Sunday, July 27, 2014

The Halo Around Centaurus A

This image shows the stunning elliptical galaxy Centaurus A. Recently, astronomers have used the NASA/ESA Hubble Space Telescope to probe the outskirts of this galaxy to learn more about its dim halo of stars.

The galaxy's halo of stars has been found to reach much further than expected, extending across 4 degrees in the sky – equivalent to eight times the apparent width of the Moon, or almost twice the width of this image.

This image is a composite of images from Digitized Sky Survey 2 (DSS2), the MPG/ESO 2.2-meter telescope, and the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS).

The areas probed by Hubble are identified in the annotated version of this image. Hubble's unique capabilities allowed astronomers to analyze the faint stars in the halo.

Image credit: ESA/Hubble, NASA, Digitized Sky Survey, MPG/ESO; acknowledgement: Davide de Martin

Note: For more information, see Hubble Traces the Halo of a Galaxy More Accurately Than Ever Before and Hubble Traces the Halo of a Galaxy More Accurately Than Ever Before.

Saturday, July 26, 2014

Measuring Kepler-93b

Using data from NASA's Kepler and Spitzer Space Telescopes, scientists have made the most precise measurement ever of the size of a world outside our solar system, as illustrated in this artist's conception. The diameter of the exoplanet, dubbed Kepler-93b, is now known with an uncertainty of just one percent.

According to this new study, the diameter of Kepler-93b is about 11,700 miles (18,800 kilometers), plus or minus 150 miles (240 kilometers) -- the approximate distance between Washington, D.C., and Philadelphia, Pennsylvania. Kepler-93b is 1.481 times the width of Earth, the diameter of which is 7,918 miles (12,742 kilometers).

The results confirm that the exoplanet is a "super-Earth." Although super-Earths are common in the galaxy, none exist in our solar system. Exoplanets like Kepler-93b are therefore our only laboratories to study this major class of planet.

With good limits on super-Earths' sizes as well as their masses, scientists can now start to theorize about what makes up these weird worlds. Previous measurements, by the Keck Observatory in Hawaii, had put Kepler-93b's mass at about 3.8 times that of Earth. The density of Kepler-93b, derived from its mass and newly obtained radius, indicates the planet is in fact very likely made of iron and rock, like Earth.

Despite its newfound similarities in composition to Earth, Kepler-93b is far too hot for life. The exoplanet's orbital distance -- only about one-sixth that of Mercury's from the sun -- implies a scorching surface temperature around 1,400 degrees Fahrenheit (760 degrees Celsius).

The methods employed in the new study could help nail down the sizes of other exoplanets, and improve our understanding of alien worlds.

The Spitzer data for this study was obtained during the "warm mission" phase using its Infrared Array Camera. The lead author of the paper describing these findings is Sarah Ballard, a NASA Carl Sagan Fellow at the University of Washington in Seattle.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see The Most Precise Measurement of an Alien World's Size.

Friday, July 25, 2014

Comet C/2013 UQ4 (Catalina)

Comet C/2013 UQ4 (Catalina) appeared to be a highly active comet one day past perihelion on July 7, 2014.

Image credit: NASA/JPL-Caltech

Note: For more information, see PIA18652: NEOWISE Spots Comet Catalina and NEOWISE Spots a Comet That Looked Like an Asteroid.

Thursday, July 24, 2014

Star Cluster NGC 3293

In this image from the Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory in Chile young stars huddle together against a backdrop of clouds of glowing gas and lanes of dust. The star cluster, known as NGC 3293, would have been just a cloud of gas and dust itself about ten million years ago, but as stars began to form it became the bright group we see here. Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve.

Image credit: ESO/G. Beccari

Note: For more information, see Lives and Deaths of Sibling Stars.

Wednesday, July 23, 2014

Four Supernova Remnants

In commemoration of the 15th anniversary of NASA's Chandra X-ray Observatory, four newly processed images of supernova remnants dramatically illustrate Chandra's unique ability to explore high-energy processes in the cosmos (see the accompanying press release).

The images of the Tycho and G292.0+1.8 supernova remnants show how Chandra can trace the expanding debris of an exploded star and the associated shock waves that rumble through interstellar space at speeds of millions of miles per hour. The images of the Crab Nebula and 3C58 show how extremely dense, rapidly rotating neutron stars produced when a massive star explodes can create clouds of high-energy particles light years across that glow brightly in X-rays.

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of the exploded star produced a shock wave moving outward into the surrounding interstellar gas, and another, reverse shock wave moving back into the expanding stellar debris. This Chandra image of Tycho reveals the dynamics of the explosion in exquisite detail. The outer shock has produced a rapidly moving shell of extremely high-energy electrons (blue), and the reverse shock has heated the expanding debris to millions of degrees (red and green). There is evidence from the Chandra data that these shock waves may be responsible for some of the cosmic rays - ultra-energetic particles - that pervade the Galaxy and constantly bombard the Earth.

At a distance of about 20,000 light years, G292.0+1.8 is one of only three supernova remnants in the Milky Way known to contain large amounts of oxygen. These oxygen-rich supernovas are of great interest to astronomers because they are one of the primary sources of the heavy elements (that is, everything other than hydrogen and helium) necessary to form planets and people. The X-ray image from Chandra shows a rapidly expanding, intricately structured, debris field that contains, along with oxygen (yellow and orange), other elements such as magnesium (green) and silicon and sulfur (blue) that were forged in the star before it exploded.

The Crab Nebula:
In 1054 AD, Chinese astronomers and others around the world noticed a new bright object in the sky. This “new star” was, in fact, the supernova explosion that created what is now called the Crab Nebula. At the center of the Crab Nebula is an extremely dense, rapidly rotating neutron star left behind by the explosion. The neutron star, also known as a pulsar, is spewing out a blizzard of high-energy particles, producing the expanding X-ray nebula seen by Chandra. In this new image, lower-energy X-rays from Chandra are red, medium energy X-rays are green, and the highest-energy X-rays are blue.

3C58 is the remnant of a supernova observed in the year 1181 AD by Chinese and Japanese astronomers. This new Chandra image shows the center of 3C58, which contains a rapidly spinning neutron star surrounded by a thick ring, or torus, of X-ray emission. The pulsar also has produced jets of X-rays blasting away from it to both the left and right, and extending trillions of miles. These jets are responsible for creating the elaborate web of loops and swirls revealed in the X-ray data. These features, similar to those found in the Crab, are evidence that 3C58 and others like it are capable of generating both swarms of high-energy particles and powerful magnetic fields. In this image, low, medium, and high-energy X-rays detected by Chandra are red, green, and blue respectively.

Image credit: NASA/CXC/SAO

Monday, July 21, 2014

Venus Express and Transit of Venus

This movie was compiled from images taken by the Venus Monitoring Camera on Venus Express as it approached the planet on its elliptical orbit on 1 June 2012. Initially, the spacecraft is looking at the south side of the planet from a distance of 63,000 km and clouds can be seen moving below. As the spacecraft draws closer, Venus starts filling the field of view and the equatorial regions can be seen. The sequence finishes with observations of cloud features at high latitudes.

Video credit: ESA/MPS/DLR/IDA

Note: For more information, see Venus Express Rises Again.

Sunday, July 20, 2014

Asteroid 21 Lutetia

This ethereal image shows a stunning sliver of large main-belt asteroid Lutetia from the viewpoint of ESA’s Rosetta spacecraft, taken as Rosetta passed by on its 10-year voyage towards comet 67P/Churyumov–Gerasimenko.

This week marks four years since Rosetta flew by this ancient rocky body, on 10 July 2010. As the spacecraft swung past Lutetia it snapped hundreds of high-resolution photographs with its Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) as well as obtaining valuable spectra, and maps of the surface temperature using other instruments.

This image was taken as Rosetta had passed its closest approach, at just under 3170 km from Lutetia’s surface, and was beginning its journey away from the asteroid.

As a result of this flyby, astronomers have been able to characterize Lutetia, viewing the wide range of craters and geological features scarring the asteroid’s surface and gauging its mass and volume–and thus density and composition. These measurements showed that Lutetia is primordial, likely having formed just under 4 billion years ago during the very early phases of the Solar System.

This asteroid is one of just two that Rosetta has closely flown past, the other being asteroid Steins in 2008.

Rosetta was launched in 2004 and, after 10 years in space, will finally rendezvous with its target comet in August. It will study the comet’s surface, dust and gases in unprecedented detail, deploy a lander onto its surface, and follow the comet for over a year as it orbits around the Sun.


Saturday, July 19, 2014

Lunar Occultation of Saturn

What happened to half of Saturn? Nothing other than Earth's Moon getting in the way. As pictured above on the far right, Saturn is partly eclipsed by a dark edge of a Moon itself only partly illuminated by the Sun. This year the orbits of the Moon and Saturn have led to an unusually high number of alignments of the ringed giant behind Earth's largest satellite. Technically termed an occultation, the above image captured one such photogenic juxtaposition from Buenos Aires, Argentina that occurred early last week. Visible to the unaided eye but best viewed with binoculars, there are still four more eclipses of Saturn by our Moon left in 2014. The next one will be on August 4 and visible from Australia, while the one after will occur on August 31 and be visible from western Africa at night but simultaneously from much of eastern North America during the day.

Image credit: Carlos Di Nallo

Friday, July 18, 2014

Comet 67P/Churyumov-Gerasimenko Rotating

This animated sequence combines 36 interpolated images of comet 67P/Churyumov-Gerasimenko, each separated by 20 minutes. This comet is the destination for the European Space Agency's Rosetta mission, which includes three NASA instruments in its 21-instrument science payload. The images were obtained by the spacecraft's Onboard Scientific Imaging System (OSIRIS) on July 14, 2014 from a distance of approximately 7,500 miles (12,000 kilometers).

Launched in 2004, the Rosetta spacecraft includes an orbiter and lander. The mission's objectives upon arrival at comet 67P/Churyumov-Gerasimenko in August 2014 are to study the celestial object up close in unprecedented detail, prepare for landing a probe on the comet's nucleus in November, and track its changes as it sweeps past the sun.

Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. Rosetta's lander will obtain the first images taken from a comet's surface and will provide the first analysis of a comet's composition by drilling into the surface. Rosetta also will be the first spacecraft to witness at close proximity how a comet changes as it is subjected to the increasing intensity of the sun's radiation. Observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.


Note: For more information, see PIA18402: Rosetta Mission's Destination: Comet 67P/Churnyumov-Gerasimenko, Comet on 14 July 2014 – Processed View, The Dual Personality of Comet 67P/C-G, Rosetta Spacecraft Approaching Twofold Comet, and Rosetta Comet May Be a Contact Binary.

For earlier stories, see Rosetta Closing in on Comet, The Three Faces of Rosetta's Comet, Rosetta's Comet: Expect the Unexpected, How Big is Rosetta Compared to the Comet?, Comet on 4 July 2014, and Are We There Yet?

Thursday, July 17, 2014

Comet C2012 S1 ISON

Analysis of data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft has revealed that comet 2012/S1 (ISON) stopped producing dust and gas shortly before it raced past the Sun and disintegrated.

Shown here is the SUMER image from 18:01 GMT on 28 November 2013. The white line indicates the bisector of the tail. Red dots mark the predicted position of the comet's nucleus at one minute intervals for the previous 10 minutes. The red cross is the position at the time of this image. The tail is offset from the comet trajectory, curved, and pointed with a length of at least 240,000 kilometers. The observations are consistent with models indicating that the comet stopped producing dust and gas hours earlier.

The white arrow indicates the direction of the Sun.

Image credit: MPS

Note: For more information, see Comet ISON's Dramatic Final Hours.

Wednesday, July 16, 2014

Comet Shoemaker-Levy 9 Fragment W Impact With Jupiter

These four images of Jupiter and the luminous night-side impact of fragment W of Comet Shoemaker-Levy 9 were taken by the Galileo spacecraft on July 22, 1994. The spacecraft was 238 million kilometers (148 million miles) from Jupiter at the time, and 621 million kilometers from Earth. The spacecraft was about 40 degrees from Earth's line of sight to Jupiter, permitting this direct view. The images were taken at intervals of 2 1/3 seconds, using the green filter (visible light). The first image, taken at an equivalent time to 8:06:10 Greenwich Mean Time (1:06 a.m. Pacific Daylight Time), shows no impact. In the next three images, a point of light appears, brightens so much as to saturate its picture element, and then fades again, seven seconds after the first picture. The location is approximately 44 degrees south as predicted, dark spots to the right are from previous impacts. Jupiter is approximately 60 picture elements in diameter.

Image credit: NASA/JPL

Note: For more information, see Looking Back at the Jupiter Crash 20 Years Later.

Tuesday, July 15, 2014

NGC 1433

This view, captured by the NASA/ESA Hubble Space Telescope, shows a nearby spiral galaxy known as NGC 1433. At about 32 million light-years from Earth, it is a type of very active galaxy known as a Seyfert galaxy — a classification that accounts for 10% of all galaxies. They have very bright, luminous centers comparable to that of our galaxy, the Milky Way.

Image credit: ESA/Hubble & NASA

Monday, July 14, 2014

Artist's Conception of an Exploding Blue Supergiant Star

This artist’s impression depicts a region of an exploding blue supergiant. These stars are quite rare in the relatively nearby Universe, but are thought to have been very common in the early Universe, with almost all of the first stars having evolved into them over the course of their short lives.

Astronomers used a number of space- and ground-based observatories, including ESA's XMM-Newton to study the gamma-ray burst GRB130925A – a flash of very energetic radiation streaming from a blue supergiant in a galaxy 5.6 billion light years from Earth. They found evidence that this star contained very little in the way of elements heavier than hydrogen and helium. The same was true for the first stars to form in the Universe, making GRB130925A a remarkable analogue for similar explosions that occurred just a few hundred million years after the Big Bang.

The illustration shows a hot cocoon of gas (shown in red) surrounding a relativistic jet emerging from the blue supergiant.

Illustration credit: NASA/Swift/A. Simonnet, Sonoma State University

Note: For more information, see Bizarre Nearby Blast Mimics Universe's Most Ancient Stars.

Sunday, July 13, 2014

Star Superclusters Forming Near Two Galaxies Merging in Galactic Cluster SDSS J1531+3414

This new NASA/ESA Hubble Space Telescope image shows two galaxies from the cluster SDSS J1531+3414.

The two galaxies have been found to be merging into one and a "chain" of young stellar superclusters are seen winding around the galaxies' nuclei. The galaxies are surrounded by an egg-shaped blue ring caused by the immense gravity of the cluster bending light from other galaxies beyond it.

Image credit: NASA, ESA/Hubble and Grant Tremblay (European Southern Observatory)

Acknowledgements: M. Gladders & M. Florian (University of Chicago, USA), S. Baum, C. O'Dea & K. Cooke (Rochester Institute of Technology, USA), M. Bayliss (Harvard-Smithsonian Center for Astrophysics, USA), H. Dahle (University of Oslo, Norway), T. Davis (European Southern Observatory), J. Rigby (NASA Goddard Space Flight Center, USA), K. Sharon (University of Michigan, USA), E. Soto (The Catholic University of America, USA) and E. Wuyts (Max-Planck-Institute for Extraterrestrial Physics, Germany).

Note: For more information, see Merging Galaxies and Droplets of Starbirth and Droplets of Star Formation and Two Merging Galaxies in SDSS J1531+3414.

Saturday, July 12, 2014

Artist’s Impression of Dust Formation Around a Supernova

This artist’s impression shows dust forming in the environment around a supernova explosion. VLT observations have shown that these cosmic dust factories make their grains in a two-stage process, starting soon after the explosion, but continuing long afterwards.

Illustration credit: ESO/M. Kornmesser

Note: For more information, see VLT Clears Up Dusty Mystery.

Friday, July 11, 2014

Reddish Bands on Europa

This colorized image of Europa is a product of clear-filter grayscale data from one orbit of NASA's Galileo spacecraft, combined with lower-resolution color data taken on a different orbit. The blue-white terrains indicate relatively pure water ice, whereas the reddish areas contain water ice mixed with hydrated salts, potentially magnesium sulfate or sulfuric acid. The reddish material is associated with the broad band in the center of the image, as well as some of the narrower bands, ridges, and disrupted chaos-type features. It is possible that these surface features may have communicated with a global subsurface ocean layer during or after their formation.

Part of the terrain in this previously unreleased color view is seen in the monochrome image, PIA01125.

The image area measures approximately 101 by 103 miles (163 km by 167 km). The grayscale images were obtained on November 6, 1997, during the Galileo spacecraft's 11th orbit of Jupiter, when the spacecraft was approximately 13,237 miles (21,700 kilometers) from Europa. These images were then combined with lower-resolution color data obtained in 1998, during the spacecraft's 14th orbit of Jupiter, when the spacecraft was 89,000 miles (143,000 km) from Europa.

Image credit: NASA/JPL-Caltech/SETI Institute

Thursday, July 10, 2014

First Waver Vapor Detected From Comet 67P/Churyumov–Gerasimenko

Even when it is still about half way between Jupiter and Mars, some 583 million kilometers from the Sun, comet 67P/Churyumov–Gerasimenko is losing the equivalent of two 150 ml glasses of water a second (roughly the size of the plastic cups in vending machines and water coolers). At this rate, the comet would fill an Olympic-sized swimming pool in about 100 days. But, as the comet gets closer to the Sun, the water vapor production rate will increase significantly.

The observations were made on 6 June 2014 by Rosetta's MIRO microwave instrument, some 350,000 km from the comet.

The comet nucleus in this image is an artist impression.

Image credit: ESA

Note: For more information, see Rosetta's Comet 'Sweats' Two Glasses of Water a Second and Rosetta's Comet Target 'Releases' Plentiful Water.

Wednesday, July 9, 2014

NGC 201

Discovered by astronomer William Herschel in the late 1700s, NGC 201 is a barred spiral galaxy similar to our own galaxy, the Milky Way. It lies 200 million light-years from Earth in the constellation of Cetus (The Sea Monster), and is invisible to the naked eye.

This new NASA/ESA Hubble Space Telescope image of NGC 201 shows the galaxy in striking detail, capturing the bright center and the barred spiral arms — arms that do not start directly from the galactic center, but instead seem to be offset and stem from a "bar" of stars cutting through the middle of the galaxy.

Along with three of its closest galactic neighbors (outside the frame), NGC 201 belongs to a group known as the HCG 7 compact galactic group. Hickson Compact Groups (HCG) are relatively small and isolated systems containing a handful of bright, compact galaxies that lie close to one another. As the galaxies within these groups move closer together they interact strongly, dragging galactic material out into space and distorting the structure of the other group members.

Eventually, all the galaxies within one HCG will merge together. Simulations have shown that within a billion years, the galaxies within one HCG have merged to form a giant fossil galaxy. It is possible that this is the final fate of all galactic groups.

Image credit: ESA/Hubble & NASA

Tuesday, July 8, 2014

Rotating Comet 67P Churyumov-Gerasimenko

This animated sequence comprises 36 images taken with Rosetta's OSIRIS narrow-angle camera on 27-28 June 2014, and shows comet 67P/Churyumov–Gerasimenko spinning with a period of 12.4 hours. On 28 June, about 86,000 km separated the comet and spacecraft.


Note: For more information, see The Comet Takes Shape, One Pixel at a Time! and Comet on 28 June 2014.

Monday, July 7, 2014

Frozen Exoplanet Found Around Binary Star

This artist's rendering shows a newly discovered planet (far right) orbiting one star (right) of a binary star system. The discovery, made by a collaboration of international research teams and led by researchers at The Ohio State University, expands astronomers' notions of where to look for planets in our galaxy. The research was funded in part by NASA.

A newly discovered planet in a binary, or twin, star system located 3,000 light-years from Earth is expanding astronomers' notions of where Earth-like -- and even potentially habitable -- planets can form, and how to find them.

At twice the mass of Earth, the planet orbits one of the stars in the binary system at almost exactly the same distance at which Earth orbits the sun. However, because the planet's host star is much dimmer than the sun, the planet is much colder than Earth -- a little colder, in fact, than Jupiter's icy moon Europa.

Four international research teams, led by professor Andrew Gould of The Ohio State University in Columbus, published their discovery in the July 4 issue of the journal Science. The research is partly funded by NASA.

The study provides the first evidence that terrestrial planets can form in orbits similar to Earth's, even in a binary star system where the stars are not very far apart. Although this planet itself is too cold to be habitable, the same planet orbiting a sun-like star in such a binary system would be in the so-called "habitable zone" -- the region where conditions might be right for life.

"This greatly expands the potential locations to discover habitable planets in the future," said Scott Gaudi, professor of astronomy at Ohio State. "Half the stars in the galaxy are in binary systems. We had no idea if Earth-like planets in Earth-like orbits could even form in these systems."

Earlier evidence that planets form in binary star systems came from NASA's Kepler and Spitzer space telescopes (see and, but the planets and dust structures in those studies were not similar to those of Earth.

The technique astronomers use to find the planet, called OGLE-2013-BLG-0341LBb, is called gravitational microlensing. In this method, the light of a distant star is magnified by a closer star that happens to pass in front -- if a planet is also present around the foreground star, it will further alter and distort the light of the background star. The telescopes used in this study are part of several projects, including the OGLE (Optical Gravitational Lensing Experiment), MOA (Microlensing Observations in Astrophysics), MicroFUN (the Microlensing Follow Up Network), and the Wise Observatory.

Searching for planets within binary systems is tricky for most techniques, because the light from the second star complicates the interpretation of the data. "But in gravitational microlensing," Gould explained, "we don't even look at the light from the star-planet system. We just observe how its gravity affects light from a more distant, unrelated star. This gives us a new tool to search for planets in binary star systems."

NASA's proposed WFIRST-AFTA (Wide-Field Infrared Survey Telescope - Astrophysics Focused Telescope Assets) mission would use the microlensing technique to find and characterize hundreds of thousands of planets in binary systems.

Image credit: Cheongho Han, Chungbuk National University, Republic of Korea

Sunday, July 6, 2014

Comet C/2012 K1 Pan-STARRS and NGC 3726

NASA's NEOWISE mission captured this series of pictures of comet C/2012 K1 -- also known as comet Pan-STARRS -- as it swept across our skies on May 20, 2014. The comet is relatively close to us -- it was only about 143 million miles (230 million kilometers) from Earth when this picture was taken. It is seen passing a much more distant spiral galaxy, called NGC 3726, which is about 55 million light-years from Earth, or 2 trillion times farther away than the comet.

The image was made from data collected by the two infrared channels onboard the NEOWISE spacecraft, with the longer-wavelength channel (centered at 4.5 microns) mapped to red and the shorter-wavelength channel (3.4 microns) mapped to cyan.

Image credit: NASA/JPL-Caltech

Note: For more information, see Comet Pan-STARRS Marches Across the Sky.

Saturday, July 5, 2014

Gum 15

This richly detailed new view from the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile shows the star formation region Gum 15. This little-known object is located in the constellation of Vela (The Sails), some 3000 light-years from Earth. The glowing cloud is a stunning example of an HII region. It also has a similarity to a more famous HII region, the Trifid Nebula (Messier 20).

Image credit: ESO

Note: For more information, see A Stellar Womb Shaped and Destroyed by its Ungrateful Offspring.

Friday, July 4, 2014

Titan's Ocean Perhaps as Salty as the Dead Sea

Researchers found that Titan's ice shell, which overlies a very salty ocean, varies in thickness around the moon, suggesting the crust is in the process of becoming rigid.

Scientists analyzing data from NASA's Cassini mission have firm evidence the ocean inside Saturn's largest moon, Titan, might be as salty as Earth's Dead Sea.

The new results come from a study of gravity and topography data collected during Cassini's repeated flybys of Titan during the past 10 years. Using the Cassini data, researchers presented a model structure for Titan, resulting in an improved understanding of the structure of the moon's outer ice shell. The findings are published in this week's edition of the journal Icarus.

"Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we're unlocking new mysteries as fast as we solve old ones," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, who was not involved in the study.

Additional findings support previous indications the moon's icy shell is rigid and in the process of freezing solid. Researchers found that a relatively high density was required for Titan's ocean in order to explain the gravity data. This indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulfur, sodium and potassium. The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.

"This is an extremely salty ocean by Earth standards," said the paper's lead author, Giuseppe Mitri of the University of Nantes in France. "Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past."

Cassini data also indicate the thickness of Titan's ice crust varies slightly from place to place. The researchers said this can best be explained if the moon's outer shell is stiff, as would be the case if the ocean were slowly crystallizing and turning to ice. Otherwise, the moon's shape would tend to even itself out over time, like warm candle wax. This freezing process would have important implications for the habitability of Titan's ocean, as it would limit the ability of materials to exchange between the surface and the ocean.

A further consequence of a rigid ice shell, according to the study, is any outgassing of methane into Titan's atmosphere must happen at scattered "hot spots" -- like the hot spot on Earth that gave rise to the Hawaiian Island chain. Titan's methane does not appear to result from convection or plate tectonics recycling its ice shell.

How methane gets into the moon's atmosphere has long been of great interest to researchers, as molecules of this gas are broken apart by sunlight on short geological timescales. Titan's present atmosphere contains about five percent methane. This means some process, thought to be geological in nature, must be replenishing the gas. The study indicates that whatever process is responsible, the restoration of Titan's methane is localized and intermittent.

"Our work suggests looking for signs of methane outgassing will be difficult with Cassini, and may require a future mission that can find localized methane sources," said Jonathan Lunine, a scientist on the Cassini mission at Cornell University, Ithaca, New York, and one of the paper's co-authors. "As on Mars, this is a challenging task."

Image credit: NASA/JPL-Caltech/SSI/Univ. of Arizona/G. Mitri/University of Nantes

Note: For more information, see Saturn's Moon Titan Has a Very Salty Ocean.

Thursday, July 3, 2014

Messier 106's Anomalous Spiral Arms

A galaxy about 23 million light-years away is the site of impressive, ongoing, fireworks. Rather than paper, powder, and fire, this galactic light show involves a giant black hole, shock waves, and vast reservoirs of gas.

This galactic fireworks display is taking place in NGC 4258 (also known as M106), a spiral galaxy like the Milky Way. This galaxy is famous, however, for something that our galaxy doesn't have -- two extra spiral arms that glow in X-ray, optical, and radio light. These features, or anomalous arms, are not aligned with the plane of the galaxy, but instead intersect with it.

The anomalous arms are seen in this new composite image of NGC 4258, where X-rays from NASA's Chandra X-ray Observatory are blue, radio data from the NSF's Karl Jansky Very Large Array are purple, optical data from NASA's Hubble Space Telescope are yellow and blue, and infrared data from NASA's Spitzer Space Telescope are red.

A new study of these anomalous arms made with Spitzer shows that shock waves, similar to sonic booms from supersonic planes, are heating large amounts of gas -- equivalent to about 10 million suns. What is generating these shock waves? Radio data shows that the supermassive black hole at the center of NGC 4258 is producing powerful jets of high-energy particles. Researchers think that these jets strike the disk of the galaxy and generate shock waves. These shock waves, in turn, heat some of the gas -- composed mainly of hydrogen molecules -- to thousands of degrees. As shown in our additional, composite image, part of the evidence for this heating process comes from the similarity in location between the hydrogen and X-ray emission, both thought to be caused by shocks, and the radio jets.

The Chandra X-ray image reveals huge bubbles of hot gas above and below the plane of the galaxy. These bubbles indicate that much of the gas that was originally in the disk of the galaxy has been heated to millions of degrees and ejected into the outer regions by the jets from the black hole.

The ejection of gas from the disk by the jets has important implications for the fate of this galaxy. Researchers estimate that all of the remaining gas will be ejected within the next 300 million years -- very soon on cosmic time scales -- unless it is somehow replenished. Because most of the gas in the disk has already been ejected, less gas is available for new stars to form. Indeed, the researchers used Spitzer data to estimate that stars are forming in the central regions of NGC 4258, at a rate which is about ten times less than in the Milky Way galaxy.

The European Space Agency's Herschel Space Observatory, for which NASA plays an important role, was used to confirm the estimate from Spitzer data of the low star-formation rate in the central regions of NGC 4258. Herschel was also used to make an independent estimate of how much gas remains in the center of the galaxy. After allowing for the large boost in infrared emission caused by the shocks, the researchers found that the gas mass is ten times smaller than had been previously estimated.

Because NGC 4258 is relatively close to Earth, astronomers can study how this black hole is affecting its galaxy in great detail. The supermassive black hole at the center of NGC 4258 is about ten times larger than the one in the Milky Way, and is also consuming material at a faster rate, potentially increasing its impact on the evolution of its host galaxy.

Image credit: NASA/CXC/JPL-Caltech/STScI/NSF/NRAO/VLA

Note: For more information, see PIA18462: Black Hole Jets Make Shock Waves, NGC 4258 (M106): Galactic Pyrotechnics On Display and Black Hole Fireworks in Nearby Galaxy.

Wednesday, July 2, 2014

Artist's Concept of a Protostar within the Orion A Molecular Cloud

Orion A, a star-forming nebula lying about 1500 light-years from Earth, as viewed by ESA's Herschel space observatory. Orion A is located within the 'sword of Orion' – below the three main stars that form the belt of the Orion constellation.

Embedded in the gaseous and dusty environment of this molecular cloud is the prolific stellar nursery called OMC2 FIR4 (highlighted with a red circle).

Astronomers studying OMC2 FIR4 with Herschel have discovered that at least one of the embryo stars that are taking shape in this protostellar cocoon is gusting a powerful wind of very energetic particles.

The inset shows an illustration of the wind blown by this newborn star. When the energetic particles hit the surrounding material, they may collide with atoms that are present in the star's environment, break them apart and produce new elements.

Our Sun likely gusted a similar wind of particles in its early days; this could explain the origin of a puzzling isotope of beryllium, whose traces are found in meteorites.

Image credit: Herschel image: ESA/Herschel/Ph. André, D. Polychroni, A. Roy, V. Könyves, N. Schneider for the Gould Belt survey Key Programme; inset and layout: ESA/ATG medialab

Note: For more information, see Young Sun's Violent History Solves Meteorite Mystery.

Tuesday, July 1, 2014

Saturn's Shadows and Mimas

It may seem odd to think of planets casting shadows out in the inky blackness of space, but it is a common phenomenon. Earth’s shadow obscures the Moon during a lunar eclipse, and Jupiter’s moons cast small shadows onto their parent planet.

One of the best places in our Solar System to spot intriguing and beautiful celestial shadows is at Saturn. On 1 July, the international Cassini mission celebrates 10 years of exploring Saturn, its rings and its moons, an endeavor that has produced invaluable science but also stunning images like this.

Drifting along in the foreground, small and serene, is Saturn’s icy moon Mimas. The blue backdrop may at first appear to be the gas giant’s famous and impressive set of rings, with pale and dark regions separated by long inky black slashes, but it is actually the northern hemisphere of Saturn itself. The dark lines slicing across the frame are shadows cast by the rings onto the planet.

Although we may not associate the color blue with Saturn, when Cassini arrived at the planet the northernmost regions displayed the delicate blue palette shown in this image. As this region of Saturn is generally quite free of cloud, scattering by molecules in the atmosphere causes sunlight to take a longer path through the atmosphere. The light is scattered predominantly at shorter – bluer – wavelengths. This is similar to why the sky on Earth appears blue to our eyes.

Seasonal changes over the years since this photo was taken have turned the blue into Saturn's more familiar golden hue. The reverse is occurring in the south, which is slowly becoming bluer.

This image is composed of infrared, optical and ultraviolet observations from Cassini’s narrow-angle camera on 18 January 2005. The colors closely match what the scene would look like in true color.

This image was first published on the NASA Cassini website, in 2005.

Image credit: NASA/JPL/Space Science Institute

Friday, June 27, 2014

Necklaces of Solar Activity

Back in 1998, the Sun was behaving as expected. The approximately 11-year cycle of activity was proceeding smoothly, heading towards a peak in 2001.

The Solar and Heliospheric Observatory (SOHO) captured this image on 9 November 1998 through its ultraviolet telescope, showing radiation from iron atoms bathed in a gas of around a million degrees Celsius.

This textbook image of solar activity shows two brighter bands circling the Sun at the same latitude in each hemisphere.

At visible wavelengths these bright loops and patches are associated with dark smudges known as sunspots. They are produced when loops of magnetism become buoyant and rise from inside the Sun into the atmosphere.

When the cycle begins, the active regions appear at high latitudes in sparse numbers, disappearing after a few weeks or so. As the cycle proceeds, new and often larger active regions appear more frequently at successively lower latitudes. Many can be larger than Earth, and they sometimes persist for months.

This activity takes place in both hemispheres simultaneously, and about five or six years into the cycle sunspots reach lower latitudes closer to the equator. This is known as solar maximum.

After this, the number of spots begins to decline until they virtually disappear and the cycle starts again at high latitudes. It is one of the enduring mysteries of the Sun why this cycle happens. Certainly, it is linked to the way the Sun generates magnetism deep inside its gaseous layers but the details remain elusive.

In recent years, the Sun has deviated from this textbook behavior. The current cycle was about two years late in starting, the hemispheres are behaving differently and the peak of activity is relatively modest. The next cycle is expected to continue in this new vein. It may even be weaker than the current cycle.

Image credit: SOHO (ESA & NASA)

Thursday, June 26, 2014

Water's Early Journey in a Solar System

The building blocks of comets, and apparently Saturn's largest moon, Titan, formed under similar conditions in the disk of gas and dust that formed the sun.

NASA's Spitzer Space Telescope observed a fledgling solar system like the one depicted in this artist's concept, and discovered deep within it enough water vapor to fill the oceans on Earth five times. This water vapor starts out in the form of ice in a cloudy cocoon (not pictured) that surrounds the embryonic star, called NGC 1333-IRAS 4B (buried in center of image). Material from the cocoon, including ice, falls toward the center of the cloud. The ice then smacks down onto a dusty pre-planetary disk circling the stellar embryo (doughnut-shaped cloud) and vaporizes. Eventually, this water might make its way into developing planets.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see Titan's Building Blocks Might Pre-date Saturn.

Wednesday, June 25, 2014

Perseus Galaxy Cluster in X-Rays

A new study of the Perseus galaxy cluster, shown in this image, and others using Chandra and XMM-Newton has revealed a mysterious X-ray signal in the data. The signal is also seen in over 70 other galaxy clusters using XMM-Newton. This unidentified signal requires further investigation to confirm both its existence and nature, but one possibility is that it represents the decay of ‘sterile neutrinos’, one proposed candidate to explain dark matter.

Image credit: Chandra: NASA/CXC/SAO/E.Bulbul, et al.; XMM-Newton: ESA)

Note: For more information, see Puzzling X-Rays Point to Dark Matter, Perseus Galaxy Cluster, and Perseus A: Mysterious X-ray Signal Intrigues Astronomers.

Tuesday, June 24, 2014

Molecular Cloud W48

Just as children are sorted into age groups at school, so the seeds of new stars can also be found in ‘classes’ of others of similar ages. This is especially true when the birth of stars in a cloud of gas and dust is triggered by an external event, like the explosion of a nearby supernova.

This image from ESA’s Herschel space observatory shows a sequence of star-forming regions in the molecular cloud W48, some 10,000 light-years away in the constellation Aquila (the Eagle).

The blue, jellyfish-shaped cloud at the lower left is the oldest stellar nursery in the image. Young and massive stars embedded within it have shaped it into a bubble and heated the diffuse gas, making it shine at the longest wavelengths probed by Herschel.

To its right, another glowing cloud conceals clumps that will evolve into massive stars. These clumps, some of which are visible as bright blotches of light, are also lined up by their age: the older ones at the lower-left and the younger ones to the upper-right. The youngest in this sequence is the small cyan lump at the center of the image, harboring the seeds of future massive stars.

Astronomers believe that this sequence of stellar birth is the result of dozens of supernovas that exploded over 10 million years ago in a region called Aquila Supershell, beyond the left edge of this image. Compressing the surrounding material, these supernovas may have initiated a wave of star formation that sparked, one by one, these stellar cribs.

The image is a composite of the wavelengths of 70 microns (blue), 160 microns (green) and 250 microns (red) and spans about one degree on the long side. North is to the upper-left and east is to the lower left. The data were acquired with Herschel’s PACS and SPIRE instruments in September 2010, as part of a larger map of the W48 molecular complex in the HOBYS Key Programme. This was first published in a paper by Q. Nguyen Luong, et al. 2011. A more detailed study of the star-forming regions shown in this image is presented in a paper by K.L.J. Rygl, et al. 2014.

Image credit: ESA/Herschel/PACS/SPIRE/HOBYS Key Programme Consortium

Monday, June 23, 2014

Earth’s Ever-Changing Magnetic Field

This animation shows changes in Earth’s magnetic field from January to June 2014 as measured by ESA’s Swarm trio of satellites.

The magnetic field protects us from cosmic radiation and charged particles that bombard Earth, but it is in a permanent state of flux. Magnetic north wanders, and every few hundred thousand years the polarity flips so that a compass would point south instead of north. Moreover, the strength of the magnetic field constantly changes – and it is currently showing signs of significant weakening.

The field is particularly weak over the South Atlantic Ocean – known as the South Atlantic Anomaly. This weak field has indirectly caused many temporary satellite ‘hiccups’ (called Single Event Upsets) as the satellites are exposed to strong radiation over this area.

Video credit: ESA/Dot2Dot

Note: For more information, see June 2014 Magnetic Field.