On 24 January 2001, Cluster’s spacecraft observed shock reformation in the Earth’s magnetosphere, predicted only in theory, over 20 years ago. Cluster provided the first opportunity ever to observe such an event, the details of which have been published in a paper on 9 March this year.
The shock wave that sits above the Earth’s surface is a natural phenomenon. It is located on the side facing the Sun, at approximately one quarter of the distance to the Moon, and is caused by the flow of electrically charged particles from the Sun.
This flow of electrically charged particles known as solar wind is emitted in a gusty manner by the Sun. When it collides with the Earth’s magnetic field, it is abruptly slowed down and this causes a barrier of electrified gas, called the bow shock, to build up. It behaves in the same way as water being pushed out of the way by the front of a ship.
On 24 January 2001, the four Cluster spacecraft were flying at an approximate altitude of 105 000 kilometres, in tetrahedron formation. Each spacecraft was separated from the others by a distance of about 600 kilometres. With such a distance between them, as they approached the bow shock, scientists expected that every spacecraft would record a similar signature of the passage through this region.
Instead, the readings they got were highly contradictory. They showed large fluctuations in the magnetic and electric field surrounding each spacecraft. They also revealed marked variations in the number of solar wind protons that were reflected by the shock and streaming back to Sun.
“The features derived from three different scientific experiments on the Cluster satellites provide the first convincing evidence in favour of the shock reformation model,” says Vasili Lobzin of the Centre National de la Recherche Scientifique, Orléans, France, who headed this study.
Vladimir Krasnoselskikh, also of the Centre National de la Recherche Scientifique, Orléans, France, who is a collaborator on this new research, had predicted the shock reformation model theoretically in 1985. It is a little similar to the way waves in the ocean build up and then break onto the shore, only to reform again, some way out to sea.
The detection has implications for the way astronomers investigate larger bow shocks around distant celestial objects. Bow shocks are related to some of the most energetic events in the Universe. Exploding stars and strong stellar winds from young stars cause them. Reforming bow shocks can also accelerate particles to extremely high energies and throw them across space.
Although the conditions that cause the reformation of a shock wave are rare around the Earth, they are common around these other celestial objects. “In astrophysical situations, the conditions needed for the bow shock to overturn and reform is almost always met,” says Krasnoselskikh.
The fact that Cluster has given scientists their first concrete data from such a bow shock reformation event is a valuable gift to space physicists. “This is a unique opportunity to study distant astrophysical objects in the kind of detail not available in any laboratory,” says Krasnoselskikh.
Philippe Escoubet | alfa
Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT
Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
06.12.2016 | Materials Sciences
06.12.2016 | Medical Engineering
06.12.2016 | Power and Electrical Engineering