Unusual Changing Feature in Titan's Ligeia Mare

These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn's moon Titan. The views, taken during three different Cassini flybys of Titan, show that this feature was not visible in earlier radar images of the same region and its appearance changed between 2013 and 2014.

In the images, the dark areas represent the sea, which is thought to be composed of mostly methane and ethane. Most of the bright areas represent land surface above or just beneath the water line. The mysterious bright feature appears off the coast below center in the middle and right images.

The mystery feature had not been seen in preceding SAR observations of the region from 2007 to 2009. After its first appearance in early July 2013, it was not visible in observations by Cassini's Visible and Infrared Mapping Spectrometer, obtained later in July and in September 2013. Low-resolution SAR images obtained in October 2013 also failed to recover the feature.

The SAR observation from Cassini's August 21, 2014 Titan flyby shows that the feature was still visible, although its appearance changed during the 11 months since it was last observed. The feature seems to have changed in size between the images from 2013 and 2014 -- doubling from about 30 square miles (about 75 square kilometers) to about 60 square miles (about 160 square kilometers). Ongoing analyses of these data may eliminate some of the explanations previously put forward, or reveal new clues as to what is happening in Titan's seas.

The Cassini radar team is investigating possible origins for the feature, including surface waves, rising bubbles, floating solids, solids that are suspended just below the surface or perhaps something more exotic. Researchers suspect that the appearance of this feature could be related to changing seasons on Titan, as summer draws near in the moon's northern hemisphere. Monitoring such changes is a major goal for Cassini's current extended mission.

The upper half of the middle image uses data from the April 26, 2007 Titan flyby. That area did not receive SAR coverage during the July 10, 2013 encounter, so the earlier data was used to fill-in the scene.

Image credit: NASA/JPL-Caltech/ASI/Cornell

Landing Site J - Comet 67P/Churyumov-Gerasimenko (21 September 2014)

Rosetta's navigation camera (NAVCAM) took this image of Comet 67P/Churyumov-Gerasimenko on 21 September, from a distance of 27.8 km from the comet center. The image covers an area of about 2 x 1.9 km and focuses on the smaller of the two comet lobes. The primary landing site J is 'above' the distinctive depression in this view. Click here for a context image.

Image credit: ESA/Rosetta/NAVCAM

Note: For more information, see Rosetta to Deploy Lander on 12 November (ESA), Rosetta to Deploy Lander on November 12 (JPL), and Rosetta Mission Status.

Comet 67P/Churyumov-Gerasimenko (21 September 2014)

Single frame (and cropped) NAVCAM image of Comet 67P/Churyumov-Gerasimenko on 21 September 2014.

Image credit: ESA/Rosetta/NAVCAM

Comet 67P/Churyumov-Gerasimenko (24 September 2014)

Four-image NAVCAM mosaic of Comet 67P/Churyumov-Gerasimenko, using images taken on 24 September 2014 when Rosetta was 28.5 km from the comet.

Image credit: ESA/Rosetta/NAVCAM

Dwarf Galaxy DDO 68

This image from the NASA/ESA Hubble Space Telescope shows a cosmic oddity, dwarf galaxy DDO 68.

This ragged collection of stars and gas clouds looks at first glance like a recently-formed galaxy in our own cosmic neighborhood.

Image credit: ESA/NASA

Note: For more information, see A Galaxy of Deception - Hubble Snaps What Looks Like a Young Galaxy in the Local Universe.

Clear Skies on HAT-P-11b

A Neptune-size planet with a clear atmosphere is shown crossing in front of its star in this artist's depiction. Such crossings, or transits, are observed by telescopes like NASA's Hubble and Spitzer to glean information about planets' atmospheres. As starlight passes through a planet's atmosphere, atoms and molecules absorb light at certain wavelengths, blocking it from the telescope's view. The more light a planet blocks, the larger the planet appears. By analyzing the amount of light blocked by the planet at different wavelengths, researchers can determine which molecules make up the atmosphere.

The problem with this technique is that sometimes planets have thick clouds that block any light from coming through, hiding the signature of the molecules in the atmosphere. This is particularly true of the handful of Neptune-size and super-Earth planets examined to date, all of which appear to be cloudy.

As a result, astronomers were elated to find clear skies on a Neptune-size planet called HAT-P-11b, as illustrated here. Without clouds to block their view, they were able to identify water vapor molecules in the planet's atmosphere. The blue rim of the planet in this image is due to scattered light, while the orange rim on the part of the planet in front of the star indicates the region where water vapor was detected.

Image credit: NASA/JPL-Caltech

Note: For more information, see PIA18838: A Sunny Outlook for 'Weather' on Exoplanets (Artist's Concept), PIA18839: Transmission Spectrum of HAT-P-11b, NASA Telescopes Find Clear Skies and Water Vapor on Exoplanet, and Clear Skies on Exo-Neptune - Smallest Exoplanet Ever Found to Have Water Vapor.

Rainbow Aurora

Auroras occur when particle radiation from the Sun hits Earth’s upper atmosphere, making it glow in a greenish blue light. ESA astronaut Alexander Gerst has one of our planet’s best views of this phenomenon, circling 400 km up on the Station.

Here, the last remnants of sunlight can be seen as a blue streak on the left side. Above it is the yellow hue of our atmosphere reflecting the sunlight. This thin band is all that protects us from solar radiation.

In the foreground, the Space Station’s Canadarm2 robotic arm is stowed, waiting to receive the next supply spacecraft to visit the microgravity laboratory.

Image credit: ESA/NASA

Saturn's North Polar Hexagon

The giant planet Saturn is mostly a gigantic ball of rotating gas, completely unlike our solid home planet. But Earth and Saturn do have something in common: weather, although the gas giant is home to some of the most bizarre weather in our Solar System, such as the swirling storm shown in this Cassini view.

Known as “the hexagon”, this weather feature is an intense, six-sided jet stream at Saturn’s north pole. Spanning some 30,000 km across, it hosts howling 320 km/h winds that spiral around a massive storm rotating anticlockwise at the heart of the region.

Numerous small vortices rotate in the opposite direction to the central storm and are dragged around with the jet stream, creating a terrifically turbulent region. While a hurricane on Earth may last a week or more, the hexagon has been raging for decades, and shows no signs of letting up.

This false-color image of the hexagon was made using ultraviolet, visible and infrared filters to highlight different regions.

The dark center of the image shows the large central storm and its eye, which is up to 50 times bigger than a terrestrial hurricane eye. The small vortices show up as pink-red clumps. Towards the lower right of the frame is a white-tinted oval storm that is bigger than any of the others — this is the largest of the vortices at some 3500 km across, twice the size of the largest hurricane ever recorded on Earth.

The darker blue region within the hexagon is filled with small haze particles, whereas the paler blue region is dominated by larger particles. This divide is caused by the hexagonal jet stream acting as a shepherding barrier — large particles cannot enter the hexagon from the outside.

These large particles are created when sunlight shines onto Saturn’s atmosphere, something that only started relatively recently in the northern hemisphere with the beginning of northern spring in August 2009.

Cassini will continue to track changes in the hexagon, monitoring its contents, shape and behavior as summer reaches Saturn’s northern hemisphere in 2017.

An animated version is available here.

Image credit: NASA/JPL-Caltech/SSI/Hampton University

Hooke Crater and Argyre Planitia

Color-coded topography map of a region of the Argyre basin, featuring Hooke crater and part of the floor of the basin known as Argyre Planitia. White and red show the highest terrains, while blue and purple show the deepest. The image is based on a digital terrain model of the region, from which the topography of the landscape can be derived. The region clearly slopes to the south (left).

The image was acquired by the High Resolution Stereo Camera on Mars Express on 20 April 2014 during orbit 13,082. The ground resolution is about 63 m per pixel. Hooke crater is located at about 46°S / 316°E. North is right and East is down.

Image credit: ESA/DLR/FU Berlin

Dwarf Galaxy M60-UDC1

This NASA/ESA Hubble Space Telescope image shows the dwarf galaxy M60-UDC1. Lying about 50 million light-years away, M60-UCD1 is a tiny galaxy with a diameter of 300 light-years – just 1/500th of the diameter of the Milky Way! Despite its size it is pretty crowded, containing some 140 million stars.

The dwarf galaxy may actually be the stripped remnant of a larger galaxy that was torn apart during a close encounter with its neighbor, a massive galaxy called Messier 60.

Circumstantial evidence for this comes from the recent discovery of a monster black hole, which is not visible in this image, at the center of the dwarf. The black hole makes up 15 percent of the mass of the entire galaxy, making it much too big to have formed inside a dwarf galaxy.

Image credit: NASA, ESA and A. Seth (University of Utah, USA)

Note: For more information, see Big Surprises Can Come in Small Packages - Hubble Helps Astronomers Find Smallest Known Galaxy With Supermassive Black Hole.

Comet 67P/Churyumov-Gerasimenko (19 September 2014)

Four-image NAVCAM mosaic of Comet 67P/Churyumov-Gerasimenko, using images taken on 19 September 2014 when Rosetta was 28.6 km from the comet.

Image credit: ESA/Rosetta/NAVCAM

NGC 6872 and IC 4970

This picture, taken by the NASA/ESA Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC2), shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused by its interactions with the smaller galaxy that can be seen just above NGC 6872, called IC 4970. They both lie roughly 300 million light-years away from Earth.

From tip to tip, NGC 6872 measures over 500,000 light-years across, making it the second largest spiral galaxy discovered to date. In terms of size it is beaten only by NGC 262, a galaxy that measures a mind-boggling 1.3 million light-years in diameter! To put that into perspective, our own galaxy, the Milky Way, measures between 100,000 and 120,000 light-years across, making NGC 6872 about five times its size.

The upper left spiral arm of NGC 6872 is visibly distorted and is populated by star-forming regions, which appear blue on this image. This may have been be caused by IC 4970 recently passing through this arm — although here, recent means 130 million years ago! Astronomers have noted that NGC 6872 seems to be relatively sparse in terms of free hydrogen, which is the basis material for new stars, meaning that if it weren’t for its interactions with IC 4970, NGC 6872 might not have been able to produce new bursts of star formation.

Image credit: ESA/Hubble & NASA

Note: For more information, see PIA17808: Hubble Feathers the Peacock.

Artist's Conception of WASP-18b

WASP-18: An exoplanet about ten times Jupiter’s mass located some 330 light years from Earth.

The artist's illustration featured in the main part of this graphic depicts a star and its planet, WASP-18b, a giant exoplanet that orbits very close to it. A new study using Chandra data has shown that WASP-18b is making the star that it orbits act much older than it actually is. The lower inset box reveals that no X-rays were detected during a long Chandra observation. This is surprising given the age of the star, suggesting the planet is weakening the star’s magnetic field through tidal forces.

Scale: Inset image is about 5.3 arcmin across (about 0.5 light years).

Image credit: X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS; Illustration: NASA/CXC/M.Weiss

Note: For more information, see WASP-18: NASA's Chandra X-ray Observatory Finds Planet That Makes Star Act Deceptively Old.

Distribution of Molecular Gas in 30 Merging Galaxies

Each of the colorful objects in this image illustrates one of 30 merging galaxies. The contours in the individual galaxies show the signal strength from carbon monoxide while the color represents the motion of gas. Gas that is moving away from us appears red while the blue color shows gas that is approaching. The contours together with the transition from red to blue indicate a gaseous disc that is rotating about the center of the galaxy.

Image credit: ALMA (ESO/NAOJ/NRAO)/SMA/CARMA/IRAM/J. Ueda et al.

Note: For more information, see Violent Origins of Disc Galaxies Probed by ALMA.

Pulsar PSR J1640-4631

The blue dot in this image marks the spot of an energetic pulsar -- the magnetic, spinning core of star that blew up in a supernova explosion. NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, discovered the pulsar by identifying its telltale pulse -- a rotating beam of X-rays, that like a cosmic lighthouse, intersects Earth every 0.2 seconds.

The pulsar, called PSR J1640-4631, lies in our inner Milky Way galaxy about 42,000 light-years away. It was originally identified by as an intense source of gamma rays by the High Energy Stereoscopic System (H.E.S.S.) in Namibia. NuSTAR helped pin down the source of the gamma rays to a pulsar.

The other pink dots in this picture show low-energy X-rays detected by NASA's Chandra X-ray Observatory.

In this image, NuSTAR data is blue and shows high-energy X-rays with 3 to 79 kiloelectron volts; Chandra data is pink and shows X-rays with 0.5 to 10 kiloeletron volts.

Image credit: NASA/JPL-Caltech/SAO

Note: For more information, see Pulse of a Dead Star Powers Intense Gamma Rays.

Philae Secondary Landing Site - Site C

Site C was chosen as the backup site for Rosetta’s lander Philae during the Landing Site Selection Group meeting held on 13–14 September 2014.

The image was taken by Rosetta's narrow-angle camera from a distance of about 70 km. The resolution is 1.5 meters/pixel.

Full story: 'J' marks the spot for Rosetta's lander

Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Note: For more information, see 'J' Marks the Spot for Rosetta's Lander.

Philae's Primary Landing Site - Site J

Philae’s primary landing site will target Site J, the center of which is indicated by the cross in this OSIRIS narrow-angle image.

Site J is located on the head of Comet 67P/Churyumov–Gerasimenko and is close to the candidate site B, the large depression to the right of the image.

Site J offers the minimum risk to the lander in comparison to the other candidate sites, and is also scientifically interesting, with signs of activity nearby. At Site J, the majority of slopes are less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. Site J also appears to have relatively few boulders and receives sufficient daily illumination to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase.

Full story: 'J' marks the spot for Rosetta's lander

Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Note: For more information, see:
* Philae’s Primary Landing Site Close-Up
* Philae’s Primary Landing Site in Context
* Philae’s Primary Landing Site in 3D
* 'J' Marks the Spot for Rosetta's Lander (ESA Science)
* PIA18809: Rosetta Lander's Primary Landing Site
* PIA18810: Rosetta Lander's Backup Landing Site
* 'J' Marks the Spot for Rosetta's Lander (JPL)
* Announcement of the Selected Rosetta Primary Landing Site and a Backup
* Replay: Rosetta Landing Site Announcement (Video)

For more information about Philae and the mission, see:
* Philae's Panoramic Camera
* Philae’s Descent and Science on the Surface
* How to Orbit a Comet (all of the above are videos)
* Rosetta and Philae at Comet

Supernova Gaia14aaa and Its Host Galaxy

This image shows the supernova named Gaia14aaa as seen on 10 September 2014 with the robotic Liverpool Telescope on La Palma, in the Canary Islands, Spain. This is a Type Ia supernova – the explosion of a white dwarf locked in a binary system with a companion star – and it was discovered in the data collected with ESA’s Gaia satellite on 30 August.

In the left panel, the image from the Liverpool Telescope shows both Gaia14aaa and its host galaxy, named SDSS J132102.26+453223.8, which is about 500 million light-years away. In this image, the supernova is slightly offset from the galaxy’s core.

The central panel shows an image of the same galaxy, taken as part of the Sloan Digital Sky Survey, several years before the explosion of Gaia14aaa could be observed from Earth.

The right panel was obtained by subtracting the second image, which contains the light emitted by the galaxy, from the first one, which depicts both the galaxy and the supernova. The difference between the two images clearly shows the appearance of Gaia14aaa.

Image credit: M. Fraser/S. Hodgkin/L. Wyrzykowski/H. Campbell/N. Blagorodnova/Z. Kostrzewa-Rutkowska/Liverpool Telescope/SDSS

Note: For more information, see Gaia Discovers Its First Supernova.

Comet 67P/Churyumov-Gerasimenko (11 August 2014) From Earth

Since early August 2014, Rosetta has been enjoying a close-up view of comet 67P/Churyumov–Gerasimenko. Meanwhile, astronomers on Earth have been busy following the comet with ground-based telescopes. As Rosetta is deep inside the ‘atmosphere’ coma – it was 100 km from the nucleus on 6 August, and has been getting much closer since then – the only way to view the whole comet is to ‘stand back’ and observe it from Earth.

This image was recorded on 11 August 2014 using one of the 8 m-diameter telescopes of the European Southern Observatory’s Very Large Telescope in Chile.

Although faint, the comet is clearly active, revealing a dusty coma extending at least 19,000 km from the nucleus. The comet's dusty veil is not symmetrical as the dust is swept away from the Sun – located beyond the lower-right corner of the image – to begin forming a tail.

At the moment, the comet is visible only from the southern hemisphere and, at more than 500 million km from the Sun, it is still very faint. In addition, it currently sits in a patch of the sky where it is camouflaged against the crowded starry background of the Milky Way. For these reasons, the image was compiled by superimposing 40 individual exposures, each lasting about 50 seconds, and removing background stars.

A large collaboration of astronomers across the world has been working to make the most of the unique opportunity to observe the comet from the ground while Rosetta is performing measurements at the comet. The Very Large Telescope is taking images every two nights on average. These short exposures monitor the comet’s activity by studying how its brightness changes. The results are used by the Rosetta team to help plan spacecraft operations.

Image credit: C. Snodgrass/ESO/ESA

Comet 67P/Churyumov-Gerasimenko (10 September 2014)

Four image NAVCAM mosaic of Comet 67P/Churyumov-Gerasimenko, using images taken on 10 September when Rosetta was 27.8 km from the comet.

Image credit: ESA/Rosetta/NAVCAM

SNR Puppis A

Puppis A: A supernova remnant located about 7,000 light years from Earth.

The destructive results of a powerful supernova explosion are seen in a delicate tapestry of X-ray light in this new image. The remnant is called Puppis A, which could have been witnessed on Earth about 3,700 years ago and is about 10 light years across. This image is the most complete and detailed X-ray view of Puppis A ever obtained, made by combining a mosaic of different Chandra and XMM-Newton observations. In this image, low-energy X-rays are shown in red, medium-energy X-rays are in green and high energy X-rays are colored blue.

Scale: Image is about 1.5 degrees across (About 180 light years).

Image credit: X-ray: NASA/CXC/IAFE/G.Dubner et al & ESA/XMM-Newton

Note: For more information, see Puppis A: An X-Ray Tapestry.

Terrain Map of Comet 67P/Churyumov-Gerasimenko

This view of the "belly" and part of the "head" of comet 67P/Churyumov-Gerasimenko indicates several morphologically different regions.

Scientists have analyzed images of the comet's surface taken by OSIRIS, Rosetta's scientific imaging system, and defined several different regions, each of which has a distinctive physical appearance. This analysis provides the basis for a detailed scientific description of 67P's surface.

The comet has areas dominated by cliffs, depressions, craters, boulders and even parallel grooves. While some of these areas appear to be quiet, others seem to be shaped by the comet's activity, in which grains emitted from below the surface fall back to the ground in the nearby area.

As both comet 67P and Rosetta travel closer to the sun during the next few months, the OSIRIS team and other instruments on the payload will monitor the surface to look for changes. While scientists do not expect the borderlines they have identified for the comet's various regions to vary dramatically, even subtle transformations of the surface may help to explain how cometary activity created such a breathtaking world.

Image credit: ESA/Rosetta/MPS for OSIRIS Team/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Note: For more information, see First Map of Rosetta's Comet.

Earth Images from the International Space Station

This timelapse video was made from images taken by ESA astronaut Alexander Gerst orbiting Earth on the International Space Station.

The video is offered in Ultra High Definition, the highest available to consumers. Be sure to change the settings in YouTube if your computer or television can handle it for the full effect.

The montage is made from a long sequence of still photographs taken at a resolution of 4256 x 2832 pixels at a rate of one every second. The high resolution allowed the ESA production team to create a 3840 x 2160 pixel movie, also known as Ultra HD or 4K.

Playing these sequences at 25 frames per second, the film runs 25 times faster than it looks for the astronauts in space.

The artistic effects of the light trails from stars and cities at night are created by superimposing the individual images and fading them out slowly.

Alexander Gerst is a member of the International Space Station Expedition 40 crew. He is spending five and a half months living and working on the ISS for his Blue Dot mission.

Video credit: ESA/NASA

Rosetta and Comet 67P/Churyumov-Gerasimenko (7 September 2014) by Philae

Using the CIVA camera on Rosetta’s Philae lander, the spacecraft have snapped a ‘selfie’ at comet 67P/Churyumov–Gerasimenko. The image was taken on 7 September from a distance of about 50 km from the comet, and captures the side of the Rosetta spacecraft and one of Rosetta’s 14 m-long solar wings, with 67P/C-G in the background. Two images with different exposure times were combined to bring out the faint details in this very high contrast situation.

Image credit: ESA/Rosetta/Philae/CIVA

Messier 54

This image from the VLT Survey Telescope at ESO’s Paranal Observatory in northern Chile shows the globular cluster Messier 54. This cluster looks very similar to many others, but it has a secret. Messier 54 doesn’t belong to the Milky Way, but actually is part of a small satellite galaxy, the Sagittarius Dwarf Galaxy. This unusual parentage has allowed astronomers to use the Very Large Telescope (VLT) to test whether unexpectedly low levels of the element lithium in stars are also found in stars outside the Milky Way.

Image credit: ESO

Note: For more information, see This Star Cluster Is Not What It Seems.

Comet 67P/Churyumov-Gerasimenko (7 September 2014)

Four-image montage comprising images taken by Rosetta's navigation camera on 7 September from a distance of 51 km from comet 67P/Churyumov-Gerasimenko. The comet nucleus is about 4 km across. For more details, see the Rosetta blog post: CometWatch 7 September

Image credit: ESA/Rosetta/NAVCAM

Note: For more information, see Comet on 7 September 2014 – NavCam (A), Comet on 7 September 2014 – NavCam (B), and Comet on 7 September 2014 – NavCam (D).

COSMOS Field

Millions of galaxies populate the patch of sky known as the COSMOS field, short for Cosmic Evolution Survey, a portion of which is shown here. Even the smallest dots in this image are galaxies, some up to 12 billion light-years away. The square region in the center of bright objects is where the telescope was blinded by bright light. However, even these brightest objects in the field are more than ten thousand times fainter than what you can see with the naked eye.

The picture is a combination of infrared data from Spitzer (red) and visible-light data (blue and green) from Japan's Subaru telescope atop Mauna Kea in Hawaii. These data were taken as part of the SPLASH (Spitzer large area survey with Hyper-Suprime-Cam) project.

Image credit: NASA/JPL-Caltech

Note: For more information, see Spitzer's SPLASH Project Dives Deep for Galaxies.

Comet 67P/Churyumov-Gerasimenko (5 September 2014)

Jagged cliffs and prominent boulders are visible in this image taken by OSIRIS, Rosetta’s scientific imaging system, on 5 September 2014 from a distance of 62 kilometers from comet 67P/Churyumov-Gerasimenko. The left part of the image shows a side view of the comet’s 'body', while the right is the back of its 'head'. One pixel corresponds to 1.1 meters.

Image credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Plate Tectonics on Europa

Scientists have found evidence of plate tectonics on Jupiter's moon Europa. This conceptual illustration of the subduction process (where one plate is forced under another) shows how a cold, brittle, outer portion of Europa's 20-30 kilometer-thick (roughly 10-20 mile) ice shell moved into the warmer shell interior and was ultimately subsumed. A low-relief subsumption band was created at the surface in the overriding plate, alongside which cryolavas may have erupted.

Illustration credit: NASA/Noah Kroese, I.NK

Note: For more information, see Scientists Find Evidence of 'Diving' Tectonic Plates on Europa.

Evidence for Supernovas Near Earth

Once every 50 years, more or less, a massive star explodes somewhere in the Milky Way. The resulting blast is terrifyingly powerful, pumping out more energy in a split second than the sun emits in a million years. At its peak, a supernova can outshine the entire Milky Way.

It seems obvious that you wouldn't want a supernova exploding near Earth. Yet there is growing evidence that one did—actually, more than one. About 10 million years ago, a nearby cluster of supernovas went off like popcorn. We know because the explosions blew an enormous bubble in the interstellar medium, and we're inside it.

Astronomers call it "the Local Bubble." It is peanut-shaped, about 300 light years long, and filled with almost nothing. Gas inside the bubble is very thin (0.001 atoms per cubic centimeter) and very hot (roughly a million degrees)—a sharp departure from ordinary interstellar material.

The Local Bubble was discovered gradually in the 1970s and 1980s. Optical and radio astronomers looked carefully for interstellar gas in our part of the galaxy, but couldn't find much in Earth's neighborhood. Meanwhile, x-ray astronomers were getting their first look at the sky using sounding rockets and orbiting satellites, which revealed a million-degree x-ray glow coming from all directions. It all added up to Earth being inside a bubble of hot gas blown by exploding stars.

However, not all researchers agreed.

"Within the last decade, some scientists have been challenging the [supernova] interpretation, suggesting that much or all of the soft X-ray diffuse background is instead a result of charge exchange," says F. Scott Porter of the Goddard Space Flight Center.

"Charge exchange": Basically, it happens when the electrically-charged solar wind comes into contact with a neutral gas. The solar wind can steal electrons from the neutral gas, resulting in an X-ray glow that looks a lot like the glow from an old supernova. Charge exchange has been observed many times in comets.

So, is the X-ray glow that fills the sky a sign of peaceful "charge exchange" in the solar system or evidence of terrifying explosions in the distant past?
image

To find out, an international team researchers including Porter and led by physics professor Massimiliano Galeazzi at the University of Miami in Coral Gables, developed an X-ray detector that could distinguish between the two possibilities. The device was named DXL, for Diffuse X-ray emission from the Local Galaxy.

On December 12, 2012, DXL launched from White Sands Missile Range in New Mexico atop a NASA Black Brant IX sounding rocket, reaching a peak altitude of 160 miles and spending five minutes above Earth's atmosphere. That was all the time they needed to measure the amount of "charge exchange" X-rays inside the solar system.

The results, published online in the journal Nature on July 27, indicate that only about 40 percent of the soft X-ray background originates within the solar system. The rest must come from a Local Bubble of hot gas, the relic of ancient supernovas outside the solar system.

Obviously, those supernovas were not close enough to exterminate life on Earth—but they were close enough to wrap our solar system in a bubble of hot gas that persists millions of years later.

"This is a significant discovery,' said Galeazzi. "[It] affects our understanding of the area of the galaxy close to the sun, and can, therefore, be used as a foundation for future models of the galaxy structure."

Galeazzi and collaborators are already planning the next flight of DXL, which will include additional instruments to better characterize the emission. The launch is currently planned for December 2015.


More information:

How did DXL distinguish between X-rays from charge exchange in the solar system vs. X-rays from hot gas in the Local Bubble?

Answer: Basically, there is a stream of interstellar helium atoms that flows through the solar system. You can read about it here. Every year in December, Earth passes through the "helium focusing cone," a region where this neutral helium is concentrated by the gravitational influence of the sun. The researchers figured the helium focusing cone was probably the strongest source of charge exchange x-rays in the solar system. Using the sounding rocket, they measured the X-ray glow of the helium and found that it could not account for all of the X-rays astronomers had been seeing. There must be a Local Bubble of hot gas to account for the difference.

Video credit: NASA; Illustration credit & copyright: Linda Huff (American Scientist), Priscilla Frisch (U. Chicago)

Comet 067P Churyumov-Gerasimenko Darker Than Charcoal

A NASA instrument aboard the European Space Agency’s (ESA's) Rosetta orbiter has successfully made its first delivery of science data from comet 67P/Churyumov-Gerasimenko.

The instrument, named Alice, began mapping the comet’s surface last month, recording the first far-ultraviolet light spectra of the comet’s surface. From the data, the Alice team discovered the comet is unusually dark -- darker than charcoal-black -- when viewed in ultraviolet wavelengths. Alice also detected both hydrogen and oxygen in the comet’s coma, or atmosphere.

Rosetta scientists also discovered the comet’s surface so far shows no large water-ice patches. The team expected to see ice patches on the comet’s surface because it is too far away for the sun’s warmth to turn its water into vapor.

"We’re a bit surprised at just how unreflective the comet’s surface is and how little evidence of exposed water-ice it shows," said Alan Stern, Alice principal investigator at the Southwest Research Institute in Boulder, Colorado.

Alice is probing the origin, composition and workings of comet 67P/Churyumov-Gerasimenko, to gather sensitive, high-resolution insights that cannot be obtained by either ground-based or Earth-orbiting observation. It has more than 1,000 times the data-gathering capability of instruments flown a generation ago, yet it weighs less than nine pounds (four kilograms) and draws just four watts of power. The instrument is one of two full instruments on board Rosetta that are funded by NASA. The agency also provided portions of two other instrument suites.

Other U.S. contributions aboard the spacecraft are the Microwave Instrument for Rosetta Orbiter (MIRO), the Ion and Electron Sensor (IES), part of the Rosetta Plasma Consortium Suite, and the Double Focusing Mass Spectrometer (DFMS) electronics package for the Rosetta Orbiter Spectrometer for Ion Neutral Analysis (ROSINA). They are part of a suite of 11 total science instruments aboard Rosetta.

MIRO is designed to provide data on how gas and dust leave the surface of the nucleus to form the coma and tail that gives comets their intrinsic beauty. IES is part of a suite of five instruments to analyze the plasma environment of the comet, particularly the coma.

To obtain the orbital velocity necessary to reach its comet target, the Rosetta spacecraft took advantage of four gravity assists (three from Earth, one from Mars) and an almost three-year period of deep space hibernation, waking up in January 2014 in time to prepare for its rendezvous with 67P/Churyumov-Gerasimenko.

Rosetta also carries a lander, Philae, which will drop to the comet’s surface in November 2014.

The comet observations will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in providing Earth with water, and perhaps even life.

Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Text credit: Science@NASA

Note: For more information, see NASA Instrument on Rosetta: First Science Results and Rosetta’s Imaging and Spectroscopy Instruments.

Lupus 4

The Wide Field Imager (WFI) on the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile captured this view of dark cloud Lupus 4 blotting out background stars. Lupus 4 is a dense pocket of gas and dust where new stars are expected to form. The cloud is located about 400 light-years away from Earth, on the border between the constellations of Lupus (The Wolf) and Norma (The Carpenter's Square).

Image credit: ESO

Note: For more information, see Cosmic Forecast: Dark Clouds Will Give Way to Sunshine.

Comet 67P/Churyumov-Gerasimenko (2 September 2014)

Corner image of the four-image montage of comet 67P/Churyumov-Gerasimenko taken by Rosetta's navigation camera on 2 September.

Image credit: ESA/Rosetta/NAVCAM

Magnetar 3XMM J185246.6+003317 Below Supernova Remnant Kesteven 79

Massive stars end their life with a bang, exploding as supernovas and releasing massive amounts of energy and matter. What remains of the star is a small and extremely dense remnant: a neutron star or a black hole.

Neutron stars come in several flavors, depending on properties such as their ages, the strength of the magnetic field concealed beneath their surface, or the presence of other stars nearby. Some of the energetic processes taking place around neutron stars can be explored with X-ray telescopes, like ESA's XMM-Newton.

This image depicts two very different neutron stars that were observed in the same patch of the sky with XMM-Newton. The green and pink bubble dominating the image is Kesteven 79, the remnant of a supernova explosion located about 23,000 light-years away from us.

From the properties of the hot gas in Kesteven 79 and from its size, astronomers estimate that it is between 5000 and 7000 years old. Taking account of the time needed for light to travel to Earth, this means that the supernova that created it must have exploded almost 30,000 years ago. The explosion left behind a young neutron star with a weak magnetic field, which can be seen as the blue spot at the center of Kesteven 79.

Beneath it, a blue splotch indicates an entirely different beast: a neutron star boasting an extremely strong magnetic field, known as a magnetar. Astronomers discovered this magnetar, named 3XMM J185246.6+003317, in 2013 by looking at images that had been taken in 2008 and 2009. After the discovery, they looked at previous images of the same patch of the sky, taken before 2008, but did not find any trace of the magnetar. This suggests that the detection corresponded to an outburst of X-rays released by the magnetar, likely caused by a dramatic change in the structure of its magnetic field.

While the neutron star in the supernova remnant is relatively young, the magnetar is likely a million years old; the age difference means that it is very unlikely that the magnetar arose from the explosion that created Kesteven 79, but must have formed much earlier.

This false-color image is a composite of 15 observations performed between 2004 and 2009 with the EPIC MOS camera on board XMM-Newton. The image combines data collected at energies from 0.3 to 1.2 keV (shown in red), 1.2 to 2 keV (shown in green) and 2 to 7 keV (shown in blue).

Image credit: ESA/XMM-Newton/ Ping Zhou, Nanjing University, China

Dark Nebula Dobashi 4173 and Reflection Nebula [B77] 63

This new NASA/ESA Hubble Space Telescope image shows a variety of intriguing cosmic phenomena.

Surrounded by bright stars, towards the upper middle of the frame we see a small young stellar object (YSO) known as SSTC2D J033038.2+303212. Located in the constellation of Perseus, this star is in the early stages of its life and is still forming into a fully grown star. In this view from Hubble’s Advanced Camera for Surveys (ACS) it appears to have a murky chimney of material emanating outwards and downwards, framed by bright bursts of gas flowing from the star itself. This fledgling star is actually surrounded by a bright disc of material swirling around it as it forms — a disc that we see edge-on from our perspective.

However, this small bright speck is dwarfed by its cosmic neighbor towards the bottom of the frame, a clump of bright, wispy gas swirling around as it appears to spew dark material out into space. The bright cloud is a reflection nebula known as [B77] 63, a cloud of interstellar gas that is reflecting light from the stars embedded within it. There are actually a number of bright stars within [B77] 63, most notably the emission-line star LkHA 326, and its very near neighbor LZK 18.

These stars are lighting up the surrounding gas and sculpting it into the wispy shape seen in this image. However, the most dramatic part of the image seems to be a dark stream of smoke piling outwards from [B77] 63 and its stars — a dark nebula called Dobashi 4173. Dark nebulae are incredibly dense clouds of pitch-dark material that obscure the patches of sky behind them, seemingly creating great rips and eerily empty chunks of sky. The stars speckled on top of this extreme blackness actually lie between us and Dobashi 4173.

Image credit: ESA

Superfast Coronal Mass Ejection

A coronal mass ejection (CME) detected by SOHO's LASCO C2 camera at 06:54 UT on 20 January 2005. The CME can be seen at the 2 o'clock position. Subsequent studies have shown that this was one of the fastest CME's during solar cycle 23, with a velocity that peaked at about 3000 km/s at a distance of between 3 and 50 solar radii, before slowing to 1000 km/s as it approached Earth. The typical speed of particles in the solar wind is 400-700 km/s.

Image credit: SOHO (ESA & NASA)

Note: For more information, see A Mixed-up Magnetic Storm.

Comet 67P/Churyumov-Gerasimenko (31 August 2014)

Four-image montage comprising images taken by Rosetta's navigation camera on 31 August from a distance of 61 km from comet 67P/Churyumov-Gerasimenko. The comet nucleus is about 4 km across.

Image credit: ESA/Rosetta/NAVCAM

SN 2014J in Messier 82

In January 2014, a supernova was discovered in the nearby galaxy M82. At a distance of about 11.5 million light-years from Earth, SN2014J as it is known, is the closest of its type to be detected in decades.

This composite Hubble image shows the supernova in visible light, obtained on 31 January with Hubble's Wide Field Camera 3, superimposed on a mosaic of the entire galaxy taken in 2006 with Hubble's Advanced Camera for Surveys.

Image credit: NASA/ESA/A. Goobar (Stockholm University)/Hubble Heritage Team (STScI/AURA)

Note: For more information, see INTEGRAL Catches Dead Star Exploding in a Blaze of Glory and Supernova Explosion.

Eta Carinae

Eta Carinae: A double star system that contains one of the largest most massive stars in the Milky Way galaxy.

The Eta Carinae double star system contains one of the biggest and brightest stars in our Galaxy, weighing at least 90 times the mass of the Sun. It is also extremely volatile and is expected to have at least one supernova explosion in the future. Astronomers are using Chandra to learn more about Eta Carinae through the X-rays it generates. This new Chandra image shows Eta Carinae with low energy X-rays in red, medium energy X-rays in green, and high energy X-rays in blue. The Chandra data are helping to reveal, among other things, how the powerful winds from the two stars in this system interact.

Scale: Image is about 2 arcmin across (about 4.6 light years).

Image credit: NASA/CXC/GSFC/K.Hamaguchi, et al.

Note: For more information, see Eta Carinae: Our Neighboring Superstars.