A Natural Law for Rotating Galaxies… What Does This Mean for Dark Matter?

An image of the nearby galaxy Messier 81, created with data from NASA's Spitzer Space Telescope.

Distant galaxies, black holes, exotics worlds…these are not just the stuff of science fiction; they are also the stuff that makes up our reality. Our quest to understand the universe is thrilling, challenging, and often confusing. Even the basic question “What is the universe made of?” isn’t easy to answer.

Adding new pieces to this puzzle, researchers from Case Western Reserve University and the University of Oregon recently discovered a natural law for rotating galaxies. Their surprising result is the subject of a new paper coming out later this week in Physical Review Letters that could have serious implications for the theory of dark matter.

The planets in our solar system rotate around the sun because of gravity. In the early 1600s, astronomer Johannes Kepler worked out a mathematical relationship between a planet’s distance from the sun and its orbital period, the time it takes to go completely around the sun. This is known as Kepler’s third law of planetary motion, and it reveals that planets farther from the sun travel around it with slower speeds. Isaac Newton later generalized Kepler’s law for all orbital systems.

There’s a problem though. The law doesn’t appear to hold for stars orbiting the centre of their galaxy. Astronomer Vera Rubin highlighted this discrepancy in the 1970s and since then, astronomers have verified time and again that stars on the outskirts of a galaxy rotate around the centre at the same speed as stars closer the centre. This result gave rise to the idea that galaxies have a halo of dark matter. If this is the case, stars do follow Newton’s law once the missing mass, made up of dark matter, is accounted for.

In this new research, work by astronomers Stacy McGaugh and Federico Lelli (Case Western) and Jim Schombert (Oregon) reveals that galaxies obey a natural law just like planets. It’s just not the same one.

The missing mass problem is the result of a difference in how we expect stars within a galaxy to behave and the way that they actually behave. Instead of assuming that these two should match, McGaugh, Lelli, and Schombert compared the observed orbital speed of stars within a galaxy (described by their radial velocity) to the predicted value that assumes what you see is what you get—no dark matter. Then they looked at the relationship between these results for a large number of galaxies.

Their work relied on data from NASA’s Spitzer Space Telescope, a space-based observatory that studies objects in infrared light. Over the years Spitzer has observed many types of galaxies, collecting information on how gas and stars are distributed within them. This information can be used to estimate the visible mass of a galaxy, which can be used to predict the radial velocity of its stars. Using 2,693 data points from 153 very different galaxies, the researchers modelled the radial velocity based on the visible mass of each galaxy.

Next, the scientists graphed these results against observed, published results of radial velocity for the same galaxies. When they got to that point, says McGaugh, “There was the result on the screen: Far better than we had ever hoped. It just fell right out.” There was a clear mathematical relationship between the observed radial velocity of a star in a galaxy to the distribution of visible matter.

If dark matter ultimately dominates the mass of galaxies, as many scientists think, then there’s no reason to assume that the amount of visible matter should be directly related to the amount of dark matter. But that’s just what this work implies. If two galaxies with very different properties have the same distribution of visible mass, the observed radial acceleration is the same. If you know one, you know the other. Not only is this surprising, it’s a big deal.

The authors suggest that their result can be explained in three ways.

1.It represents the end product of galaxy formation.
2.It represents new "dark sector" physics.
3.It is the result of new dynamical laws rather than dark matter.

None of these explanations are completely satisfying, say the authors. Their paper doesn’t go into the details, but it falls right in the middle of an ongoing discussion about the validity of the dark matter model. This work demonstrates a regularity in the data, says McGaugh. “How you interpret that is a whole 'nother can o' worms.” There’s no doubt that scientists will be elbow deep in that can before long.

—Kendra Redmond

NASA-funded science rocket discovers mysterious X-ray emissions in space

It’s a new mystery for astronomers: About a quarter of the high-energy X-rays picked up by the NASA-funded DXL sounding rocket on its most recent 15-minute flight must have come from somewhere else, and we don’t know where that somewhere might be.

Let’s step back and explain what’s going on first. A sounding rocket (also called a research rocket) is a rocket designed to take measurements and perform experiments in sub-orbital flights. DXL is short for Diffuse X-ray emission from the Local galaxy, which is exactly what the rocket was sent to measure. On this run, the instrument solved a longstanding question about the origins of the dim X-ray fog blanketing the entire sky. Evidence it collected confirms predictions that our solar system is moving through a region called the Local Hot Bubble, which may have been blasted clear by supernova explosions during the past 20 million years.

In addition to confirming the LHB, the rocket’s readings show the relative contribution of the solar wind and the LHB to the sum total of X-rays in the fog: about 40% of the observed X-rays come from the solar wind, and we find those mostly along the ecliptic. The LHB accounts for most of the rest. But DXL also found some high-energy X-band photons whose origins are still unexplained.

“We think that around 10 million years ago, a supernova exploded and ionized the gas of the Local Hot Bubble,” said study co-author Massimiliano Galeazzi. “But one supernova wouldn’t be enough to create such a large cavity and reach these temperatures — so it was probably two or three supernova over time, one inside the other.”

The high-energy X-rays, though, are too high-energy to have come from either the solar wind or the LHB, even in the wake of double or triple supernovae. “These sources contribute less than a quarter of the X-ray emission,” said lead author Youaraj Uprety. “So there’s an unknown source of X-rays in this energy range.”

To get the best readings on solar wind versus interstellar helium, DXL waited to launch this mission until Earth was passing through the sun’s helium-focusing cone. The helium-focusing cone is comparable with the sun’s wake: a region of space “behind” the sun, with respect to its axis of travel, where neutral helium from the LHB is much denser than in the rest of the inner solar system.

“The solar system is moving through interstellar space at about 15 miles per second,” said Uprety. “This space is filled with hydrogen and helium. The helium is a little heavier, so it carves around the sun to form a tail.” DXL flew right into that tail and took readings to figure out just where the X-rays it picked up had come from. Our galaxy has lots of neutral gas that would absorb X-rays coming from distant sources — meaning that these X-rays must originate somewhere near our solar system. At the same time, there’s nothing nearby that looks responsible; the LHB just isn’t hot enough to produce X-ray emissions at those energies, said Uprety.

“So we’re left with an open question on the source of these X-rays,” he said.

ESO's dust buster reveals hidden stars

In this new image of the nebula Messier 78, young stars cast a bluish pall over their surroundings, while red fledgling stars peer out from their cocoons of cosmic dust. To our eyes, most of these stars would be hidden behind the dust, but ESO's Visible and Infrared Survey Telescope for Astronomy (VISTA) sees near-infrared light, which passes right through dust. The telescope is like a giant dust buster that lets astronomers probe deep into the heart of the stellar environment.

Click on the images to enlarge

Messier 78, or M78, is a well-studied example of a reflection nebula. It is located approximately 1600 light-years away in the constellation of Orion (The Hunter), just to the upper left of the three stars that make up the belt of this familiar landmark in the sky. In this image, Messier 78 is the central, bluish haze in the centre; the other reflection nebula towards the right goes by the name of NGC 2071. The French astronomer Pierre Méchain is credited with discovering Messier 78 in 1780. However, it is today more commonly known as the 78th entry in French astronomer Charles Messier's catalogue, added to it in December of 1780.

M78 RA:  00h 00m 51.6s   DEC:+00° 05'  36"    Magnitude +8.3

When observed with visible light instruments, like ESO's Wide Field Imager at the La Silla Observatory, Messier 78 appears as a glowing, azure expanse surrounded by dark ribbons (see eso1105). Cosmic dust reflects and scatters the light streaming from the young, bluish stars in Messier 78's heart, the reason it is known as a reflection nebula.

The dark ribbons are thick clouds of dust that block the visible light originating behind them. These dense, cold regions are prime locations for the formation of new stars. When Messier 78 and its neighbours are observed in the submillimetre light between radio waves and infrared light, for example with the Atacama Pathfinder Experiment (APEX) telescope, they reveal the glow of dust grains in pockets just barely warmer than their extremely cold surroundings (see eso1219). Eventually new stars will form out of these pockets as gravity causes them to shrink and heat up.

In between visible and submillimetre light lies the near-infrared part of the spectrum, where the Visible and Infrared Survey Telescope for Astronomy (VISTA) provides astronomers with crucial information. Beyond dusty reflections and through thinner portions of obscuring material, the luminous stellar sources within Messier 78 are visible to VISTA's eyes. In the centre of this image, two blue supergiant stars, called HD 38563A and HD 38563B, shine brightly. Towards the right of the image, the supergiant star illuminating NGC 2071, called HD 290861, is also seen.

Besides big, blue, hot stars, VISTA can also see many stars that are just forming within the cosmic dust strewn about this region, their reddish and yellow colours shown clearly in this image. These colourful fledgling stars can be found in the dust bands around NGC 2071 and along the trail of dust running towards the left of the image. Some of these are T Tauri stars. Although relatively bright, they are not yet hot enough for nuclear fusion reactions to have commenced in their cores. In several tens of millions of years, they will attain full "star hood," and will take their place alongside their stellar brethren lighting up the Messier 78 region.

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.

The 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.

Astronomers shed light on different galaxy types

In 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. 

Dr 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.

“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.

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

The 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

 

 

 

 

 

 

 

 

 

 

 

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.

One 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.

After 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.

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

By 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.

“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 6000ºC, 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

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

Picture postcards from Jupiter sent by NASA’s Juno probe

 

 

 

 

 

 

Please click on these images to enlarge

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

50th Anniversary of Lunar Orbiter 1 Mission

Today is the 50th anniversary of the launch of the first of five lunar orbiters that returned images of 99 percent of both the near- and far-side surfaces of the moon. The orbiters sent back a total of 3,062 photos.

Lunar Orbiter 1, built by The Boeing Co., was launched Aug. 10, 1966 on an Atlas SLV-3 Agena-D rocket from Cape Canaveral in Florida. It was designed primarily to photograph smooth areas of the moon’s surface for selection of landing sites for the Surveyor and Apollo missions.

Radiation experiments on the orbiters also confirmed that the design of Apollo spacecraft hardware would protect astronauts from short-term exposure to solar particle events.

The orbiters were commanded to crash on the moon before their attitude control gas ran out so they would not be a navigational or communications hazard to Apollo flights.

The program was managed by NASA Langley Research Center in Hampton, Virginia.

Young stars in Sagittarius cluster excite astronomers

M18 – NGC 6613 | RA 18h 17m  DEC – 5 deg 09’ | Mag +7.5 | Size 7 arc minutes |

Messier 18 was discovered and catalogued in 1764 by Charles Messier — for whom the Messier Objects are named — during his search for comet-like objects. It lies within the Milky Way, approximately 4600 light-years away in the constellation of Sagittarius, and consists of many sibling stars loosely bound together in what is known as an open cluster.

There are over 1000 known open star clusters within the Milky Way, with a wide range of properties, such as size and age, that provide astronomers with clues to how stars form, evolve and die. The main appeal of these clusters is that all of their stars are born together out of the same material.

[Click on the images to enlarge]

In Messier 18 the blue and white colours of the stellar population indicate that the cluster’s stars are very young, probably only around 30 million years old. Being siblings means that any differences between the stars will only be due to their masses, and not their distance from Earth or the composition of the material they formed from. This makes clusters very useful in refining theories of star formation and evolution.

Astronomers now know that most stars do form in groups, forged from the same cloud of gas that collapsed in on itself due to the attractive force of gravity. The cloud of leftover gas and dust — or molecular cloud — that envelops the new stars is often blown away by their strong stellar winds, weakening the gravitational shackles that bind them. Over time, loosely bound stellar siblings like those pictured here will often go their separate ways as interactions with other neighbouring stars or massive gas clouds nudge, or pull, the stars apart. Our own star, the Sun, was most likely once part of a cluster very much like Messier 18 until its companions were gradually distributed across the Milky Way.

The dark lanes that snake through this image are murky filaments of cosmic dust, blocking out the light from distant stars. The contrasting faint reddish clouds that seem to weave between the stars are composed of ionised hydrogen gas. The gas glows because young, extremely hot stars like these are emitting intense ultraviolet light which strips the surrounding gas of its electrons and causes it to emit the faint glow seen in this image. Given the right conditions, this material could one day collapse in on itself and provide the Milky Way with yet another brood of stars — a star formation process that may continue indefinitely.

This mammoth 30 577 x 20 108 pixel image was captured using the OmegaCAM camera, which is attached to the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile.

Celebrate the Royal Greenwich Observatory

45 Years-ago the magnificent 28 inch refractor returned to the Royal Greenwich Observatory after a period of safe keeping. It was housed at Herstmonceux Castle for a while, then on 23 October 1971 Sir Patrick Moore was on hand to record the event for the BBC Sky at Night program.

In July I went back to the Royal Greenwich Observatory to meet the Curator Dr Louise Devoy, who was kind enough to show me around and learn something about the other telescopes their. Then I went over to see the 28 inch refractor itself. It is the 10th biggest refractor telescope in the world today, and the only one that visitors can look through on observational nights at Greenwich.

The Royal Greenwich Observatory was established in 1675 by King Charles II to find a means of measuring Longitude so mariners would not get lost at sea. The King appointed John Flamsteed as the first astronomer Royal.

The Cassini Solstice mission roles on as planet’s shadow shortens

Turning a midsummer night's dream into reality, NASA's Cassini spacecraft began its new mission extension -- the Cassini Solstice Mission – in September 2010. The mission extension takes Cassini a few months past Saturn's northern summer solstice (or midsummer) through September 2017.

A complete seasonal period on Saturn has never been studied at this level of detail.

The shadow of Saturn on the rings, which stretched across all of the rings earlier in Cassini's mission (see PIA08362), now barely makes it past the Cassini division.

The changing length of the shadow marks the passing of the seasons on Saturn. As the planet nears its northern-hemisphere solstice in May 2017, the shadow will get even shorter. At solstice, the shadow's edge will be about 28,000 miles (45,000 kilometres) from the planet's surface, barely making it past the middle of the B ring.

The moon Mimas is a few pixels wide, near the lower left in this image.

This view looks toward the sunlit side of the rings from about 35 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on May 21, 2016.

The view was obtained at a distance of approximately 2.0 million miles (3.2 million kilometres) from Saturn. Image scale is 120 miles (190 kilometres) per pixel.

Rainer Weiss wins Kavli Prize in Astrophysics

LIGO inventor shares award for direct detection of gravitational waves.

Rainer Weiss, emeritus professor of physics, is a recipient of the 2016 Kavli Prize in Astrophysics. The Kavli Prizes are awarded biennially to recognize scientists who have made seminal advances in three categories: astrophysics, nanoscience, and neuroscience.

Weiss will share the prize, including a cash award of $1 million, with Ronald Drever, emeritus professor of physics at Caltech, and Kip Thorne, Caltech’s Richard P. Feynman Professor of Theoretical Physics, emeritus. The three scientists, who are co-founders of the Laser Interferometer Gravitational-wave Observatory (LIGO), have received the prize for the direct detection of gravitational waves, according to the award citation:

“This detection has, in a single stroke and for the first time, validated Einstein’s General Theory of Relativity for very strong fields, established the nature of gravitational waves, demonstrated the existence of black holes with masses 30 times that of our sun, and opened a new window on the universe.”

On September 14, 2015, LIGO’s two interferometers — one in Washington, the other in Louisiana — picked up a signal that lasted just one-fifth of a second. For the next few months, LIGO scientists around the world would carefully analyse, verify, and verify again, to determine that this signal represented the first direct detection of gravitational waves — ripples across the universe, created by extreme cataclysmic events billions of years ago.

The scientists determined that the incredibly faint signal was produced by the spectacularly violent collision of two black holes, each about 30 times as massive as the sun, 1.3 billion light years away.

Announcing the Kavli Astrophysics recipients, in an address in Oslo, Norway, Mats Carlsson, chair of the astrophysics committee, read from the award citation:

“The detection of gravitational waves is an achievement for which hundreds of scientists, engineers, and technicians around the world share credit. Drever, Thorne, and Weiss stand out: Their ingenuity, inspiration, intellectual leadership, and tenacity were the driving force behind this epic discovery.”

Pushing for a signal

In 1972, Weiss had worked out the basic concept for an interferometer to detect gravitational waves — an idea he originally drew up as an exercise for students in his general relativity course at MIT. His concept would eventually serve as the essential blueprint for LIGO.

From LIGO’s earliest days to its most recent detection, “Weiss provided technical leadership and devoted his extraordinary experimental acumen over the next decades, contributing to every aspect of the final apparatus,” the citation reads.

In 1974, a research team led by physicists Russell Hulse and Joseph Taylor made the first detection of gravitational waves, by analysing the behaviour of two orbiting neutron stars — a detection for which the pair was awarded the Nobel Prize in physics in 1993. The detection, however, was not a direct one.

In 1975, Weiss and Thorne met for the first time at a NASA committee meeting in Washington, D.C., where they began to think about how Weiss’ interferometer design could be scaled up to make a direct detection of gravitational waves. Since the 1960s, Thorne had been evaluating how extreme events such as colliding black holes and neutron stars generate gravitational waves, and how those waves might be detected from Earth.

Weiss and Thorne pushed the concept of LIGO through numerous hurdles in funding and design, and eventually oversaw the observatory’s construction, in the form of two identical and massive instruments, each 4 kilometres long and 3,000 kilometres apart.

In 1979, Drever joined the team as the third co-founder of LIGO, and helped to perfect the design and operation of the interferometers, devising ways to increase the power and efficiency of the optical systems central to LIGO’s sensitivity.

“For the first time in history we can explore the universe’s mysteries in three regimes: electromagnetic, particle, and gravitational regime,” said France Córdova, director of the National Science Foundation, who spoke as part of the awards announcement.

“Humming with signals”

Weiss received his BS in 1955 and his PhD in 1962, both from MIT. After appointments at Tufts University and Princeton University, Weiss returned to MIT as a faculty member in 1964. He has also served as an adjunct professor of physics at Louisiana State University since 2011. Weiss is a co-founder and science advisor of the NASA Cosmic Background Explorer (COBE) satellite mission, which measured the spectrum of cosmic microwave background radiation supporting the Big Bang scenario. 

Weiss has received numerous awards and honours, including the 2003 Medaille de l’ADION, the 2006 Gruber Prize in Cosmology, and the 2007 Einstein Prize of the American Physical Society. He is a fellow of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, and the American Physical Society, as well as a member of the National Academy of Sciences. Earlier this year, Weiss received a Special Breakthrough Prize in Fundamental Physics and the 2016 Gruber Prize in Cosmology, both shared with Drever and Thorne. Most recently, the three co-founders were also awarded the Shaw Prize in Astronomy.

Today, Weiss and Thorne watched a live broadcast of the Kavli Prize announcement from New York, as part of the World Science Festival. As their names were announced, the pair, who are close friends, shared a hug, to a standing ovation.

In a panel held after the Kavli Prize announcement to discuss the significance of each Kavli Prize, Nergis Malvalvala, who is the Curtis and Kathleen Marble Professor of Astrophysics and associate head of the Department of Physics at MIT, a LIGO team member, and a former student of Weiss’, said of LIGO’s future: “We have so much still to do. We’ve really just uncovered the very first signal. The universe is humming with signals we have yet to pick up.”

NASA peers inside a rocket plume imaged for the first time

You’ve never truly seen what a rocket plume looks like. They are extremely bright and therefore, have never been photographed properly and unless you want to stare directly into one, it’ll be nearly impossible to imagine. Although that’s difficult, considering there haven’t been cameras that could capture its image before.

However, NASA unveiled a new camera during its recent space launch test, which is able to show the detail in a rocket plume. And it looks pretty spectacular.

Normally cameras can’t properly capture something like a rocket plume. You can fiddle with the exposure settings, but reducing them darkens the rest of the image. Most cameras also only record one exposure at a time.

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However, the new High Dynamic Range Stereo X (HiDyRS-X) project overcomes this by being able to record multiple slow motion exposures at once and combining them into a more high-quality video. It uses a similar technique to what night photographers use when they splice multiple images together in post to get an impressive image.

The photo below is of the plume taken without the camera, so you can clearly see the difference.

Photo credit: NASA

According to a statement from NASA, scientists tried out the camera while testing its booster, QM-2. They monitored the camera from a safe distance, but its automatic timer failed to go off, meaning scientists had to start it manually.

And apparently, the force of the booster test was so great that it disconnected the camera’s power source. So NASA got confirmation that its camera works, but also that its rocket is very powerful.

Currently, this is just a prototype. Scientists plan to build a second one with more advanced capabilities, including with alignment. We’re looking forward to seeing more amazing photos, NASA! Don’t keep us waiting.

Comet Panstarrs X1 is a spectacle in the celestial hare

2016 July 24 18h04m UT, FLI PL16200, ASA 12" f/3.6. LRGB 8/4/4/4 min., Farm Tivoli, Namibia, Remote © 2016 Gerald Rhemann

Despite being rather faint, Mag 12, Panstarrs X1 is putting on a nice show for observers in the southern hemisphere. The comet is in the constellation of Hydra and lies close to the stat Pi Hydrae.

On 14 August the comet can be found at:

RA 14h 19m 52.7s DEC –29 53’ 08”

The above photograph was taken on the night of 24 July 2016 when Panstarrs X1 was in the constellation of Centaurus.

The Night Sky for 15 August

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This is the night sky at 10pm for the middle of August. The Summer Triangle is prominent, it is made up from the bright stars Deneb in Cygnus, Vega in Lyra, and Altair in Aquila the eagle. The constellations of Autumn are now rising in the East, so the great Andromeda galaxy (M31) is on display for binocular observers. Scan across the Milky Way and you will many nice star clusters, and in the constellation of Hercules try to view the bright globular cluster (M13). Click on the image for more detailed information about the planets & constellations now on view in The Sky at Night.

A postcard from Dawn: Liber crater

Another postcard from NASA’s Dawn spacecraft.

This view features Liber Crater (14 miles, 23 kilometres wide) in Ceres' northern hemisphere, at right.

Dawn took this image on June 17, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 kilometres) above the surface. The image resolution is 120 feet (35 meters) per pixel.

Image Credit: NASA/JPL Caltech/UCLA/MPS/DLR/IDA

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In the next program of Astronomy & Space we will be looking at the Asteroids of the solar system. Including NASA's new asteroid-sampling mission OSIRIS-REx. It will be available to watch from 29 August.

Scientists discover Ceres to be an icy ‘slush ball’ in space

The minor planet Ceres is the largest of the Minor planets, situated in the large gap between the planets Mars & Jupiter. It is 427 miles in diameter and takes just over 4 1/2 years to orbit around the Sun.

NASA’s Dawn spacecraft has been in orbit around Ceres for the last year taking hundreds of photographs, and making careful science observations.

Since gravity dominates Dawn's orbit at Ceres, scientists can measure variations in Ceres’ gravity by tracking subtle changes in the motion of the spacecraft. Using data from Dawn, scientists have mapped the variations in Ceres' gravity for the first time in a new study in the journal Nature, which provides clues to the dwarf planet's internal structure.

"The new data suggest that Ceres has a weak interior, and that water and other light materials partially separated from rock during a heating phase early in its history," said Ryan Park, the study’s lead author and the supervisor of the solar system dynamics group at NASA’s Jet Propulsion Laboratory, Pasadena, California.

Ceres' gravity field is measured by monitoring radio signals sent to Dawn, and then received back on Earth, by NASA’s Deep Space Network. This network is a collection of large antennas at three locations around the globe that communicate with interplanetary spacecraft. Using these signals, scientists can measure the spacecraft's speed to a precision of 0.004 inches (0.1 millimetres) per second, and then calculate the details of the gravity field.

Ceres has a special property called "hydrostatic equilibrium," which was confirmed in this study. This means that Ceres' interior is weak enough that its shape is governed by how it rotates. Scientists reached this conclusion by comparing Ceres' gravity field to its shape. Ceres' hydrostatic equilibrium is one reason why astronomers classified the body as a dwarf planet in 2006.

The data indicate that Ceres is “differentiated,” which means that it has compositionally distinct layers at different depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less dense than Earth, the moon, giant asteroid Vesta (Dawn’s previous target) and other rocky bodies in our solar system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the study shows separated from the rocky material and rose to the outer layer along with other light materials.

"We have found that the divisions between different layers are less pronounced inside Ceres than the moon and other planets in our solar system," Park said. “Earth, with its metallic core, semi-fluid mantle and outer crust, has a more clearly defined structure than Ceres," Park said.

Scientists also found that high-elevation areas on Ceres displace mass in the interior. This is analogous to how a boat floats on water: the amount of displaced water depends on the mass of the boat. Similarly, scientists conclude that Ceres’ weak mantle can be pushed aside by the mass of mountains and other high topography in the outermost layer as though the high-elevation areas "float" on the material below. This phenomenon has been observed on other planets, including Earth, but this study is the first to confirm it at Ceres.

The internal density structure, based on the new gravity data, teaches scientists about what internal processes could have occurred during the early history of Ceres. By combining this new information with previous data from Dawn about Ceres' surface composition, they can reconstruct that history: Water must have been mobile in the ancient subsurface, but the interior did not heat up to the temperatures at which silicates melt and a metallic core forms.

"We know from previous Dawn studies that there must have been interactions between water and rock inside Ceres," said Carol Raymond, a co-author and Dawn’s deputy principal investigator based at JPL. "That, combined with the new density structure, tells us that Ceres experienced a complex thermal history."

The 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 sulphur dioxide gas that can extend up to 300 miles (480 kilometres) 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 sulphur 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 sulphur dioxide gas settles as frost on the moon’s surface. The atmosphere redevelops as the surface warms once the moon returns to full sunlight.

“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 kilometres) 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.