ESA Herschel Telescope finds WATER !!!
'Silver sensation' seeks cold cosmos
By Jonathan Amos
Science reporter, BBC News
Stare into the curve of Herschel's mirror too long and you get a slightly giddy feeling that comes from not being able to judge where its surface really starts.
It is enchanting, spectacular and - at 3.5m in diameter - it will soon become the biggest telescope mirror in space, surpassing that of Hubble.
The great 18th Century astronomer William Herschel would have been astonished by the silver sensation that now bears his name.
The design keeps Herschel's critical detectors in an ultra-cold state
The European Space Agency (Esa) is certainly very proud of its new observatory. It has been working on the venture for more than 20 years.
"The mirror is an enormous piece of hardware," enthused Thomas Passvogel, Esa's programme manager on the Herschel space observatory.
"It's a ceramic mirror; it's the biggest piece ever made from silicon carbide. It's very hard but much, much lighter than glass and the performance is excellent."
This week, the finished observatory will be flown to Europe's Kourou spaceport in South America. There, it will be bolted to an Ariane rocket and hurled into orbit.
It will take up a vantage point a million-and-a-half kilometres from Earth, to open up what scientists expect to be an utterly fascinating new vista on the Universe.
"Very simply, the science pillars of Herschel are to understand better how stars and galaxies form and how they evolve," Göran Pilbratt, Esa's project scientist on Herschel, told BBC News.
Unlike Hubble, which is tuned to see the cosmos in the same light that is visible to our eyes, Herschel will go after much longer wavelength radiation - in the far-infrared and sub-millimetre range.
It will permit Herschel to see past the dust that scatters Hubble's visible wavelengths, and to gaze at really cold places and objects in the Universe - from the birthing clouds of new stars to the icy comets that live far out in the Solar System.
Some of these targets, though, are frigid in the extreme (between five and 50K; or -268 to -223C); and for Herschel to register them requires an even colder state be achieved on the observatory itself.
This involves the use of a cryostat. It is akin to a giant "thermos" bottle. Filled with more than 2,000 litres of liquid helium, its systems will plunge Herschel's science instruments into the deepest of chills.
Critical detectors will be taken to just fractions of a degree above absolute zero (0K; -273C), from where they can make the most of their remarkable design performance.
"Imagine one million, million, millionth of the brightness of a 60W lightbulb - that's what we can detect with one of our detectors," explained Professor Matt Griffin, who leads the international consortium behind SPIRE (Spectral and Photometric Imaging Receiver), one of Herschel's three instruments.
"Turning that around - imagine observing one of our very faint sources; let's say a very distant galaxy. If we were to observe it with SPIRE for a billion years, we would collect enough energy to light that 60W lightbulb for just one-twentieth of a second," the Cardiff University, UK, researcher said.
Herschel's other instruments are HIFI (the Heterodyne Instrument for the Far Infrared) and PACS (Photodetector Array Camera and Spectrometer).
With the entire package, the observatory can investigate a broad range of wavelengths (55-672 microns), including a swathe that has hitherto been missed by orbiting telescopes.
The classic "Pillars of Creation", great columns of gas and dust. Viewing the star-forming region at progressively longer wavelengths opens up new features
(A) Visible light: Reflected light from the nebula is seen (0.5µm)
(B) Near-infrared: Nebula suddenly becomes transparent (1-2µm)
(C) Even longer: Possible to see emission from the nebula itself (7µm)
(D) Longer still: Different structures start to become apparent (50µm)
Herschel's interest will be piqued near and far.
Close to home, it will study the mountainous balls of ice, dust and rock (some of them comets) that orbit our Sun beyond Neptune. The nature of these "primitive" objects has an important bearing on the story of how our Solar System came into being.
And beyond our little corner of space, Herschel's vision will allow it to see inside the clouds of gas and dust that give rise to stars in the Milky Way galaxy today, to see the conditions "in the womb". Studying these embryonic events will give astronomers further insights into the Solar System's beginnings 4.5 billion years ago.
Once the liquid helium boils off, Herschel's instruments will go blind
Another key target for Herschel's investigations will be those galaxies that thrived when the Universe was roughly a half to a fifth of its present age. It is a period in cosmic history when it is thought star formation was at its most prolific.
Herschel will need to look deep into space to make these observations. The data will be used by scientists to test their models of how and when the galaxies formed their stars and how successive generations of those stars produced the abundance of heavy elements (everything heavier than hydrogen and helium) that now exist in the Universe.
Professor Griffin summed up the Esa mission in this way: "Herschel is not about studying mature stars or galaxies; it is really about studying the processes by which they are created.
"We know very little about that and we need to understand it in order to put together a picture of how the Universe we live in today grew from the earliest stages after the Big Bang."
A double deal
Herschel's launch will be doubly significant because it sees Esa loft two major science missions on a single rocket. The other passenger on the Ariane will be the Planck telescope, which will look at even longer wavelength (microwave) radiation.
Herschel will share its ride with the Planck telescope
Read about Esa's Planck mission
One reason for the dual launch, says Esa's head of science projects, Jacques Louet, is logistics. Both telescopes have been designed to operate at the so-called Lagrange Point 2, a gravitational "sweet spot" in space where the observatories can stay fixed in the same location relative to the Earth and the Sun.
"The other reason is that we have coupled them industrially," he told BBC News.
"Both spacecraft share the same service module, so there is an economy in building them together. And because you build them together, you have basically the same timing on each mission. So, overall, I think it is a good strategy, but a risky strategy."
At a combined value for Hershel and Planck of approximately 1.7 billion euros, you get an idea of just how risky this strategy is. If the rocket fails, both missions are lost.
One is tempted to say "good luck"; but as Göran Pilbratt points out, when you have put as much effort into these missions as Esa has over the past 20 years, "luck doesn't come into it".
Herschel-Planck Mission Will Be ESA's Highest-Stake Science Endeavor Ever
Apr 5, 2009
| By Michael A. Taverna |
Of all the uncertainties that bewilder astronomers, none is more puzzling than what transpired in the first millionth of a second after the Big Bang. Understanding what occurred then will help unravel some of the best-kept secrets in the universe - including the density and nature of matter, the existence of "dark energy," and the origins of stars and galaxies.
That will be the objective of a €1.3-billion ($1.7-billion) twin-telescope mission due to lift off from the European spaceport at Kourou, French Guiana, at the end of April.
Herschel - the larger of the two telescopes - will study the formation and evolution of galaxies and stars. Like its predecessor, the Infrared Space Observatory (ISO), and earlier probes from the U.S. (Spitzer) and Japan (Akari), this mission will make observations in infrared wavelengths, not in visible light, as does the big Hubble Space Telescope. This will make it possible to view relatively cool and diffuse matter, such as interstellar and circumstellar dust and gas, or hidden stars and galaxies, which have gone largely unseen so far. "By observing in the infrared, we can study how things get formed, the very early steps, because formation processes very often happen in cool and dusty places," explains Goran Pilbratt, the European Space Agency's Herschel project scientist.
Named after the British astronomer William Herschel, who discovered infrared radiation (as well as the planet Uranus), the three-axis stabilized spacecraft - which is about 7.5 meters (24.5 ft.) high and weighs 3,300 kg. (7,260 lb.) - will operate in the far infrared to submillimeter wavelengths (60-670 microns). These are the bands in which - because of a displacement known as the red shift - the light from the most distant and youngest galaxies (which existed in the initial period after the Big Bang) emit. In addition to its primary mission, Herschel will study the chemical composition of the atmosphere around celestial bodies - in particular, interesting objects discovered in earlier missions - and explore the molecular chemistry of the universe, notably by studying the atmospheres of comets.
Initially called the Far Infrared and Submillimeter Telescope (First), Herschel is equipped with a primary mirror 3.5 meters in diameter that is half again as big as the one on Hubble. It will remain the largest until Hubble's successor, the James Webb Space Telescope (JWST), is launched around 2013.
The second telescope on this mission, Planck, will survey the whole sky to help scientists understand the origin and evolution of the large structures that inhabited the universe immediately after the Big Bang. Carrying on from NASA's Cosmic Background Explorer, launched in 1989, and the Wilkinson Microwave Anisotropy Probe, sent aloft in 2001, the 1,800-kg. Planck will measure the temperature fluctuations (or anisotropies) of the cosmic microwave background (CMB) with unprecedented resolution and sensitivity. Astronomers hope that such ultra-precise measurements will help determine fundamental cosmological conundrums - such as the density parameter and the Hubble constant - that have long eluded their grasp. A further objective of the mission, which will observe the sky simultaneously in nine frequency channels from 30-900 GHz., will be to derive the polarization state of the CMB, which has never been done before.
Moreover, there is a possibility that Planck - which was named after the German physicist Max Planck, the founder of quantum theory - will detect a slight distortion of the CMB caused by a suspected period in cosmic history known as the inflationary epoch. Inflationary theory postulates that the universe underwent a period of enormously accelerated expansion just after the Big Bang that should cause the whole of space to ripple in a special way. This slight ripple might show up in the Planck data. "Of all the exiting science that we will do, this is the most exciting possible measurement of all," says Jan Tauber, the Planck project scientist.
Herschel and Planck will be lofted into orbit by the same Ariane 5 ECA heavy-lift rocket. The two spacecraft will then journey independently to the L2 Lagrange point, 1.5 million km. (930,000 mi.) from Earth, where they will operate unaffected by Earth, lunar or solar gravity effects. Upon arrival, 60 days after launch, they will be inserted into Lissajous formation, with Herschel in the larger of two concentric orbits and Planck in the smaller one. Herschel is expected to remain in operation for at least 3.5 years and Planck, for 18 months - long enough to map at least 95% of the sky twice.
The telescopes were combined in a single mission in an attempt to save money for ESA's perennially underfunded science program. However, the complexities involved in readying two such sophisticated telescopes at the same time caused a €180-million cost overrun and pushed back liftoff well beyond the initial February 2007 launch date. "It was a nightmare," acknowledged Jacques Louet, ESA's head of science projects (AW&ST Apr. 24, 2006, p. 38). The experience convinced planners to opt for a different approach based on sharing bus, instruments and subsystems in single, smaller missions, as has been done on Mars Express and Venus Express.
Both Herschel and Planck employ cutting-edge technologies, in particular reflectors and cryogenic coolers, which caused the most design headaches. Thales Alenia Space, which built ISO, is prime contractor for the twin mission.
Thales Alenia's Italian arm is supplying the bus for the two satellites, while EADS Astrium is responsible for Herschel payload and integration. Numerous subcontractors and institutes from nations - including the U.S., Russia, Israel and Taiwan - are participating.
Herschel's primary mirror - which replaced a carbon-fiber composite design that NASA had initially planned to contribute - is made entirely of silicon carbide (SiC), a lightweight composite that makes it possible to build very large mirrors with excellent thermal, mechanical and acoustic properties without incurring a prohibitive weight penalty. Unlike the beryllium JWST mirror, which will be 6.5 meters in diameter, the Herschel unit will be monolithic, not folding.
Despite its size, the 3-mm. thick Herschel reflector will weigh barely 320 kg., versus 1,000 kg. for that on Hubble.
Engineers at Boostec, an Astrium affiliate that built the mirror, say the primary difficulty in single-piece constructions of this size is brazing the 12 petals together within tolerances that guarantee optical performance.
Specifications require that the mirror surface roughness be less than 30 nanometers and reflectivity, better than 0.97 (AW&ST Feb. 23, 2004, p. 95). The same SiC technology will be used in ESA's Gaia observatory, to be launched in late 2011, and Japan's Spica, a cooperative mission with ESA that will work in shorter IR wavelengths than Herschel.
Herschel will also feature an advanced cryostat, derived from experience with ISO, that will allow instruments to operate at 1.7 Kelvin (-271C) - a fraction above absolute zero - to prevent it from emitting infrared emissions and thus obscuring incoming infrared light. The spacecraft will always be facing the Sun to maximize energy from the solar panels. A shield will help protect it from the Sun's glare.
Designing the cryostat - with a main tank designed to hold 2,250 liters of liquid helium and a 50-liter buffer tank that keeps the main tank cold while on the ground - posed the biggest technology challenge in the Herschel-Planck mission. The cryostat could complicate launch arrangements, too, because it will be unable to tolerate a flight slip of more than 24 hr. If delayed beyond that point, it will be necessary to roll back the rocket to the assembly building so the cryostat main tank can be emptied, refilled and subcooled.
Planck will use a special low-spin platform equipped with a 1.5-meter offset Cassegrain telescope designed to focus cosmic background radiation toward its detectors. The reflector was developed by the Danish Space Research Institute and ESA. The telescope's high-frequency detectors are passively cooled by means of a cooling chain (comprising a 20K hydrogen sorption cooler, a compressor-driven 4K cooler and a dilution cooler) that maintain the temperature at 0.1K, essential for obtaining high sensitivity. Sensitivity will be better than 2 X 10-6 and angular resolution, 10 arcminutes.
Herschel will carry:
·The Heterodyne Instrument for the Far Infrared (HIFI), built by Frank Helmich of the Netherlands Institute for Space Research in Groningen. HIFI will perform high- and very-high-resolution spectroscopy in the 250-600-micron range, useful for obtaining information on chemical composition and kinematics.
·A Photodetector Array Camera and Spectrometer (PACS), built by a consortium led by Albrecht Poglitsch of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. PACS will handle image line spectroscopy and photometry in the 80-210-micron bands.
·The Spectral and Photometric Imaging Receiver (Spire), an incoherent bolometric instrument assembled by a team led by Matthew Griffin of Cardiff University in Wales. Spire will run photometry measurements simultaneously in three bands and spectroscopy across the whole 260-670-micron wavelength range.
The Planck package comprises low- and high-frequency instruments (LFI/HFI). The LFI - developed by Nazzareno Mandolesi at the Institute of Space Astrophysics in Bologna, Italy - consists of an array of tuned radiometers that use 56 high-electron-mobility-transistor detectors; these will convert microwaves into radiation intensity for each frequency. The HFI, led by Jean-Loup Puget of the Institute for Space Astrophysics in Paris, will investigate the 100-857-GHz. frequency range using 48 bolometric detectors, useful for pinpointing and measuring small amounts of thermal radiation.
Astronomers expect measurements from the five instruments to provide the most detailed picture yet of different aspects of the cold cosmos, setting the stage for missions to follow at the end of the next decade.
|A bit of History about Infrared|
|The discovery of Infrared Radiation|
|William Herschel, an amateur astronomer famous for the discovery of Uranus in 1781, made an important discovery in 1800. Herschel was familiar with Newton’s discovery that sunlight could be separated into that separate chromatic components via refraction through a glass prism. Herschel thought that the colors themselves might contain different levels of heat, so he devised a clever experiment to investigate this. Herschel passed sunlight through a glass prism to create a spectrum (the rainbow created when light is divided into its color components) and measured the temperatures of the different colors. He used three thermometers with blackened bulbs and placed one bulb in each color while the other two were placed outside the spectrum as controls.|
|Sunlight passes through a prism forming the usual rainbow spectrum. A row of thermometers is positioned on a table beyond the red end of the spectrum. Thermometer 1, aligned with the spectrum, registers a rise in temperature, while the control thermometers 2 and 3 do not.|
|As he measured the temperature of the violet, blue, green, yellow, orange and red light, he noticed that all the colors had temperatures higher than the controls and that the temperature increased from the violet to the red part of the spectrum. After understanding this pattern, Herschel measured the temperature just beyond the red portion of the spectrum and found this area had the highest temperature of all and thus contained the most heat. What Herschel discovered was a form of light beyond red light. Herschel’s experiment was important not only because it lead to the discovery of infrared light, but because it was the first experiment that showed there were forms of light not visible to the human eye.|
|Beginning with Herschel’s observations we now understand the full nature of electromagnetic radiation and have developed a wide range of technologies to observe it and exploit it to man’s benefit.|
The mission, formerly titled the Far Infrared and Sub-millimetre Telescope (FIRST), will be the first space observatory to cover the full far infrared and submillimetre waveband. At 3.5 meters wide, its telescope will incorporate the largest mirror ever deployed in space. The light will be focused onto three instruments with detectors kept at temperatures below 2 K. The instruments will be cooled with liquid helium, boiling away in a near vacuum at a temperature of approximately 1.4 K. The 2,000 litres of helium on board the satellite will limit its operational lifetime. The satellite is expected to be operational for at least 3 years.
Herschel will carry aboard three detectors:
- PACS (Photodetecting Array Camera and Spectrometer)
- An imaging camera and low-resolution spectrometer covering 55 to 210 micrometres. The spectrometer will have a resolution between 1000 and 5000 and be able to detect signals as weak as a few times 10-18 W/m². The imaging camera will be able to image simultaneously in two bands (either 60-85/85-130 micrometres and 130-210 micrometres) with a detection limit of a few millijanskys.
- SPIRE (Spectral and Photometric Imaging Receiver)
- An imaging camera and low-resolution spectrometer covering 194 to 672 micrometres. The spectrometer will have a resolution between 40 and 1000 at wavelengths of 250 micrometres and be able to image point sources with brightnesses around 100 millijanskys (mjy) and extended sources with brightnesses of around 500 mjy. The imaging camera has three bands, centered at 250, 350 and 500 micrometres, each with 139, 88 and 43 pixels respectively. It should be able to detect point sources with brightness above 2 mjy and between 4 and 9 mjy for extended sources. A prototype of the SPIRE imaging camera flew on the BLAST high-altitude balloon.
- HIFI (Heterodyne Instrument for the Far Infrared)
- A detector with a spectral resolution as high as 107. The spectrometer can be operated within two wavelength bands, from 157 to 212 micrometres and from 240 to 625 micrometres.
Herschel will specialise in collecting light from objects in our Solar System as well as the Milky Way and even extragalactic objects billions of light-years away, such as newborn galaxies, and is charged with four primary areas of investigation:
- Galaxy formation in the early universe and the evolution of galaxies;
- Star formation and its interaction with the interstellar medium;
- Chemical composition of atmospheres and surfaces of Solar System bodies, including planets, comets and moons;
- Molecular chemistry across the universe.
Launch and orbit
The satellite, built in the Cannes Mandelieu Space Center with a joint launch cost of €1.1 billion (US$1.7 billion), will be carried with the Planck satellite into space by an Ariane 5 ECA rocket, scheduled for 14 May 2009.
In July 2009, app. sixty days after launch, it will enter a Lissajous orbit of 800,000 km average radius around the second Lagrangian point (L2) of the Earth-Sun system, 1.5 million kilometres from the Earth. The mission is named after Sir William Herschel, the discoverer of the infrared spectrum.
With HIFI it will be possible for the first time ever to get a complete inventory of the most important rotational lines of water and its isotopomers. It therefore provides a really unique possibility to trace the water evolution from its origins to its dissociation. This water trail will be one of the key science subjects for HIFI.
Water has many lines available with intrinsic strengths that vary over several orders of magnitude and at energy levels from almost zero to several thousands K. Different water lines will therefore probe vastly different environments
Here we display some examples of the vastly different environments where water is (expected to be) found, "The Water Universe".
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