University student maps plasma tubes in the sky
Using theMurchison Widefield Array (MWA) radio telescope in theWestern Australia desert, a Sydney University student, Cleo Loi, has discovered enormous plasma pipes in the Earth’s upper atmosphere. Thought to beresponsible for possible radio interference with satellite navigation systems,the presence of these objects has been predicted for over 60 years, but neverbefore seen. By imaginatively using the radio telescope to observe in 3D, Loiwas able to image large areas of the sky using the fast photographycapabilities of the MWA to produce a movie that shows the motions of the plasmain real-time.
The Earthis surrounded in space by the magnetosphere. This layer is believed to begenerated by the movement of liquid iron inside a shell of iron, nickel andother metals, deep within the center of the earth’s core, which creates amagnetic field that extends out beyond the confines of the Earth to wrap ourplanet in a protective layer that deflects many types of ionizing radiation.
Theinnermost level of the magnetosphere is the ionosphere, and the layer beyondthat is the plasmasphere. It is in this region of magnetic fields that atoms inthe upper atmosphere are ionized (that is, have electrons stripped away) by thesolar wind constantly flowing out from the sun, generating great plumes ofplasma and vast swathes of free electrons in the sky. Here, in an area riddled with manydifferent types of plasma structures, is where the new plasma tubes have beenlocated and where they interact with the magnetic field to createmagnetic-line-following ducts.
"Wemeasured their position to be about 600 kilometers above the ground, in theupper ionosphere, and they appear to be continuing upwards into theplasmasphere," said Loi, from the School of Physics at the University of Sydney. "This is around where the neutral atmosphere ends, and we aretransitioning to the plasma of outer space. The discovery of the structures is importantbecause they cause unwanted signal distortions that could, as one example,affect our civilian and military satellite-based navigation systems. So we needto understand them."
Whilestill an undergraduate, Loi and her colleagues used the 7 sq km (2.7 sq mile) MWAarray as a type of binocular apparatus, by dividing the 128 antennas of thearray into two separate receiving areas. In this way they effectively createdtwo "eyes" which, when combined with triangulation, enabled them tobuild a three-dimensional dynamic map of the plasma tubes over a large area.
"Thisis like turning the telescope into a pair of eyes, and by that we were able toprobe the 3D nature of these structures and watch them move around," Loi said. "We saw astriking pattern in the sky where stripes of high-density plasma neatlyalternated with stripes of low-density plasma. Thispattern drifted slowly and aligned beautifully with the Earth's magnetic fieldlines, like aurorae.”
Already adominant instrument in the multi-continent Square Kilometre Array (SKA), usingthe MWA to provide 3D vision of objects is already piquing the interests ofscientists to conduct a great deal more analysis on the formation of these plasmastructures.
"Werealized we may be onto something big and things got even better when we inventeda new way of using the MWA," revealed Loi. "We were able to measure the spacingbetween them, their height above the ground and their steep inclination. Thishas never been possible before and is a very exciting new technique."
However, before any such research could be made a reality, Loi first had to overcome the skepticism of senior colleagues who thought thather results from the observations may have been a little too enthusiastic andpremature.
"Itis to Cleo's great credit that she not only discovered this but also convincedthe rest of the scientific community," said Loi's supervisor Dr Tara Murphy, also of the School of Physics at the University of Sydney. "As an undergraduate student with no priorbackground in this, that is an impressive achievement. When they first saw the data, many of her senior collaborators thoughtthe results were literally 'too good to be true' and that the observationprocess had somehow corrupted the findings. But over the next few months, Cleomanaged to convince them that they were both real and scientificallyinteresting."
A betterknowledge of the make-up of these ducts also means that astronomers can takesuch phenomena into account when using radio telescopes. Especially as, whendealing with such fundamentally weak radio signals coming in from astronomicalobjects such as quasars, pulsars, and black holes. The more interference thatcan be cut out and the clearer the signal received, the better the resolutionand data gathering will be.
The shortvideo below shows a reconstruction in 3D of the plasma tubes floating above theEarth.
Source: The University of Sydney