Press Release

Unique gathering of spacecraft yields new views, clues on Jupiter’s Magnetosphere

By SpaceRef Editor
February 27, 2002
Filed under , ,

A space probe carrying British-designed and operated instruments has helped
scientists to understand the magnetosphere surrounding Jupiter better than
ever before.

Its magnetosphere was observed to contract in response to shock waves
generated at the Sun, the first time scientists have been able to clearly
observe how changes in the solar wind affect the magnetosphere of this giant

In addition an unexplained pulsating X-ray hot spot near Jupiter’s North
pole has been observed that does not appear to be influenced by the solar
wind but by some as yet unknown factor inside the magnetosphere itself.

The Cassini probe, launched in 1997, used a flyby of Jupiter in late 2000
and early 2001 to gather a gravitational boost to ‘sling-shot’ it on to
Saturn, its mission destination.

As it flew by, scientists collected important data on Jupiter’s
magnetosphere that were later combined with simultaneous observations made
from the orbiting Galileo spacecraft and also from the Hubble Space
Telescope and the Chandra X-ray observatory orbiting around Earth to provide
a unique observational data set.

Today 82 scientists from around the world present their findings from this
once-in-a-lifetime opportunity in a series of papers in Nature*1.

“The unique opportunity of having two spacecraft observe a planet other than
the Earth at the same time and at close range has yielded a very rich
science harvest,” said Dr Michele Dougherty of the department of physics at
Imperial College, London, Acting Principal Investigator of the Cassini
magnetometer team, and co-author of three of the papers.

“It has allowed us for the first time to simultaneously connect disturbances
in the solar wind to changes within the magnetosphere of Jupiter,” said Dr

Cassini flew along the dusk flank of the magnetosphere, at a distance of 10
million kilometres from Jupiter. Jupiter is 600 million kilometres from

Dr Dougherty’s contributions to these research findings relate to the first
clear evidence of the influence the solar wind has on the magnetosphere of
Jupiter, and the investigation of a pulsating auroral X-ray hotspot on the

“The magnetosphere can be likened to a bubble of charged gas rotating under
the control of the magnetic field of the planet,” said Dr Dougherty. “But it
is continually buffeted, squeezed and stretched by the solar wind of charged
particles speeding away from the Sun.”

The two spacecraft, Cassini and Galileo, some 9 million kilometres apart,
both encountered the boundary of the magnetospheric bubble while this bubble
was contracting due to an increase in solar wind pressure. The presence of
both spacecraft proved critical in enabling scientists to prove that the
magnetosphere is indeed controlled by the solar wind.

Research on the auroral effects revealed that most of the northern auroral
X-rays at Jupiter are coming from a hot spot located much closer to the pole
than previously thought.

The hot spot X-rays pulsate every 45 minutes, a periodicity previously
observed near Jupiter in radio and energetic electron bursts. However, no
clear correlation between any changes in the solar wind and these auroral
X-rays was observed, implying that such oscillations arise from some as yet
unknown internal processes within the magnetosphere itself.

“Being able to understand the link between the solar wind effects and
changes within Jupiter’s magnetosphere will allow us to better understand
our own planet’s smaller magnetosphere and also the environments around
Jupiter-sized planets in other solar systems and galaxies,” said Dr

As part of NASA’s distributed operations network, there is a mini-control
centre at Imperial College directly connected to the Spacecraft Control
Centre at the Jet Propulsion Laboratories (JPL) in Pasadena, California.
Magnetic field data from the spacecraft arrives in Pasadena and is
immediately transferred over to Imperial College where the magnetometer team
downloads, processes and begins analysing it.

A further benefit of the Jupiter flyby was to serve as a ‘test run’ for the
Cassini spacecraft, originally launched in 1997, to check its operational
capabilities as it heads for Saturn where it is due to arrive in 2004.

The Huygens probe will land on Saturn’s largest moon, Titan, and investigate
its atmosphere and surface. Cassini will orbit Saturn and carry out a four
year detailed study of the planet.

British Scientists have taken part in the building of eight of the eighteen
scientific instruments on the Cassini-Huygens, which is a joint NASA/ESA
mission. The UK involvement in the project, including the input into the
magnetometer instrument and research undertaken by the Imperial College
team, is funded by the Particle Physics and Astronomy Research Council

Professor Ian Halliday, Chief Executive of PPARC said:

“This is an amazing collaboration which illustrates how, by sharing data
from different missions, scientists are able to gain a much greater
understanding of phenomena in our solar system. Through such partnerships
discoveries are being made which would not have been achievable through
isolated missions from single nations.”


Pictures of Jupiter’s hotspot are available on request. Please contact Gill
Ormrod in the PPARC Press office (contact details below).

Useful web sites

UK Cassini-Huygens mission home page

The Cassini-Huygens mission home page

For more information please contact:

Dr Michele Dougherty

Department of Physics

Imperial College, London

Tel: +44 (0)20 7594 7757


Gill Ormrod

PPARC Press Office

Tel: +44 (0) 1793 442012

Fax: +44 (0) 1793 442002


Tom Miller

Imperial College Press Office

Tel: +44 (0)20 7594 6704

Mob: +44 (0)7803 886248


Notes to Editors:

1. The research is published in a series of papers in the scientific
journal, Nature on 28 February. Dr Dougherty of Imperial College is
co-author on three papers: ‘Control of Jupiter’s radio emission and aurorae
by the solar wind’; ‘The dusk flank of Jupiter’s magnetosphere’; ‘A
pulsating auroral X-ray hot spot on Jupiter’.

2. Cassini-Huygens is a joint NASA-ESA mission, launched in 1997, to study
Saturn and its rings and moons. British Scientists have taken part in the
development of eight of the eighteen instruments on Cassini and Huygens. In
particular, British scientists have headed the international teams that
built the Dual Technique Magnetometer (headed by Dr Michele Dougherty) and
the Surface Science Package (headed by Dr John Zarnecki of the Open

The mission is named after Gian Domenico Cassini, an Italian astronomer who
found a large gap in Saturn’s rings

3. The Particle Physics and Astronomy Research Council (PPARC) is the UK’s
strategic science investment agency. It funds research, education and public
understanding in four broad areas of science – particle physics, astronomy,
cosmology and space science.

PPARC is government funded and provides research grants and studentships to
scientists in British universities, gives researchers access to world-class
facilities and funds the UK membership of international bodies such as the
European Organisation for Nuclear Research, CERN, and the European Space
Agency. It also contributes money for the UK telescopes overseas on La
Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at
the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.

PPARC’s Public Understanding of Science and Technology Awards Scheme
provides funding to both small local projects and national initiatives aimed
at improving public understanding of its areas of science.

4. Imperial College of Science, Technology and Medicine is the largest
applied science, technology and medicine university institution in the UK.
In the December 2001 Research Assessment Exercise, 75 per cent of staff
achieved a 5* rating, the highest proportion in any UK university.

SpaceRef staff editor.