Sculpting Solar Systems

ESO - European Southern Observatory logo.

9 November 2016

ESO’s SPHERE instrument reveals protoplanetary discs being shaped by newborn planets

Protoplanetary discs observed with SPHERE

Sharp new observations have revealed striking features in planet-forming discs around young stars. The SPHERE instrument, mounted on ESO’s Very Large Telescope, has made it possible to observe the complex dynamics of young solar systems — including one seen developing in real-time. The recently published results from three teams of astronomers showcase SPHERE’s impressive capability to capture the way planets sculpt the discs that form them — exposing the complexities of the environment in which new worlds are formed.

Three teams of astronomers have made use of SPHERE, an advanced exoplanet-hunting instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory, in order to shed light on the enigmatic evolution of fledgling planetary systems. The explosion in the number of known exoplanets in recent years has made the study of them one of the most dynamic fields in modern astronomy.

Disc around the young star RX J1615

Today it is known that planets form from vast discs of gas and dust encircling newborn stars, known as protoplanetary discs. These can extend for thousands of millions of kilometres. Over time, the particles in these protoplanetary discs collide, combine and eventually build up into planet-sized bodies. However, the finer details of the evolution of these planet-forming discs remain mysterious.

SPHERE is a recent addition to the VLT’s array of instruments and with its combination of novel technologies, it provides a powerful method to directly image the fine details of protoplanetary discs [1]. The interaction between protoplanetary discs and growing planets can shape the discs into various forms: vast rings, spiral arms or shadowed voids. These are of special interest as an unambiguous link between these structures and the sculpting planets is yet to be found; a mystery astronomers are keen to solve. Fortunately, SPHERE’s specialised capabilities make it possible for research teams to observe these striking features of protoplanetary discs directly.

Disc around the star HD 97048

For example, RX J1615 is a young star, which lies in the constellation of Scorpius, 600 light-years from Earth. A team led by the Jos de Boer, of Leiden Observatory in the Netherlands, found a complex system of concentric rings surrounding the young star, forming a shape resembling a titanic version of the rings that encircle Saturn. Such an intricate sculpting of rings in a protoplanetary disc has only been imaged a handful of times before, and even more excitingly, the entire system seems to be only 1.8 million years old. The disc shows hints of being shaped by planets still in the process of formation.

The age of the newly detected protoplanetary disc makes RX J1615 an outstanding system, as most other examples of protoplanetary discs detected so far are relatively old or evolved. De Boer’s unexpected result was quickly echoed by the findings of a team led by Christian Ginski, also of Leiden Observatory. They observed the young star HD 97048, located in the constellation of Chamaeleon, about 500 light-years from Earth. Through painstaking analysis, they found that the juvenile disc around this star has also formed into concentric rings. The symmetry of these two systems is a surprising result, as most protoplanetary systems contain a multitude of asymmetrical spiral arms, voids and vortexes. These discoveries significantly raise the number of known systems with multiple highly symmetrical rings.

Disc around the star HD 135344B

A particularly spectacular example of the more common asymmetric disc was captured by a group of astronomers led by Tomas Stolker of the Anton Pannekoek Institute for Astronomy, the Netherlands. This disc surrounds the star HD 135344B, about 450 light-years away. Although this star has been well-studied in the past, SPHERE allowed the team to see the star’s protoplanetary disc in more detail than ever before. The large central cavity and two prominent spiral arm-like structures are thought to have been created by one or multiple massive protoplanets, destined to become Jupiter-like worlds.

In addition, four dark streaks, apparently shadows thrown by the movement of material within HD 135344B's disc, were observed. Remarkably, one of the streaks noticeably changed in the months between observing periods: a rare example of observing planetary evolution occur in real time, hinting at changes occurring in the inner disc regions that can not be directly detected by SPHERE. As well as producing beautiful images, these flickering shadows provide a unique way of probing the  dynamics of innermost disc regions.

As with the concentric rings found by de Boer and Ginski, these observations by Stolker’s team prove that the complex and changing environment of the discs surrounding young stars are still capable of producing surprising new discoveries. By building an impressive body of knowledge about these protoplanetary discs, these teams are stepping closer to understanding how planets shape the discs that form them — and therefore understanding planet formation itself.

Notes:

[1] SPHERE had first light in June 2014. The instrument uses advanced adaptive optics to remove atmospheric distortion, a coronagraph to block most of the light from the central star and a combination of differential imaging and polarimetry to isolate the light from features in the disc.

More information:

The research of de Boer, Ginski and Stolker and their colleagues in the SPHERE consortium is now accepted for publication in the journal Astronomy and Astrophysics. Their papers are entitled: "Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE"; "Shadows cast on the transition disk of HD 135344B: Multi-wavelength VLT/SPHERE polarimetric differential imaging", and "Multiple rings in the transition disk and companion candidates around RX J1615.3-3255: High contrast imaging with VLT/SPHERE". All three of papers have been created in the framework of the SPHERE GTO program, led by Carsten Dominik, University of Amsterdam.

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 by Jos de Boer et al.: http://www.eso.org/public/archives/releases/sciencepapers/eso1640/eso1640a.pdf

Research paper by Christian Ginski et al.: http://www.eso.org/public/archives/releases/sciencepapers/eso1640/eso1640b.pdf

Research paper by Tomas Stolker et al.: http://www.eso.org/public/archives/releases/sciencepapers/eso1640/eso1640c.pdf

SPHERE: http://www.eso.org/public/teles-instr/vlt/vlt-instr/sphere/

Very Large Telescope (VLT): http://www.eso.org/public/teles-instr/paranal/

ESO’s Paranal Observatory: https://en.wikipedia.org/wiki/Paranal_Observatory

Images, Text, Credits: ESO/Richard Hook/Leiden University/J. de Boer et al./Anton Pannekoek Institute for Astronomy/T. Stolker et al.

Best regards, Orbiter.ch

CERN - Linac 4 reached its energy goal

CERN - European Organization for Nuclear Research logo.

November 8, 2016

Image above: Linac 4 during its installation in 2015. This photo was taken as part of the 2015 Photowalk competition (Image: Federica Piccinni/CERN).

CERN’s new linear accelerator (Linac 4) has now accelerated a beam up to its design energy, 160 MeV. This important milestone of the accelerator’s commissioning phase took place on  25 October.

Linac 4 is scheduled to become the source of proton beams for the CERN accelerator complex, including the Large Hadron Collider (LHC) after the long shutdown in 2019-2020. It will replace the existing Linac 2 as the first link in the accelerator chain, which is currently accelerating protons at 50 MeV. The new 30-metre-long accelerator will accelerate hydrogen ions – protons surrounded by two electrons – at 160 MeV, before sending them to the Proton Synchrotron Booster. Here, the ions are stripped of their two electrons to leave only the protons that will be further accelerated before finishing their race in the LHC.

Linac 4 comprises four types of accelerating structures to bring particles in several stages to higher and higher energies. These accelerating structures have been commissioned one by one: in November 2013, the first hydrogen ion beam was accelerated to the energy of 3 MeV and two years after, the Linac 4 accelerator has reached an energy of 50 MeV – the energy Linac 2 runs at. Then, on the 1 July 2016, it crossed the 100 MeV threshold.

Note:

CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related links:

CERN accelerator complex: http://home.cern/about/accelerators

Linac 2: http://home.cern/about/accelerators/linear-accelerator-2

Proton Synchrotron Booster: http://home.cern/about/accelerators/proton-synchrotron-booster

For more information about European Organization for Nuclear Research (CERN), Visit: http://home.cern/

Image (mentioned), Text, Credits: CERN/Stefania Pandolfi.

Greetings, Orbiter.ch

Flying the fantastic four

ESA - GALILEO Programme logo.

8 November 2016

This month, a single Ariane 5 rocket is set to propel four Galileo satellites into orbit for the navigation constellation’s first-ever quadruple launch. Mission controllers are training intensively for the complex space delivery.

On 17 November, an Ariane 5 will use a new payload dispenser to release four identical satellites into orbit in one go.

Quad sats see space

This will be the eighth Galileo launch, and will bring the number of satellites in space to 18. Once complete, the system will sport 24 operational satellites and a ground network to provide positioning, navigation and timing services.

Four times complex mission control

To date, Soyuz rockets have carried two satellites at a time. This quadruple launch presents several technical challenges, including the new dispenser and the need to establish control over four independent satellites almost simultaneously.
The ascent into the medium-altitude orbit will take three and a half hours. Then, after the satellites separate, a combined team from ESA and France’s CNES space agency will take over, establishing control and shepherding them through their early orbits, lasting nine days for one pair and 13 days for the other.

“At the time that the four satellites separate two by two, we’ll have two shifts of the mission team working in the control room at the CNES centre in Toulouse, France, each shift managing two satellites – so it will be an intense period,” says Liviu Stefanov, co-flight director from ESA.

Galileo control room

“This is the same team who conducted the previous Galileo early orbit phases, so we’re familiar with the satellites themselves,” says Hélène Cottet, lead flight director from CNES.

“What’s different this time is managing four satellites, sometimes in sequence and sometimes in parallel. We have concentrated a lot of effort on planning and training for the first few hours in space.”

Since 2011, the joint team have conducted the Galileo initial flight operations alternately from ESA’s centre in Darmstadt, Germany, and the CNES centre in Toulouse.

Target orbit: 23 200 km

Separation will mark the start of a set of critical activities and manoeuvres to ensure the four are ready for handover to the Galileo Control Centre in Oberpfaffenhofen, Germany for the rest of their mission.

This includes ensuring that each have opened their solar wings and are ‘power positive’, establishing a data link via a set of ground stations, conducting extensive health checks and then switching the craft into a stable Earth-pointing mode, ready for subsequent manoeuvres.

Cut-away foursome

Each must make three engine firings at roughly one-day intervals to get onto their ‘drift’ orbits, after which control will be passed from the joint team to the Galileo Control Centre.

“After a few days, we expect things to settle down, and we’ll be able to concentrate on manoeuvring two satellites while babysitting the other two,” says ESA’s Tom Cowell, one of four spacecraft operations managers.

“After handover of the first pair to Oberpfaffenhofen, we can manoeuvre the other two just as we’ve done for previous dual launches.”

Teamwork

Even after handover, specialists will continue determining the orbits and computing manoeuvres to position the satellites in their final orbits at around 23 200 km, expected early in 2017.

Training, simulating, preparing

Since summer, everyone involved in this Galileo launch has worked through multiple simulations, mostly focused on preparing for if things go wrong.

This week, the training will end with an intensive three-day live simulation in Toulouse.

After a network countdown practice on 14 November, the live network countdown for the actual launch will start a couple of hours after midnight on 17 November, with lift off from the European Spaceport in Kourou, French Guiana, set for the same day at 13:06 GMT (14:06 CET).

“It will be a challenge, but having already taken 14 Galileo satellites into orbit, our joint teams are confident of our abilities and skills,” says Hervé Côme, co-flight director from ESA.

“We know we can rely on teamwork and expertise, and we’re looking forward to a smooth lift off for Galileo’s first quad launch.”

Related links:

Launching Galileo website: http://www.esa.int/Our_Activities/Navigation/The_future_-_Galileo/Launching_Galileo

Galileo Tour: http://esamultimedia.esa.int/multimedia/Galileo_tour/galileo.swf?lang=gb&mylang=gb

EC Galileo website: http://ec.europa.eu/growth/sectors/space/galileo/index_en.htm

European GNSS Agency: http://www.gsa.europa.eu/

Images, Text, Credits: ESA/P. Carril/J. Mai/CNES/E. Grimault, 2015.

Best regards, Orbiter.ch

Crew Sets up for Earth and Radiation Studies Before Next Trio Launches

ISS - Expedition 50 Mission patch.

November 8, 2016

The Expedition 50 trio orbiting on the International Space Station is conducting maintenance while getting ready for Earth observations and radiation exposure studies today. In Kazakhstan, three new crew members are waiting as their Soyuz rocket is prepared for launch.

Commander Shane Kimbrough started work on the U.S. segment’s Oxygen Generation System (OGS), which will undergo maintenance throughout the week. Today, Kimbrough tagged up with ground specialists and replaced a hydrogen sensor and will continue to work on OGS through Wednesday. The system is currently shut down due to a low voltage signature within the Hydrogen Orbital Replacement Unit (ORU) that contains the electrolyzing cell stack. The Russian Elektron system is providing oxygen for the crew at this time.

Image above: Middle school children programmed a space station camera to photograph this portion of the Sahara desert seen in western Libya in October. Image Credits: Sally Ride EarthKAM.

The two flight engineers, new cosmonaut Sergey Ryzhikov and veteran station commander Andrey Borisenko, are handing over a set of radiation detectors to Kimbrough. The NASA astronaut, who is on his second trip in space, will install the Radi-N2 detectors in the Destiny laboratory for a week to help doctors understand the radiation risk to crew health and develop protective measures.

Ryzhikov is also setting up a camera that will allow middle school students to photograph targets on Earth and downlink the imagery. The Sally Ride EarthKAM gear will be set up in the Harmony module’s Earth-facing hatch window and use internet-based tools to promote the learning process.

Another trio of Expedition 50 members is counting down to its Nov. 17 launch and two-day trip to the space station from the Baikonur Cosmodrome. Veteran station residents Peggy Whitson of NASA and Oleg Novitskiy of Roscosmos, along with first-time space flyer Thomas Pesquet of the European Space Agency, are in final training before they liftoff aboard the Soyuz MS-03 spacecraft. This will be Whitson’s third station mission and Novitskiy’s second.

Image above: Expedition 50-51 crew members (from left) Peggy Whitson, Oleg Novitskiy and Thomas Pesquet try on their spacesuits and check out the Soyuz MS-01 spacecraft in Kazakhstan. Image Credits: NASA/Alexander Vysotsky.

Thomas Pesquet, Peggy Whitson and Oleg Novitskiy have tried on their spacesuits and checked out the Soyuz MS-03 spacecraft they will blast off in Nov. 17. After launch, the trio will take a two-day trip to their new home in space where they will live until May. Today, the new crew is participating in flag-raising and tree-planting ceremonies at the Baikonur Cosmodrome launch site.

The orbiting crew of Commander Shane Kimbrough and Flight Engineers Sergey Ryzhikov and Andrey Borisenko are conducting critical space science while maintaining station systems.

Related links:

Expedition 50: http://www.nasa.gov/mission_pages/station/expeditions/expedition50/index.html

Radi-N2 detectors: http://www.nasa.gov/mission_pages/station/research/experiments/898.html

Sally Ride EarthKAM: http://www.nasa.gov/mission_pages/station/research/experiments/90.html

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Text, Credits: NASA/Mark Garcia.

Greetings, Orbiter.ch

Weekly Recap From the Expedition Lead Scientist, Week of Oct. 24, 2016

ISS - International Space Station logo.

Nov. 7, 2016

(Highlights: Week of Oct. 24, 2016) - It’s harvesting time for many crops in North America as winter approaches, but it’s planting season on the International Space Station as new crew members kicked off another run of an investigation that could help food production efforts on Earth.

NASA astronaut Shane Kimbrough configured and installed the hardware for the Veg-03 investigation, including planting six small plant pillows that will grow red romaine lettuce plants. Future long-duration space missions will require crew members to grow their own food. Understanding how plants respond to microgravity is an important step. Crew members on the station have previously grown lettuce and flowers in the Veggie facility. This new series of the study expands on previous validation tests. After the lettuce is harvested, crew members will attempt to grow cabbage in orbit. The investigation has scheduled four harvests over the course of two months.

Image above: NASA astronauts Kate Rubins, left, and Shane Kimbrough install the Veggie hardware to begin growing another crop of lettuce on the International Space Station. Image Credit: NASA.

Veggie provides lighting and necessary nutrients for plants in the form of a low-cost growth chamber and planting pillows, which deliver nutrients for the root system. The Veggie pillow concept is a low-mass, low-maintenance, modular system that requires no additional energy beyond a special light to help the plants grow. It supports a variety of plant species that can be cultivated for fresh food, and even for education experiments.

Crew members have commented that space gardening is fun, and investigators believe growing plants could provide a psychological benefit to crew members on long-duration missions, just as gardening is often a fun hobby for people on Earth. Data from this investigation could benefit agricultural practices on Earth by designing systems that use valuable resources, such as water, more efficiently.

Image above: Russian cosmonaut Anatoly Ivanishi, left, and JAXA astronaut Takuya Onishi take one last peek out of the Earth-facing portal in the cupola to enjoy another sunset on the International Space Station before they returned to Earth with NASA astronaut Kate Rubins Oct. 29. Image Credit: NASA.

Kimbrough installed hardware for the University of Nebraska-Lincoln Detector for the Analysis of Solar Neutrons investigation. When spacecraft components are exposed to solar neutrons for an extended period, degradation issues may result. Neutron radiation is also a concern for humans. There is a risk of low-energy neutron exposure while in space, with the potential to suffer from adverse health consequences as a result. Accurate measurement of the neutron environment inside space vehicles advances development of more effective radiation-shielding materials and methods. This project involves installation of a new type of detector to improve the reliability of identifying these electrically neutral particles. An efficient and compact detector requiring no operational power is well-suited for use aboard spacecraft. The detector uses special crystals and a thin film of the boron isotope to absorb neutrons, leaving a distinct signature which is then processed and analyzed to determine radiation levels.

Neutron sources also are widely used in scientific research, including medical and commercial applications. A small and sensitive slow-neutron detector is useful for neutron radiation monitoring.

Image above: The solar arrays of the Cygnus cargo vehicle can be seen as the space station orbited over the Bahamas. Image Credit: NASA.

A similar study monitoring solar radiation is the Dose Distribution Inside the International Space Station-3D (DOSIS-3D) investigation. As one of his last tasks in orbit before returning to Earth on Oct. 29, JAXA (Japan Aerospace Exploration Agency) astronaut Takuya Onishi retrieved 11 detectors for further study. The DOSIS-3D investigation uses several active and passive detectors to determine the radiation doses. The goal of the ESA (European Space Agency) investigation is creating a 3-D radiation map covering all sections of the outpost, documenting the nature and distribution of the radiation field inside the orbiting laboratory. On Earth, flight crews and nuclear plant workers are exposed to greater-than-average radiation. DOSIS-3D also provides insight into combining different devices for dosage monitoring and lessons in how to monitor real-time data. This could improve radiation monitoring for commercial and military airline crews, as well as other workers exposed to radiation on Earth.

Progress was made on other investigations and facilities this week, including JAXA Protein Crystal Growth, Meteor, JAXA EPO, ACE T-1, EML Batch 1.2c, FLEX-2, MSL Batch 2b, SODI DCMIX, BEAM, Biomolecule Sequencer and Manufacturing Device.

Other human research investigations conducted this week include Airway Monitoring, Biochem Profile, EDOS-2, IMMUNO-2, Fine Motor Skills, Habitability, IPVI, Neuromapping, Dose Tracker, and Space Headaches.

Related links:

Japan Aerospace Exploration Agency (JAXA): http://global.jaxa.jp/

European Space Agency (ESA): http://www.esa.int/ESA

Veg-03 investigation: http://www.nasa.gov/mission_pages/station/research/experiments/1294.html

Veggie facility: http://www.nasa.gov/mission_pages/station/research/experiments/383.html

University of Nebraska-Lincoln Detector for the Analysis of Solar Neutrons investigation: http://www.nasa.gov/mission_pages/station/research/experiments/2296.html

International Space Station-3D (DOSIS-3D): http://www.nasa.gov/mission_pages/station/research/experiments/184.html

JAXA Protein Crystal Growth: http://www.nasa.gov/mission_pages/station/research/experiments/157.html

Meteor: http://www.nasa.gov/mission_pages/station/research/experiments/1323.html

JAXA EPO: http://www.nasa.gov/mission_pages/station/research/experiments/970.html

ACE T-1: http://www.nasa.gov/mission_pages/station/research/experiments/2033.html

FLEX-2: http://www.nasa.gov/mission_pages/station/research/experiments/480.html

MSL Batch 2b: http://www.nasa.gov/mission_pages/station/research/experiments/1978.html

SODI DCMIX: http://www.nasa.gov/mission_pages/station/research/experiments/1175.html

BEAM: http://www.nasa.gov/mission_pages/station/research/experiments/1804.html

Biomolecule Sequencer: http://www.nasa.gov/mission_pages/station/research/experiments/2181.html

Manufacturing Device: http://www.nasa.gov/mission_pages/station/research/experiments/2198.html

Airway Monitoring: http://www.nasa.gov/mission_pages/station/research/experiments/1172.html

Biochem Profile: http://www.nasa.gov/mission_pages/station/research/experiments/1008.html

EDOS-2: http://www.nasa.gov/mission_pages/station/research/experiments/619.html

IMMUNO-2: http://www.nasa.gov/mission_pages/station/research/experiments/1790.html

Fine Motor Skills: http://www.nasa.gov/mission_pages/station/research/experiments/1767.html

Habitability: http://www.nasa.gov/mission_pages/station/research/experiments/1772.html

IPVI: http://www.nasa.gov/mission_pages/station/research/experiments/1950.html

Neuromapping: http://www.nasa.gov/mission_pages/station/research/experiments/1007.html

Dose Tracker: http://www.nasa.gov/mission_pages/station/research/experiments/1933.html

Space Headaches: http://www.nasa.gov/mission_pages/station/research/experiments/181.html

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Images (mentioned), Text, Credits: NASA/Vic Cooley, Lead Increment Scientist Expeditions 49 & 50/Kristine Rainey.

Best regards, Orbiter.ch

Ring Details on Display

NASA - Cassini Mission to Saturn patch.

Nov. 7, 2016

This view from NASA's Cassini spacecraft showcases some of the amazingly detailed structure of Saturn's rings.

The rings are made up of many smaller ringlets that blur together when seen from a distance. But when imaged up close, the rings' structures display quite a bit of variation. Ring scientists are debating the nature of these features — whether they have always appeared this way or if their appearance has evolved over time.

This view looks toward the sunlit side of the rings from about 4 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Sept. 24, 2016.

The view was acquired at a distance of approximately 283,000 miles (456,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 32 degrees. Image scale is 17 miles (27 kilometers) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org and ESA's website http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Image, Text,  Credits: NASA/JPL-Caltech/Space Science Institute/Tony Greicius.

Greetings, Orbiter.ch

Mars' ionosphere shaped by crustal magnetic fields

ESA - Mars Express Mission patch.

07 November 2016

Scattered pockets of magnetism across the surface of Mars have a significant influence on the planet's upper atmosphere, according to observations from ESA's Mars Express. Understanding these effects may be crucial for ensuring safe radio communications between Mars and Earth and, eventually, between explorers on the surface of the planet.

Earth's magnetic field is dominated by a single, strong source: the dynamo deep below the planet's surface. However, the same cannot be said for Mars. Rather than possessing a single source of magnetic field, Mars has many.

Image above: Mars as viewed by the Visual Monitoring Camera on Mars Express. Image Credits: ESA/D. O'Donnell - CC BY-SA IGO.

The Red Planet has numerous pockets of strong magnetism locked up within its crust, remnants from its earliest days. Modern-day Mars may be known for its relative lack of magnetism but young Mars was likely a different world; it was probably warmer and wetter, with a denser atmosphere and a hotter core. Scientists believe the young planet also had a sizeable magnetic field, driven by the circulating motion of molten material within its core (known as a planetary dynamo).

This global field switched off long ago – likely as the core cooled and solidified, freezing the dynamo in place – but the planet still boasts anomalous patches of strong remnant magnetism spread across its surface, known as 'crustal fields'.

Magnetic memories of early Mars

Parts of Mars' crust and rock remain magnetised today due to a phenomenon known as 'ferro-magnetism', which lasts even when the external magnetic field is no longer present (as is the case with Mars).

Magnetic map of Mars. Image Credit: NASA

Mars' crust cooled to below a specific temperature – known as the Curie temperature [1] – when the planet's core dynamo, and thus its magnetic field, was still active and present, causing residual magnetism to become permanently locked within ferrous (iron-containing) material in the crust. Similar crustal magnetic fields are also found on the Earth and the Moon.

These fields can later be removed by reheating material to above the Curie temperature – via large impacts, for example – and then allowing it to cool again in the absence of a magnetic field.

Magnetism is thought to have been wiped out from sizeable patches of the martian crust in this way, but large portions of the southern, and smaller parts of the northern, hemisphere of Mars remain magnetised to some degree, with pockets scattered planet-wide. These crustal fields are strong enough to drive features in Mars' upper atmosphere akin to the aurorae seen on Earth – such features have been seen by ESA's Mars Express).

Image above: Mars Express aurora detections. Image Credits: Based on data from J.-C. Gérard et al. (2015).

"They may be weak in terms of absolute strength – hundreds of nanotesla in the upper atmosphere on average, or between 0.1 and 1 per cent of the field strength produced by the Earth's dynamo at the equivalent altitude – but Mars' crustal fields are significantly stronger than those found on the Earth or the Moon," says Markus Fraenz of the Max Planck Institute for Solar System Research in Göttingen, Germany. "This indicates that Mars' dynamo field was once at least as strong as Earth's – but in order to produce such strong patches of remnant crustal magnetisation, it was probably stronger than our planet's has ever been."

Unfortunately no lander or rover has yet reached these sites of strong magnetisation, but comprehensive observations from long-lived orbiters such as NASA's Mars Global Surveyor and ESA's Mars Express have helped scientists to characterise Mars' magnetic environment.

Mars Express has been in orbit around Mars since 2003, and has completed numerous studies using its MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) and ASPERA-3 (Analyzer of Space Plasmas and Energetic Atoms) instruments to explore the effect these crustal fields have on Mars' ionosphere.

"Mars' crustal fields appear to strongly control the plasma in the planet's upper atmosphere," says David Andrews of the Swedish Institute of Space Physics in Uppsala. More specifically, they affect a layer of weakly ionised gas known as the ionosphere, which sits sandwiched between the bulk of Mars' neutral atmosphere and the intense radiation of outer space (including the solar wind, a stream of charged particles – protons and electrons – emanating from the Sun).

Climbing plasma in Mars' ionosphere

Mars' ionosphere is quite similar to Earth's in many respects, such as the typical densities, altitudes, and so on. "Earth's ionosphere is a bit more complex in terms of its structure, and has a larger number of distinct layers," says Andrews. "This is partly due to Earth's atmosphere being a mix of nitrogen and oxygen, unlike the CO₂-dominated martian atmosphere."

Mars' crustal fields affect the motion and dynamics of its ionospheric plasma, influencing how it circulates, accumulates, and escapes to space. For example, plasma soars to far higher altitudes than expected in regions with vertically-oriented crustal fields, and areas with stronger crustal fields are topped by denser and more extensive layers of ionosphere than weaker or absent fields.

The magnetic and plasma environment at Mars. Image Credit: ESA

Mars' ionosphere sits at the boundary between Mars' lower atmosphere and the solar wind, which floods out into space from the Sun. The solar wind also drags the solar magnetic field out into the Solar System as it travels, creating the interplanetary magnetic field (IMF).

When dragged into Mars' vicinity, IMF field lines can connect with the field lines emanating from some regions of Mars' crust (a process known as 'magnetic reconnection'). This process allows plasma to race upwards along the newly-created lines and escape to space, creating narrow cavities within Mars' ionosphere that are comparatively lacking in electrons.

"The big question, however, is whether or not these crustal fields affect the rate at which Mars loses its atmosphere to space and if so, how," says Andrews. "It's likely that while plasma is reconfigured in regions where the field is strong, the long-term averages of atmospheric escape are not massively different – but we're unsure."

From day to night

The behaviour and properties of the ionosphere differ between the region nearest the Sun (the 'dayside', between Mars and the Sun) and that stretching away from it (the 'night side', tailing away from Mars towards the outer Solar System).

Mars Express data have shown the dayside ionosphere to be surprisingly complex and variable, with electron densities and structured layers of plasma that change abruptly and inconsistently. The satellite has also flagged up how much there is to understand about the night side, and why some of its properties differ considerably from the dayside.

The process of plasma escape via magnetic reconnection, for example, is especially efficient at the day-night boundary (the regions surrounding this boundary, or terminator, are sometimes named 'morning' and 'evening' or 'dawn' and 'dusk'). Similarly, the ionosphere on the dayside is both denser and stretches to higher altitudes over crustal anomalies than on the night side. Plasma also appears to flow towards Mars on the dayside, and away at the day-night boundary.

In general, the number and density of electrons in the ionosphere increases with field strength during the day and at the boundary between day and night – but on the night side, the opposite is true. Mars' night side ionosphere is patchy; it is replenished by some of the plasma from the dayside ionosphere, and by precipitating electrons from the solar wind and magnetosphere (the region of space over which Mars' small intrinsic magnetic field dominates).

"This all reinforces the idea that Mars' plasma environment is strongly influenced by both the levels of incoming solar radiation, and the strength and distribution of the planet's crustal fields," says Eduard Dubinin of the Max Planck Institute for Solar System Research in Göttingen, Germany. "We need to understand much more about these interactions and about Mars' ionosphere in general to paint a detailed picture of Mars' longer-term evolution in terms of climate, habitability, loss of water and atmosphere, and more."

Issues for Red Planet radio?

As well as forming a better scientific understanding of Mars as a planet, knowing more about the martian ionosphere and crustal fields is vital for missions currently at Mars, and for those planned in the future (including crewed missions).

For example, the ionosphere dictates how, when, and where Mars Express' radar equipment (MARSIS) can operate. The dayside ionosphere of Mars is denser and more reflective of radio waves. MARSIS can thus probe Mars' ionosphere on the dayside, as the plasma there reflects incoming radar pulses at the appropriate frequencies (~MHz). On the night side, however, MARSIS performs subsurface sounding. The instrument's radio waves reach through the comparatively sparse ionosphere and can make it far further before being reflected, reaching Mars' surface and up to about 10 km below.

Mars Express with MARSIS antenna unfurled. Image Credit: ESA

"MARSIS can exploit the varying properties of the ionosphere, making it a great instrument to probe both the ionosphere and subsurface of Mars," says Dmitri Titov, project scientist for ESA's Mars Express.

The variability of the martian ionosphere could be an issue, however, for any communications on the surface of Mars.

Landers and rovers on Mars communicate with Earth via an orbiter, which in turn uses high enough radio frequencies (GHz) that the ionosphere is not a huge obstacle. However, this may become a larger issue if and when humans set foot on the planet.

"Shortwave radio communications (MHz) on the surface may be affected by variability of Mars' ionosphere, especially around stronger crustal fields, and our understanding here is still incomplete," adds Titov. "Understanding more about Mars' magnetic and plasma environment is key. Findings such as these from Mars Express are crucial to our continued exploration of the Solar System, whether with robots or human crews."

Background Information:

[1] The Curie temperature is the temperature above which some materials lose their permanent magnetic properties.

Contributing studies include:

Martian ionosphere observed by Mars Express. 1. Influence of the crustal magnetic fields, by E. Dubinin et al., Planetary and Space Science, Vol. 124, May 2016, pp.62-75; doi: 10.1016/j.pss.2016.02.004 (http://dx.doi.org/10.1016/j.pss.2016.02.004)

Empirical model of the Martian dayside ionosphere: Effects of crustal magnetic fields and solar ionizing flux at higher altitudes, by F. Nemec et al., Journal of Geophysical Research: Space Physics, Vol. 121, February 2016, pp. 1760-1771; doi: 10.1002/2015JA022060 (http://dx.doi.org/10.1002/2015JA022060)

The morphology of the topside ionosphere of Mars under different solar wind conditions: Results of a multi-instrument observing campaign by Mars Express in 2010, by P. Withers et al., Planetary and Space Science, Vol. 120, January 2016, pp. 24-34; doi: 10.1016/j.pss.2015.10.013 (http://dx.doi.org/10.1016/j.pss.2015.10.013)

Control of the topside Martian ionosphere by crustal magnetic fields, by D. Andrews et. al., Journal of Geophysical Research: Space Physics, Vol. 120, April 2015, pp. 3042-3058; doi: 10.1002/2014JA020703 (http://dx.doi.org/10.1002/2014JA020703)

The measurements were conducted by the Mars Express Analyzer for Space Plasmas and Energetic Atoms (ASPERA-3) plasma instrument suite and the Mars Advanced Radar for Sub-Surface and Ionospheric Sounding (MARSIS).

Related links:

Looking at Mars: http://www.esa.int/Our_Activities/Space_Science/Mars_Express

More about...

Mars Express overview: http://www.esa.int/Our_Activities/Space_Science/Mars_Express_overview

Mars Express 10 year brochure: http://esamultimedia.esa.int/multimedia/publications/BR-312/

Images (mentioned), Text, Credits: ESA/Dmitri Titov/Max Planck Institute for Solar System Research/Markus Fraenz/Eduard Dubinin/Swedish Institute of Space Physics/David Andrews.

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