New Ceres Images Show Bright Craters

NASA - Dawn Mission patch.

April 19, 2016

Image above: Ceres' Haulani Crater, with a diameter of 21 miles (34 kilometers), shows evidence of landslides from its crater rim. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Craters with bright material on dwarf planet Ceres shine in new images from NASA's Dawn mission.

In its lowest-altitude mapping orbit, at a distance of 240 miles (385 kilometers) from Ceres, Dawn has provided scientists with spectacular views of the dwarf planet.

Haulani Crater, with a diameter of 21 miles (34 kilometers), shows evidence of landslides from its crater rim. Smooth material and a central ridge stand out on its floor. An enhanced false-color view allows scientists to gain insight into materials and how they relate to surface morphology. This image shows rays of bluish ejected material. The color blue in such views has been associated with young features on Ceres.

Image above: NASA's Dawn spacecraft took images of Haulani Crater at a distance of 240 miles (385 kilometers) from the surface of Ceres. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

"Haulani perfectly displays the properties we would expect from a fresh impact into the surface of Ceres. The crater floor is largely free of impacts, and it contrasts sharply in color from older parts of the surface," said Martin Hoffmann, co-investigator on the Dawn framing camera team, based at the Max Planck Institute for Solar System Research, Göttingen, Germany.

The crater's polygonal nature (meaning it resembles a shape made of straight lines) is noteworthy because most craters seen on other planetary bodies, including Earth, are nearly circular. The straight edges of some Cerean craters, including Haulani, result from pre-existing stress patterns and faults beneath the surface.

Image above: Oxo Crater is unique because of the relatively large "slump" in its crater rim. Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

A hidden treasure on Ceres is the 6-mile-wide (10-kilometer-wide) Oxo Crater, which is the second-brightest feature on Ceres (only Occator's central area is brighter). Oxo lies near the 0 degree meridian that defines the edge of many Ceres maps, making this small feature easy to overlook. Oxo is also unique because of the relatively large "slump" in its crater rim, where a mass of material has dropped below the surface. Dawn science team members are also examining the signatures of minerals on the crater floor, which appear different than elsewhere on Ceres.

"Little Oxo may be poised to make a big contribution to understanding the upper crust of Ceres," said Chris Russell, principal investigator of the mission, based at the University of California, Los Angeles.

Unveiling Ceres

Video above: NASA's Dawn spacecraft has revealed marvelous sights on dwarf planet Ceres during its first year in orbit. Video Credits: NASA/JPL.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants, visit:
http://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites:

http://dawn.jpl.nasa.gov
http://www.nasa.gov/dawn

Images (mentioned), Video (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Elizabeth Landau.

Best regards, Orbiter.ch

Lone Planetary-Mass Object Found in Family of Stars

NASA - WISE Mission logo.

April 19, 2016

In 2011, astronomers announced that our galaxy is likely teeming with free-floating planets. In fact, these lonely worlds, which sit quietly in the darkness of space without any companion planets or even a host sun, might outnumber stars in our Milky Way galaxy. The surprising discovery begged the question: Where did these objects come from? Are they planets that were ejected from solar systems, or are they actually light-weight stars called brown dwarfs that formed alone in space like stars?

A new study using data from NASA's Wide-field Infrared Survey Explorer, WISE, and the Two Micron All Sky Survey, or 2MASS, provides new clues in this mystery of galactic proportions. Scientists have identified a free-floating, planetary-mass object within a young star family, called the TW Hydrae association. The newfound object, termed WISEA J114724.10−204021.3, or just WISEA 1147 for short, is estimated to be between roughly five to 10 times the mass of Jupiter.

Image above: A young, free-floating world sits alone in space in this illustration. The object, called WISEA J114724.10−204021.3, is thought to be an exceptionally low-mass "brown dwarf," which is a star that lacked enough mass to burn nuclear fuel and glow like a star. Astronomers using data from NASA's WISE and 2MASS sky surveys found the object in TW Hydrae – a young, 10-million-year-old association of stars. Image Credits: NASA/JPL-Caltech.

WISEA 1147 is one of the few free-floating worlds where astronomers can begin to point to its likely origins as a brown dwarf and not a planet. Because the object was found to be a member of the TW Hydrae family of very young stars, astronomers know that it is also very young -- only 10 million years old. And because planets require at least 10 million years to form, and probably longer to get themselves kicked out of a star system, WISEA 1147 is likely a brown dwarf. Brown dwarfs form like stars but lack the mass to fuse atoms at their cores and shine with starlight.

"With continued monitoring, it may be possible to trace the history of WISEA 1147 to confirm whether or not it formed in isolation," said Adam Schneider of the University of Toledo in Ohio, lead author of a new study accepted for publication in The Astrophysical Journal.

Of the billions of possible free-floating worlds thought to populate our galaxy, some may be very low-mass brown dwarfs, while others may in fact be bona fide planets, kicked out of nascent solar systems. At this point, the fraction of each population remains unknown. Tracing the origins of free-floating worlds, and determining whether they are planets or brown dwarfs, is a difficult task, precisely because they are so isolated.

"We are at the beginning of what will become a hot field – trying to determine the nature of the free-floating population and how many are planets versus brown dwarfs," said co-author Davy Kirkpatrick of NASA's Infrared Processing and Analysis Center, or IPAC, at the California Institute of Technology in Pasadena.

Astronomers found WISEA 1147 by sifting through images taken of the entire sky by WISE, in 2010, and 2MASS, about a decade earlier. They were looking for nearby, young brown dwarfs. One way to tell if something lies nearby is to check to see if it's moved significantly relative to other stars over time. The closer an object, the more it will appear to move against a backdrop of more distant stars. By analyzing data from both sky surveys taken about 10 years apart, the close objects jump out.

Finding low-mass objects and brown dwarfs is also well suited to WISE and 2MASS, both of which detect infrared light. Brown dwarfs aren't bright enough to be seen with visible-light telescopes, but their heat signatures light up when viewed in infrared images.

Image above: A sky map taken by NASA's Wide-field Infrared Survey Explorer, or WISE, shows the location of the TW Hydrae family, or association, of stars, which lies about 175 light-years from Earth and is centered in the Hydra constellation. The stars are thought to have formed together around 10 million years ago. Recently, data from WISE and its predecessor, the Two Micron All Sky Survey, or 2MASS, found the lowest-mass free-floating object in this family -- a likely brown dwarf called WISEA J114724.10−204021.3. Image Credits: NASA/JPL-Caltech.

The brown dwarf WISEA 1147 was brilliantly "red" in the 2MASS images (where the color red had been assigned to longer infrared wavelengths), which means that it's dusty and young.

"The features on this one screamed out, 'I'm a young brown dwarf,'" said Schneider.

After more analysis, the astronomers realized that this object belongs to the TW Hydrae association, which is about 150 light-years from Earth and only about 10 million years old. That makes WISEA 1147, with a mass between about five and 10 times that of Jupiter, one of the youngest and lowest-mass brown dwarfs ever found.

Interestingly, a second, very similar low-mass member of the TW Hydrae association was announced just days later (2MASS 1119-11) by a separate group led by Kendra Kellogg of Western University in Ontario, Canada.

Another reason that astronomers want to study these isolated worlds is that they resemble planets but are easier to study. Planets around other stars, called exoplanets, are barely perceptible next to their brilliant stars. By studying objects like WISEA 1147, which has no host star, astronomers can learn more about their compositions and weather patterns.

"We can understand exoplanets better by studying young and glowing low-mass brown dwarfs," said Schneider. "Right now, we are in the exoplanet regime."

Other authors of the study include: James Windsor and Michael Cushing of the University of Toledo; and Ned Wright of UCLA, who was also the principal investigator of the WISE mission.

NASA's Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA's Science Mission Directorate in Washington. The spacecraft was put into hibernation mode in 2011, after it scanned the entire sky twice, completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.

The 2MASS mission was a joint effort between the California Institute of Technology, Pasadena; the University of Massachusetts, Amherst; and JPL. Caltech manages JPL for NASA.

WISE, NEOWISE and 2MASS data are archived at IPAC.

For more information about WISE (Wide-field Infrared Survey Explorer), visit: http://www.nasa.gov/mission_pages/WISE/main/index.html

Images (mentioned), Text, Credits: NASA/Tony Greicius/JPL/Whitney Clavin.

Greetings, Orbiter.ch

Venus Express' swansong experiment sheds light on Venus' polar atmosphere

ESA - Venus Express Mission patch.

19 April 2016

Some of the final results sent back by ESA's Venus Express before it plummeted down through the planet's atmosphere have revealed it to be rippling with atmospheric waves – and, at an average temperature of -157°C, colder than anywhere on Earth.

Venus Express aerobraking. Credit: ESA - C. Carreau

As well as telling us much about Venus' previously-unexplored polar regions and improving our knowledge of our planetary neighbour, the experiment holds great promise for ESA's ExoMars mission, which is currently winging its way to the Red Planet. The findings were published in the journal Nature Physics on 11 April 2016.

ESA's Venus Express arrived at Venus in 2006. It spent eight years exploring the planet from orbit, vastly outliving the mission's planned duration of 500 days, before running out of fuel. The probe then began its descent, dipping further and further into Venus' atmosphere, before the mission lost contact with Earth (November 2014) and officially ended (December 2014).

However, Venus Express was industrious to the end; low altitude orbits were carried out during the final months of the mission, taking the spacecraft deep enough to experience measurable drag from the atmosphere. Using its onboard accelerometers, the spacecraft measured the deceleration it experienced as it pushed through the planet's upper atmosphere – something known as aerobraking.

Venus Express aerobraking. Image Credit: ESA - C. Carreau

"Aerobraking uses atmospheric drag to slow down a spacecraft, so we were able to use the accelerometer measurements to explore the density of Venus' atmosphere," said Ingo Müller-Wodarg of Imperial College London, UK, lead author of the study. "None of Venus Express' instruments were actually designed to make such in-situ atmosphere observations. We only realised in 2006 – after launch! – that we could use the Venus Express spacecraft as a whole to do more science."

When Müller-Wodarg and colleagues gathered their observations Venus Express was orbiting at an altitude of between 130 and 140 kilometres near Venus' polar regions, in a portion of Venus' atmosphere that had never before been studied in situ.

Previously, our understanding of Venus' polar atmosphere was based on observations gathered by NASA's Pioneer Venus probe in the late 1970s. These were of other parts of Venus' atmosphere, near the equator, but extrapolated to the poles to form a complete atmospheric reference model.

These new measurements, taken as part of the Venus Express Atmospheric Drag Experiment (VExADE) from 24 June to 11 July 2014, have now directly tested this model – and reveal several surprises.

Graphic above: Density profiles of Venus' polar atmosphere. Credit: Figure courtesy of I. Müller-Wodarg (Imperial College London, UK).

For one, the polar atmosphere is up to 70 degrees colder than expected, with an average temperature of -157°C (114 K). Recent temperature measurements by Venus Express' SPICAV instrument (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus) are in agreement with this finding.

The polar atmosphere is also not as dense as expected; at 130 and 140 km in altitude, it is 22% and 40% less dense than predicted, respectively. When extrapolated upward in the atmosphere, these differences are consistent with those measured previously by VExADE at 180 km, where densities were found to be lower by almost a factor of two.

"This is in-line with our temperature findings, and shows that the existing model paints an overly simplistic picture of Venus' upper atmosphere," added Müller-Wodarg. "These lower densities could be at least partly due to Venus' polar vortices, which are strong wind systems sitting near the planet's poles. Atmospheric winds may be making the density structure both more complicated and more interesting!"

Additionally, the polar region was found to be dominated by strong atmospheric waves, a phenomenon thought to be key in shaping planetary atmospheres – including our own.

"By studying how the atmospheric densities changed and were perturbed over time, we found two different types of wave: Atmospheric gravity waves and planetary waves," explained co-author Sean Bruinsma of the Centre National D'Etudes Spatiales (CNES), France. "These waves are tricky to study, as you need to be within the atmosphere of the planet itself to measure them properly. Observations from afar can only tell us so much."

Image above: Mapping the density waves in Venus' lower thermosphere. Credit: ESA/Venus Express/VExADE/Müller-Wodarg et al., 2016.

Atmospheric gravity waves are similar to waves we see in the ocean, or when throwing stones in a pond, only they travel vertically rather than horizontally. They are essentially a ripple in the density of a planetary atmosphere – they travel from lower to higher altitudes and, as density decreases with altitude, become stronger as they rise. The second type, planetary waves, are associated with a planet's spin as it turns on its axis; these are larger-scale waves with periods of several days.

We experience both types on Earth. Atmospheric gravity waves interfere with weather and cause turbulence, while planetary waves can affect entire weather and pressure systems. Both are known to transfer energy and momentum from one region to another, and so are likely to be hugely influential in shaping the characteristics of a planetary atmosphere.

"We found atmospheric gravity waves to be dominant in Venus' polar atmosphere," added Bruinsma. "Venus Express experienced them as a kind of turbulence, a bit like the vibrations you feel when an aeroplane flies through a rough patch. If we flew through Venus' atmosphere at those heights we wouldn't feel them because the atmosphere just isn't dense enough, but Venus Express' instruments were sensitive enough to detect them."

Venus Express found atmospheric waves at an altitude of 130-140 km that the team think originated from the upper cloud layer in Venus' atmosphere, which sits at and below altitudes of approximately 90 km, and a planetary wave that oscillated with a period of five days. "We checked carefully to ensure that the waves weren't an artefact of our processing," said co-author Jean-Charles Marty, also of CNES.

This is not just a first for Venus Express; while the aerobraking technique has been used for Earth satellites, and was previously used on NASA-led missions to Mars and Venus, it had never before been used on any ESA planetary mission.

However, ESA's ExoMars Trace Gas Orbiter, which launched earlier this year, will use a similar technique. "During this activity we will extract similar data about Mars' atmosphere as we did at Venus," added Håkan Svedhem, project scientist for ESA's ExoMars 2016 and Venus Express missions.

"For Mars, the aerobraking phase would last longer than on Venus, for about a year, so we'd get a full dataset of Mars' atmospheric densities and how they vary with season and distance from the Sun," added Svedhem. "This information isn't just relevant to scientists; it's crucial for engineering purposes as well. The Venus study was a highly successful test of a technique that could now be applied to Mars on a larger scale – and to future missions after that."

Background information:

The findings were published in a paper entitled "In situ observations of waves in Venus' polar lower thermosphere with Venus Express aerobraking" by Muller-Wodarg et al., in Nature Physics on 11 April 2016 (doi: 10.1038/NPHYS3733):
http://dx.doi.org/10.1038/nphys3733

Venus Express is Europe's first mission to Venus. It was launched from Baikonur Cosmodrome on 9 November 2005 on a Soyuz-Fregat launcher, and was inserted into Venus orbit on 11 April 2006. The payload includes a combination of spectrometers, spectro-imagers, and imagers covering a wavelength range from ultraviolet to thermal infrared, a plasma analyser and a magnetometer. Between May and July 2014, an aerobraking campaign was performed with Venus Express – the first performed by an ESA spacecraft – resulting in unique observations of the planet's rarefied outer atmosphere and a change in the spacecraft's orbital period from 24 hours to 22 hours 20 minutes.

Science highlights from the Venus Express mission can be found here: http://sci.esa.int/venus-express/54062-1-shape-shifting-polar-vortices/

Related links:

ESA's ExoMars Trace Gas Orbiter: http://exploration.esa.int/mars/46475-trace-gas-orbiter/

ESA's ExoMars: http://exploration.esa.int/

Related article:

Venus Express goes gently into the night:
http://orbiterchspacenews.blogspot.ch/2014/12/venus-express-goes-gently-into-night.html

For more information about Venus Express mission, visit: http://www.esa.int/Our_Activities/Space_Science/Venus_Express

Images, Text, Credits: ESA/Håkan Svedhem/CNES/Sean Bruinsma/Jean-Charles Marty/Blackett Laboratory, Imperial College London, UK/Ingo Müller-Wodarg.

Greetings, Orbiter.ch

15 years of Europe on the International Space Station

ESA - European Space Agency International patch / NASA - STS-100 Mission patch.

19 April 2016

On 23 April 2001, Italian ESA Umberto Guidoni made history as the first European astronaut to board the International Space Station.

Guidoni had been launched on four days earlier, on 19 April, on Space Shuttle Endeavour as part of its seven-strong STS-100 crew from Kennedy Space Centre, with a liftoff at 20:41 CEST.

The 11-day STS-100 mission was the ninth Shuttle visit to the Space Station and would feature two space walks. The Shuttle docked with the International Space Station some 260 km above Earth on 21 April. The hatches between Endeavour and the Space Station were opened another two days later, on 23 April, allowing the Shuttle crew and Station occupants to greet one another for the first time.

Guidoni and his six colleagues were delivering elements and equipment required for the ongoing assembly of the International Space Station. In particular, the Shuttle carried the Raffaello Multi-Purpose Logistics Module (MPLM), provided by the Italian space agency ASI, as well as the Space Station Remote Manipulator System, the Canadian robotic arm that would be used extensively to assemble the Space Station over the coming years.

Launch STS-100

Guidoni’s specific role on STS-100 was as ‘loadmaster’ in charge of MPLM logistical operations, overseeing the activation and deactivation of Raffaello and, in a backup role, helping to operate the Shuttle's robotic arm during the spacewalks.

Endeavour also boosted the Space Station’s altitude and performed a fly-around survey of the Station, including recording views with an IMAX camera in the Shuttle’s cargo bay. All objectives were completed without incident, and the Shuttle returned safely to Earth on 1 May 2001. During this mission, astronaut Chris Hadfield made the first spacewalk by a Canadian.

Since Guidoni’s flight, there have been another 16 Europeans staying for a cumulative total of over 1400 days on the orbiting outpost.

Umberto Guidoni, the first European astronaut to fly to the ISS, 2001

ESA astronaut Roberto Vittori (IT) became the first European to make second and third visits to the Station. Frank De Winne (BE), André Kuipers (NL), Paolo Nespoli (IT) and Christer Fuglesang (SE) have all made second visits.

The first ESA astronaut to stay on board in an expedition was Thomas Reiter (DE) in 2006. Tim Peake (GB) is currently serving on a six-month long-duration mission.

Related links:

Guidoni makes history as first European astronaut on Space Station: http://www.esa.int/About_Us/Welcome_to_ESA/Guidoni_makes_history_as_first_European_astronaut_on_Space_Station

Related news:

First European astronaut visits the International Space Station: http://www.esa.int/About_Us/Welcome_to_ESA/First_European_astronaut_visits_the_International_Space_Station

ISS astronauts need to be versatile:
http://www.esa.int/Our_Activities/Human_Spaceflight/Astronauts/ISS_astronauts_need_to_be_versatile

Images, Text, Credit: European Space Agency (ESA).

Best regards, Orbiter.ch

NASA's SDO Captures Images of a Mid-Level Solar Flare

NASA - Solar Dynamics Observatory (SDO) patch.

April 18, 2016

The sun emitted a mid-level solar flare, peaking at 8:29 pm EDT on April 17, 2016. NASA’s Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel.

Animation above: NASA's Solar Dynamics Observatory captured this imagery of a solar flare – as seen in the bright flash – around 8:30 p.m. EDT on April 17, 2016. A loop of solar material can also be seen rising up off the right limb of the sun. Animation Credits: NASA/SDO/Goddard.

NOAA's Space Weather Prediction Center states that "moderate radio blackouts were observed" during the peak of the flare. Such radio blackouts are only ongoing during the course of a flare, and so they have since subsided. NOAA's Space Weather Prediction Center is the U.S. government's official source for space weather forecasts, watches, warnings and alerts.

This flare is classified as an M6.7 class flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

Image above: A black spot on the sun is visible in the upper right of this image captured by NASA's Solar Dynamics Observatory. Such spots are evidence that this is an area of complex magnetic activity on the sun, which can sometimes lead to solar eruptions sending light and radiation out into space. This region produced a solar flare at 8:29 p.m. EDT on April 17, 2016. Image Credits: NASA/SDO/Goddard.

This flare came from an area of complex magnetic activity on the sun – known as an active region, and in this case labeled Active Region 2529 – which has sported a large dark spot, called a sunspot, over the past several days. This sunspot has changed shape and size as it slowly made its way across the sun’s face over the past week and half. For much of that time, it was big enough to be visible from the ground without magnification and is currently large enough that almost five Earths could fit inside. This sunspot will rotate out of our view over the right side of the sun by April 20, 2016.  Scientists study such sunspots in order to better understand what causes them to sometimes erupt with solar flares.

What is a solar flare?

For answers to this and other space weather questions, please visit the Space weather Frequently Asked Questions page: http://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html

Related Links:

NOAA's Space Weather Prediction Center: http://spaceweather.gov/

View Past Solar Activity: http://www.nasa.gov/mission_pages/sunearth/solar-events-news/index.html

For more information about Solar Dynamics Observatory (SDO), visit: http://www.nasa.gov/mission_pages/sdo/main/index.html

Image (mentioned), Animation (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Karen C. Fox/Rob Garner.

Greetings, Orbiter.ch

NASA's Fermi Telescope Poised to Pin Down Gravitational Wave Sources

NASA Fermi Gamma-ray Space Telescope logo.

April 18, 2016

On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA's Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light.

Visualisation of Merging Black Holes and Gravitational Waves

Video above: This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun’s mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its "ringdown" phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA's Ames Research Center. Video Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC).

“This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers,” said Valerie Connaughton, a GBM team member at the National Space, Science and Technology Center in Huntsville, Alabama, and lead author of a paper on the burst now under review by The Astrophysical Journal.

Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi's GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

Image above: This image, taken in May 2008 as the Fermi Gamma-ray Space Telescope was being readied for launch, highlights the detectors of its Gamma-ray Burst Monitor (GBM). The GBM is an array of 14 crystal detectors. Image Credits: NASA/Jim Grossmann.

With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together. These same systems also are suspected to be prime producers of gravitational waves.

"With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB," said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. "There is an incredible synergy between the two observations, with gamma rays revealing details about the source's energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event." He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.  

“That's a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that’s what our instrument is designed to do," said Eric Burns, a GBM team member at the University of Alabama in Huntsville. "A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack." 

Fermi and LIGO Hone in on Gravity Wave Source

Video above: Fermi's GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections. Image Credits: NASA's Goddard Space Flight Center.

Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position.      

The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi's view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible.

The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

NASA Fermi Gamma-ray Space Telescope. Image Credit: NASA

Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Related links:

Laser Interferometer Gravitational-Wave Observatory (LIGO): https://www.ligo.caltech.edu/

Science paper: http://arxiv.org/abs/1602.03920

For more information about NASA's Fermi Gamma-ray Space Telescope, please visit: http://www.nasa.gov/fermi

Images (mentioned), Videos (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Francis Reddy/Ashley Morrow.

Greetings, Orbiter.ch

Comets ISON & PanSTARRS: Comets in the "X"-Treme

NASA - Chandra X-ray Observatory logo.

April 18, 2016

For millennia, people on Earth have watched comets in the sky. Many ancient cultures saw comets as the harbingers of doom, but today scientists know that comets are really frozen balls of dust, gas, and rock and may have been responsible for delivering water to planets like Earth billions of years ago.

While comets are inherently interesting, they can also provide information about other aspects of our Solar System. More specifically, comets can be used as laboratories to study the behavior of the stream of particles flowing away from the Sun, known as the solar wind.

Recently, astronomers announced the results of a study using data collected with NASA's Chandra X-ray Observatory of two comets -- C/2012 S1 (also known as "Comet ISON") and C/2011 S4 ("Comet PanSTARRS").

Image above: The Comets ISON and PanSTARRS in optical images taken by an astrophotographer, with insets showing the X-ray images from Chandra. Images Credits: X-ray: NASA/CXC/Univ . of CT/B.Snios et al, Optical: DSS, Damian Peach (damianpeach.com).

Chandra observed these two comets in 2013 when both were relatively close to Earth, about 90 million and 130 million miles for Comets ISON and PanSTARRS respectively. These comets arrived in the inner Solar System after a long journey from the Oort cloud, an enormous cloud of icy bodies that extends far beyond Pluto's orbit.

The graphics show the two comets in optical images taken by an astrophotographer, Damian Peach, from the ground during the comets' close approach to the sun that have been combined with data from the Digitized Sky Survey to give a larger field of view. (The greenish hue of Comet ISON is attributed to particular gases such as cyanogen, a gas containing carbon and nitrogen, escaping from the comet's nucleus.)

The insets show the X-rays detected by Chandra from each comet. The different shapes of the X-ray emission (purple) from the two comets indicate differences in the solar wind at the times of observation and the atmospheres of each comet. Comet ISON, on one hand, shows a well-developed, parabolic shape, which indicates that the comet had a dense gaseous atmosphere. On the other hand, Comet PanSTARRS has a more diffuse X-ray haze, revealing an atmosphere with less gas and more dust.

Scientists have determined that comets produce X-ray emission when particles in the solar wind strike the atmosphere of the comet. Although most of the particles in the solar wind are hydrogen and helium atoms, the observed X-ray emission is from "heavy" atoms (that is, elements heavier than hydrogen and helium, such as carbon and oxygen). These atoms, which have had most of their electrons stripped away, collide with neutral atoms in the comet's atmosphere. In a process called "charge exchange," an electron is exchanged between one of these neutral atoms, usually hydrogen, and a heavy atom in the solar wind. After such a collision, an X-ray is emitted as the captured electron moves into a tighter orbit.

The Chandra data allowed scientists to estimate the amount of carbon and nitrogen in the solar wind, finding values that agree with those derived independently using other instruments such as NASA's Advanced Composition Explorer (ACE). New measurements of the amount of neon in the solar wind were also obtained.

The detailed model developed to analyze the Chandra data on comets ISON and PanSTARRS demonstrates the value of X-ray observations for deriving the composition of the solar wind. The same techniques can be used, together with Chandra data, to investigate interactions of the solar wind with other comets, planets, and the interstellar gas.

Chandra X-ray Observatory. Image Credits: NASA/CXC

A paper describing these results appeared in February 20th, 2016 issue of The Astrophysical Journal and is available online: http://arxiv.org/abs/1601.06622. The authors are Bradford Snios and Vasili Kharchenko (University of Connecticut), Carey Lisse (Johns Hopkins University), Scott Wolk (Harvard-Smithsonian Center for Astrophysics), Konrad Dennerl (Max Planck Institute for Extraterrestrial Physics) and Michael Combi (University of Michigan).

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

Read More from NASA's Chandra X-ray Observatory: http://chandra.si.edu/photo/2016/comets/

For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra

Images (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Molly Porter/Chandra X-ray Center/Megan Watzke.

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