Paris, 10 April 1998
The discovery, which may provide an important clue to the origin of water in the Solar System, is reported in an article in Astrophysical Journal Letters, to be published on 20 April. This Information Note is distributed simultaneously with a Press Release on the same subject from Cornell University, Johns Hopkins University, the Harvard/Smithsonian Center for Astrophysics, and NASA's Ames Research Center.
The water vapour is in the Orion Molecular Cloud, a giant interstellar mass composed primarily of hydrogen molecules. The observations were carried out in October 1997 with the Long Wavelength Spectrometer, devised by a British-led team as one of four instruments on board ISO.
Looking at long infrared wavelengths, the astronomers saw the characteristic signature of emission by water vapour.
"The interstellar gas cloud that we observed is being pummelled by shock waves that compress and heat the gas," says Martin Harwit of Cornell University, an ISO mission scientist and lead author on the article reporting the finding. "These shock waves are the result of the violent early stages of starbirth, in which a young star spews out gas that slams into its surroundings at high speed. The heated water vapour that we observed is the result of that collision."
Harwit also suggests that shock waves are a cause of starbirth as well as a result. "In the future," he says, "they may also trigger the formation of additional stars and planets as they compress the gas cloud that we observed, but only if surplus heat can be radiated away. Even though the interstellar gas is composed primarily of hydrogen molecules, water vapour is a particularly efficient radiator at far-infrared wavelengths and plays a critical role in cooling the gas and facilitating the star formation process. Because the Earth's own wet atmosphere is completely opaque at the wavelengths of interest, the observations that we are reporting today are possible only from space with the use of the ISO satellite."
"An enhanced concentration of water is precisely what we expected in this gas cloud," comments team member Gary Melnick of the Harvard-Smithsonian Center for Astrophysics. "We are looking at a region of interstellar space where shock waves have made the gas abnormally warm. For the past 25 years, astrophysicists have been predicting that whenever the temperature exceeds about 100 °C, chemical reactions will convert most of the oxygen atoms in the interstellar gas into water. And that's exactly what we've observed in Orion."
"The interstellar gas cloud that we observed in Orion seems to be a huge chemical factory," Neufeld says, "generating enough water molecules in a single day to fill the Earth's oceans sixty times over. Eventually that water vapour will cool and freeze, turning into small solid particles of ice. Similar ice particles were presumably present within the gas cloud from which the Solar System originally formed. It seems quite plausible that much of the water in the Solar System was originally produced in a giant water-vapour factory like the one we have observed in Orion."
Panels showing two examples of measurements carried out on board the ISO, together with an image of the Orion nebula taken with the Wide Field Planetary Camera 2 on NASA's Hubble Space Telescope can be seen on the World Wide Web at:
http://www.pha.jhu.edu/~neufeld/orionwater.html
Cornell University
April 9, 1998
The amount of water vapor measured in Orion is 20 times larger than that observed in other interstellar gas clouds in our galaxy, the Milky Way. The discovery was made within the Orion molecular cloud, a giant interstellar gas cloud, a trillion miles across, composed primarily of hydrogen molecules.
The measurements were made with the long-wavelength spectrometer aboard the Infrared Space Observatory (ISO) launched in November 1995 by the European Space Agency with the participation of NASA. The observations were made in October 1997 and are reported today (April 20) in the Astrophysical Journal Letters.
Looking in the far-infrared region of the electromagnetic spectrum, the astronomers observed the characteristic signature of emission by water vapor. "The interstellar gas cloud that we observed is being pummeled by shock waves that compress and heat the gas," says Harwit, who is a Cornell professor emeritus, an ISO mission scientist and lead author on the research report. "These shock waves are the result of the violent early stages of star birth in which a young star spews out gas that slams into its surroundings at high speed. The heated water vapor that we observed is the result of that collision," he says.
Such a high concentration of water in Orion's giant gas cloud, which swirls around millions of stars along our spiral arm of the Milky Way, 1,500 light years from the sun, could have implications for the origin of water in the solar system, says ISO team member David Neufeld, professor of physics and astronomy at Johns Hopkins University. "The interstellar gas cloud that we observed in Orion seems to be a huge chemical factory generating enough water molecules in a single day to fill the Earth's oceans 60 times over."
Eventually, he says, the water vapor will freeze, becoming small ice particles. Similar ice particles are thought to have been present within the gas cloud from which the solar system originally formed. "It seems quite plausible that much of the water in the solar system was originally produced in a giant water vapor factory like the one we have observed in Orion," Neufeld says.
Cornell's Harwit speculates that the shock waves observed in the Orion gas cloud could be a cause as well as the result of star birth. The shock waves might also trigger the formation of additional stars and planets as they compress the gas cloud -- if the heat can be radiated away, says Harwit. "Water vapor is a particularly efficient radiator at far-infrared wavelengths and plays a critical role in cooling the gas and facilitating star formation," he notes.
The concentration of water vapor measured by the team was about one part in 2,000 by volume. The new observations confirm predictions by astrophysicists over the past 25 years that whenever the temperature exceeds 200 degrees Fahrenheit, chemical reactions will convert most of the oxygen atoms in interstellar gas into water.
"An enhanced concentrator of water is precisely what we expected in this gas cloud," says team member Gary Melnick of the Harvard-Smithsonian Center for Astrophysics. He adds that the strength of the water radiation detected from Orion was in perfect agreement with theoretical predictions published in the doctoral thesis of team member Michael Kaufman, a former Johns Hopkins graduate student now at NASA's Ames Research Center.
Panels showing two examples of measurements carried out on board the ISO, together with an image of the Orion nebula taken with the Wide Field Planetary Camera 2 on NASA's Hubble Space Telescope, can be seen on the World Wide Web at http://www.pha.jhu.edu/~neufeld/orionwater.html
PHOTO CAPTION:
The panels at the upper left and lower right show two examples of flux measurements carried out by the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). They indicate the presence of a large concentration of water vapor.
The central panel is an image of the Orion nebula taken with the Wide Field Planetary Camera 2 (WFPC2) on NASA's Hubble Space Telescope (HST) and shows the region of space where the water vapor was detected.
ESA
Paris, 9 April 1998
At 07:00 on 8 April 1998, engineers at ESA's ground station at Villafranca near Madrid reported that ISO's telescope was beginning to warm up, above its nominal operating temperature close to absolute zero. This was the sign that ISO had exhausted the superfluid helium used to achieve the very low temperatures necessary for infrared astronomy.
Observations ceased at 23h07 when the temperature of the instruments had risen above -269?C. At that time, ISO was observing the galaxy NGC 1808 with the camera (ISOCAM) for Prof. J. Hough (UK). The astronomers then handed ISO over to the engineering team for check-outs and decommissioning. The spacecraft will be switched off in about 28 days' time.
Infrared rays come from cool places in the sky, and ISO would have been dazzled by its own heat unless its optical system were extremely cold. At its launch in November 1995, ISO carried a supply of 2000 litres of superfluid helium, which boils at -271 degrees C. Slow venting of the helium into space maintained the low temperature of the optical system.
How did ISO achieve its extended life? Three months came from a prudent safety margin in the engineering calculations of the rate of loss of helium. Two months were the result of favourable circumstances in the launch campaign at Kourou in French Guiana. During a technical check of the Ariane 44P launcher, ISO's engineers seized the chance to recharge the helium, and the quick launch that followed meant that the outer parts of the cryogenic system of the spacecraft had little time to warm up in Kourou's tropical climate.
Finally, the daily loss of helium turned out to be 17 less than expected, at the lower end of a range of possibilities considered by the engineers. That gave ISO an estimated five months of additional life.
The date for the helium to run out remained somewhat uncertain, and astronomers and engineers have been alert to the possibility of its exhaustion for the past few weeks. The huge bonus to astronomers, from ISO's long operating life, is only one of their reasons to be grateful for the highly successful engineering and operations of ISO. The pointing accuracy of ISO's telescope was ten times better than required by the specification, and its jitter was one-fifth of what would have been considered tolerable. Smooth, well-planned operations were extended on a daily basis by a US ground station supporting ESA's Villafranca station. ISO was observing selected targets in the sky for 90-95 of the time available.
Even in between the planned observations a "serendipity" programme with the ISOPHOT instrument charted cool objects as ISO slewed from one target to the next.
Although ISO's observations are now completed, astronomers will be analysing them for years to come, assisted by a team of mission experts who will continue their work at Villafranca and other centres worldwide until 2001.
Commenting on the completion of ISO's observational phase, ESA's director of science, Roger Bonnet, says: We always knew that ISO's helium would run out one day, and we can be grateful that it has lasted for so long. This is a time for celebration, not sorrow, and I congratulate the VILSPA, ESTEC and ESOC staff who have operated so efficiently the spacecraft as well as European industry which developed such an excellent mission and our scientists who built such an outstanding payload . I wish European astronomers as well as their colleagues from the USA and Japan to now fully exploit the image data acquired by ISO".
ESA
Paris 7 April 1998
ISO's operational teams at ESA's ground station at Villafranca near Madrid have been hurrying to provide the world's astronomers with as many observations as possible. They have long anticipated the exhaustion of ISO's vital supply of liquid helium, which cooled the infrared telescope and its instruments to their operating temperatures, close to absolute zero. Two weeks after ISO was put into orbit on 17 November 1995 by an Ariane 44P launcher, the external parts of the cooling system had settled to the operating temperature. The specification required that ISO should then operate for at least 18 months -- implying that operations might have to end in May 1997.
Thanks to superb engineering by European industry, which built the spacecraft and its super-cool telescope, ISO has given astronomers almost a year longer than that. During the extra time the count of ISO's observations of cosmic objects has risen from 16,000 to about 26,000. Among the benefits of ISO's longevity has been the chance to examine an important region of the sky, in and around the constellation of Orion. This was not accessible in the nominal mission but has now been observed in two periods.
Four inter national teams, supported by national funding agencies, supplied the instruments to analyse the infrared rays received by ISO's telescope. The principal investigators leading the teams are Dietrich Lemke (Heidelberg, Germany) for the versatile photometer ISOPHOT, Catherine Cesarsky (Saclay, France) for the camera ISOCAM, Thijs de Graauw (Groningen, the Netherlands) for the Short Wavelength Spectrometer SWS, and Peter Clegg (London, UK) for the Long Wavelength Spectrometer LWS.
As previously reported, ISO has identified stony materials, tarry compounds of carbon, and vapours and ices like water and carbon monoxide. Together they give the first clear picture of how Mother Nature prepares, from elements manufactured in stars, the ingredients needed for planets and for life itself.
Particularly striking for the human imagination are ISO's repeated discoveries of water in the deserts of space. They encourage expectations of life elsewhere in the Universe. Water has turned up around dying stars, newborn stars, in the general interstellar medium, in the atmospheres of the outer planets and in other galaxies too. A link to the Earth's oceans and the water we live by comes in the water- ice long known to be a major ingredient of comets, which are relics from the era of planet-building.
A further link to the investigation of the origin of life is the apparent detection of water vapour in the mysterious atmosphere of Saturn's largest moon, Titan. A preliminary announcement comes from an international team headed by Athena Coustenis of Paris Observatory and Alberto Salama of the ISO Science Operations Center at Villafranca.
The team used ISO's Short Wavelength Spectrometer during several hours of observations last December, when Titan was at its farthest from Saturn as seen by ISO. Emissions at wavelengths of 39 and 44 microns showed up, as an expected signature of water vapour. The news will excite the scientists involved in ESA's probe Huygens, launched last year aboard NASA's Cassini spacecraft. It will parachute into Titan's atmosphere to see what the chemistry of the Earth may have been like before life began.
"Water vapour makes Titan much richer," comments Athena Coustenis. "We knew there was carbon monoxide and carbon dioxide in Titan's atmosphere, so we expected water vapour too. Now that we believe we've found it, we can expect to better understand the organic chemistry taking place on Titan and also the sources of oxygen in the Saturnian System. After ISO, the Huygens probe will reveal the actual degree of complexity in a mixture of elaborate organic molecules closely resembling the chemical soup on the young Earth."
Other well-known nebulae in the Orion region include NGC 2068 and NGC 2071. Emission by carbon compounds (polycyclic aromatic hydrocarbons or PAH) makes the infrared nebulae spectacular, as seen by ISOCAM. And thanks to ISOCAM's sensitivity and the ability of infrared rays to penetrate a dust cloud better than visible light, ballet corps of young stars appear on the stage, seen as spots in the centre of these two nebulae. This is not surprising, because the dense, dusty regions called molecular clouds are often the breeding grounds of new stars, but ISOCAM detects fainter and more obscured objects.
"We have used ISOCAM to make a census of families of young stars," comment Lennart Nordh and Goran Olofsson of Stockholm University, who lead a team of astronomers from Sweden, France, Italy, the UK and ESA. "By comparing the intensities of the point-like objects at different infrared wavelengths we can efficiently identify the ensemble of young stars still embedded in its parental molecular clouds."
From their study of ISO's early observations of four star-forming clouds, the astronomers report the detection of small stars. "Almost 300 young stars have been identified to date, many of which were previously not recognized," Nordh and Olofsson say. "Most of the latter objects have luminosities 10-100 times lower than revealed by earlier observations. Our preliminary analysis indicates that at least ten per cent of the embedded young stars will become small brown dwarfs, or ownerless super-planets, less than one-tenth of the mass of the Sun."
A famous pair of colliding galaxies called the Antennae was one of the first objects to be examined by ISO. Continuing study of the Antennae over the past two years has revealed a clear picture of a starburst occurring exactly where the dense disks of the galaxies intersect. The nuclei of the two galaxies are plainly distinguished too.
Centaurus A is a galaxy that first attracted the attention of astronomers by its strong of radio emissions. In its visible appearance, a large, round (elliptical) galaxy has a dark band across its face. This too turns out to be the result of a galactic collision. The dark band is a flat, disk-shaped galaxy seen almost edge-on. Centaurus A is the nearest case of a phenomenon seen elsewhere by ISO, in which a flat galaxy has merged with an elliptical galaxy while preserving its flat configuration.
ISOCAM gives an image of Centaurus A in which the disk galaxy is the more conspicuous object. The orientation of the disk becomes clear. It is at right angles to the axis of the radio-emitting regions, which are powered by jets of electrons driven by a black hole in the centre of the galaxy. Excited emissions detected by ISO's Short Wavelength Spectrometer also indicate the presence of an active black hole.
"Centaurus A is an example of ISO's magic," says Catherine Cesarsky of CEA Saclay in France, leader of the ISOCAM instrument team. "It transforms opaque clouds seen by visible light into glowing scenes in the infrared. The same thing happens in dust clouds hiding newborn stars, and on a huge scale in dusty starburst galaxies -- which become infrared beacons lighting our way deep into the Universe."
Both for ISO and the Hubble Space Telescope these holes have been special targets for observations with long exposures, to reveal faint galaxies. ISOCAM results through the northern hole, by a Japanese-led team, were reported last year in an ESA Information Note (25.97) and a picture release (ESA/ISO 97:8/1). They revealed many infrared-luminous galaxies billions of light- years away, from an era corresponding with about half the present age of the Universe. Even more distant and earlier galaxies may be present in ISO's observations, including some objects not yet seen by visible light.
Results released at the London press briefing on ISO include "deep field" examinations by groups of astronomers led by Catherine Cesarsky of CEA Saclay and Michael Rowan Robinson of Imperial College, London, analysing the northern and southern images respectively. In the northern deep field, when ISOCAM observations are superimposed on a Hubble picture of the same region, they pick out spiral galaxies experiencing starbursts. A different signature comes from large elliptical galaxies whose visible light has been shifted into the infrared by the expansion of the Universe. The astronomers estimate that some of the objects seen by ISOCAM are so far away that the Universe was only one-third of its present age when they emitted the radiation seen today.
The first ISO images from the opposite direction in the sky, in the southern deep field, show similar objects, again at great distances. A preliminary analysis indicates the presence of of 30-40 remote galaxies seen at a wavelength of 7 microns and 22-30 at 15 microns. One interesting source, bright in the infrared, is not seen by visible light even in a prolonged examination by the CTIO 4-metre telescope in Chile (A. Walker). Astronomers suspect that this object is undergoing an especially violent period of star formation. The interpretation can be checked when Hubble and other telescopes have a chance to examine this scene.
Besides illuminating the evolution of the galaxies, ISO's deep field results are encouraging for scientists planning another of ESA's astronomical space projects, FIRST. Its longer wavelengths will penetrate even deeper into the unknown.
Activity concerning ISO will continue at the Villafranca ground station until the year 2001, long after the completion of the observational phase of the mission. During the space operations, the main objective was to make as many observations as possible. Thorough analysis and interpretation of the results will take several years.
"We still have plenty to do," says Martin Kessler, ESA's project scientist for ISO. "Our team at Villafranca is preparing a complete archive of ISO data on 500-1000 compact disks, after reprocessing with improved software. We'll release part of this archive to the world-wide astronomical community in the autumn of this year, and the rest in 1999. We shall also advise the astronomers who have used ISO, about the particular requirements for handling the data from each instrument, and we'll be doing some astronomy ourselves. There are far more results still to come from ISO."
Europe's infrared astronomers are already busy preparing ESA's FIRST and Planck missions, due for launch early in the new century. FIRST will observe long infrared wavelengths in the sub-millimetre range, while Planck will map the cosmic microwave background far more accurately than NASA's COBE mission did, to reveal the clumps of matter from which galaxies evolved. Also under study by ESA is a possible interferometer mission using a combination of infrared telescopes. In principle it might observe and characterize planets in orbit around other stars.
Meanwhile, Europe's space astronomy programme continues apace in other directions. ESA's participation in the Hubble Space Telescope and its eventual successor assures access to those important instruments for Europe's astronomers. The release in 1997 of the catalogues from ESA's unique star-mapping mission Hipparcos provided all astronomer with amazingly precise data for sizing up the stars and the wider Universe. Next year will see the launch of ESA's XMM satellite to observe X-rays from the Universe with the most ingenious and sensitive X-ray telescopes ever made. It will be followed by Integral in 2001, which will investigate cosmic gamma-rays with clever imaging devices called coded masks, and ultra-sensitive detectors.
"Our aim in space astronomy is that every ESA mission should be the best in the world at the time of its launch," says Roger Bonnet, ESA's director of science. "ISO is a shining example. It has revolutionized infrared astronomy. It has given us wonderful insights into cool and hidden places in the Universe, and into the origins of water and other materials to which we owe our very existence. A mission of this scale and complexity was feasible for Europe only through the multinational collaboration coordinated by ESA."
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