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COMING EVENTS Band Concert

Public Observing Downtown Lawrence

South Park west of Mass St.

Schedule to be determined

9:30 PM

President

Rick Heschmeyer rcjbm@sbcglobal.net

Webmaster Howard Edin

howard@howardedin.com

Observing Clubs Doug Fay

dfay@ku.edu

ALCOR William Winkler

billwink10@yahoo.com

University Advisor Dr. Bruce Twarog

Report from the Officers We ended the Spring semester meetings with a big bang, in every way possible. About 75 people showed up to hear Prof. Feldman explain the fundamental observations of Cosmology that lead to the conclusion that the Uni-verse began about 13.8 billion years ago with the mass-energy concentrated into an almost infinitesimally small region of spacetime. Equally important, the recent BICEP observations of polarization in the cosmic microwave background radiation, if confirmed, supply direct observa-tional evidence of an event known as inflation, when the universe expanded by a factor of ~10

44 on a timescale of

10-33 sec. The gravitational waves created during this extraordinary expansion created a signature in the back-ground radiation which has been seen for the first time.

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Volume 40 Number 05 MAY 2014

INSIDE THIS ISSUE

Officer Report (continued) 2

El Gordo Cluster 3

NASA Space Place 4

Cool Solar Neighbors 5

Galaxies—Young & Mature 6

Galaxies (continued) 7

Alma (continued) 7

Massive Stars—ALMA 8

Ganymede Sandwich 9

El Gordo (continued) 10

Cool Neighbor (continued) 10

Meeting web page:http://www.slasonline.org/msral2014.html May 16, 2014 – Last day to reserve MSRAL rooms at the Knight Center at the $99 convention rate. May 26, 2014 - Early Registration ends, price $35 per person Banquet, Star-B-Q and lunches will also increase June 1, 2014 - Last Day to Register for Banquet and Meals June 6, 2014 - Friday Night Star-B-Q, Telescope Viewing, Planetarium Sky Show, Laserium Shows June 7, 2014 - AM/PM Paper Presentations, Annual Business Meeting, Earth and Planetary Science Center (E&PSC) tours

June 8, 2014 - AM - Astrophotography, Night Sky Network Training

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About the Astronomy Associates of Lawrence

The club is open to all people interested in sharing their love for astronomy. Monthly meetings are typically on the second Friday of each month and often feature guest speakers, presentations by club members, and a chance to exchange amateur astronomy tips. Approximately the last Sunday of each month we have an open house at the Prairie Park Nature Center. Periodic star parties

are scheduled as well. For more information, please contact the club officers: president, Rick Heschmeyer at

rcjbm@sbcglobal.net; webmaster, Howard Edin, at howard@howardedin.com; AlCor William Winkler, at

billwink10@yahoo.com; or faculty advisor, Prof. Bruce Twarog at btwarog@ku.edu. Because of the flexibility of the schedule due to holidays and alternate events, it is always best to check the Web site for the exact Fridays and Sundays when events are

scheduled. The information about AAL can be found at http://groups.ku.edu/~astronomy

Copies of the Celestial Mechanic can also be found on the web at http://groups.ku.edu/~astronomy/celestialmechanic

Dr. Hume Feldman, Chair of Physics & Astronomy and an internationally re-nowned cosmologist., (left) had no trouble filling the 75 minute presentation with amazing facts and insight which the audience clearly appreciated. If you missed it, you missed an exciting event. Finally! Our last public observing ses-sion for the Spring semester at Prairie Park Nature Center went off without a hitch. The skies were dark and the temperatures comfortable. Club mem-bers were joined by the KU SEDS (Space Exploration and Development Society) club, who brought along their

newly acquired telescope for checkout and testing. Though not as populated as the talk on Friday, everyone had a good time learning a little about observing the sky. We will try again in late May, picking up our usual schedule of observing downtown after the Wednesday Band Concerts as soon as the schedule for the concerts is officially posted.

ALCON 2014 Website is now "LIVE" The annual Astronomical League Convection this year is in San Antonio, Texas – July 10, 11, & 12, 2014. Log on to the site (http://alcon2014.astroleague.org/) and check the plans and registration in detail. Perspectives on the Monuments of Mount Oread: A Stop Day Walking Tour of Kansas University

Conducted by Professor Emeritus Ted Johnson, Sponsored by the Department of Humanities and Western Civilization The traditional marathon Stop Day walking tour of the campus consisting of informal, peripatetic, Socratic dialogues growing out of various sites will take place on Friday, May 9, 2014, from 9 a.m. to about 6 p.m. (bring friends and come and go as you please). The walking tour begins in front of the Natural History Museum, 14th Street and Jayhawk Boulevard, at 9 a.m.. For further information, please contact the Department of Humanities and Western Civilization at hwc@ku.edu or Professor John-son at jtj@ku.edu. Special Android Application now available from the NASA Space Place Program

For those of you familiar with our monthly SpacePlace column from NASA, Space Place Prime is now available on Android! A spinoff of NASA’s popular kids’ Space Place website (spaceplace.nasa.gov), Space Place Prime has timely, educational, and easy-to-read articles and activities from the Space Place and other science websites, the latest and most impressive NASA space and Earth imagery, and a wide array of informational movies. There is plenty to keep everyone occupied and informed. Content is updated daily, http://tinyurl.com/lyqme53.

Any suggestions for improving the club or the newsletter are always welcome.

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Hubble Finds That Monster 'El Gordo' Galaxy Cluster Is Bigger Than Thought

NASA's Hubble Space Telescope has weighed the largest known galaxy cluster in the distant universe and found that it definitely lives up to its nickname: El Gordo (Spanish for "the fat one").

By precisely measuring how much the gravity from the cluster's mass warps images of far-more-distant background galaxies, a team of astronomers has calculated the cluster's mass to be as much as 3 million billion times the mass of our Sun. The Hubble data show that the cluster is roughly 43 percent more massive than earlier estimates based on X-ray and dynamical studies of the unusual cluster.

"It's given us an even stronger probability that this is really an amazing system very early in the universe," said

team lead James Jee of the University of California at Davis.

A fraction of this mass is locked up in several hundred galaxies that inhabit the cluster and a larger fraction is in hot

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This is a Hubble Space Telescope image of the most massive cluster of galaxies ever seen to exist when the uni-verse was just half of its current age of 13.8 billion years. The cluster, catalogued as ACT-CL J0102-4915, contains several hundred galaxies swarming around under the collective gravitational pull. The total mass of the cluster, as refined in new Hubble measurements, is estimated to weigh as much as 3 million billion stars like our Sun (about 3,000 times as massive as our own Milky Way galaxy) — though most of the mass is hidden away as dark matter. The location of the dark matter is mapped out in the blue overlay. Because dark matter doesn't emit any radiation, Hubble astronomers instead precisely measure how its gravity warps the images of far background galaxies like a funhouse mirror. This allowed them to come up with a mass estimate for the cluster. The cluster was nicknamed El Gordo (Spanish for "the fat one") in 2012 when X-ray observations and kinematic studies first suggested it was unu-sually massive for the time in the early universe when it existed. The Hubble data have confirmed that the cluster is undergoing a violent merger between two smaller clusters.

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The Power of the

Sun's Engines

By Dr. Ethan Siegel

Here on Earth, the sun provides us with the vast majority of our energy, striking the top of the atmosphere with up to 1,000 Watts of power per square meter, albeit highly dependent on the sunlight's angle-of-incidence. But remember that the sun is a whopping 150 million kilometers away, and sends an equal amount of radiation in all directions; the Earth-facing direction is noth-ing special. Even considering sunspots, solar flares, and long-and-short term variations in solar irradiance, the sun's energy output is always constant to about one-part-in-1,000. All told, our parent star consistently outputs an esti-mated 4 × 1026 Watts of power; one second of the sun's emissions could power all the world's energy needs for over 700,000 years.

That's a literally astronomical amount of energy, and it comes about thanks to the hugeness of the sun. With a radi-us of 700,000 kilometers, it would take 109 Earths, lined up from end-to-end, just to go across the diameter of the sun once. Unlike our Earth, however, the sun is made up of around 70% hydrogen by mass, and it's the individual protons -— or the nuclei of hydrogen atoms — that fuse together, eventually becoming helium-4 and releasing a tremendous amount of energy. All told, for every four protons that wind up becoming helium-4, a tiny bit of mass — just 0.7% of the original amount — gets converted into energy by E=mc2, and that's where the sun's power origi-nates.

You'd be correct in thinking that fus-ing ~4 × 1038 protons-per-second gives off a tremendous amount of energy, but remember that nuclear fusion occurs in a huge region of the sun: about the innermost quarter (in radius) is where 99% of it is actively taking place. So there might be 4 × 1026 Watts of power put out, but that's spread out over 2.2 × 1025 cu-bic meters, meaning the sun's energy output per-unit-volume is just 18 W / m3. Compare this to the average human being, whose basal metabolic rate is equivalent to around 100 Watts, yet takes up just 0.06 cubic meters of space. In other words, you emit 100 times as much energy-per-unit-volume as the sun! It's only because the sun is so large and massive that its power is so great.

It's this slow process, releasing huge amounts of energy per reaction over an incredibly large volume, that has powered life on our world throughout its entire history. It may not appear so impressive if you look at just a tiny region, but — at least for our sun — that huge size really adds up!

Check out these “10 Need-to-Know Things About the Sun”: http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun.

Kids can learn more about an intriguing solar mystery at NASA’s Space Place: http://spaceplace.nasa.gov/sun-corona.

Composite of 25 images of the sun, showing solar outburst/activity over a 365 day

period; NASA / Solar Dynamics Observatory / Atmospheric Imaging Assembly / S.

Wiessinger; post-processing by E. Siegel.

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NASA's Spitzer and WISE Telescopes Find Close, Cold Neighbor of Sun

NASA's Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescope have discovered what appears to be the coldest "brown dwarf" known -- a dim, star-like body that surprisingly is as frosty as Earth's North Pole.

Images from the space tele-scopes also pinpointed the object's distance to 7.2 light-years away, earning it the title for fourth closest system to our sun. The closest system, a trio of stars, is Alpha Centauri, at about 4 light-years away.

"It's very exciting to discover a new neighbor of our solar sys-tem that is so close," said Kev-in Luhman, an astronomer at Pennsylvania State Universi-ty's Center for Exoplanets and Habitable Worlds, University

Park. "And given its extreme tem-perature, it should tell us a lot about the atmospheres of planets, which often have similarly cold tempera-tures."

Brown dwarfs start their lives like stars, as collapsing balls of gas, but they lack the mass to burn nuclear fuel and radiate starlight. The new-found coldest brown dwarf is named WISE J085510.83-071442.5. It has a chilly tempera-ture between minus 54 and 9 de-grees Fahrenheit (minus 48 to mi-nus 13 degrees Celsius). Previous record holders for coldest brown dwarfs, also found by WISE and Spitzer, were about room tempera-ture.

WISE was able to spot the rare ob-ject because it surveyed the entire sky twice in infrared light, observing some areas up to three times. Cool objects like brown dwarfs can be invisible when viewed by visible-light telescopes, but their thermal glow -- even if feeble -- stands out in infra-red light. In addition, the closer a body, the more it appears to move in images taken months apart. Airplanes are a good example of this effect: a closer, low-flying plane will appear to fly

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This artist's conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Brown dwarfs are dim star-like bodies that lack the mass to burn nuclear fuel as stars do. WISE J085510.83-071442.5 is as cold as the North Pole (or between minus 54 and 9 degrees Fahrenheit, which is minus 48 to minus 13 degrees Celsius). The color of the brown dwarf in this image is arbitrary; it would have different colors when viewed in different wavelength ranges.

This celestial orb is also the fourth closest to our sun, at 7.2 light-years from Earth. In this illustration, the sun is the bright star directly to the right of the brown dwarf. Our sun's closest neighboring system (not pictured) is Alpha Centauri, at 4 light-years from Earth.

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Herschel discovers mature galaxies in the young Universe New Herschel results have given us a remarkable insight into the internal dynamics of two young galaxies. Surprisingly,

they have shown that just a few billion years after the Big Bang, some galaxies were rotating in a mature way, seemingly

having completed the accumulation of their gas reservoirs.

When galaxies form, they accumulate mass by gravitationally attracting vast, external gas clouds. As the gas clouds enter the galaxy, they fall into haphazard orbits. These disordered paths cause turbulence in the host galaxies, which can drive star formation.

To investigate the internal conditions of forming galaxies James Rhoads and Sangeeta Malhotra, both from Arizona State University, and col-leagues targeted two young galaxies, known as S0901 and the Clone. The light from both galax-ies has taken 10 billion years to reach us across space. Thus, we are seeing them when they were comparatively young.

"The purpose of this project is to study the physi-cal conditions of gas in those galaxies. We want-ed to know: are they similar to the galaxies around us or is there some difference in their physical conditions," says Rhoads.

The two galaxies they choose to study are aver-age galaxies for that time in cosmic history. This means that they are about 10-20 per cent the size of our Milky Way, which is considered an average

galaxy in the present-day Universe.

Studying galaxies so far away is usually hampered because they appear too dim to study effectively but in this case, the research-ers were helped by a cosmic magnifier known as a gravitational lens. The two galaxies both sit behind intervening groups of galax-ies, whose gravity warps space. As described by Albert Einstein's General Theory of Relativity, this warping acts like a lens. Alt-hough it distorts the images of the young galaxies, it helps by magnifying their light, thus bringing them within reach of Her-schel's HIFI instrument.

The researchers used HIFI to investigate the infrared light of ion-ized carbon, which is emitted at a wavelength of 158 micrometres (a frequency of 1900 GHz). This spectral line is produced in the clouds that surround star-forming regions. HIFI showed the line was broadened into a double peak, and this allowed the motion of the gas to be fitted with a model.

Firstly, the team fitted the overall rotation of the galaxy, and then the turbulence in the gas clouds. To their surprise they found that galaxy S0901 was extremely well behaved. Instead of turbulence, it was found to be in orderly rotation, much more akin to the ma-jestic galaxies of today.

"Usually, when astronomers examine galaxies at this early era, they find that turbulence plays a much greater role than it does in modern galaxies. But S0901 is a clear exception to that pattern, and the Clone could be another," says Rhoads.

The Clone, the second galaxy in their study, could also be fitted by an orderly rotation. However, because it was somewhat dimmer, the quality of the data was not so good. This meant that the data could also be fitted with a highly turbulent model, as conventional wisdom would expect.

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Lensed image of galaxy S0901. Credit: NASA/STScI; S. Allam and team; and the Master Lens Database (masterlens.org), L. A. Mousta-kas, K. Stewart, et al. (2014)

Herschel spectrum of the galaxy S0901. Credit: ESA/Herschel/HIFI. Acknowledgments: James Rhoads and Sangeeta Malhotra, Arizona State University, USA

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"Galaxies 10 billion years ago were making stars more ac-tively than they do now," says Malhotra, "They usually also show more turbulence, likely because they are accumulat-ing gas faster than a modern galaxy does. But here we have cases of early galaxies that combine the 'calm' rota-tion of a modern one with the active star formation of their early peers. This suggests first that these galaxies have finished accumulating their gas, at least for now. But it also seems that turbulence is not actually required to trigger that early, active star formation."

Malhotra acknowledges the preliminary nature of their study. "This is not the last word on this. We need a bigger sample to be sure of our conclusions," she says. But that bigger sample will not be investigated by Herschel. As pre-dicted, the liquid helium coolant needed to keep HIFI and Herschel's other instruments working ran out in April 2013. Instead the researchers hope to continue the work pio-neered by Herschel using the Atacama Large Millimeter/submillimeter Array (ALMA), a ground-based array of 66 radio dishes in Chile.

"It is mind-boggling that with Herschel/HIFI – admittedly with the help of gravitational lensing – it has been possible to study the internal gas kinematics in galaxies when the Uni-verse was only a few billion years old, and what we can learn about them this way. This pioneering work by Her-schel is bound to be continued," says Göran Pilbratt, Her-schel Project Scientist at ESA.

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Herschel spectrum of the galaxy S0901. Credit: ESA/Herschel/HIFI. Acknowledgments: James Rhoads and Sangeeta Malhotra, Arizona State Uni-versity, USA

revealed the distribution. The distribution of the emissions from the 1700 degrees Celsius water molecules was similar to that of the jet observed via the SiO maser. The team interpreted this to mean that water molecules in the jet from Source I are emitting the radio maser. The radiation from water molecules at 2700 degrees Celsi-us was found to have a structure similar to that of Source I at the base of the jet. Interestingly, the team found that this hot gas seems to have a disk-like shape. Detailed analysis indicates that the rotational velocity of the disk is 10 km per second.

The team also found; the temperature of the rotating disk reaches 3000 degrees Celsius or higher, the central star should have at least 7 times more mass than the Sun., and the diameter of the disk is estimated as about 80 times larger than the Solar System. The radio emissions come from a rotating ring-like structure or limb of the disk viewed edge-on.One of the team members, Mareki Honma, said, "Our observations uncovered the nature of Source I, and we can understand the previous observational results about Source I in a consistent manner. These are all thanks to ALMA. Thanks to this state-of-the-art telescope, we can observe the tar-get at higher frequency and higher resolution. In addition, thanks

to VERA, we have a good distance estimate to Source I. This

results in accurate estimates for the size of the disk and other physical quantities." This study settles the long-standing problem; is Source I a jet or a gas disk. The result clearly shows that Source I is a gas disk.

The team wants to learn the more detailed structure and dynamics of Source I by using ALMA with higher resolu-tion and sensitivity at higher frequency. Such observations should reveal the mysteries of the evolution of Source I. Hirota said, "It is also important that the physical conditions of a circumstellar disk depend on the mass of the cen-tral protostar. The circumstellar disk around a massive star is heated up to 3000 degrees Celsius. Dust that is the material for planets should melt away at such high temperatures. I wonder if planets can form under such condition. I’m interested in the dependence of planet formation on stellar mass and physical conditions."

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Distribution of the radio emission from water mol-ecule at 336 GHz observed by ALMA. The color indicates the motion of the water molecule; blue means the gas moving toward us and orange indicates the gas moving away from us. The gray dots shows the distribution of the SiO maser emission detected by VERA. Researchers inter-prets that the SiO maser traces the root of the jet.

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ALMA Helps to Explain Massive Stars Mysterious Formation

A research team led by Tomoya Hirota (National Astronomical Observatory of Japan: NAOJ) discovered a hot circumstellar disk around a massive proto-star by using the Atacama Large Millimeter/Submillimeter Array (ALMA) and the VLBI Exploration of Radio Astrometry (VERA) . The formation process of a massive star has been a long-standing problem. The research results favor disk accretion for the formation of massive stars, similar to the formation of low to intermediate mass stars such as the Sun.

The team observed a radio source called Source I in Orion KL, the nearest massive star-forming region. ALMA detected radio signals from hot water vapor with high angular resolution. The gas temperature reaches around 3000 degrees Celsius. Combining this data with the data taken by VERA, the team confirmed that the hot gas containing water vapor is actually a circum-stellar disk around Source I. Thanks to an accurate estimated distance to Source I based on VERA observations, the disk diameter can be estimated at about 80 times larger than the distance between the Sun and Earth.

Thanks to recent intensive studies, the formation process of low to intermedi-ate mass stars is now well understood. On the other hand, we know little about how massive stars form. Low and intermediate mass stars are formed by mass accretion from a circumstellar disk. Is this process the same for massive stars? Massive stars could form via stellar collisions as another the-

ory suggests. We cannot answer such a simple question.

A radio telescope is essential to study the process of star formation because stars form in gas and dust, and a radio telescope observes such interstellar matter. For high resolution, observations by a radio array have a great ad-vantage. Until very recently, the resolution and sensitivity of observational instruments were not high enough for detailed investigations of molecular clouds in which massive stars are forming. To make matters worse, most such clouds are located far from our Solar System. Now, ALMA enables researchers to study actual formation sites of massive stars.

The research team selected the nearest region of massive star-formation, Orion KL, for the ALMA observation. Stars with 8 times more mass than the Sun are forming in Orion KL. The distance to Orion KL is estimated to be about 1400 light-years, and it has been well studied since its discovery in 1967 because of its vicinity. The re-search team carried out observations of Source I in Orion KL with VERA. The team observed the launching point of a bipolar outflow, and found a cluster of vibrationally ex-cited SiO masers tracing an outflow arising from the sur-face of the disk. The team uncovered a high-speed jet from the region surrounding Source I by observing the SiO masers. The other research group found a compact radio continuum source associated with the center of these vibrationally excited SiO masers. This radio source is interpreted as an edge-on disk. However, the nature of Source I is still controversial. The structure of this region is complex. Many large and small jets are blowing off in various directions. Thus, interpretation of the observa-tions was sometimes different and some researchers deny the existence of the disk and jets.

Previously, the research team successfully found radio signals emitted by high temperature water vapor by ana-lyzing ALMA’s data. When the data was taken, ALMA was in the science verification phase before full operation so the resolution was not high enough to uncover the nature of the molecular gas associated with the hot water vapor. Hirota, the leader of this study, said, "We proposed additional ALMA observations to understand Source I. We got very good quality data! The resolution is three times higher than the previous data set." The team used the two radio lines emitted by water molecules at the frequencies of 321 GHz and 336 GHz, which are thought to corre-spond to gas temperatures of 1700 and 2700 degrees Celsius, respectively. Thus, these lines are suitable tracers to study the closest region of Source I. The team detected the two lines from the hot water molecules and clearly

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Antenna locations of the VERA array. Credit: NAOJ

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Jupiter's moon Ganymede may harbor 'club sandwich' of oceans and ice

The largest moon in our solar system, a companion to Jupiter named Ganymede, might have ice and oceans stacked up in several layers like a club sandwich, ac-cording to new NASA-funded research that models the moon's makeup. Previously, the moon was thought to harbor a thick ocean sandwiched between just two layers of ice, one on top and one on bottom. "Ganymede's ocean might be organized like a Dag-wood sandwich," said Steve Vance of NASA's Jet Pro-pulsion Laboratory in Pasadena, Calif., explaining the moon's resemblance to the "Blondie" cartoon charac-ter's multi-tiered sandwiches. The study, led by Vance, provides new theoretical evidence for the team's "club sandwich" model, first proposed last year. The re-search appears in Planetary and Space Science. The results support the idea that primitive life might have possibly arisen on the icy moon. Scientists say that places where water and rock interact are important for the development of life; for example, it's possible life began on Earth in bubbling vents on our sea floor. Prior

to the new study, Ganymede's rocky sea bottom was thought to be coated with ice, not liquid -- a problem for the emer-gence of life. The "club sandwich" findings suggest otherwise: the first layer on top of the rocky core might be salty water. "This is good news for Ganymede," said Vance. "Its ocean is huge, with enormous pressures, so it was thought that dense ice had to form at the bottom of the ocean. When we added salts to our models, we came up with liquids dense enough to sink to the sea floor."

NASA scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon, which is bigger than Mercury. In the 1990s, NASA's Galileo mission flew by Ganymede, confirming the moon's ocean, and showing it extends to depths of hundreds of miles. The spacecraft also found evidence for salty seas, likely containing the salt magnesium sulfate. Previous models of Ganymede's oceans assumed that salt didn't change the properties of liquid very much with pressure. Vance and his team showed, through laboratory experiments, how much salt really increases the density of liquids under the extreme conditions inside Ganymede and similar moons. It may seem strange that salt can make the ocean denser, but you can see for yourself how this works by adding plain old table salt to a glass of water. Rather than increasing in volume, the liquid shrinks and becomes denser. This is because the salt ions attract water molecules.

The models get more complicated when the different forms of ice are taken into account. The ice that floats in your drinks is called "Ice I." It's the least dense form of ice and lighter than water. But at high pressures, like those in crush-ingly deep oceans like Ganymede's, the ice crystal structures become more compact. "It's like finding a better arrange-ment of shoes in your luggage -- the ice molecules become packed together more tightly," said Vance. The ice can become so dense that it is heavier than water and falls to the bottom of the sea. The densest and heaviest ice thought to persist in Ganymede is called "Ice VI." By modeling these processes using computers, the team came up with an ocean sandwiched between up to three ice layers, in addition to the rocky seafloor. The lightest ice is on top, and the saltiest liquid is heavy enough to sink to the bottom. What's more, the results demonstrate a possible bizarre phenome-non that causes the oceans to "snow upwards." As the oceans churn and cold plumes snake around, ice in the upper-most ocean layer, called "Ice III," could form in the seawater. When ice forms, salts precipitate out. The heavier salts would thus fall downward, and the lighter ice, or "snow," would float upward. This "snow" melts again before reaching the top of the ocean, possibly leaving slush in the middle of the moon sandwich. "We don't know how long the Dag-wood-sandwich structure would exist," said Christophe Sotin of JPL. "This structure represents a stable state, but vari-ous factors could mean the moon doesn't reach this stable state.

Sotin and Vance are both members of the Icy Worlds team at JPL, part of the multi-institutional NASA Astrobiology Institute based at the Ames Research Center in Moffett Field, Calif. The results can be applied to exoplanets too, plan-ets that circle stars beyond our sun. Some super-Earths, rocky planets more massive than Earth, have been proposed as "water worlds" covered in oceans. Could they have life? Vance and his team think laboratory experiments and more detailed modeling of exotic oceans might help find answers. Ganymede is one of five moons in our solar system thought to support vast oceans beneath icy crusts. The other moons are Jupiter's Europa and Callisto and Saturn's Titan and Enceladus. The European Space Agency is developing a space mission, called JUpiter ICy moons Explorer or JUICE, to visit Europa, Callisto and Ganymede in the 2030s. NASA and JPL are contributing to three instruments on the mission, which is scheduled to launch in 2022 (see http://www.jpl.nasa.gov/news/news.php?release=2013-069).

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gas that fills the entire volume of the cluster. The rest is tied up in dark matter, an invisible form of matter that makes up the bulk of the mass of the universe. Though galaxy clusters as massive are found in the nearby universe, such as the so-called Bullet Cluster, nothing like this has ever been seen to exist so far back in time, when the universe was roughly half of its current age of 13.8 billion years. The team suspects such monsters are rare in the early uni-verse, based on current cosmological models.

The immense size of El Gordo was first reported in January 2012. Astronomers estimated its huge mass based on observations from NASA's Chandra X-ray Observatory and galaxy velocities measured by the European Southern Observatory's Very Large Telescope array in Paranal, Chile. They were able to put together estimates of the clus-ter's mass based on the motions of the galaxies moving inside the cluster and the very high temperatures of the hot gas between the cluster galaxies. The challenge was that they noticed that the cluster (catalogued as ACT-CL J0102-4915) looked as if it might have been the result of a titanic collision between a pair of galaxy clusters the re-searchers describe as "seeing two cannonballs hit each other."

"We wondered what happens when you catch a cluster in the midst of a major merger and how the merger process influences both the X-ray gas and the motion of the galaxies," explained John Hughes of Rutgers University. "So the bottom line is that because of the complicated merger state, it left some questions about the reliability of the mass estimates we were making."

"That's where the Hubble data came in," said Felipe Menanteau of the University of Illinois at Urbana-Champaign. "We were in dire need for an independent and more robust mass estimate given how extreme this cluster is and how rare its existence is in the current cosmological model. There was all this kinematic energy that could be unac-counted for and could potentially suggest that we were actually underestimating the mass." The expectation of "unaccounted energy" comes from the fact that the merger is occurring tangentially to the observers' line of sight. This means they are potentially missing a good fraction of the kinetic energy of the merger because their spectro-scopic measurements only track the radial speeds of the galaxies.

The team used Hubble to measure how strongly the mass of the cluster warped space. Hubble's high resolution allowed measurements of so-called "weak lensing," where the cluster's immense gravity subtly distorts space like a funhouse mirror and warps images of background galaxies. The greater the warping, the more mass is locked up in the cluster. "What I did is basically look at the shapes of the background galaxies that are farther away than the cluster itself," explained Jee.

The team's next step with Hubble will be to try to get a large mosaic image of the cluster. It doesn't fit into Hubble's field of view. It's like looking at a giant's head and shoulders from the side, say researchers. "We can tell it's a pretty big El Gordo, but we don't know what kind of legs he has, so we need to have a larger field of view to get the com-plete picture of the giant," said Menanteau.

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overhead more rapidly than a high-flying one.

"This object appeared to move really fast in the WISE data," said Luhman. "That told us it was something special."

After noticing the fast motion of WISE J085510.83-071442.5 in March of 2013, Luhman spent time analyzing addi-tional images taken with Spitzer and the Gemini South telescope on Cerro Pachon in Chile. Spitzer's infrared ob-servations helped determine the frosty temperature of the brown dwarf. Combined detections from WISE and Spitzer, taken from different positions around the sun, enabled the measurement of its distance through the paral-lax effect. This is the same principle that explains why your finger, when held out right in front of you, appears to jump from side to side when you alternate left- and right-eye views.

"It is remarkable that even after many decades of studying the sky, we still do not have a complete inventory of the sun's nearest neighbors," said Michael Werner, the project scientist for Spitzer at NASA's Jet Propulsion Laborato-ry in Pasadena, Calif. JPL manages and operates Spitzer. "This exciting new result demonstrates the power of exploring the universe using new tools, such as the infrared eyes of WISE and Spitzer."

WISE J085510.83-071442.5 is estimated to be 3 to 10 times the mass of Jupiter. With such a low mass, it could be a gas giant similar to Jupiter that was ejected from its star system. But scientists estimate it is probably a brown dwarf rather than a planet since brown dwarfs are known to be fairly common. If so, it is one of the least massive brown dwarfs known.

In March of 2013, Luhman's analysis of the images from WISE uncovered a pair of much warmer brown dwarfs at a distance of 6.5 light years, making that system the third closest to the sun. His search for rapidly moving bodies also demonstrated that the outer solar system probably does not contain a large, undiscovered planet, which has been referred to as "Planet X" or "Nemesis."

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