturn’s winds are stronger than Jupiter’s, its banded cloud patterns and populations of hurricane-like vortices differ considerably, and its magnetic field, which is almost symmetrical about its axis — a puzzle in its own right — contrasts with Jupiter’s tilted dipole,” he notes. “These contrasts indicate that the planets are cousins rather than twins, whose intriguing mix of similarities as well as differences will keep planetary scientists engaged for years to come.”

Second image caption: An image of Saturn from NASA’s Cassini spacecraft, clearly showing the ‘geographic’ South Pole of the planet (at the center of the circle of clouds, lower left). The bulk rotation of the planet is around an axis passing through the South Pole and Saturn’s clouds (of ammonia ice) are organized into dark ‘belts’ and light ‘zones’ that are generally aligned with lines of latitude, indicating the influence of the planet’s rotation on its meteorology.

Source: Nature

July 29, 2009December 24, 2015 by Anne Minard

Closest-Ever Look At Betelgeuse Reveals its Fiery Secret

Artist’s impression of the supergiant star Betelgeuse as it was revealed with ESO’s Very Large Telescope. Credit: ESO/L.Calçada

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The giant star Betelgeuse churns out gas bubbles that match its own size — and that’s how it can shed an entire solar mass in 10,000 years.

That according to the sharpest-ever images of Orion’s second-brightest star, released this week by the European Organisation for Astronomical Research in the Southern Hemisphere (ESO). At left is an artist’s impression of the supergiant star Betelgeuse as it was revealed in the new images (courtesy of ESO and L.Calçada). The actual images follow …

This collage shows the Orion constellation in the sky (Betelgeuse is identified by the marker), a zoom towards Betelgeuse, and the sharpest ever image of this supergiant star, which was obtained with NACO on ESO’s Very Large Telescope. Credit: ESO, P.Kervella, Digitized Sky Survey 2 and A. Fujii

Betelgeuse, the second brightest star in the constellation of Orion (the Hunter), is a red supergiant, one of the biggest stars known, and almost 1,000 times larger than our Sun. It is also one of the most luminous stars known, emitting more light than 100,000 Suns.

Red supergiants still hold several unsolved mysteries. One of them is just how these behemoths shed such tremendous quantities of material — about the mass of the Sun — in only 10,000 years.

With an age of only a few million years, the Betelgeuse star is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.

Using ESO’s Very Large Telescope, two independent teams of astronomers have obtained the sharpest ever views of the supergiant star.

The first team used the adaptive optics instrument, NACO, combined with a so-called “lucky imaging” technique, to obtain the sharpest ever image of Betelgeuse, even with Earth’s turbulent, image-distorting atmosphere in the way. With lucky imaging, only the very sharpest exposures are chosen and then combined to form an image much sharper than a single, longer exposure would be.

The resulting NACO images almost reach the theoretical limit of sharpness attainable for an 8-metre telescope. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground.

“Thanks to these outstanding images, we have detected a large plume of gas extending into space from the surface of Betelgeuse,” said Pierre Kervella from the Paris Observatory, who led the team. The plume extends to at least six times the diameter of the star, corresponding to the distance between the Sun and Neptune. “This is a clear indication that the whole outer shell of the star is not shedding matter evenly in all directions.”

Two mechanisms could explain this asymmetry. One assumes that the mass loss occurs above the polar caps of the giant star, possibly because of its rotation. The other possibility is that such a plume is generated above large-scale gas motions inside the star, known as convection — similar to the circulation of water heated in a pot.

To arrive at a solution, Keiichi Ohnaka from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and his colleagues used ESO’s Very Large Telescope Interferometer. The astronomers were able to detect details four times finer still than the NACO images had allowed — in other words, the size of a marble on the ISS, as seen from the ground.

“Our AMBER observations are the sharpest observations of any kind ever made of Betelgeuse. Moreover, we detected how the gas is moving in different areas of Betelgeuse’s surface — the first time this has been done for a star other than the Sun,” Ohnaka said.

The AMBER observations revealed that the gas in Betelgeuse’s atmosphere is moving vigorously up and down, and that these bubbles are as large as the supergiant star itself. The astronomers are proposing that these large-scale gas motions roiling under Betelgeuse’s red surface are behind the ejection of the massive plume into space.

Source: European Organisation for Astronomical Research in the Southern Hemisphere (ESO). Two related papers are here and here.

July 27, 2009December 24, 2015 by Anne Minard

Galaxy Zoo Discovers New Group of Galaxies: ‘Green Peas’

The newly discovered Green Pea galaxies. (Photo: Carolin Cardamone and Sloan Digital Sky Survey.)

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Citizen scientists from the Galaxy Zoo project have discovered rare galaxies they’re calling the “Green Peas.” They’re small in size, bright green in color, and proficient at churning out new stars — plus, they could reveal unique insights into how galaxies form stars in the early universe.

The newly discovered galaxies appear in the image at left, from Carolin Cardamone and the Sloan Digital Sky Survey.

“These are among the most extremely active star-forming galaxies we’ve ever found,” said Cardamone, an astronomy graduate student at Yale University and lead author of a new paper on the discovery. The results will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

Galaxy Zoo users volunteer their spare time to help classify galaxies in an online image bank. Cardamone said of the one million galaxies that make up Galaxy Zoo’s image bank, the team found only 250 Green Peas.

“No one person could have done this on their own,” she said. “Even if we had managed to look through 10,000 of these images, we would have only come across a few Green Peas and wouldn’t have recognized them as a unique class of galaxies.”

The Green Peas boast “some of the highest specific star formation rates seen in the local Universe,” write Cardamone and her co-authors, “yielding doubling times for their stellar mass of hundreds of millions of years.”

The authors say evidence points to recent or ongoing mergers, adding that the Peas are similar in size, mass, luminosity and metallicity to Luminous Blue Compact Galaxies.

“They are also similar to high redshift UV-luminous galaxies, e.g., Lyman-break galaxies and Lyman-alpha emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies,” they write.

The galaxies, which are between 1.5 billion and 5 billion light years away, are 10 times smaller than our own Milky Way galaxy and 100 times less massive. But they are forming stars 10 times faster than the Milky Way.

Kevin Schawinski, a postdoctoral associate at Yale and one of Galaxy Zoo’s founders, said the Green Peas would have been normal in the early universe, “but we just don’t see such active galaxies today. Understanding the Green Peas may tell us something about how stars were formed in the early universe and how galaxies evolve.”

The Galaxy Zoo volunteers who discovered the Green Peas—and who call themselves the “Peas Corps” and the “Peas Brigade”—began discussing the strange objects in the online forum. (The original forum thread was called “Give peas a chance.”)

Cardamone asked the volunteers, many of whom had no previous astronomy background or experience, to refine the sample of objects they detected in order to determine which were bona fide Green Peas and which were not, based on their colors. By analyzing their light, Cardamone determined how much star formation is taking place within the galaxies.

“This is a genuine citizen science project, where the users were directly involved in the analysis,” Schawinski said, adding that 10 Galaxy Zoo volunteers are acknowledged in the paper as having made a particularly significant contribution. “It’s a great example of how a new way of doing science produced a result that wouldn’t have been possible otherwise.”

Source: Yale University, via the American Astronomical Society press wire. The paper is here, and here is a link to the Galaxy Zoo project.

July 22, 2009December 24, 2015 by Anne Minard

Northern & Southern Aurorae Are Siblings, But Not Twins

Asymmetrical aurorae, courtesy of Karl Magnus Laundal and Nature

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Seen the Northern Lights and you’ve seen them all, hm? Not so.

It is commonly assumed that the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere are mirror images of each other — but new research has revealed differences between the events.

The aurorae, commonly known as the Northern and Southern Lights, are spectacular natural light displays in the Earth’s upper atmosphere. The phenomenon is caused by charged particles from the solar wind striking atoms and molecules in the atmosphere.

It’s intuitive to think the Northern and Southern Lights are identical, because the charged particles causing the aurora follow the symmetric magnetic field lines connecting the two hemispheres.

But study co-authors Nikolai Østgaard and Karl Magnus Laundal, both of the University of Bergen in Norway, report in the journal Nature this week that there are differences between the phenomena.

“Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere,” they write. “The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.”

Østgaard and Laundal based their report on observations from a new set of global imaging cameras at each pole. The authors suggest that the observed asymmetry confirms the existence of inter-hemispheric, field-aligned currents related to the seasons, which had been predicted but never before observed.

Source: Nature

July 22, 2009December 24, 2015 by Anne Minard

Mystery Solved? New Clues Point to a Liquid Ocean on Enceladus.

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A liquid plume is spewing from Saturn’s icy moon Enceladus — but is it coming from heated ice on the surface, or a liquid ocean underneath?

Analysis of the plume’s chemistry, detailed in the Cassini (CICLOPS) image above and reported in Nature this week, may put the debate to rest.

Lead author Jack Hunter (J.H.) Waite, of the Southwest Research Institute in San Antonio, Texas and his colleagues say ammonia detected in the jets from Enceladus’ south pole provides the strongest evidence yet for the existence of liquid water beneath the surface.

A previous paper led by Frank Postberg of the University of Heidelberg in Germany, published in Nature just last month, reported the discovery of salts in E-ring particles derived from the plume, also suggestive of a liquid reservoir.

But Susan Kieffer of the University of Illinois at Urbana–Champaign and her colleagues proposed in a 2006 Science paper that warm ice is heated near the surface, causing dissociation of clathrate hydrates. And Nicholas Schneider, of the University of Colorado at Boulder, and his colleagues published a paper in the same Nature issue as Postberg’s team (June 24) — reporting that there’s not enough sodium in the plume to support a liquid ocean.

The ammonia may tip the scales, say the authors of the new paper.

“The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180K have been measured near the fractures from which the jets emanate,” the authors write. “We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.”

Besides ammonia, the authors detected various organic compounds and deuterium — ‘heavy’ hydrogen abundant in the oceans of Earth. Ammonia, together with methanol and salts, acts as an antifreeze, allowing liquid water to exist at below-freezing temperatures. The authors suggest that preserving even a residual oceanic layer during cooling episodes would maintain conditions necessary for tidal heating and geologic activity.

Enceladus is one of only three moons in the Solar System known to be volcanically active. The plume of gas and particles is thought to make up Saturn’s outermost ‘E’ ring.

UT ran a story last month, when Nature ran two papers with different ideas about whether Enceladus harbors a liquid ocean. See that story here.

Source for text: Nature. Source for images: Cassini Imaging Central Laboratory for Operations (CICLOPS), with thanks to study co-author William Lewis for the tip.