26 Sep 2016

Hubble Spots Water Plumes Erupting on Jupiter's Moon Europa

Astronomers using NASA's Hubble Space Telescope have imaged what may be water vapour plumes erupting off the surface of Jupiter's moon Europa. This finding bolsters other Hubble observations suggesting the icy moon erupts with high-altitude water vapour plumes.

The observation increases the possibility that missions to Europa may be able to sample Europa's ocean without having to drill through miles of ice.

"Europa's ocean is considered to be one of the most promising places that could potentially harbour life in the solar system," said Geoff Yoder, acting associate administrator for NASA's Science Mission Directorate in Washington, D.C.. "These plumes, if they do indeed exist, may provide another way to sample Europa's subsurface."

The plumes are estimated to rise about 125 miles (200 kilometres) before, presumably, raining material back down onto Europa's surface. Europa has a huge global ocean containing twice as much water as Earth's oceans, but it is protected by a layer of extremely cold and hard ice of unknown thickness. The plumes provide a tantalizing opportunity to gather samples originating from under the surface without having to land or drill through the ice.

hs-2016-33-b-web_printThe team, led by William Sparks of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, observed these finger-like projections while viewing Europa's limb as the moon passed in front of Jupiter.

The original goal of the team's observing proposal was to determine whether Europa has a thin, extended atmosphere, or exosphere. Using the same observing method that detects atmospheres around planets orbiting other stars, the team also realized if there was water vapour venting from Europa's surface, this observation would be an excellent way to see it.

"The atmosphere of an extrasolar planet blocks some of the starlight that is behind it," Sparks explained. "If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter."

In 10 separate occurrences spanning 15 months, the team observed Europa passing in front of Jupiter. They saw what could be plumes erupting on three of these occasions.

This work provides supporting evidence for water plumes on Europa. In 2012, a team led by Lorenz Roth of Southwest Research Institute in San Antonio, Texas, detected evidence for water vapour erupting from the frigid south polar region of Europa and reaching more than 100 miles (160 kilometres) into space. Although both teams used Hubble's Space Telescope Imaging Spectrograph (STIS) instrument, each used a totally independent method to arrive at the same conclusion.

"When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it's pretty similar to what Roth and his team found," Sparks said. "The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work."

But as of yet, the two teams have not simultaneously detected the plumes using their independent techniques. Observations thus far have suggested the plumes could be highly variable, meaning that they may sporadically erupt for some time and then die down. For example, observations by Roth's team within a week of one of the detections by Sparks' team failed to detect any plumes.

If confirmed, Europa would be the second moon in the solar system known to have water vapour plumes. In 2005, NASA's Cassini orbiter detected jets of water vapour and dust spewing off the surface of Saturn's moon Enceladus.

Scientists may use the infrared vision of the James Webb Space Telescope, which is scheduled to launch in 2018, to confirm venting or plume activity on Europa. NASA also is formulating a mission to Europa with a payload that could confirm the presence of plumes and study them from close range during multiple flybys.

"Hubble's unique capabilities enabled it to capture these plumes, once again demonstrating Hubble's ability to make observations it was never designed to make," said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington, D.C. "This observation opens up a world of possibilities, and we look forward to future missions — such as the James Webb Space Telescope — to follow-up on this exciting discovery."

The work by Sparks and his colleagues will be published in the Sept. 29 issue of The Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

22 Sep 2016

Astronomers shed light on different galaxy types

Stephans-Quintet-500x313In research published today, Australian scientists have taken a critical step towards understanding why different types of galaxies exist throughout the Universe.

The research, made possible by cutting-edge AAO instrumentation, means that astronomers can now classify galaxies according to their physical properties rather than human interpretation of a galaxy’s appearance.

For the past 200 years, telescopes have been capable of observing galaxies beyond our own galaxy, the Milky Way.

Only a few were visible to begin with but as telescopes became more powerful, more galaxies were discovered, making it crucial for astronomers to come up with a way to consistently group different types of galaxies together.

In 1926, the famous American astronomer Edwin Hubble refined a system that classified galaxies into categories of spiral, elliptical, lenticular or irregular shape. This system, known as the Hubble sequence, is the most common way of classifying galaxies to this day.

Despite its success, the criteria on which the Hubble scheme is based are subjective, and only indirectly related to the physical properties of galaxies. This has significantly hampered attempts to identify the evolutionary pathways followed by different types of galaxies as they slowly change over billions of years. 

SAMIplugging-500x451Dr Luca Cortese, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said the world’s premier astronomical facilities are now producing surveys consisting of hundreds of thousands of galaxies rather than the hundreds that Hubble and his contemporaries were working with.

“We really need a way to classify galaxies consistently using instruments that measure physical properties rather than a time consuming and subjective technique involving human interpretation,” he said.

In a study led by Dr Cortese, a team of astronomers has used a technique known as Integral Field Spectroscopy to quantify how gas and stars move within galaxies and reinterpret the Hubble sequence as a physically based two-dimensional classification system.

“Thanks to the development of new technologies, we can map in great detail the distribution and velocity of different components of galaxies. Then, using this information we’re able to determine the overall angular momentum of a galaxy, which is the key physical quantity affecting how the galaxy will evolve over billions of years.

sami-classification_sml-500x375“Remarkably, the galaxy types described by the Hubble scheme appear to be determined by two primary properties of galaxies–mass and angular momentum. This provides us with a physical interpretation for the well known Hubble sequence whilst removing the subjectiveness and bias of a visual classification based on human perception rather than actual measurement.”

The new study involved 488 galaxies observed by the 3.9m Anglo Australian Telescope in New South Wales and an instrument attached to the telescope called the Sydney-AAO Multi-object Integral-field spectrograph or ‘SAMI’.

The SAMI project, led by the University of Sydney and the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), aims to create one of the first large-scale resolved survey of galaxies, measuring the velocity and distribution of gas and stars of different ages in thousands of systems.

“Australia has a lot of expertise with this type of astronomy and is really at the forefront of what’s being done,” said Professor Warrick Couch, Director of the Australian Astronomical Observatory and CAASTRO Partner Investigator.

“For the SAMI instrument we succeeded in putting 61 optical fibres within a distance that’s less than half the width of a human hair.

“That’s no small feat, it’s making this type of work possible and attracting interest from astronomers and observatories from around the world.”

Future upgrades of the instrument are planned that will allow astronomers to obtain even sharper maps of galaxies and further their understanding of the physical processes shaping the Hubble sequence.

“As we get better at doing this and the instruments we’re using are upgraded, we should be able to look for the physical triggers that cause one type of galaxy to evolve into another—that’s really exciting stuff,” Dr Cortese said.

17 Sep 2016

OSIRIS REx NASA’s mission to Bennu

Running time: 35 minutes

Acknowledgements: Damian Peach for his image of Saturn; NASA JPL the European Southern Observatory for their kind permission to use images & graphics in this month’s program.

OSIRIS REx is due to launch on 8 September to Bennu, an asteroid that is possibly on a collision course with Earth. This is NASA’s first sample return mission to study a Near Earth Asteroid.

In this month’s program we examine the European Southern Observatory’s remarkable discovery of an Earth-like planet in orbit around Proxima Centauri, our nearest star. Take a detailed look at the OSIRIS spacecraft along with its mission, and asteroids in general.

Historic first image of Pluto in X-rays

PIA21061The first detection of Pluto in X-rays has been made using NASA's Chandra X-ray Observatory in conjunction with observations from NASA's New Horizons spacecraft.

As New Horizons approached Pluto in late 2014 and then flew by the planet during the summer of 2015, Chandra obtained data during four separate observations. During each observation, Chandra detected low-energy X-rays from the small planet. The main panel in this graphic is an optical image taken from New Horizons on its approach to Pluto, while the inset shows an image of Pluto in X-rays from Chandra.

There is a significant difference in scale between the optical and X-ray images. New Horizons made a close flyby of Pluto but Chandra is located near the Earth, so the level of detail visible in the two images is very different. The Chandra image is 180,000 miles across at the distance of Pluto, but the planet is only 1,500 miles across. Pluto is detected in the X-ray image as a point source, showing the sharpest level of detail available for Chandra or any other X-ray observatory. This means that details over scales that are smaller than the X-ray source cannot be seen here.

Detecting X-rays from Pluto is a somewhat surprising result given that Pluto - a cold, rocky world without a magnetic field - has no natural mechanism for emitting X-rays. However, scientists knew from previous observations of comets that the interaction between the gases surrounding such planetary bodies and the solar wind - the constant streams of charged particles from the sun that speed throughout the solar system -- can create X-rays.

The researchers were particularly interested in learning more about the interaction between the gases in Pluto's atmosphere and the solar wind. The New Horizon spacecraft carries an instrument designed to measure that activity up-close -- Solar Wind Around Pluto (SWAP) -- and scientists examined that data and proposed that Pluto contains a very mild, close-in bow shock, where the solar wind first "meets" Pluto (similar to a shock wave that forms ahead of a supersonic aircraft) and a small wake or tail behind the planet.

The immediate mystery is that Chandra's readings on the brightness of the X-rays are much higher than expected from the solar wind interacting with Pluto's atmosphere. The Chandra detection is also surprising since New Horizons discovered Pluto's atmosphere was much more stable than the rapidly escaping, "comet-like" atmosphere that many scientists expected before the spacecraft flew past in July 2015. In fact, New Horizons found that Pluto's interaction with the solar wind is much more like the interaction of the solar wind with Mars, than with a comet. While Pluto is releasing enough gas from its atmosphere to make the observed X-rays, there isn't enough solar wind flowing directly at Pluto at its great distance from the Sun to make them according to certain theoretical models.

There are several suggested possibilities for the enhanced X-ray emission from Pluto. These include a much wider and longer tail of gases trailing Pluto than New Horizons detected using its SWAP instrument. Because Pluto is so small compared to the size of a Chandra point source, scientists may be unable to detect such a tail in X-rays. Other possibilities are that interplanetary magnetic fields are focusing more particles than expected from the solar wind into the region around Pluto, or the low density of the solar wind in the outer solar system at the distance of Pluto could allow for the formation of a doughnut, or torus, of neutral gas cantered around Pluto's orbit. It will take deeper and higher resolution images of X-rays from Pluto's environment than we currently have from Chandra to distinguish between these possibilities. 

Image Credit:
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Center/Chandra X-Ray Center
 

Ed Beshore's Rocket Ride Into the Sunset

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With the OSIRIS-REx spacecraft successfully launched and bound for the asteroid Bennu, the deputy principal investigator of the UA-led mission will retire in three weeks, and Heather Enos will take over as second in command to Dante Lauretta.

astr-1-image-16256-navcamOne week post-launch, NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft remains healthy and is on track for its two-year journey to the asteroid Bennu.  As of noon EDT Thursday, the spacecraft was approximately 2 million miles (3.2 million kilometres) from Earth, traveling at approximately 12,300 miles per hour (19,800 kilometres per hour) relative to Earth.  All of the spacecraft’s subsystems are operating as expected.

This is the first image from the OSIRIS-REx star tracker taken on Monday, Sept. 12. Similar to the way early sailors used the stars to navigate, the star tracker on OSIRIS-REx takes images of the stars and compares them to an on-board catalogue, which then tells the spacecraft navigation systems its attitude, or which way it is pointing. Credits: NASA

The OSIRIS-REx spacecraft is designed to rendezvous with, study, and return a sample of Bennu to Earth. This sample of a primitive asteroid will help scientists understand the formation of our solar system more than 4.5 billion years ago.

28902011064_f80becded5_zAfter lift-off at 7:05 p.m. EDT on Sept. 8, the United Launch Alliance Atlas V rocket performed flawlessly and positioned the OSIRIS-REx spacecraft exactly where the mission’s navigation team expected it to be. By 1:30 p.m. EDT on Sept. 9, approximately 18 1/2 hours after launch, the OSIRIS-REx spacecraft had crossed the orbital path of the moon at 240,000 miles (386,500 kilometres). By that evening, the spacecraft transitioned from launch operations into its outbound cruise phase.

On Sept. 12, OSIRIS-REx took its first image from it star tracker navigational camera, proving the system is functioning properly.  The star tracker takes images of the stars and compares them to an on-board catalogue, which then tells the spacecraft navigation systems its attitude, or which way it is pointing.

Next week, the engineers controlling the OSIRIS-REx spacecraft will conduct checkouts of the science instruments on board the spacecraft.

Goddard Space Flight Center provides overall mission management, systems engineering and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator. Lockheed Martin Space Systems in Denver built the spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the agency’s New Frontiers Program for its Science Mission Directorate in Washington.

16 Sep 2016

New spacecraft Proba-3 is set to study the Sun’s Corona

Proba-3_satellites_form_artificial_eclipse_largeBy converging in orbit, a pair of small satellites will open a new view on the source of the largest structure in the Solar System: the Sun’s ghostly atmosphere, extending millions of kilometres out into space.

The two satellites together are called Proba-3, set for launch in late 2019. Through precise formation flying, one will cast a shadow across the second to open up an unimpeded view of the inner area of the ‘corona’, which is a million times fainter than the blindingly brilliant solar disc.

“When I first heard of the idea I said ‘Wow! That’s just what we need’,” said Andrei Zhukov of the Royal Observatory of Belgium, serving as Principal Investigator for Proba-3’s solar instrument.

“The best way to observe the corona from the ground is during a solar eclipse, although we still have to cope with stray light – we cannot correct for the influence of Earth’s atmosphere. 


“The next best method is by using ‘coronagraphs’ to create an artificial eclipse, either on ground telescopes or inside Sun-watching satellites such as SOHO and Stereo.

“The problem is that stray light bending around the edge of the occulting disc limits our view of the most important inner portion of the corona. SOHO’s coronagraph, for instance, can observe no closer in than 1.1 Sun-diameters. Others can see closer, but with strong stray light making detailed observation impossible.

A_fiery_solar_explosion_node_full_image_2“With Proba-3 we aim to see extremely close to the solar surface in visible light, by flying the occulted and coronagraph on separate satellites some 150 m apart.

“This should give us a ringside seat on the most interesting segment of the corona, where a lot of interesting physics is going on, where the solar wind is born and ‘coronal mass ejections’ originate – gigantic solar eruptions with the potential to affect our terrestrial infrastructure.”

While the Sun’s surface is a comparatively cool 6000ÂșC, the corona averages a sizzling million degrees. The mystery is how energy travels from the cool Sun to the hot corona, in apparent defiance of the laws of thermodynamics.

“By mapping the fine structure of the inner corona for a prolonged time – we are targeting around six hours – our hope is that we gain insight into the kind of energy flows that are taking place,” notes Dr Zhukov. 

“Our standard observing mode will be once per minute, but we could speed that up to a few seconds within a selected field of view, for instance when tracing the rapid evolution of a mass ejection.

“The ultimate goal is to be able to solve the physics of space weather, in order to forecast coronal mass ejections, which are known to have dramatic effects on terrestrial electricity grids and other infrastructure.”

Proba-3 is first and foremost a technology demonstration, exploring the potential of precise formation flying in orbit, but achieving meaningful scientific results will also help to prove its approach works.     

Saturn, Approaching Northern Summer

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Since NASA's Cassini spacecraft arrived at Saturn in mid-2004, the planet's appearance has changed greatly. The shifting angle of sunlight as the seasons march forward has illuminated the giant hexagon-shaped jet stream around the north polar region, and the subtle bluish hues seen earlier in the mission have continued to fade. Earlier views obtained in 2004 and 2009 (see PIA06077 and PIA11667) demonstrate how drastically the illumination has changed.

This view shows Saturn's northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Saturn's year is nearly 30 Earth years long, and during its long time there, Cassini has observed winter and spring in the north, and summer and fall in the south. The spacecraft will complete its mission just after northern summer solstice, having observed long-term changes in the planet's winds, temperatures, clouds and chemistry.

Cassini scanned across the planet and its rings on April 25, 2016, capturing three sets of red, green and blue images to cover this entire scene showing the planet and the main rings. The images were obtained using Cassini's wide-angle camera at a distance of approximately 1.9 million miles (3 million kilometres) from Saturn and at an elevation of about 30 degrees above the ring plane. The view looks toward the sunlit side of the rings from a sun-Saturn-spacecraft angle, or phase angle, of 55 degrees. Image scale on Saturn is about 111 miles (178 kilometres) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute

3 Sep 2016

Picture postcards from Jupiter sent by NASA’s Juno probe

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Please click on these images to enlarge

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On 27 August the JUNO spacecraft made its first close approach to giant Jupiter, and JUNO CAM captured all these images released by NASA during the course of 2 September 2016 with more to follow.