Tuesday, December 31, 2013

Hubble Sees Cloudy Super-Worlds with Chance for More Clouds

Artwork Credit: NASA, ESA, and G. Bacon (STScI)
Science Credit: NASA, ESA, L. Kreidberg and J. Bean (University of Chicago), 
and H. Knutson (California Institute of Technology)
Highest-quality download options 

Credit: NASA, ESA, and A. Feild and G. Bacon (STScI)

Weather forecasters on exoplanet GJ 1214b would have an easy job. Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more clouds.

Two teams of scientists using NASA's Hubble Space Telescope report they have characterized the atmospheres of a pair of planets with masses intermediate between gas giants, like Jupiter, and smaller, rockier planets, like Earth. A survey by NASA's Kepler space telescope mission showed that objects in this size range are among the most common type of planets in our Milky Way galaxy. The researchers described their work as an important milestone on the road to characterizing potentially habitable, Earth-like worlds beyond the solar system.

The findings appear in separate papers in the January 2 issue of the journal Nature.

The two planets studied are known as GJ 436b and GJ 1214b. GJ 436b is categorized as a "warm Neptune" because it is much closer to its star than frigid Neptune is to our Sun. The planet is located 36 light-years away in the constellation Leo.

GJ 1214b is known as a "super-Earth" type planet. Super-Earths are planets with masses between that of Earth and Neptune. Because no such planet exists in our solar system, the physical nature of super-Earths is largely unknown. GJ1214b is located just 40 light-years from Earth, in the constellation Ophiuchus.

Both GJ 436b and GJ 1214b can be observed passing in front of, or transiting, their parent stars. This provides an opportunity to study these planets in more detail as starlight filters through their atmospheres.

An atmospheric study of GJ 436b based on such transit observations with Hubble over the last year is presented in one of the papers, led by Heather Knutson of the California Institute of Technology in Pasadena, Calif. The news is about what they didn't find. The Hubble spectra were featureless and revealed no chemical fingerprints whatsoever in the planet's atmosphere. "Either this planet has a high cloud layer obscuring the view, or it has a cloud-free atmosphere that is deficient in hydrogen, which would make it very unlike Neptune," said Knutson. "Instead of hydrogen, it could have relatively large amounts of heavier molecules such as water vapor, carbon monoxide, and carbon dioxide, which would compress the atmosphere and make it hard for us to detect any chemical signatures."

Observations similar to those obtained for GJ 436b had been previously obtained for GJ 1214b. The first spectra of this planet were also featureless and presented a similar puzzle: The planet's atmosphere either was predominantly water vapor or hydrogen-dominated with high-altitude clouds.

A team of astronomers led by Laura Kreidberg and Jacob Bean of the University of Chicago used Hubble to obtain a deeper view of GJ 1214b that revealed what they consider definitive evidence of high clouds blanketing the planet. These clouds hide any information about the composition and behavior of the lower atmosphere and surface. The new Hubble spectra also revealed no chemical fingerprints whatsoever in the planet's atmosphere, but the high precision of the new data enabled them to rule out cloud-free compositions of water vapor, methane, nitrogen, carbon monoxide, or carbon dioxide for the first time.

"Both planets are telling us something about the diversity of planet types that occur outside of our own solar system; in this case we are discovering that we may not know them as well as we thought," said Knutson. "We'd really like to determine the size at which these planets transition from looking like mini-gas giants to something more like a water world or a rocky, scaled-up version of the Earth. Both of these observations are fundamentally trying to answer that question."

Models of GJ 436b and GJ 1214b predict clouds that could be made out of potassium chloride or zinc sulfide at the scorching temperatures of several hundred degrees Fahrenheit predicted to be found in these atmospheres. "You would expect very different kinds of clouds to form on these planets than you would find, say, on Earth," said Kreidberg.

The Chicago team had to make a big effort to conclusively determine the nature of GJ 1214b's cloudy atmosphere. Kreidberg explained, "We really pushed the limits of what is possible with Hubble to make this measurement — our work devoted more Hubble time to a single exoplanet than ever before. This advance lays the foundation for characterizing other Earths with similar techniques." Added Bean, "I think it's very exciting that we can use a telescope like Hubble that was never designed with this in mind, do these kinds of observations with such exquisite precision, and really nail down some aspect of a super-Earth atmosphere."

Knutson continued, "For exoplanets, clouds are incredibly frustrating because they can hide the bulk composition of the atmosphere that we want to measure." However, more will be learned with the launch of the James Webb Space Telescope later this decade. Said Kreidberg, "Looking forward, the James Webb Space Telescope will be transformative. The new capabilities of this telescope will allow us to peer through the clouds on GJ 1214b and similar exoplanets."

CONTACT


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514

dweaver@stsci.edu / villard@stsci.edu


Messier 65 through the yearsMessier 65 through the years

Credit: ESA/Hubble & NASA 

The 1st of March 1780 was a particularly productive night for Charles Messier. Combing the constellation of Leo for additions to his grand astronomical catalogue, he struck on not one, but two, new objects. 

One of those objects is seen here: Messier 65. "Nebula discovered in Leo: It is very faint and contains no star," he jotted down in his notebook. But he was wrong — as we now know, Messier 65 is a spiral galaxy containing billions upon billions of stars. 

All Messier saw was a faint diffuse light, nothing like the fine detail here, so we can forgive his mistake. If he had had access to a telescope like Hubble, he could have spied these stunning, tightly wound purple spiral arms and dark dust lanes, encircling a bright centre crammed with stars. 

Almost exactly 233 years later in March of this year, one of the stars within Messier 65 went supernova (not seen in this image), rivalling the rest of the entire galaxy in brightness. This, the first Messier supernova of 2013, is now fading, and the serene beauty of M65 is returning. 



Friday, December 27, 2013

Flat as a pancake

Credit: ESA/HUBBLE & NASA

Located some 25 million light-years away, this new Hubble image shows spiral galaxy ESO 373-8. Together with at least seven of its galactic neighbours, this galaxy is a member of the NGC 2997 group. We see it side-on as a thin, glittering streak across the sky, with all its contents neatly aligned in the same plane.

We see so many galaxies like this — flat, stretched-out pancakes — that our brains barely process their shape. But let us stop and ask: Why are galaxies stretched out and aligned like this?

Try spinning around in your chair with your legs and arms out. Slowly pull your legs and arms inwards, and tuck them in against your body. Notice anything? You should have started spinning faster. This effect is due to conservation of angular momentum, and it’s true for galaxies, too.

This galaxy began life as a humungous ball of slowly rotating gas. Collapsing in upon itself, it spun faster and faster until, like pizza dough spinning and stretching in the air, a disc started to form. Anything that bobbed up and down through this disc was pulled back in line with this motion, creating a streamlined shape.

Angular momentum is always conserved — from a spinning galactic disc 25 million light-years away from us, to any astronomer, or astronomer-wannabe, spinning in his office chair.




Tuesday, December 24, 2013

Massive stars mark out Milky Way’s ‘missing arms’

This artist’s impression shows our Galaxy, the Milky Way, as the spiral shape in the background. The massive stars referred to in the new study are indicated by red circles. The position of the Solar System is marked by a black dot and circle at the top centre. Credit: J. Urquhart et al. Background image by Robert Hurt of the Spitzer Science Center. Credit: J. Urquhart et al. Background image by Robert Hurt of the Spitzer Science Center. Click here for a larger image

A 12-year study of massive stars has reaffirmed that our Galaxy has four spiral arms, following years of debate sparked by images taken by NASA’s Spitzer Space Telescope that only showed two arms.

The new research, which is published online in the Monthly Notices of the Royal Astronomical Society, is part of the RMS Survey, which was launched by academics at the University of Leeds.

Astronomers cannot see what our Galaxy, which is called the Milky Way, looks like because we are on the inside looking out. But they can deduce its shape by careful observation of its stars and their distances from us.

"The Milky Way is our galactic home and studying its structure gives us a unique opportunity to understand how a very typical spiral galaxy works in terms of where stars are born and why," said Professor Melvin Hoare, a member of the RMS Survey Team in the School of Physics & Astronomy at the University of Leeds and a co-author of the research paper.

In the 1950s astronomers used radio telescopes to map our Galaxy. Their observations focussed on clouds of gas in the Milky Way in which new stars are born, revealing four major arms. NASA’s Spitzer Space Telescope, on the other hand, scoured the Galaxy for infrared light emitted by stars. It was announced in 2008 that Spitzer had detected about 110 million stars, but only found evidence of two spiral arms.

The astronomers behind the new study used several radio telescopes in Australia, USA and China to individually observe about 1650 massive stars that had been identified by the RMS Survey. From their observations, the distances and luminosities of the massive stars were calculated, revealing a distribution across four spiral arms.

“It isn’t a case of our results being right and those from Spitzer’s data being wrong – both surveys were looking for different things,” said Professor Hoare. “Spitzer only sees much cooler, lower mass stars – stars like our Sun – which are much more numerous than the massive stars that we were targeting.”

Massive stars are much less common than their lower mass counterparts because they only live for a short time – about 10 million years. The shorter lifetimes of massive stars means that they are only found in the arms in which they formed, which could explain the discrepancy in the number of galactic arms that different research teams have claimed.

“Lower mass stars live much longer than massive stars and rotate around our Galaxy many times, spreading out in the disc. The gravitational pull in the two stellar arms that Spitzer revealed is enough to pile up the majority of stars in those arms, but not in the other two,” explains Professor Hoare. “However, the gas is compressed enough in all four arms to lead to massive star formation.”

Dr James Urquhart from the Max Planck Institute for Radio Astronomy in Bonn, Germany, and lead author of the paper, said: “It's exciting that we are able to use the distribution of young massive stars to probe the structure of the Milky Way and match the most intense region of star formation with a model with four spiral arms.”

Professor Hoare concludes, “Star formation researchers, like me, grew up with the idea that our Galaxy has four spiral arms. It’s great that we have been able to reaffirm that picture.”



Media contacts

(To arrange interviews with Professor Melvin Hoare)
Sarah Reed
Press Officer
University of Leeds
Tel: +44 (0)113 343 4196

s.j.reed@leeds.ac.uk

Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035

rm@ras.org.uk



Further information

The new work appears in the paper “The RMS survey: galactic distribution of massive star formation”, J. S. Urquhart, C. C. Figura, T. J. T. Moore, M. G. Hoare, S. L. Lumsden, J. C. Mottram, M. A. Thompson and R. D. Oudmaijer, Monthly Notices of the Royal Astronomical Society, published by Oxford University Press. The paper is available from http://mnras.oxfordjournals.org/content/early/2013/11/13/mnras.stt2006


Notes for editors

University of Leeds
The University of Leeds is one of the largest higher education institutions in the UK and a member of the Russell Group of research-intensive universities.

The 2008 Research Assessment Exercise showed the University of Leeds to be the UK's eighth biggest research powerhouse and the University's vision is to secure a place among the world's leading universities by 2015.
www.leeds.ac.uk

Royal Astronomical Society

The Royal Astronomical Society (RAS, www.ras.org.uk ),  founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

Follow the RAS on Twitter via @royalastrosoc


Monday, December 23, 2013

NASA's Asteroid Hunter Spacecraft Returns First Images after Reactivation

NASA's NEOWISE spacecraft opened its "eyes" after more than two years of slumber to see the starry sky. Image credit: NASA/JPL-Caltech.  Full image and caption

This is one of the first images captured by the revived NEOWISE mission, after more than two years of hibernation. Image credit: NASA/JPL-Caltech. Full image and caption - enlarge image

Probe Will Assist Agency in Search for Candidates to Explore
 
NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), a spacecraft that made the most comprehensive survey to date of asteroids and comets, has returned its first set of test images in preparation for a renewed mission. 

NEOWISE discovered more than 34,000 asteroids and characterized 158,000 throughout the solar system during its prime mission in 2010 and early 2011. It was reactivated in September following 31 months in hibernation, to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects (NEOs). NEOWISE also can assist in characterizing previously detected asteroids that could be considered potential targets for future exploration missions. 

"NEOWISE not only gives us a better understanding of the asteroids and comets we study directly, but it will help us refine our concepts and mission operation plans for future, space-based near-Earth object cataloging missions," said Amy Mainzer, principal investigator for NEOWISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The spacecraft is in excellent health, and the new images look just as good as they were before hibernation. Over the next weeks and months we will be gearing up our ground-based data processing and expect to get back into the asteroid hunting business, and acquire our first previously undiscovered space rock, in the next few months." 

Some of the deep-space images taken by the spacecraft include a previously detected asteroid named (872) Holda. With a diameter of 26 miles (42 kilometers), this asteroid orbits the sun between Mars and Jupiter in a region astronomers call the asteroid belt. The images tell researchers the quality of the spacecraft's observations is the same as during its primary mission. 

The spacecraft uses a 16-inch (40-centimeter) telescope and infrared cameras to seek out and discover unknown NEOs and characterize their size, albedo or reflectivity, and thermal properties. Asteroids reflect, but do not emit visible light, so data collected with optical telescopes using visible light can be deceiving. 

Infrared sensors, similar to the cameras on NEOWISE, are a powerful tool for discovering, cataloging and understanding the asteroid population. Some of the objects about which NEOWISE will be collecting data could become candidates for the agency's announced asteroid initiative. 

NASA's initiative will be the first mission to identify, capture and relocate an asteroid. It represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities that will help protect our home planet. The asteroid initiative brings together the best of NASA's science, technology and human exploration efforts to achieve President Obama's goal of sending humans to an asteroid by 2025. 

"It is important that we accumulate as much of this type of data as possible while the spacecraft remains a viable asset," said Lindley Johnson, NASA's NEOWISE program executive in Washington. "NEOWISE is an important element to enhance our ability to support the initiative." 

NEOWISE began as WISE. The prime mission, which was launched in December 2009, was to scan the entire celestial sky in infrared light. WISE captured more than 2.7 million images in multiple infrared wavelengths and cataloged more than 747 million objects in space, ranging from galaxies faraway to asteroids and comets much closer to Earth. NASA turned off most of WISE's electronics when it completed its primary mission in February 2011. 

Upon reactivation, the spacecraft was renamed NEOWISE, with the goal of discovering and characterizing asteroids and comets whose orbits approach within 28 million miles (45 million kilometers) from Earth's path around the sun. 

More information about NEOWISE is available online at: http://www.nasa.gov/wise
 
For more information on the asteroid initiative, visit: http://www.nasa.gov/asteroidinitiative
 
JPL manages the project for NASA's Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colo., built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.

agle@jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington

Dwayne.c.brown@nasa.gov

 

Friday, December 20, 2013

The Rise and Fall of Galactic Cities


The collection of red dots seen near the center of this image show one of several very distant galaxy clusters discovered by combining ground-based optical data from the National Optical Astronomy Observatory's Kitt Peak National Observatory with infrared data from NASA's Spitzer Space Telescope. This galaxy cluster, named ISCS J1434.7+3519, is located about 9 billion light-years from Earth. 

The large white and yellow dots in this picture are stars in our galaxy, while the rest of the smaller dots are distant galaxies. The cluster, comprised of red dots near the center, includes more than 100 massive galaxies.
Spitzer was able to capture prodigious levels of star formation occurring in the galaxies that live in this cluster. Some of them are forming stars hundreds of times faster than our own Milky Way galaxy.

Infrared light in this image has been colored red; and visible light, blue and green. Credit: NASA/JPL-Caltech/M. Brodwin (UMKC)

In the fable of the town and country mice, the country mouse visits his city-dwelling cousin to discover a world of opulence. In the early cosmos, billions of years ago, galaxies resided in the equivalent of urban or country environments. Those that dwelled in crowded areas called clusters also experienced a kind of opulence, with lots of cold gas, or fuel, for making stars. 

Today, however, these galactic metropolises are ghost towns, populated by galaxies that can no longer form stars.  How did they get this way and when did the fall of galactic cities occur?

A new study from NASA's Spitzer Space Telescope finds evidence that these urban galaxies, or those that grew up in clusters, dramatically ceased their star-making ways about 9 billion years ago (our universe is 13.8 billion years old). These galactic metropolises either consumed or lost their fuel. Galaxies in the countryside, by contrast, are still actively forming stars.

"We know the cluster galaxies we see around us today are basically dead, but how did they get that way?" wondered Mark Brodwin of the University of Missouri-Kansas City, lead author of this paper, published in the Astrophysical Journal. "In this study, we addressed this question by observing the last major growth spurt of galaxy clusters, which happened billions of years ago."

Researchers studying distant galaxies get a peek into the past since the galaxies' light takes time, sometimes billions of years, to reach us. Brodwin and his colleagues used Spitzer to study 16 galaxy clusters that existed between the time our universe was 4.3 and 6 billion years old. Spitzer's infrared vision allows it see the dust warmed by new stars, revealing star-formation rates. NASA's Hubble Space Telescope and the W.M. Keck Observatory were used to measure the galaxies' distances from Earth. 

This is one of the most comprehensive looks at distant galaxy clusters yet, revealing new surprises about their environments. Previous observations of relatively nearby clusters suggested that the urban, cluster galaxies produced all their stars early in the history of our universe in one big burst. This theory, called monolithic collapse, predicted that these tight-knit galaxies would have used all their fuel at once in an early, youthful frenzy. But the new study shows this not to be the case: The urban galaxies continued to make stars longer than expected, until suddenly production came to a halt around 9 billion years ago, or about 3 billion years later than previously thought.

A second study using observations from the Herschel Space Observatory, led by Stacey Alberts at the University of Massachusetts-Amherst and published in the Monthly Notices of the Royal Astronomical Society journal, finds a similar transition epoch. Alberts and colleagues observed 300 clusters over a longer period of time, dating back to when the universe was 4 to 10 billion years old. Herschel, which ran out of coolant in April of 2013 as expected, detected longer wavelengths of infrared light than Spitzer, which is still up and running. The two telescopes complement each other, allowing scientists to confirm results and probe different aspects of cosmic conundrums. 

"We find that around 9 billion years ago, cluster galaxies were as active as their counterparts outside of clusters; however, their rate of star formation decreases dramatically between then and now, much more quickly than we see in isolated galaxies," said Alberts. 

Why do the urban galaxies shut down their star formation sooner and more rapidly than the country bumpkins? Brodwin says this may have to do with galaxy mergers. The more crowded a galactic environment, as is the case in young, growing galaxy clusters, the more often two galaxies will collide and merge. Galaxy mergers induce bursts of fuel-consuming star formation, and also feed growing supermassive black holes, which then blast out radiation that heats up the gas and quickly shuts off the star formation. 

"It's as if boom times for galaxies in clusters ended with a sudden widespread collapse," said Peter Eisenhardt of NASA's Jet Propulsion Laboratory, Pasadena, Calif., who led a previous study that identified the distant galaxy cluster sample used by Brodwin and Alberts.  "They go from vibrantly forming new stars to the quiescent state they've been in for the last half of the history of the universe, and the switch happens surprisingly fast."

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.



A stellar sneezing fit

Credit: ESA/Hubble & NASA
Acknowledgement: Gilles Chapdelaine
 
Look at the bright star in the middle of this image. Achoo! It has just sneezed. This sight will only last for a few thousand years — a blink of an eye in the young star's life.

If you could carry on watching for a few years you would realise it's not just one sneeze, but a sneezing fit. This young star is firing off salvos of super-hot, super-fast gas — Achoo! Achoo! — before it finally exhausts itself. These bursts of gas have shaped the turbulent surroundings, creating structures known as Herbig-Haro objects.

These objects are formed from the star's energetic "sneezes". These salvos can contain as much mass as our home planet, and cannon into nearby clouds of gas at hundreds of kilometres per second. Shock waves form, such as the U-shape below this star. Unlike most other astronomical phenomena, as the waves crash outwards, they can be seen moving across human timescales. Soon, this star will stop sneezing, and grow up to be a star like the Sun.

This region is actually home to several interesting objects. The star at the centre of the frame is a variable star named V633 Cassiopeiae, with Herbig-Haro objects HH 161 and HH 164 forming parts of the horseshoe-shaped loop emanating from it. The slightly shrouded star just to the left is known as V376 Cassiopeiae, another variable star that has succumbed to its neighbour's infectious sneezing fits; this star is also sneezing, creating yet another Herbig-Haro object — HH 162. Both stars are very young and are still surrounded by dusty material left over from their formation, which spans the gap between the two

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Gilles Chapdelaine.

For more information about these objects, see Hubblecast 49: Supersonic jets from newborn stars.




Thursday, December 19, 2013

Nearby Failed Stars May Harbor Planet


Image of Luhman 16AB 
Courtesy NASA / JPL / Gemini Observatory / AURA / NSF

Pasadena, CA— Astronomers, including Carnegie’s Yuri Beletsky, took precise measurements of the closest pair of failed stars to the Sun, which suggest that the system harbors a third, planetary-mass object.The research is published as a letter to the editor in Astronomy & Astrophysics available online at http://arxiv.org/abs/1312.1303.

Failed stars are known as brown dwarfs and have a mass below 8% of the mass of the Sun—not massive enough to burn hydrogen in their centers. This particular system, Luhman 16AB, was discovered earlier this year and is only 6.6 light-years away.

After the discovery announcement, several teams of astronomers, including the one with Beletsky, used a variety of telescopes to characterize the neighbouring couple.

After two-months of observations and extensive data analysis, Beletsky’s team, led by Henri Boffin of the European Southern Observatory (ESO), found that both objects have a mass between 30 and 50 Jupiter masses. By comparison, the Sun has a mass of about 1,000 Jupiter masses.

“The two brown dwarfs are separated by about three times the distance between the Earth and the Sun. Binary brown dwarf systems are gravitationally bound and orbit about each other. Because these two dwarfs have so little mass, they take about 20 years to complete one orbit,” explained Beletsky.

The team used the FORS2 instrument on ESO’s Very Large Telescope at Paranal to image the brown dwarf couple in the best possible conditions, every 5 or 6 days over the period April 14, to June 22, 2013. Because of the instrument enabled the observers to make very precise measurements, the scientists were already able to detect tiny displacements of the two objects in their orbit during only this the two-month period.

The astronomers were able to measure the positions of the two brown dwarfs with ten times better accuracy than before and thereby detect even small perturbations of their orbit.

“We have been able to measure the positions of these two objects with a precision of a few milli-arcseconds,” said Boffin. “That is like a person in Paris being able to measure the position of someone in New York with a precision of 10 centimetres.”

The measurements were so fine that the astronomers were able to see some very small deviations from the expected motion of the two brown dwarfs around each other. The fact that the deviations appear correlated is a strong indication that a companion perturbs the motion of one of the two brown dwarfs. This companion is most likely a planetary-mass object, which has an orbital period between two months and a year.

“Further observations are required to confirm the existence of a planet,” concludes Boffin. “But it may well turn out that the closest brown dwarf binary system to the Sun turns out to be a triple system!”

The team is composed of Henri Boffin, Kora Muzic, Valentin Ivanov, Andrea Mehner, Jean-Philippe Berger, Julien Girard, and Dimitri Mawet (ESO, Chile), Dimitri Pourbaix (Université Libre de Bruxelles, Belgium), Rudy Kurtev (Universidad de Valparaiso, Chile), and Yuri Beletsky (Carnegie Observatories at Las Campanas Observatory, Chile).




Wednesday, December 18, 2013

J075141 and J174140: Doubling Down With Rare White Dwarf Systems

Illustration of J075141 & J174140
Credit X-ray: NASA/CXC/Univ of Oklahoma/M.Kilic et al, Optical: SDSS, 
Illustration: NASA/CXC/M.Weiss 
 
  video
J075141 and J174140 Animations 

In the middle of the twentieth century, an unusual star was spotted in the constellation of Canes Venatici (Latin for "hunting dogs"). Years later, astronomers determined that this object, dubbed AM Canum Venaticorum (or, AM CVn, for short), was, in fact, two stars. These stars revolve around each other every 18 minutes, and are predicted to generate gravitational waves - ripples in space-time predicted by Einstein.

The name AM CVn came to represent a new class of objects where one white dwarf star is pulling matter from a very compact companion star, such as a second white dwarf. (White dwarf stars are dense remains of Sun-like stars that have run out of fuel and collapsed to the size of the Earth.) The pairs of stars in AM CVn systems orbit each other extremely rapidly, whipping around one another in an hour, and in one case as quickly as five minutes. By contrast, the fastest orbiting planet in our Solar System, Mercury, orbits the Sun once every 88 days.

Despite being known for almost 50 years, the question has remained: where do AM CVn systems come from? New X-ray and optical observations have begun to answer that with the discovery of the first known systems of double stars that astronomers think will evolve into AM CVn systems.

The two binary systems - known by their shortened names of J0751 and J1741 - were observed in X-rays by NASA's Chandra X-ray Observatory and ESA's XMM-Newton telescope. Observations at optical wavelengths were made using the McDonald Observatory's 2.1-meter telescope in Texas, and the Mt. John Observatory 1.0-meter telescope in New Zealand.

The artist's illustration depicts what these systems are like now and what may happen to them in the future. The top panel shows the current state of the binary that contains one white dwarf (on the right) with about one-fifth the mass of the Sun and another much heavier and more compact white dwarf about five or more times as massive (unlike Sun-like stars, heavier white dwarfs are smaller).

As the two white dwarfs orbit around each other, gravitational waves will be given off causing the orbit to become tighter. Eventually the smaller, heavier white dwarf will start pulling matter from the larger, lighter one, as shown in the middle panel, forming an AM CVn system. This process continues until so much matter accumulates on the more massive white dwarf that a thermonuclear explosion may occur in about 100 million years.

Credit: X-ray: NASA/CXC/Univ of Oklahoma/M.Kilic et al, 
Optical: SDSS

One possibility is that the thermonuclear explosion could destroy the larger white dwarf completely in what astronomers call a Type Ia supernova (the type of supernova used to mark large distances across the Universe by serving as so-called standard candles.) However, it's more likely that a thermonuclear explosion will occur only on the surface of the star, leaving it scarred but intact. The resulting outburst is likely to be about one tenth the brightness of a Type Ia supernova. Such outbursts have been named - somewhat tongue-in-cheek - as .Ia supernovae. Such .Ia outbursts have been observed in other galaxies, but J0751 and J1741 are the first binary stars known which can produce .Ia outbursts in the future.

The optical observations were critical in identifying the two white dwarfs in these systems and ascertaining their masses. The X-ray observations were needed to rule out the possibility that J0751 and J1741 contained neutron stars. A neutron star - which would disqualify it from being a possible parent to an AM CVn system - would give off strong X-ray emission due to its magnetic field and rapid rotation. Neither Chandra nor XMM-Newton detected any X-rays from these systems.

AM CVn systems are of interest to scientists because they are predicted to be sources of gravitational waves, as noted above. This is important because even though such waves have yet to be detected, many scientists and engineers are working on instruments that should be able to detect them in the near future. This will open a significant new observational window to the universe.

The paper reporting these results is available online and is published in the Monthly Notices of the Royal Astronomical Society Letters. The authors are Mukremin Kilic, from the University of Oklahoma in Norman, OK; J.J. Hermes from the University of Texas at Austin in TX; Alexandros Gianninas from the University of Oklahoma; Warren Brown from Smithsonian Astrophysical Observatory in Cambridge, MA; Craig Heinke from University of Alberta, in Edmonton, Canada; Marcel Agüeros from Columbia University in New York, NY; Paul Chote and Denis Sullivan from Victoria University of Wellington, New Zealand; and Keaton Bell and Samuel Harrold from University of Texas at Austin.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Mass., controls Chandra's science and flight operations.

Fast Facts for J075141: 

Scale: Image is 7 arcmin across (about 11 light years). 
Category: White Dwarfs & Planetary Nebulas
Coordinates (J2000): RA 07h 51m 41.20s | Dec -01° 41' 20.90" 
Constellation: Monoceros
Observation Dates: 22 Dec 2012 
Observation Time: 1 hours 7 min 
Obs. IDs: 14608 
Instrument: ACIS
References: Kilic, M. et al, 2013, MNRAS Letters (in press); arxiv:1310.6359
Color Code: X-ray (Pink); Optical (Red, Green, Blue) 
Distance Estimate: About 5,500 light years 



Tuesday, December 17, 2013

RS Puppis puts on a spectacular light show [heic1323]

The NASA/ESA Hubble Space Telescope has observed the variable star RS Puppis over a period of five weeks, showing the star growing brighter and dimmer as it pulsates. These pulsations have created a stunning example of a phenomenon known as a light echo, where light appears to reverberate through the murky environment around the star. 

Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration. Acknowledgment: H. Bond (STScI and Penn State University)
 
Copyright: ESA/Hubble & ESO


  Watch a Star Blast Out Light Echoes 
Credit: NASA, ESA, G. Bacon (STScI), the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration, and H. Bond (STScI and Pennsylvania State University)
 
For most of its life, a star is pretty stable, slowly consuming the fuel at its core to keep it shining brightly.

However, once most of the hydrogen that stars use as fuel has been consumed, some stars evolve into very different beasts – pulsating stars. They become unstable, expanding and shrinking over a number of days or weeks and growing brighter and dimmer as they do so.

A new and spectacular Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable [1]. As variable stars go, Cepheids have comparatively long periods. RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days.

RS Puppis is unusual as it is shrouded by a nebula – thick, dark clouds of gas and dust. Hubble observed this star and its murky environment over a period of five weeks in 2010, capturing snapshots at different stages in its cycle and enabling scientists to create a time-lapse video of this ethereal object (heic1323a).

The apparent motion shown in these Hubble observations is an example of a phenomenon known as a light echo [2]. The dusty environment around RS Puppis enables this effect to be shown with stunning clarity. As the star expands and brightens, we see some of the light after it is reflected from progressively more distant shells of dust and gas surrounding the star, creating the illusion of gas moving outwards. This reflected light has further to travel, and so arrives at the Earth after light that travels straight from star to telescope [3]. This is analogous to sound bouncing off surrounding objects, causing the listener to hear an audible echo.

While this effect is certainly striking in itself, there is another important scientific reason to observe Cepheids like RS Puppis. The period of their pulsations is known to be directly connected to their intrinsic brightness, a property that allows astronomers to use them as cosmic distance markers. A few years ago, astronomers used the light echo around RS Puppis to measure its distance from us, obtaining the most accurate measurement of a Cepheid's distance (eso0805). Studying stars like RS Puppis helps us to measure and understand the vast scale of the Universe.

Notes

[1] RS Puppis is over ten times more massive than our Sun, and around 15 000 times more luminous. It lies around 6500 light-years away from us.

[2] This light echo enabled astronomers to measure the distance to RS Puppis very accurately back in 2008. This measurement is the most accurate ever calculated for a Cepheid.

[3] This effect can make it appear that this propagation of light is happening at speeds greater than the speed of light, but this is just an illusion.

Notes for editors

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Contacts

Nicky Guttridge
Hubble/ESA
Garching bei München, Germany
Tel: +49-89-3200-6855
Email:
nguttrid@partner.eso.org




SMA Reveals Giant Star Cluster in the Making

The Smithsonian's Submillimeter Array (SMA) has peered through the dusty fog to provide the first clear view of this stellar nursery. The SMA revealed an active site of star formation being fed by streamers of infalling gas.

"We were amazed by all the features we saw in the SMA images," says lead author Roberto Galván-Madrid, who conducted this research at the Harvard-Smithsonian Center for Astrophysics (CfA) and the European Southern Observatory (ESO).

W49A is located about 36,000 light-years from Earth, on the opposite side of the Milky Way. It represents a nearby example of the sort of vigorous star formation seen in so-called "starburst" galaxies, where stars form 100 times faster than in our galaxy.

The heart of W49A holds a giant yet surprisingly compact star cluster. About 100,000 stars already exist within a space only 10 light-years on a side. In contrast, fewer than 10 stars lie within 10 light-years of our Sun. In a few million years, the giant star cluster in W49A will be almost as crowded as a globular cluster.

The SMA also revealed an intricate network of filaments feeding gas into the center, much like tributaries feed water into mighty rivers on Earth. The gaseous filaments in W49A form three big streamers, which funnel star-building material inward at speeds of about 4,500 miles per hour (2 km/sec).

"Move over, Mississippi!" quips co-author Qizhou Zhang of the CfA.

Being denser than average will help the W49A star cluster to survive. Most star clusters in the galactic disk dissolve rapidly, migrating away from each other under the influence of gravitational tides. This is why none of the Sun's sibling stars remain nearby. Since it is so compact, the cluster in W49A might remain intact for billions of years.

The Submillimeter Array mapped the molecular gas within W49A in exquisite detail. It showed that central 30 light-years of W49A is several hundred times denser than the average molecular cloud in the Milky Way. In total, the nebula contains about 1 million suns' worth of gas, mostly molecular hydrogen.
"We suspect that the organized architecture seen in W49A is rather common in massive stellar cluster-formation," adds co-author Hauyu Baobab Liu of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan.

The team expects to continue analyzing the SMA data for some time to come.

"It's a mine of information," says Galván-Madrid.

Their research was published in the December 2013 Astrophysical Journal.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462

daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463

cpulliam@cfa.harvard.edu




Monday, December 16, 2013

Planetary Nebula Sh2-71

This composite image was obtained through the filters Hα (red, 3×120s), Sloan r´ (green, 3×30s) and [OIII] (blue, 3×120s) using the Wide Field Camera on the Isaac Newton Telescope on the 21st of October, 2013. Images were reduced using THELI, and processed using FITS Liberator and MATLAB. Field of view is 9×6 arcminutes, North up, East left. Credits: Teo Mocnik (ING) [ JPEG | TIFF ]

The bipolar planetary nebula (PN) Sh2-71 lies in the constellation of Aquila at a distance of 1 kpc. It was discovered by Rudolph Minkowski in 1946. Shortly after the discovery, the central star (the brightest star in the centre of the nebula) was identified to be a variable with a quasi-sinusoidal lightcurve with an amplitude of 0.8 magnitudes. Later observations showed sharp brightness dips, possibly eclipses, with a period of 17.2 days. Besides an unusual lightcurve, it also exhibits pronounced spectral variations. 
Astronomers believe that the central star is a close binary, which could explain the observed variability as well as the necessary mechanism for collimating the outflowing material. 

However, some astronomers claim that the real central star is actually a much dimmer star located to the North-West of the bright one. The true nature of the planetary nebula Sh2-71 will remain veiled until more data are obtained and new analysis and explanations are provided.


More information:
INT's Wide-Field Camera.

Contact: Javier Méndez  (Public Relations Officer)



 

Herschel spies active argon in Crab Nebula

Herschel image and spectrum of the Crab Nebula, with emission lines from the molecular ion argon hydride. Credit: ESA/Herschel/PACS, SPIRE/MESS Key Programme Supernova Remnant Team.  Hi-Res Image
 
Herschel (red) and Hubble (blue) composite image of the Crab Nebula. Credit: ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team; NASA, ESA and Allison Loll/Jeff Hester (Arizona State University). Hi-Res Image

Using ESA's Herschel Space Observatory, a team of astronomers has found first evidence of a noble-gas based molecule in space. A compound of argon, the molecule was detected in the gaseous filaments of the Crab Nebula, one of the most famous supernova remnants in our Galaxy. While argon is a product of supernova explosions, the formation and survival of argon-based molecules in the harsh environment of a supernova remnant is an unforeseen surprise. 

Just like a group of people, the periodic table of chemical elements has its share of team players and loners. While some elements tend to react more easily with other species, forming molecules and other compounds, others hardly ever take part in chemical reactions and are mainly found in isolation. 'Inert' elements par excellence are the noble gases: helium, neon, argon, krypton, xenon and radon.

The name of one of them – argon – derives from the Greek word for idle, to emphasise its highly inert nature. But noble gases are not entirely inactive. While at first scientists doubted that chemical compounds could even contain noble gases, several such species are now known and have been extensively studied in the laboratory.

Things are more complex in space. Over the decades, astronomers have detected atoms and ions of noble gases in a variety of cosmic environments, ranging from the Solar System to the atmospheres of stars, from dense nebulae to the diffuse interstellar medium. But the search for noble-gas based compounds had until now proved unsuccessful, suggesting that these almost inert elements might have a hard time reacting with other species in space.

A new study, led by Michael Barlow from University College London, UK, and based on data from ESA's Herschel Space Observatory, has found the first evidence of such a compound in space. The results are published in the journal Science.

The team of astronomers has detected emission from argon hydride (ArH+), a molecular ion containing the noble gas argon, in the Crab Nebula. A wispy and filamentary cloud of gas and dust, the Crab Nebula is the remnant of a supernova explosion that was observed by Chinese astronomers in the year 1054.

"At first, the discovery seemed bizarre," comments Barlow.

"With hot gas still expanding at high speeds after the explosion, a supernova remnant is a harsh, hostile environment, and one of the places where we least expected to find a noble-gas based molecule," he adds.

Argon hydride is produced when ions of argon (Ar+) react with hydrogen molecules (H2), but these two species are usually found in different regions of a nebula. While ions form in the most energetic regions, where radiation from a star or stellar remnant ionises the gas, molecules take shape in the denser, colder pockets of gas that are shielded from this powerful radiation.


"But we soon realised that even in the Crab Nebula, there are places where the conditions are just right for a noble gas to react and combine with other elements.

"There, in the transition regions between ionised and molecular gas, argon hydride can form and survive," explains Barlow.

This new picture was supported by the comparison of the Herschel data with observations of the Crab Nebula performed at other wavelengths, which revealed that the regions where they had found ArH+ also exhibit higher concentrations of both Ar+ and H2. There, argon ions can react with hydrogen molecules forming argon hydride and atomic hydrogen.

In the partly ionised gas filling these regions, molecules collide frequently with ions and free electrons. These collisions excite the molecular structure of ArH+ making it rotate; in turn, molecular rotations produce the emission features detected in the spectrum of the Crab Nebula by Herschel.

"The discovery was truly serendipitous: we were observing the Crab Nebula to study its dust content. But then, on top of the emission from dust, we found two emission lines that had never been seen before," says co-author Bruce Swinyard, also from University College London.

The identification of these lines was a challenging task. To this end, the astronomers exploited two extensive databases of molecular spectra and, after lengthy investigation, they matched the observed features with two characteristic lines emitted by ArH+.

"And there's icing on the cake: from a molecule's emission, we can determine the isotope of the elements that form it – something that we can't do when we see only ions," adds Swinyard.

The Herschel data indicate that the argon hydride found in the Crab Nebula is made up of the argon isotope 36Ar. This is the first time that astronomers could identify the isotopic nature of an element in a supernova remnant.

"Finding that argon in the Crab Nebula consists of 36Ar was not surprising because this is the dominant isotope of argon across the Universe.

"And it's also the main argon isotope to be synthesised in the nuclear reactions during supernova explosions, so its detection in the Crab Nebula confirms that this iconic nebula was created by the explosive death of a massive star," explains Barlow.

The astronomers are planning further observations with other facilities to seek new emission lines in the Crab Nebula's spectrum, possibly from molecules containing different isotopes of argon. The detection of such a molecule would enable them to study the ratio of different isotopes produced by supernovae and to learn more about the nuclear reactions that take place when a massive star dies.

"This is not only the first detection of a noble-gas based molecule in space, but also a new perspective on the Crab Nebula. Herschel has directly measured the argon isotope we expect to be produced via explosive nucleosynthesis in a core-collapse supernova, refining our understanding of the origin of this supernova remnant," concludes Göran Pilbratt, Herschel Project Scientist at ESA.

Background information

The results described in this article are reported in "Detection of a Noble Gas Molecular Ion, 36ArH+, in the Crab Nebula", by M. J. Barlow et al., published in Science, 342, 6163, 1343-1345, 13 December 2013. DOI: 10.1126/science.124358213.

The argon isotope found in the Crab Nebula is different from the one that dominates in Earth's atmosphere, 40Ar, which derives from the decay of a radioactive isotope of potassium (40K) present in our planet's rocks. 
At almost one per cent, argon is the third most abundant gas in the atmosphere of Earth after nitrogen and oxygen, and was discovered at the end of the 19th century.

The study is based on data collected with the Spectral and Photometric Imaging Receiver (SPIRE) on board ESA's Herschel Space Observatory. The team of astronomers detected two emission lines corresponding to the first two rotational transitions of argon hydride (ArH+) at frequencies of 617.5 GHz and 1234.6 GHz, respectively. To identify the lines, they made use of two extensive databases of molecular lines: the Cologne Database for Molecular Spectroscopy (CDMS) and the Madrid Molecular Spectroscopy Excitation (MADEX) code.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

The SPIRE instrument contains an imaging photometer (camera) and an imaging spectrometer. The camera operates in three wavelength bands centred on 250, 350 and 500 µm, and so can make images of the sky simultaneously in three sub-millimetre colours; the spectrometer covers the wavelength range between 194 and 671 μm. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA  (UK); and NASA (USA).

Herschel was launched on 14 May 2009 and completed science observations on 29 April 2013.

Contacts

Michael J. Barlow
Department of Physics & Astronomy
University College London
London, UK
Email:
mjb@star.ucl.ac.uk
Phone: +44-20-7679-7160
Mobile: +44-77-5894-5482


Bruce M. Swinyard
Department of Physics & Astronomy
University College London
London, UK
Email
: bms@star.ucl.ac.uk; bruce.swinyard@stfc.ac.uk
Phone: +44-20-7679-1352
Mobile: +44-79-0834-3567


Göran Pilbratt
Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate
ESA, The Netherlands
Email:
gpilbratt@rssd.esa.int
Phone: +31-71-565-3621




Saturday, December 14, 2013

Multiwavelength solar view

Multiwavelength solar view
Copyright: Kosmas Gazeas (University of Athens, Greece, kgaze@phys.uoa.gr), P.Horálek - Observatory Úpice, J.Sládeček, M.Druckmüller, Proba-2 (ESA/ROB), SDO (NASA)   Hi-Res Image

A composite of space- and ground-based observations in different wavelengths gathered on the day of the solar eclipse of 3 November 2013. The result is an overall view of the Sun and its surrounding corona, extending far out into space.

Close-in views of the solar disc and its surroundings in extreme-ultraviolet light are covered by the Royal Observatory of Belgium’s SWAP instrument aboard ESA’s Proba-2 minisatellite and the AIA and HMI instruments aboard NASA’s Solar Dynamics Observatory mission. The surrounding inner corona is depicted through a combination of white-light images acquired from the ground along the path of totality, from Port Gentil in Gabon and Pokwero in Uganda. The outer corona is depicted through the white-light LASCO-C2 and C3 coronagraph instruments aboard the ESA/NASA SOHO satellite.

The planet Saturn is visible at the top left of the picture as a bright saturated object, coincidentally giving an impression of rings. To see more of the eclipse in multiple wavelengths, check this video.



 

Friday, December 13, 2013

Hubble discovers water vapour venting from Jupiter’s moon Europa

Water vapour plumes on Jupiter's moon Europa (artist's impression) 

PR Image heic1322b
Water vapour plumes on Jupiter's moon Europa (artist's impression) 

Water vapour plumes on Jupiter's moon Europa (artist's impression)

PR Image heic1322d
Water vapour plumes on Jupiter’s moon Europa (artist’s impression)
 
Water vapour plumes over Europa


Videos

Illustrated fly-by of Europa's plumes (artist's impression)
Illustrated fly-by of Europa's plumes (artist's impression)

Flying past Europa’s plumes (artist’s impression)
Flying past Europa’s plumes (artist’s impression)

The NASA/ESA Hubble Space Telescope has discovered water vapour erupting from the frigid surface of Jupiter’s moon Europa, in one or more localised plumes near its south pole.

Europa is already thought to harbour a liquid ocean beneath its icy crust, making the moon one of the main targets in the search for habitable worlds away from Earth. This new finding is the first observational evidence of water vapour being ejected off the moon's surface.

"The discovery that water vapour is ejected near the south pole strengthens Europa's position as the top candidate for potential habitability," said lead author Lorenz Roth of the Southwest Research Institute in San Antonio, Texas. "However, we do not know yet if these plumes are connected to subsurface liquid water or not." The Hubble findings will be published in the 12 December online issue of Science Express, and are being reported today at the meeting of the American Geophysical Union in San Francisco, California, USA.

The Hubble discovery makes Europa only the second moon in the Solar System known to have water vapour plumes. In 2005, plumes of water vapour and dust were detected by NASA's Cassini orbiter spewing off the surface of the Saturnian moon Enceladus.

The Europa plumes were discovered by Hubble observations in December 2012. The Space Telescope Imaging Spectrograph (STIS) detected faint ultraviolet light from an aurora at the moon's south pole. This aurora is driven by Jupiter's intense magnetic field, which causes particles to reach such high speeds that they can split the water molecules in the plume when they hit them, resulting in oxygen and hydrogen ions which leave their telltale imprint in the colours of the aurora.

So far, only water vapour has been detected — unlike the plumes on Enceladus, which also contain ice and dust particles.

"We pushed Hubble to its limits to see this very faint emission," said co-lead author and principal investigator of the Hubble observing campaign Joachim Saur of the University of Cologne, Germany. "Only after a particular camera on the Hubble Space Telescope had been repaired on the last servicing mission by the Space Shuttle did we gain the sensitivity to really search for these plumes."

Roth suggests long cracks on Europa's surface, known as linea, might be venting water vapour into space. Similar fissures have been photographed near Enceladus's south pole by the Cassini spacecraft. It is unknown how deep inside Europa's crust the source of the water may be. Roth asks, "Do the vents extend down to a subsurface ocean or are the ejecta simply from warmed ice caused by friction stresses near the surface?"

Also like Enceladus, the Hubble team found that the intensity of the plumes varies with Europa's orbital position. Active geysers have only been seen when the moon is furthest from Jupiter. But the researchers could not detect any sign of venting when Europa is closer to Jupiter.

One explanation is that the long fractures in the ice crust experience more stress as gravitational tidal forces push and pull on the moon and so open vents at larger distances from Jupiter. The vents are narrowed or closed when at closest approach to the gas giant planet [1]. Team member Kurt Retherford, also of the Southwest Research Institute, points out that "the plume variability supports a key prediction that we should see this kind of tidal effect if there is a subsurface ocean on Europa".

Future space probe missions to Europa could confirm that the exact locations and sizes of vents and determine whether they connect to liquid subsurface reservoirs. It is important news for missions such as ESA's JUpiter ICy moons Explorer, a mission planned for launch in 2022, and which aims to explore both Jupiter and three of its largest moons: Ganymede, Callisto, and Europa.

Notes

[1] When Europa orbits around Jupiter, the moon experiences varying tidal forces at different points in its orbit. The tidal stresses compress the vents at the south pole region when Europa is closest to Jupiter, and stretch them when Europa is furthest away, making it possible for the vents to open up. A subsurface ocean would allow the stresses on Europa's surface to be much stronger as the interior would be malleable and flexible.

Notes for editors


The Hubble Space Telescope is a project of international cooperation between ESA and NASA.


The international team of astronomers in this study consists of L. Roth (Southwest Research Institute, USA; University of Cologne, Germany), J. Saur (University of Cologne, Germany), K. D. Retherford (Southwest Research Institute, USA), D. F. Strobel (The Johns Hopkins University, USA), P. D. Feldman (The Johns Hopkins University, USA), M. A. McGrath (NASA Marshall Space Flight Center, USA), F. Nimmo (University of California, USA).

More information

Image credit: NASA, ESA, L. Roth (Southwest Research Institute, USA/University of Cologne, Germany) and M. Kornmesser.

Links

Contacts

Lorenz Roth
Southwest Research Institute, San Antonio, Texas, USA
University of Cologne, Germany
Tel: +1-210-522-2225
Email:
lorenz.roth@swri.org

Joachim Saur
University of Cologne
Germany
Tel: +49-221-470-2310
Email:
jsaur@uni-koeln.de

Nicky Guttridge
ESA/Hubble Public Information Officer
Garching, Germany
Tel: +49-89-3200-6855
Cell: +44 7512 318322
Email:
nguttrid@partner.eso.org

Ray Villard
Space Telescope Science Institute
Baltimore, Maryland, USA
Tel: +1-410-338-4514
Email:
villard@stsci.edu