From: Particle Physics and Astronomy Research Council
Posted: Wednesday, September 17, 2003
Galileo, the NASA space probe in which UK scientists have played a key role, will dramatically end its 14-year mission when it plunges into Jupiter's dense atmosphere on the 21st September. The spacecraft, which has revealed a wealth of scientific data on Jupiter and its moons, with fuel and power exhausted, will vaporize like a meteor as its descends through the giant planet's turbulent atmosphere (an artist's impression of what this might look like is available - please see notes to editors). As well as extensive scientific data, Galileo has provided the most visually stunning images of Jupiter and its moons ever, especially Io and Europa. The probe, launched in 1989 by the Space Shuttle Atlantis, also imaged the Earth, Venus, the Moon and several asteroids during its lifetime.
The highlights of the mission include the identification of massive amounts of lightening activity in Jupiter's atmosphere, where hurricane-force winds and huge amounts of heat from the interior whip clouds of frozen ammonia into bands that encircle the planet, studded with giant storms, some of them larger than the entire Earth. The planet is richer in heavy elements than the Sun, showing that it was assembled from smaller 'planetesimals' rather than condensing in isolation as previously surmised.
Galileo also discovered that Jupiter's rings are made of small dust grains blasted off the surface of Jupiter's four innermost satellites by the impacts of meteoroids. The infrared spectrometer on Galileo took the surface temperature of Io, one of Jupiter's moons, and discovered that many of Io's active volcanoes are much hotter than Earth's, indicating a higher magnesium or iron content for the silicate lava that erupts from below Io's surface than would be expected in a terrestrial volcano.
Commenting on the mission, Prof. Ian Halliday, Chief Executive Officer of the Particle Physics and Astronomy Research Council, the UK's space science agency, said, " Galileo has been a resounding scientific success. Our understanding of Jupiter and the Jovian system has been increased enormously and UK scientists have been at the forefront of some of these amazing discoveries".
Galileo images and infrared spectra have revealed that Europa, another Jovian moon, has a salty ocean beneath its cracked and frozen surface, an impression that is reinforced by the lack of craters on the moon, which show the surface to be relatively young. Galileo has revealed that Jupiter's largest moon, Ganymede, has its own magnetic field and evidence has also been provided to support the existence of a subsurface ocean on Callisto.
Scientists from Oxford University, The Open University and Imperial College are involved in three of the eleven instruments onboard Galileo.
Professor Tony McDonnell from the Planetary and Space Sciences Research Institute (PSSRI) at The Open University is Co-Investigator on the Dust Detector Subsystem which has looked at the properties of dust particles within the Jovian system said,
"Galileo has been a truly remarkable mission. The results from the Dust Detector Subsystem indicate that much of the dust comes from outside the solar system indicating that it originates from distant stars."
Professor Fred Taylor from Oxford University, a team member for the infrared spectrometer experiment on Galileo, said : "Galileo has provided a fantastic database that will be a rich source of progress in the planetary sciences for years or decades to come. The mission has provided key information about Jupiter and its place in the solar system."
Dr Michele Dougherty from Imperial College is a team member on the Magnetometer instrument that detects magnetic fields in the spacecraft's immediate environment. She comments, "It is always sad when a mission comes to the end of its lifetime. However, Galileo has exceeded expectations and provided a wealth of scientific data resulting in the discovery of many new important facts about the Jovian system. In addition the images produced of Europa and Io are stunning."
The UK scientists are working with their US and other overseas colleagues on a massive, multi-authored book that will record the scientific results of Galileo's 30-year odyssey and form a fitting epitaph for one of the most successful of man's voyages to his planetary neighbours so far.
Notes to Editors
Gill Ormrod - PPARC Press Office
Tel: 01793 442012. Mobile: 0781 8013509
Professor Tony McDonnell - PSSRI,
Tel: 01227 761352. Email: firstname.lastname@example.org
Professor Fred Taylor - Oxford
Tel: 01865 272933. Email: email@example.com
Dr Michele Dougherty - Imperial
Tel: 020 75947757. Email: firstname.lastname@example.org
Images, including an artist's impression of Galileo plunging into Jupiter can be found at
Alternatively, please contact Gill Ormrod in the PPARC Press Office - contact details above.
Further images can be found on the NASA website listed above.
The September 21st end of mission event will be web cast live at http://www.jpl.nasa.gov/webcast/galileo/
The overall mission costs are approximately $1.5 billion. PPARC contributed £1 million to the mission costs, through the production of instruments.
Background facts on Jupiter
Jupiter reigns supreme among our nine planets, containing two-thirds of the planetary mass of the solar system. In composition it resembles a small star. Its interior pressure may reach 100 million times the pressure on Earth's surface. Jupiter's magnetic field is immense, even in proportion to the size of the planet, stretching millions of miles into the solar system. Electrical activity in Jupiter is so strong that it pours billions of watts into Earth's own magnetic field every day.
Jupiter is endowed with 16 moons, a ring system, and an immense, complex atmosphere. Its atmosphere bristles with lightning and swirls with huge storm systems, including the Great Red Spot, a storm that has persisted for at least 100 years, perhaps as long as 300 years. Some scientists theorize that beneath the atmosphere there is no solid mass at the center of Jupiter, but that the planet's unique temperature and pressure conditions sustain a core whose density is more like liquid or slush.
The reddish color of the "Great Red Spot" is a puzzle to scientists, but several chemicals, including phosphorus, have been proposed as a reason. In fact, the colors and mechanisms driving the appearance of the entire atmosphere are still not well understood. These mysteries cannot be solved by taking pictures. Direct measurements from within the atmosphere are necessary - measurements like those made by the Galileo Probe.
Jupiter's Storms and Rings
Using data from the Galileo Probe's plunge into the top cloud layers of Jupiter, Galileo has discovered that Jupiter has thunderstorms many times larger than Earth's. These storms result from the vertical circulation of water in the top layers, leaving large areas where air descends and becomes dry like the Sahara desert, and other areas where water rises to form the thunderstorms. Galileo has also found that Jupiter's rings are made of small dust grains blasted off the surface of Jupiter's four innermost satellites by the impacts of meteoroids.
Hot Active Volcanoes on Io
Now considered the solar system's most active body, Io's volcanoes were first discovered by Voyager 1 in 1979 and result from 100 meter (328 ft) tides in its solid surface. By taking Io's temperature with Galileo's instruments, scientists now know that some of Io's volcanoes are hotter than Earth's. From this, scientists surmise that lava made of silicate material rich in magnesium erupts from below Io's surface.
A Possible Ocean on Europa
Possessing more water than the total amount found on earth, Europa appears to have had a salty ocean beneath its icy cracked and frozen surface. Galileo images show ice "rafts" the size of cities that appear to have broken off and drifted apart, a frozen "puddle" smooths over older cracks, warmer material bubbles up from below to blister the surface, evaporative-type salts are exposed. A remarkable lack of craters show the surface to be relatively young. Europa has a thin oxygen atmosphere and an ionosphere.
Ganymede's Own Magnetic Field
Internal tidal friction again causes surprising effects on the solar system's largest moon. Galileo revealed that Ganymede has its own magnetic field. Perhaps from a slightly different orbit in its past, enough heat from tidal friction caused the separation of material inside Ganymede and this stirring of a molten core or iron sulfide is believed to generate Ganymede's magnetic field.
Does An Ocean Hide Beneath Callisto's Surface?
There is evidence to support the existence of a subsurface ocean on Callisto. The ocean would have to be deep enough inside the moon that it does not affect the heavily cratered surface on top. Instead the ocean could be showing itself indirectly, through the magnetic field it generates. This could come from electric flow in a salty ocean generated by Jupiter's strong magnetic field passing through it.
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, the European Space Agency and the European Southern Observatory. 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.
Issued by the Particle Physics and Astronomy Research Council on 16th September 2003.
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