Saturday, 4 March 2017

Sivan 2 to M31

From within the boundaries of the constellation Cassiopeia (left) to Andromeda (right), this telescopic mosaic spans over 10 degrees in planet Earth's skies. The celestial scene is constructed of panels that are part of a high-resolution astronomical survey of the Milky Way in hydrogen-alpha light. Processing the monochromatic image data has brought out the region's faintest structures, relatively unexplored filaments of hydrogen gas near the plane of our Milky Way Galaxy. Large but faint and also relatively unknown nebula Sivan 2 is at the upper left in the field. The nearby Andromeda Galaxy, M31, is at center right, while the faint, pervasive hydrogen nebulosities stretch towards M31 across the foreground in the wide field of view. The broad survey image demonstrates the intriguing faint hydrogen clouds recently imaged by astronomer Rogelio Bernal Andreo really are within the Milky Way, along the line-of-sight to the Andromeda Galaxy.

Sivan 2 to M31 
Image Credit & Copyright: MDW Sky Survey (David Mittelman, Dennis di Cicco, Sean Walker)

Friday, 3 March 2017

Orbiter Steers Clear of Mars Moon Phobos

NASA’s MAVEN spacecraft performed a previously unscheduled maneuver this week to avoid a collision in the near future with Mars’ moon Phobos.
The Mars Atmosphere and VolatileEvolutioN (MAVEN)spacecraft has been orbiting Mars for just over two years, studying the Red Planet’s upper atmosphere, ionosphere and interactions with the sun and solar wind. On Tuesday the spacecraft carried out a rocket motor burn that boosted its velocity by 0.4 meters per second (less than 1 mile per hour). Although a small correction, it was enough that -- projected to one week later when the collision would otherwise have occurred -- MAVEN would miss the lumpy, crater-filled moon by about 2.5 minutes.

This is the first collision avoidance maneuver that the MAVEN spacecraft has performed at Mars to steer clear of Phobos. The orbits of both MAVEN and Phobos are known well enough that this timing difference ensures that they will not collide.

MAVEN, with an elliptical orbit around Mars, has an orbit that crosses those of other spacecraft and the moon Phobos many times over the course of a year.  When the orbits cross, the objects have the possibility of colliding if they arrive at that intersection at the same time. These scenarios are known well in advance and are carefully monitored by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, which sounded the alert regarding the possibility of a collision.

With one week’s advance notice, it looked like MAVEN and Phobos had a good chance of hitting each other on Monday, March 6, arriving at their orbit crossing point within about 7 seconds of each other. Given Phobos’ size (modeled for simplicity as a 30-kilometer sphere, a bit larger than the actual moon in order to be conservative), they had a high probability of colliding if no action were taken.

Said MAVEN Principal Investigator Bruce Jakosky of the University of Colorado in Boulder, “Kudos to the JPL navigation and tracking teams for watching out for possible collisions every day of the year, and to the MAVEN spacecraft team for carrying out the maneuver flawlessly.”

Wednesday, 4 January 2017

Titan: Send in the Clouds

Floating high above the hydrocarbon lakes, wispy clouds have finally started to return to Titan's northern latitudes.

Clouds like these disappeared from Titan's (3,200 miles or 5,150 kilometers across) northern reaches for several years (from about 2010 to 2014). Now they have returned, but in far smaller numbers than expected. Since clouds can quickly appear and disappear, Cassini scientists regularly monitor the large moon, in the hopes of observing cloud activity. They are especially interested in comparing these observations to predictions of how cloud cover should change with Saturn’s seasons. Titan’s clear skies are not what researchers expected.

This view looks toward the Saturn-facing side of Titan. North on Titan is up and rotated 3 degrees to the left. The image was taken with the Cassini spacecraft narrow-angle camera on Oct. 29, 2016 using a spectral filter that preferentially admits wavelengths of near-infrared light centered at 938 nanometers.

The view was obtained at a distance of approximately 545,000 miles (878,000 kilometers) from Titan. Image scale is 3 miles (5 kilometers) per pixel.

Wednesday, 3 August 2016

New Research Reveals Fluctuating Atmosphere of Jupiter’s Volcanic Moon

Jupiter’s volcanic moon Io has a thin atmosphere that collapses in the shadow of Jupiter, condensing as ice, according to a new study by NASA-funded researchers. The study reveals the freezing effects of Jupiter’s shadow during daily eclipses on the moon’s volcanic gases.

“This research is the first time scientists have observed this remarkable phenomenon directly, improving our understanding of this geologically active moon,” said Constantine Tsang, a scientist at the Southwest Research Institute in Boulder, Colorado. The study was published Aug. 2 in the Journal of Geophysical Research.

Io is the most volcanically active object in the solar system. The volcanoes are caused by tidal heating, the result of gravitational forces from Jupiter and other moons. These forces result in geological activity, most notably volcanoes that emit umbrella-like plumes of sulfur dioxide gas that can extend up to 300 miles (480 kilometers) above Io and produce extensive basaltic lava fields that can flow for hundreds of miles.

The new study documents atmospheric changes on Io as the giant planet casts its shadow over the moon’s surface during daily eclipses. Io’s thin atmosphere, which consists primarily of sulfur dioxide (SO2) gas emitted from volcanoes, collapses as the SO2 freezes onto the surface as ice when Io is shaded by Jupiter, then is restored when the ice warms and sublimes (i.e. transforms from solid back to gas) when the moon moves out of eclipse back into sunlight.

The study used the large eight-meter Gemini North telescope in Hawaii and an instrument called the Texas Echelon Cross Echelle Spectrograph (TEXES). Data showed that Io’s atmosphere begins to “deflate” when the temperatures drop from -235 degrees Fahrenheit in sunlight to -270 degrees Fahrenheit during eclipse. Eclipse occurs two hours of every Io day (1.7 Earth days). In full eclipse, the atmosphere effectively collapses, as most of the sulfur dioxide gas settles as frost on the moon’s surface. The atmosphere redevelops as the surface warms once the moon returns to full sunlight.
Artist’s concept of the atmospheric collapse of Jupiter’s volcanic moon Io, which is eclipsed by Jupiter for two hours of each day (1.7 Earth days). The resulting temperature drop freezes sulfur dioxide gas, causing the atmosphere to “deflate,” as seen in the shadowed area on the left.
Credits: SwRI/Andrew Blanchard

“This confirms that Io’s atmosphere is in a constant state of collapse and repair, and shows that a large fraction of the atmosphere is supported by sublimation of SO2 ice,” said John Spencer, a co-author of the new study, also at the Southwest Research Institute. “Though Io’s hyperactive volcanoes are the ultimate source of the SO2, sunlight controls the atmospheric pressure on a daily basis by controlling the temperature of the ice on the surface.  We’ve long suspected this, but can finally watch it happen.”

Prior to the study, no direct observations of Io’s atmosphere in eclipse had been possible because Io’s atmosphere is difficult to observe in the darkness of Jupiter’s shadow.  This breakthrough was possible because TEXES measures the atmosphere using heat radiation, not sunlight, and the giant Gemini telescope can sense the faint heat signature of Io’s collapsing atmosphere.

The observations occurred over two nights in November 2013, when Io was more than 420 million miles (675 million kilometers) from Earth. On both occasions, Io was observed moving into Jupiter’s shadow for a period about 40 minutes before and after the start of the eclipse.

The research was funded by NASA’s Solar System Workings and Solar System Observations programs.

Monday, 11 July 2016

'Frankenstein' Galaxy Surprises Astronomers

About 250 million light-years away, there's a neighborhood of our universe that astronomers had considered quiet and unremarkable. But now, scientists have uncovered an enormous, bizarre galaxy possibly formed from the parts of other galaxies.

A new study to be published in the Astrophysical Journal reveals the secret of UGC 1382, a galaxy that had originally been thought to be old, small and typical. Instead, scientists using data from NASA telescopes and other observatories have discovered that the galaxy is 10 times bigger than previously thought and, unlike most galaxies, its insides are younger than its outsides, almost as if it had been built using spare parts.

"This rare, 'Frankenstein' galaxy formed and is able to survive because it lies in a quiet little suburban neighborhood of the universe, where none of the hubbub of the more crowded parts can bother it," said study co-author Mark Seibert of the Observatories of the Carnegie Institution for Science, Pasadena, California. "It is so delicate that a slight nudge from a neighbor would cause it to disintegrate."

Seibert and Lea Hagen, a graduate student at Pennsylvania State University, University Park, came upon this galaxy by accident. They had been looking for stars forming in run-of-the-mill elliptical galaxies, which do not spin and are more three-dimensional and football-shaped than flat disks. Astronomers originally thought that UGC 1382 was one of those.

But while looking at images of galaxies in ultraviolet light through data from NASA's Galaxy Evolution Explorer (GALEX), a behemoth began to emerge from the darkness.

"We saw spiral arms extending far outside this galaxy, which no one had noticed before, and which elliptical galaxies should not have," said Hagen, who led the study. "That put us on an expedition to find out what this galaxy is and how it formed."

Researchers then looked at data of the galaxy from other telescopes: the Sloan Digital Sky Survey, the Two Micron All-Sky Survey (2MASS), NASA's Wide-field Infrared Survey Explorer (WISE), the National Radio Astronomy Observatory's Very Large Array and Carnegie's du Pont Telescope at Las Campanas Observatory. After GALEX revealed previously unseen structures to the astronomers, optical and infrared light observations from the other telescopes allowed the researchers to build a new model of this mysterious galaxy.

As it turns out, UGC 1382, at about 718,000 light-years across, is more than seven times wider than the Milky Way. It is also one of the three largest isolated disk galaxies ever discovered, according to the study. This galaxy is a rotating disk of low-density gas. Stars don't form here very quickly because the gas is so spread out.

But the biggest surprise was how the relative ages of the galaxy's components appear backwards. In most galaxies, the innermost portion forms first and contains the oldest stars. As the galaxy grows, its outer, newer regions have the youngest stars. Not so with UGC 1382. By combining observations from many different telescopes, astronomers were able to piece together the historical record of when stars formed in this galaxy -- and the result was bizarre.

"The center of UGC 1382 is actually younger than the spiral disk surrounding it," Seibert said. "It's old on the outside and young on the inside. This is like finding a tree whose inner growth rings are younger than the outer rings."

The unique galactic structure may have resulted from separate entities coming together, rather than a single entity that grew outward. In other words, two parts of the galaxy seem to have evolved independently before merging -- each with its own history.

At first, there was likely a group of small galaxies dominated by gas and dark matter, which is an invisible substance that makes up about 27 percent of all matter and energy in the universe (our own matter is only 5 percent). Later, a lenticular galaxy, a rotating disk without spiral arms, would have formed nearby. At least 3 billion years ago, the smaller galaxies may have fallen into orbit around the lenticular galaxy, eventually settling into the wide disk seen today.

More galaxies like this may exist, but more research is needed to look for them.

"By understanding this galaxy, we can get clues to how galaxies form on a larger scale, and uncover more galactic neighborhood surprises," Hagen said.

The GALEX mission, which ended in 2013 after more than a decade of scanning the skies in ultraviolet light, was led by scientists at Caltech in Pasadena, California. NASA's Jet Propulsion Laboratory, also in Pasadena, managed the mission and built the science instrument. Data for the 2MASS and WISE missions are archived at the Infrared Processing and Analysis Center (IPAC) at Caltech. JPL is managed by Caltech for NASA.

Thursday, 28 April 2016

Light Echoes Used to Study Protoplanetary Disks

A new study published in the Astrophysical Journal uses data from NASA's Spitzer Space Telescope and four ground-based telescopes to determine the distance from a star to the inner rim of its surrounding protoplanetary disk. Researchers used a method called "photo-reverberation," also known as "light echoes." When the central star brightens, some of the light hits the surrounding disk, causing a delayed “echo.” Scientists measured the time it took for light coming directly from the star to reach Earth, then waited for its echo to arrive.

The Spitzer study marks the first time the light echo method was used in the context of protoplanetary disks.

This illustration shows a star surrounded by a protoplanetary disk. Material from the thick disk flows along the star’s magnetic field lines and is deposited onto the star’s surface. When material hits the star, it lights up brightly

Saturday, 19 March 2016

The Soyuz TMA-20M rocket launches from the Baikonur Cosmodrome in Kazakhstan

The Soyuz TMA-20M rocket launches from the Baikonur Cosmodrome in Kazakhstan on Saturday, March 19, 2016 (Friday, March 18, in the U.S.), carrying Expedition 47 Soyuz Commander Alexey Ovchinin of Roscosmos, Flight Engineer Jeff Williams of NASA, and Flight Engineer Oleg Skripochka of Roscosmos into orbit to begin their five and a half month mission on the International Space Station.

Credit: NASA/Aubrey Gemignani