First Signs of Self-interacting Dark Matter?

ESO - European Southern Observatory logo.

15 April 2015

Dark matter may not be completely dark after all

Hubble image of the galaxy cluster Abell 3827

For the first time dark matter may have been observed interacting with other dark matter in a way other than through the force of gravity. Observations of colliding galaxies made with ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have picked up the first intriguing hints about the nature of this mysterious component of the Universe.

Using the MUSE instrument on ESO’s VLT in Chile, along with images from Hubble in orbit, a team of astronomers studied the simultaneous collision of four galaxies in the galaxy cluster Abell 3827. The team could trace out where the mass lies within the system and compare the distribution of the dark matter with the positions of the luminous galaxies.

Although dark matter cannot be seen, the team could deduce its location using a technique called gravitational lensing. The collision happened to take place directly in front of a much more distant, unrelated source. The mass of dark matter around the colliding galaxies severely distorted spacetime, deviating the path of light rays coming from the distant background galaxy — and distorting its image into characteristic arc shapes.

Hubble image of galaxy cluster Abell 3827 showing dark matter distribution

Our current understanding is that all galaxies exist inside clumps of dark matter. Without the constraining effect of dark matter’s gravity, galaxies like the Milky Way would fling themselves apart as they rotate. In order to prevent this, 85 percent of the Universe’s mass [1] must exist as dark matter, and yet its true nature remains a mystery.

In this study, the researchers observed the four colliding galaxies and found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. The dark matter is currently 5000 light-years (50 000 million million kilometres) behind the galaxy — it would take NASA’s Voyager spacecraft 90 million years to travel that far.

A lag between dark matter and its associated galaxy is predicted during collisions if dark matter interacts with itself, even very slightly, through forces other than gravity [2]. Dark matter has never before been observed interacting in any way other than through the force of gravity.

Lead author Richard Massey at Durham University, explains: “We used to think that dark matter just sits around, minding its own business, except for its gravitational pull. But if dark matter were being slowed down during this collision, it could be the first evidence for rich physics in the dark sector — the hidden Universe all around us.”

Hubble view of the galaxy cluster Abell 3827

The researchers note that more investigation will be needed into other effects that could also produce a lag. Similar observations of more galaxies, and computer simulations of galaxy collisions will need to be made.

Team member Liliya Williams of the University of Minnesota adds: “We know that dark matter exists because of the way that it interacts gravitationally, helping to shape the Universe, but we still know embarrassingly little about what dark matter actually is. Our observation suggests that dark matter might interact with  forces other than gravity, meaning we could rule out some key theories about what dark matter might be.”

This result follows on from a recent result from the team which observed 72 collisions between galaxy clusters [3] and found that dark matter interacts very little with itself. The new work however concerns the motion of individual galaxies, rather than clusters of galaxies. Researchers say that the collision between these galaxies could have lasted longer than the collisions observed in the previous study — allowing the effects of even a tiny frictional force to build up over time and create a measurable lag [4].

Taken together, the two results bracket the behaviour of dark matter for the first time. Dark matter interacts more than this, but less than that. Massey added: “We are finally homing in on dark matter from above and below — squeezing our knowledge from two directions.”

Notes:

[1]  Astronomers have found that the total mass/energy content of the Universe is split in the proportions 68% dark energy, 27% dark matter and 5% “normal” matter. So the 85% figure relates to the fraction of “matter” that is dark.

[2] Computer simulations show that the extra friction from the collision would make the dark matter slow down. The nature of that interaction is unknown; it could be caused by well-known effects or some exotic unknown force. All that can be said at this point is that it is not gravity.

All four galaxies might have been separated from their dark matter. But we happen to have a very good measurement from only one galaxy, because it is by chance aligned so well with the background, gravitationally lensed object. With the other three galaxies, the lensed images are further away, so the constraints on the location of their dark matter too loose to draw statistically significant conclusions.

[3] Galaxy clusters contain up to a thousand individual galaxies.

[4] The main uncertainty in the result is the timespan for the collision: the friction that slowed the dark matter could have been a very weak force acting over about a billion years, or a relatively stronger force acting for “only” 100 million years.

More information:

This research was presented in a paper entitled “The behaviour of dark matter associated with 4 bright cluster galaxies located in the 10 kpc core of Abell 3827” to appear in the journal Monthly Notices of the Royal Astronomical Society on 15 April 2015.

The team is composed of R. Massey (Institute for Computational Cosmology, Durham University, Durham, UK), L. Williams (School of Physics & Astronomy, University of Minnesota, Minneapolis, Minnesota, USA), R. Smit (Institute for Computational Cosmology, UK), M. Swinbank (Institute for Computational Cosmology, UK), T. D. Kitching (Mullard Space Science Laboratory, University College London, Dorking, Surrey, UK), D. Harvey (Ecole Polytechnique Fédérale de Lausanne, Observatoire de Sauverny, Versoix, Switzerland), H. Israel (Institute for Computational Cosmology, UK), M. Jauzac (Institute for Computational Cosmology, UK; Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Durban, South Africa), D. Clowe (Department of Physics and Astronomy, Ohio University, Athens, Ohio, USA), A. Edge (Department of Physics, Durham University, Durham, UK), M. Hilton (Astrophysics and Cosmology Research Unit, South Africa), E. Jullo (Laboratoire d’Astrophysique de Marseille, Université d’Aix-Marseille, Marseille, France), A. Leonard (University College London, London, UK), J. Liesenborgs (Hasselt University, Diepenbeek, Belgium), J. Merten (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA; California Institute of Technology, Pasadena, California, USA), I. Mohammed (Physik-Institüt, University of Zürich, Zürich, Switzerland), D. Nagai (Department of Physics, Yale University, New Haven, Connecticut, USA), J. Richard (Observatoire de Lyon, Université Lyon, Saint Genis Laval, France), A. Robertson (Institute for Computational Cosmology, UK), P. Saha (Physik-Institüt, Switzerland), R. Santana (Department of Physics and Astronomy, Ohio University, Athens, Ohio, USA), J. Stott (Department of Physics, Durham, UK) and E. Tittley (Royal Observatory, Edinburgh, UK).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1514/eso1514a.pdf

Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/

Related links:

MUSE instrument: http://www.eso.org/public/teles-instr/vlt/vlt-instr/muse/

ESO’s Very Large Telescope (VLT): http://www.eso.org/vlt

Hubble Space Telescope: http://www.spacetelescope.org/

Images, Text, Credits: ESO/R. Massey/ESA/NASA/Video: NASA, ESA. Music: Johan B. Monell (www.johanmonell.com).

Greetings, Orbiter.ch

Design begins for ESA's Asteroid Impact Mission

ESA - European Space Agency patch.

15 April 2015

European industry has begun work on dual concept studies to design an innovative Asteroid Impact Mission for ESA. The mission is tasked to encounter and chart a distant asteroid, and then witness it being struck by another spacecraft, returning data to help guide planetary defence strategies.

Last month saw the formal start of the Asteroid Impact Mission (AIM) preliminary design phase. Two separate industrial consortia have begun work on design concepts for the mission’s satellite platform, payload accommodation and operations systems.

AIM in orbit

“Running dual industrial contracts in parallel is a tried and tested way of encouraging as much innovation as possible,” explains Karim Mellab, AIM spacecraft manager.

“A decision will be made between the two sets of results in about 15 months, following the intermediate system requirements review.”

The chosen concept will then be presented to ESA’s Council of Ministers in November 2016 for approval.

Asteroid Impact Mission

If approved, the mission concept would then become an actual ESA mission and work can begin to translate computer-aided design drawings into bent metal and cast composite.

The two contracts cover the AIM spacecraft plus ground operations concepts. The payload instruments will be sourced from scientific institutions across ESA Member States.

“The payload is typically considered the part that does the scientific discovery,” explains Andres Galvez, AIM payload engineer.

“For AIM, however, every resource will be squeezed to the last drop including the payload, which will be put to a dual use and also support spacecraft operations, to make the most of every kilogram we take with us to the target asteroids.

AIM and Didymos binary

“This approach will also be part of an innovative set of technology demonstrations, including deep-space laser communications, for future missions.”

AIM may also host an asteroid lander, currently under study by the DLR German Aerospace Center, and two or more CubeSats, which are the subject of a separate announcement of opportunity.

“AIM is proposed to be ESA’s first mission to a small body since Rosetta,” adds Karim. “So it is an undeniably ambitious endeavour, but at the same time it needs to cost around an order of magnitude cheaper than Rosetta.”

Part of that reduced price-tag comes down to the fact that AIM will be a much shorter-lived mission than the decade-spanning Rosetta, taking only a year to cruise to its target, the binary asteroid system of Didymos and its moon.

Target: Didymoon

AIM, with a maximum mass of 800 kg at launch and about the size of a large office desk, will also be much more compact than the lorry-sized Rosetta.

The rest of the savings need to be identified in this first phase of the activity, such as applying onboard autonomy to reduce the number of personnel needed to run the mission. For instance, the spacecraft might use a telecommunication carrier beacon as a streamlined means of communicating its health status.

Contact teams

The first contract has been awarded to a consortium led by German company OHB, with Politecnico di Milano performing mission analysis, Italian company Telespazio working on the ground segment and operations and Portuguese company Spin.Works focused on the guidance and navigation aspects.

The second contract has gone to a consortium led by QinetiQ Space Belgium, with GMV in Spain taking on responsibility for guidance and navigation.

Mapping Didymoon

“Guidance and navigation is a crucial part of the mission design,” comments Karim. “First, the spacecraft needs to find its way across 480 million km of space to its target asteroid. Then it needs to perform visual reckoning to manoeuvre around the Didymos system, employing a limited quantity of propellant.”

Whichever design is chosen, the mission needs to be launched in October 2020 to make the launch window to catch the asteroid and its moon.

Joint endeavour

AIM must be in position before late 2022 when NASA’s Double Asteroid Redirection Test, or DART, is planned to crash into the asteroid’s moon for detailed before-and-after impact monitoring.  These observations will help determine how far the DART kinetic impactor has moved the asteroid moon.

The two missions together are components of an international collaboration on an asteroid-deflection demonstration mission called the Asteroid Impact & Deflection Assessment (AIDA).

Asteroid collision

“AIDA is an exciting and economical concept for a mission to demonstrate multiple technologies and techniques that would provide high-value asteroid science and benefit planetary defense planning,” says Lindley Johnson, NASA’s Near-Earth Object Program Executive.

”We are delighted that ESA has completed their AIM Pre-Phase-A study, and decided to officially move on to Phase-A concept definition. Our own DART mission is scheduled to initiate its Phase-A study in a few months.”

The combined mission concepts of AIM and DART would make the joint AIDA mission the world’s first attempt to demonstrate that international space agencies working together could protect the Earth from an asteroid impact.

Related links:

ESA’s planetary defence test set for 2020: http://www.esa.int/Our_Activities/Space_Engineering_Technology/ESA_s_planetary_defence_test_set_for_2020

Asteroid Impact & Deflection Assessment mission: http://www.esa.int/Our_Activities/Space_Engineering_Technology/Asteroid_Impact_Mission/Asteroid_Impact_Deflection_Assessment_mission

AIDA science community: https://www-n.oca.eu/michel/AIDA/

OHB: https://www.ohb-system.de/

Politecnico di Milano: http://www.polimi.it/

Telespazio: http://www.telespazio.it/

Spin.Works: http://www.spinworks.pt/

QinetiQ Space: http://www.qinetiq.be/

GMV: http://www.gmv.com/

NASA Near-Earth Object Program: http://neo.jpl.nasa.gov/

Images, Text, Credits: ESA/Science Office.

Best regards, Orbiter.ch

Research for One-Year Space Station Mission Among NASA Cargo Launched Aboard SpaceX Resupply Flight

SpaceX - Falcon 9/Dragon CRS-6 patch.

April 14, 2015

Liftoff! Dragon on its Way to Station

Research that will help prepare NASA astronauts and robotic explorers for future missions to Mars is among the two tons of cargo now on its way to the International Space Station aboard SpaceX's Dragon spacecraft. Dragon launched on a Falcon 9 rocket at 4:10 p.m. EDT Tuesday, April 14 from Space Launch Complex 40 at Cape Canaveral Air Force Station. At 7 a.m. EDT on Friday, April 17, the Dragon spacecraft will catch up to the orbiting laboratory, where the Expedition 43 crew will capture it with the station's robotic arm.

Liftoff of SpaceX CRS-6

“Five years ago this week, President Obama toured the same SpaceX launch pad used today to send supplies, research and technology development to the ISS,” said NASA Administrator Charles Bolden. “Back then, SpaceX hadn’t even made its first orbital flight. Today, it’s making regular flights to the space station and is one of two American companies, along with The Boeing Company, that will return the ability to launch NASA astronauts to the ISS from U.S. soil and land then back in the United States. That’s a lot of progress in the last five years, with even more to come in the next five.”

The mission is the company's sixth cargo delivery flight to the station through NASA’s Commercial Resupply Services contract. Dragon's cargo will support approximately 40 of the more than 250 science and research investigations that will be performed during Expeditions 43 and 44, including numerous human research investigations for NASA astronaut Scott Kelly's one-year mission in space.

Images above: The series of images shows the journey the SpaceX Falcon 9 rocket and Dragon spacecraft from its launch at 4:10 p.m. EDT on Tuesday from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida, to solar array deployment. Image Credit: NASA TV.

Science payloads will support experiments in biology, biotechnology, physical science and Earth science -- research that improves life on Earth and drives progress for future space exploration. Investigations include:

- A study of potential methods for counteracting cell damage that occurs in a microgravity environment

The Cell Shape and Expression research program will provide for the first time a reliable experimental model able to highlight the relationships between microgravity, cell shape and gene expression, which may also inform pharmacological ways to counteract microgravity-induced cell damages.

- Research to improve understanding of bone cells, which could lead to treatments for osteoporosis and muscle wasting conditions

Osteo-4 studies the effects of microgravity on the function of osteocytes, which are the most common cells in bone. These cells reside within the mineralized bone and can sense mechanical forces, or the lack of them, but researchers do not know how. Osteo-4 allows scientists to analyze changes in the physical appearance and genetic expression of mouse bone cells in microgravity.

- Continued studies into astronaut vision changes

Dragon also will deliver hardware to support an ongoing one-year crew study known as Fluid Shifts. More than half of American astronauts experience vision changes and alterations to parts of their eyes during and after long-duration spaceflight. The Fluid Shifts investigation measures how much fluid shifts from the lower body to the upper body, in or out of cells and blood vessels, and determines the impact these shifts have on fluid pressure in the head and changes in vision and eye structures.

- Tests on a new material that could one day be used as a synthetic muscle for robotics explorers of the future

Robots can perform tasks too repetitive, difficult or dangerous for humans. Robots built with synthetic muscle would have more human-like capabilities, but the material would have to withstand the rigors of space. This investigation tests the radiation resistance of an electroactivepolymer called Synthetic Muscle, developed by RasLabs, which can contract and expand like real muscles.

The spacecraft also will deliver hardware needed for the installation of two International Docking Adapters scheduled for delivery on future SpaceX missions. Once installed, these adapters will enable commercial crew spacecraft to dock to the space station.

 SpaceX CRS-6 Dragon Spacecraft Separation

ESA (European Space Agency) astronaut Samantha Cristoforetti will use the space station's robotic arm to grapple Dragon to the station at 7 a.m. Friday, April 17. Expedition 43 Commander Terry Virts of NASA will assist.

After about five weeks, Dragon will depart the space station for a splashdown in the Pacific Ocean west of Baja California. The capsule will return more than 3,000 pounds of science, hardware, crew supplies and spacewalk tools.

The International Space Station is a convergence of science, technology and human innovation that enables us to demonstrate new technologies and make research breakthroughs not possible on Earth. It has been continuously occupied since November 2000 and, since then, has been visited by more than 200 people and a variety of international and commercial spacecraft. The ISS remains the springboard to NASA's next giant leap in exploration, including future missions to an asteroid and Mars.

SpaceX Dragon space Cargo. Image Credits: NASA/SpaceX

The Dragon spacecraft is on its own in orbit and operating with its arrays deployed as planned. Next stop, the International Space Station where Flight Engineer and European Space Agency Astronaut Samantha Cristoforetti and Expedition 43 Commander Terry Virts will use the station’s 57.7-foot robotic arm to reach out and capture it as they operate from the station’s cupola. Arrival is set for Friday at 7 a.m. EDT.

For more information about International Space Station science and research, visit: http://www.nasa.gov/mission_pages/station/main/index.html

For more information about the SpaceX resupply mission, visit: http://www.nasa.gov/spacex

Images (mentioned), Videos, Text, Credits: NASA/Stephanie Schierholz/Johnson Space Center/Dan Huot/SpaceX.

Greetings, Orbiter.ch

NASA's Spitzer Spots Planet Deep Within Our Galaxy

NASA - Spitzer Space Telescope logo.

April 14, 2015

NASA's Spitzer Space Telescope. Image Credits: NASA/JPL-Caltech

NASA's Spitzer Space Telescope has teamed up with a telescope on the ground to find a remote gas planet about 13,000 light-years away, making it one of the most distant planets known.

The discovery demonstrates that Spitzer -- from its unique perch in space -- can be used to help solve the puzzle of how planets are distributed throughout our flat, spiral-shaped Milky Way galaxy. Are they concentrated heavily in its central hub, or more evenly spread throughout its suburbs?

"We don't know if planets are more common in our galaxy's central bulge or the disk of the galaxy, which is why these observations are so important," said Jennifer Yee of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, and a NASA Sagan fellow. Yee is the lead author of one of three new studies that appeared recently in the Astrophysical Journal describing a collaboration between astronomers using Spitzer and the Polish Optical Gravitational Lensing Experiment, or OGLE.

Image above: This artist's map of the Milky Way shows the location of one of the farthest known exoplanets, lying 13,000 light-years away. Most of the thousands of exoplanets discovered to date are closer to our solar system, as indicated by the pink/orange areas. Image Credit: NASA/JPL-Caltech.

OGLE's Warsaw Telescope at the Las Campanas Observatory in Chile scans the skies for planets using a method called microlensing. A microlensing event occurs when one star happens to pass in front of another, and its gravity acts as a lens to magnify and brighten the more distant star's light. If that foreground star happens to have a planet in orbit around it, the planet might cause a blip in the magnification.

Astronomers are using these blips to find and characterize planets tens of thousands of light-years away in the central bulge of our galaxy, where star crossings are more common. Our sun is located in the suburbs of the galaxy, about two-thirds of the way out from the center. The microlensing technique as a whole has yielded about 30 planet discoveries so far, with the farthest residing about 25,000 light-years away.

"Microlensing experiments are already detecting planets from the solar neighborhood to almost the center of the Milky Way," said co-author Andrew Gould of The Ohio State University, Columbus. "And so they can, in principle, tell us the relative efficiency of planet formation across this huge expanse of our galaxy."

Microlensing complements other planet-hunting tools, such as NASA's Kepler mission, which has found more than 1,000 planets closer to home. But it faces one key problem: This method can't always precisely narrow down the distance to the stars and planets being observed. While a passing star may magnify the light of a more distant star, it rarely can be seen itself, making the task of measuring how far away it is challenging.

Image above: This plot shows data obtained from NASA's Spitzer Space Telescope and the Optical Gravitational Lensing Experiment, or OGLE, telescope located in Chile, during a "microlensing" event. Image Credit: NASA/JPL-Caltech/Warsaw University Observatory.

Of the approximately 30 planets discovered with microlensing so far, roughly half cannot be pinned down to a precise location. The result is like a planetary treasure map lacking in X's.

That's where Spitzer can help out, thanks to its remote Earth-trailing orbit. Spitzer circles our sun, and is currently about 128 million miles (207 million kilometers) away from Earth. That's father from Earth than Earth is from our sun. When Spitzer watches a microlensing event simultaneously with a telescope on Earth, it sees the star brighten at a different time, due to the large distance between the two telescopes and their unique vantage points. This technique is generally referred to as parallax.

"Spitzer is the first space telescope to make a microlens parallax measurement for a planet," said Yee. "Traditional parallax techniques that employ ground-based telescopes are not as effective at such great distances."

Using space telescopes to observe microlensing events is tricky. Ground telescopes send out alerts to the astronomy community when an event starts, but the activity can quickly fade, lasting on average about 40 days. The Spitzer team has scrambled to start microlensing campaigns as soon as three days after receiving an alert.

In the case of the newfound planet, the duration of the microlensing event happened to be unusually long, about 150 days. Both Spitzer and OGLE's telescopes detected the telltale planetary blip in the magnification, with Spitzer seeing it 20 days earlier.

Image above: This infographic explains how NASA's Spitzer Space Telescope can be used in tandem with a telescope on the ground to measure the distances to planets discovered using the "microlensing" technique. Image Credit: NASA/JPL-Caltech.

This time delay between viewing of the event by OGLE and Spitzer was used to calculate the distance to the star and its planet. Knowing the distance allowed the scientists also to determine the mass of the planet, which is about half that of Jupiter.

Spitzer has eyed 22 other microlensing events in collaboration with OGLE and several other ground-based telescopes. While these observations have not turned up new planets, the data are essential to learning the population statistics of stars and planets at the heart of our galaxy. Spitzer will watch approximately 120 additional microlensing events this summer.

"We've mainly explored our own solar neighborhood so far," said Sebastiano Calchi Novati, a Visiting Sagan Fellow at NASA's Exoplanet Science Institute at the California Institute of Technology, Pasadena. "Now we can use these single lenses to do statistics on planets as a whole and learn about their distribution in the galaxy."

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer

Images (mentioned), Text, Credits: NASA/Felicia Chou/JPL/Whitney Clavin.

Greetings, Orbiter.ch

Rosetta and Philae find comet not magnetised

ESA - Rosetta Mission patch.

14 April 2015

Measurements made by Rosetta and Philae during the probe’s multiple landings on Comet 67P/Churyumov-Gerasimenko show that the comet’s nucleus is not magnetised.

Studying the properties of a comet can provide clues to the role that magnetic fields played in the formation of Solar System bodies almost 4.6 billion years ago. The infant Solar System was once nothing more than a swirling disc of gas and dust but, within a few million years, the Sun burst into life in the centre of this turbulent disc, with the leftover material going into forming the asteroids, comets, moons and planets.

Rosetta and Philae investigate magnetic properties of Comet 67P/C-G

The dust contained an appreciable fraction of iron, some of it in the form of magnetite. Indeed, millimetre-sized grains of magnetic materials have been found in meteorites, indicating their presence in the early Solar System.

This leads scientists to believe that magnetic fields threading through the proto-planetary disc could have played an important role in moving material around as it started to clump together to form larger bodies.

But it remains unclear as to how crucial magnetic fields were later on in this accretion process, as the building blocks grew to centimetres, metres and then tens of metres across, before gravity started to dominate when they grew to hundreds of metres and kilometres in scale.

Some theories concerning the aggregation of magnetic and non-magnetic dust particles show that the resulting bigger objects could also remain magnetised, allowing them to also be influenced by the magnetic fields of the proto-planetary disc.

Because comets contain some of the most pristine materials in the Solar System, they offer a natural laboratory for investigating whether or not these larger chunks could have remained magnetised.

However, detecting the magnetic field of comets has proven difficult in previous missions, which have typically made rapid flybys, relatively far from comet nuclei.

It has taken the proximity of ESA’s Rosetta orbiter to Comet 67P/Churyumov-Gerasimenko, and the measurements made much closer to and at the surface by its lander Philae, to provide the first detailed investigation of the magnetic properties of a comet nucleus.

Reconstructing Philae’s trajectory

Philae’s magnetic field measuring instrument is the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP), while Rosetta carries a magnetometer as part of the Rosetta Plasma Consortium suite of sensors (RPC-MAG).

Changes in the magnetic field surrounding Rosetta allowed RPC-MAG to detect the moment when Philae was deployed in the morning of 12 November 2014.

Then, by sensing periodic variations in the measured external magnetic field and motions in its boom arm, ROMAP was able to detect the touchdown events and determine the orientation of Philae over the following hours. Combined with information from the CONSERT experiment that provided an estimate of the final landing site location, timing information, images from Rosetta’s OSIRIS camera, assumptions about the gravity of the comet, and measurements of its shape, it was possible to determine Philae’s trajectory.

The mission teams soon discovered that Philae not only touched down once at Agilkia, but also came into contact with the comet’s surface four times in fact – including a grazing collision with a surface feature that sent it tumbling towards the final touchdown point at Abydos.

This complex trajectory turned out to be scientifically beneficial to the ROMAP team.

“The unplanned flight across the surface actually meant we could collect precise magnetic field measurements with Philae at the four points we made contact with, and at a range of heights above the surface,” says Hans-Ulrich Auster, co-principal investigator of ROMAP and lead author of the results published in the journal Science and presented at the European Geosciences Union General Assembly in Vienna, Austria, today.

The non-magnetic comet

The multiple descents and ascents meant that the team could compare measurements made on the inward and outward journeys to and from each contact point, and as it flew across the surface.

ROMAP measured a magnetic field during these sequences, but found that its strength did not depend on the height or location of Philae above the surface. This is not consistent with the nucleus itself being responsible for that field.

“If the surface was magnetised, we would have expected to see a clear increase in the magnetic field readings as we got closer and closer to the surface,” explains Hans-Ulrich.  “But this was not the case at any of the locations we visited, so we conclude that Comet 67P/Churyumov-Gerasimenko is a remarkably non-magnetic object.”

Instead, the magnetic field that was measured was consistent with an external one, namely the influence of the solar wind interplanetary magnetic field near the comet nucleus.  This conclusion is confirmed by the fact that variations in the field that were measured by Philae closely agree with those seen at the same time by Rosetta.

“During Philae’s landing, Rosetta was about 17 km above the surface, and we could provide complementary magnetic field readings that rule out any local magnetic anomalies in the comet’s surface materials,” says Karl-Heinz Glassmeier, principal investigator of RPC-MAG on board the orbiter and a co-author of the Science paper.

If large chunks of material on the surface of 67P/Churyumov-Gerasimenko were magnetised, ROMAP would have recorded additional variations in its signal as Philae flew over them.

“If any material is magnetised, it must be on a scale of less than one metre, below the spatial resolution of our measurements. And if Comet 67P/Churyumov-Gerasimenko is representative of all cometary nuclei, then we suggest that magnetic forces are unlikely to have played a role in the accumulation of planetary building blocks greater than one metre in size,” concludes Hans-Ulrich.

“It’s great to see the complementary nature of Rosetta and Philae’s measurements, working together to answer this simple, but important ‘yes-no’ question as to whether the comet is magnetised,” says Matt Taylor, ESA’s Rosetta project scientist.

Notes for Editors:

“The non-magnetic nucleus of Comet 67P/Churyumov-Gerasimenko,” by H.-U. Auster et al. is published in Science Express on 14 April.

The results were also presented on 14 April at the European Geosciences Union (EGU) General Assembly 2015 in Vienna, Austria, during a dedicated Rosetta mission press briefing.

The data were collected by the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP) on board Philae and the Rosetta Plasma Consortium fluxgate magnetometer (RPC-MAG) on board Rosetta.

Overall, the data show that the comet has an upper magnetic field magnitude of less than 2 nT at the cometary surface at multiple locations, with a specific magnetic moment of < 3.1 x 10–5 Am2/kg, less than known values for lunar material and meteorites measured on Earth.

About ROMAP:

ROMAP is the Rosetta Lander Magnetometer and Plasma Monitor. The contributing institutions to ROMAP are: Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Germany; Max-Planck Institut für Sonnensystemforschung, Göttingen, Germany; Hungarian Academy of Sciences Centre for Energy Research, Hungary; and Space Research Institute Graz, Austria. The co-principal investigators are Hans-Ulrich Auster (Technische Universität, Braunschweig) and István Apáthy, KFKI, Budapest, Hungary.

About RPC-MAG:

RPC-MAG one of six instruments comprising the Rosetta Plasma Consortium. The fluxgate magnetometer (RPC-MAG) is led by Karl-Heinz Glassmeier, Technische Universität, Braunschweig, Germany.

About Rosetta:

Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta’s Philae lander was provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta is the first mission in history to rendezvous with a comet. It is escorting the comet as they orbit the Sun together. Philae landed on the comet on 12 November 2014. Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission should become the key to unlocking the history and evolution of our Solar System.

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

More about...

Rosetta overview: http://www.esa.int/Our_Activities/Space_Science/Rosetta_overview

Rosetta factsheet: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_factsheet

Frequently asked questions: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions

For the media:

Rosetta Media press kit: http://sci.esa.int/rosetta/54816-press-kit---12-november-2014---landing-on-a-comet/

Rosetta Media factsheet: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_Media_factsheet

Rosetta Media Pages: http://www.esa.int/For_Media/Photos/Highlights/Rosetta_and_Philae

In depth:

Rosetta in depth: http://sci.esa.int/rosetta

Related links:

Rosetta at Astrium: http://www.astrium.eads.net/en/programme/rosetta-1go.html

Rosetta at DLR: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10394/

Ground-based comet observation campaign: http://www.rosetta-campaign.net/home

Images, Text, Credits: ESA/Markus Bauer, ESA Science and Robotic Exploration Communication Officer/Hans-Ulrich Auster, ROMAP principal investigator, Technische Universität, Braunschweig/Karl-Heinz Glassmeier, RPC-MAG principal investigator, Technische Universität, Braunschweig/Matt Taylor, ESA Rosetta project scientist/Data: Auster et al. (2015)/Spacecraft: ESA/ATG medialab/Comet image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/Background comet image: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

Best regards, Orbiter.ch

NASA-funded Study Explains Saturn's Epic Tantrums

NASA - Cassini Mission to Saturn patch.

April 14, 2015

Image above: This series of images from NASA's Cassini spacecraft shows the development of a huge storm of the type that erupts about every 30 years on Saturn. Credit: NASA/JPL-Caltech/SSI.

The long-standing mystery of why Saturn seethes with enormous storms every 30 years may have been solved by scientists working with data from NASA's Cassini mission. The tempests, which can grow into bright bands that encircle the entire planet, are on a natural timer that is reset by each subsequent storm, the researchers report.

In 140 years of telescope observations, great storms have erupted on Saturn six times. Cassini and observers on Earth tracked the most recent of these storms from December 2010 to August 2011. During that time, the storm exploded through the clouds, eventually winding its way around Saturn.

In a paper published online today in the journal Nature Geoscience, scientists describe the effect they believe is responsible for the periodic outbursts. The basic idea is that water vapor is heavier than the hydrogen and helium that make up the bulk of Saturn's atmosphere, so once each giant storm dumps its huge mass of rain, the air within the clouds is left lighter than the atmosphere below. For a time, this situation shuts off the process of convection -- in which warm, moist air rises, and cool, dense air sinks -- that creates new clouds and storms.

"For decades after one of these storms, the warm air in Saturn's deep atmosphere is too wet, and too dense, to rise," said Cheng Li, a graduate student at the California Institute of Technology in Pasadena, who led the study. "The air above has to cool off, radiating its heat to space, before its density is greater than that of the hot, wet air below. This cooling process takes about 30 years, and then come the storms."

Li thinks the episodic nature of the storms indicates Saturn's deep atmosphere contains more water, relative to the other atmospheric constituents, than Jupiter. The researchers suggest Saturn's extra-wet interior might explain why the planet has such epic tantrums, whereas Jupiter does not. If Saturn's deep atmosphere were drier, scientists would expect continuous, smaller storms, as observed on Jupiter, Li said. Instead, Saturn's outbursts are episodic and quite explosive.

Cassini spacecraft. Image Credits: NASA/JPL-Caltech

Other observations by ground and space-based telescopes have hinted at a wet interior for Saturn. "Previous studies using spectroscopy have shown that Saturn's interior is enriched in methane and other volatiles, by two or three times, compared to Jupiter. From there, it's a short leap to expect that Saturn is also rich in oxygen, which is also a volatile and a big part of every H2O molecule," said Andrew Ingersoll, a member of the Cassini science team, also at Caltech, who co-authored the paper with Li. Volatiles are elements and chemical compounds that change from solid to liquid or gas at relatively low temperatures.

Scientists are interested in understanding the amount of oxygen and other volatile ingredients in Saturn and Jupiter. These ingredients provide important clues about the formation of the two planets -- which are thought to have formed before all the others -- and conditions in the early solar system.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL, a division of Caltech, manages the mission for NASA's Science Mission Directorate in Washington.

For previous news and images related to Saturn's giant storm: http://go.nasa.gov/1H89e3p

For more information about Cassini, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov and http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Images (mentioned), Text, Credits: NASA/JPL/Preston Dyches.

Best regards, Orbiter.ch

Unable to live on this planet

Exoplanet Science logo.

April 13, 2015

The exoplanet HD189733, located 63 light-years from Earth, has hellish weather conditions, according to a study.

Artist's view of the exoplanet HD189733b

Astronomers from the Universities of Geneva (UNIGE) and Berne have closely studied the atmosphere of the exoplanet HD189733b, thanks to new measurement techniques. Their findings were unveiled Monday. On this planet, it is 3000 degrees and altitude winds to several thousand km/h.

These infernal weather could be measured by combining both approaches. One is based on the HARPS spectrometer and the other on a new way of interpreting the signal emitted by the sodium in the atmosphere, said in a statement the University of Geneva.

Hot and Stormy at High Altitudes on Exoplanet HD 189733b

According to the alma mater Geneva, this study opens "the way to exploring the atmospheres of exoplanets with more accessible tools that giant or space telescopes." It led to publications in journals "Astronomy & Astrophysics" and "Astrophysical Journal Letters".

The exoplanet HD189733b is 63 light years from Earth in the constellation Vulpecula. studies of this planet by the Universities of Geneva and Bern were conducted as part of the national research center PlanetS.

Related links:

Universities of Geneva (UNIGE) http://www.unige.ch/

Astronomical Observatory of Geneva http://www.unige.ch/sciences/astro/fr/
English: http://www.unige.ch/sciences/astro/en/

HARPS: http://obswww.unige.ch/Instruments/HARPS/

NCCR PlanetS: http://exoplanets.ch/nccr-planets/

Images, Tex, Credits: ATS/Universities of Geneva (UNIGE)/Orbiter.ch Aerospace.

Cheers, Orbiter.ch