Andrew Yee[_1_]
July 3rd 08, 07:34 PM
ESA News
http://www.esa.int
27 June 2008
Cluster listens to the sounds of Earth
The first thing an alien race is likely to hear from Earth is chirps and
whistles, a bit like R2-D2, the robot from Star Wars. In reality, they are
the sounds that accompany the aurora. Now ESA's Cluster mission is showing
scientists how to understand this emission and, in the future, search for
alien worlds by listening for their sounds.
Scientists call this radio emission the Auroral Kilometric Radiation (AKR).
It is generated high above the Earth, by the same shaft of solar particles
that then causes an aurora to light the sky beneath. For decades,
astronomers had assumed that these radio waves travelled out into space in
an ever-widening cone, rather like light emitted from a torch. Thanks to
Cluster, astronomers now know this is not true.
By analysing 12 000 separate bursts of AKR, a team of astronomers have
determined that the AKR is beamed into space in a narrow plane. This is like
placing a mask over the torch with just a small slit in the middle for light
to escape.
"We can now determine exactly where the emission is coming from," says
Robert Mutel, University of Iowa, who conducted the three-year study with
colleagues. For each of the AKR bursts they analysed, the astronomers
pinpointed its point of origin to regions in Earth's magnetic field just a
few tens of kilometres in size. These were located a few thousand kilometres
above where the light of the aurora is formed.
"This result was only possible because of the Cluster mission's four
spacecraft," says Mutel. Consisting of four nearly identical spacecraft
flying in formation, Cluster allowed the scientists to precisely time when
the AKR washed over each of the satellites. Using this information, the
scientists triangulated the points of origin, in a similar way to the way
GPS navigation works.
AKR was discovered by satellites in the early 1970s. It is blocked from
reaching the ground by the ionosphere, the upper reaches of Earth's
atmosphere. This is just as well because otherwise it would overwhelm the
transmissions from all our radio stations. It is 10 000 times more intense
than even the strongest military radar signal. "Whenever you have aurora,
you get AKR," says Mutel. That includes aurorae on other planets, too.
Visiting spacecraft have seen aurorae and detected AKR on Jupiter and
Saturn, the two largest gas giants in our Solar System.
Not only will this new understanding of how the AKR is beamed into space
help astronomers understand the magnetic environment of those gas worlds, it
will also help them search for similar planets around other stars.
Although looking for AKR from extrasolar planets will require much larger
radio telescopes than are currently available, these instruments are on the
drawing boards. Once these planets have been identified, the AKR can be
monitored for how it winks on and off, allowing astronomers to calculate how
long the planet takes to rotate.
It also provides new routes of investigation into the magnetic fields of
other stars, many of which have magnetic fields thousands of times stronger
than the Sun. They too, will produce radiation similar to AKR and these can
be monitored.
The result is a major scientific breakthrough that gives astronomers a new
tool with which to investigate both planets and stars.
Notes for Editors:
Cluster multi-spacecraft determination of AKR angular beaming by R. Mutel,
I. Christopher and J. Pickett is published in Geophysical Research Letters.
The data used in the study was collected by the NASA Wide Band (WBD)
instrument flying onboard the four Cluster spacecraft.
For more information:
Robert Mutel, University of Iowa
Email: robert-mutel @ uiowa.edu
Philippe Escoubet, ESA Cluster Project Scientist
Email: philippe.escoubet @ esa.int
[NOTE: Images and weblinks suporting this release are available at
http://www.esa.int/esaCP/SEMLX5SHKHF_index_1.html ]
http://www.esa.int
27 June 2008
Cluster listens to the sounds of Earth
The first thing an alien race is likely to hear from Earth is chirps and
whistles, a bit like R2-D2, the robot from Star Wars. In reality, they are
the sounds that accompany the aurora. Now ESA's Cluster mission is showing
scientists how to understand this emission and, in the future, search for
alien worlds by listening for their sounds.
Scientists call this radio emission the Auroral Kilometric Radiation (AKR).
It is generated high above the Earth, by the same shaft of solar particles
that then causes an aurora to light the sky beneath. For decades,
astronomers had assumed that these radio waves travelled out into space in
an ever-widening cone, rather like light emitted from a torch. Thanks to
Cluster, astronomers now know this is not true.
By analysing 12 000 separate bursts of AKR, a team of astronomers have
determined that the AKR is beamed into space in a narrow plane. This is like
placing a mask over the torch with just a small slit in the middle for light
to escape.
"We can now determine exactly where the emission is coming from," says
Robert Mutel, University of Iowa, who conducted the three-year study with
colleagues. For each of the AKR bursts they analysed, the astronomers
pinpointed its point of origin to regions in Earth's magnetic field just a
few tens of kilometres in size. These were located a few thousand kilometres
above where the light of the aurora is formed.
"This result was only possible because of the Cluster mission's four
spacecraft," says Mutel. Consisting of four nearly identical spacecraft
flying in formation, Cluster allowed the scientists to precisely time when
the AKR washed over each of the satellites. Using this information, the
scientists triangulated the points of origin, in a similar way to the way
GPS navigation works.
AKR was discovered by satellites in the early 1970s. It is blocked from
reaching the ground by the ionosphere, the upper reaches of Earth's
atmosphere. This is just as well because otherwise it would overwhelm the
transmissions from all our radio stations. It is 10 000 times more intense
than even the strongest military radar signal. "Whenever you have aurora,
you get AKR," says Mutel. That includes aurorae on other planets, too.
Visiting spacecraft have seen aurorae and detected AKR on Jupiter and
Saturn, the two largest gas giants in our Solar System.
Not only will this new understanding of how the AKR is beamed into space
help astronomers understand the magnetic environment of those gas worlds, it
will also help them search for similar planets around other stars.
Although looking for AKR from extrasolar planets will require much larger
radio telescopes than are currently available, these instruments are on the
drawing boards. Once these planets have been identified, the AKR can be
monitored for how it winks on and off, allowing astronomers to calculate how
long the planet takes to rotate.
It also provides new routes of investigation into the magnetic fields of
other stars, many of which have magnetic fields thousands of times stronger
than the Sun. They too, will produce radiation similar to AKR and these can
be monitored.
The result is a major scientific breakthrough that gives astronomers a new
tool with which to investigate both planets and stars.
Notes for Editors:
Cluster multi-spacecraft determination of AKR angular beaming by R. Mutel,
I. Christopher and J. Pickett is published in Geophysical Research Letters.
The data used in the study was collected by the NASA Wide Band (WBD)
instrument flying onboard the four Cluster spacecraft.
For more information:
Robert Mutel, University of Iowa
Email: robert-mutel @ uiowa.edu
Philippe Escoubet, ESA Cluster Project Scientist
Email: philippe.escoubet @ esa.int
[NOTE: Images and weblinks suporting this release are available at
http://www.esa.int/esaCP/SEMLX5SHKHF_index_1.html ]