Soaring Success of the Herschel Space Observatory
What's Hot in Physics, May 2011
by Simon Mitton
The hottest news in the Physics Top Ten this time comes from the Herschel Space Observatory, which examines the coldest objects in the universe. Herschel is a project of the European Space Agency (ESA), and it was launched on May 14, 2009 on a mission to observe far away from Earth (1.5 x 106 km), tracking on a Lissajous orbit at the second Lagrangian point (L2) of the Sun-Earth-Moon system.
The observatory had been almost 30 years in the making: after ten years of feasibility studies it joined ESA’s must-do list in 1993. Assembly began in 2001. The telescope is named after William Herschel, to mark the 200th anniversary of his discovery (1800) of infrared light.
The prime science objectives of Herschel are intimately connected to the physics and processes of the interstellar medium (ISM) in the widest sense: near and far in both space and time, stretching from solar system objects, through star formation in the ISM, to the star-formation history of the universe, as well as galaxy evolution and cosmology.
The Herschel Space Observatory. From the Wiki
Commons.
Paper #1 has taken pole position on our grid because it is a frame-setting overview of this innovative ESA observing facility. Papers presenting the science outcomes usually cite #1, which covers spacecraft description, the telescope optics, the science instruments, and science operations.
The focal plane units of the instruments on Herschel must be cold enough that the thermal radiation from the detectors themselves does not overpower the weak signals from faraway objects. That’s why the cameras, spectrometers, and receivers are chilled to 2 K in a superfluid helium cryostat. But 2 K is too warm for the bolometers of the photodetector array camera and spectrometer, so they are further cooled to 0.3 K.
And of course, the read-out electronics has to work in this frigid environment. The downside of having a cryostat is that its helium slowly evaporates: with expected life of just 3.5 years, Herschel’s observers are racing against time, with only 20,000 hours of operation available.
On Herschel the telescope set-up is much larger than those used on previous infrared astronomy missions. The observational capability extends across the far-infrared and submillimeter spectral range 55- 671 µm, so Herschel bridges the gap between infrared and radio astronomy, and thereby sheds light on the cool universe.
William Herschel surely holds the record for the total amount of time any one person has spent surveying the heavens. He literally discovered the universe beyond our galaxy. It is fitting, therefore, that a large fraction of the Herschel observing time is allocated to large-scale photometric surveys in the far-infrared. The technical details of the array camera and spectrometer are described in paper #2. This general-purpose instrument operates in the range 60-210 µm. It is highly efficient, fully operational, and has achieved the pre-launch predictions.
Sir Frederick William Herschel, 15 November 1738 – 25 August 1822.
From the Wiki Commons.
Our trio of papers is completed by #3, which describes instrumentation broadly comparable to that in #2, but spanning 194-671 µm, which certainly does propel observers into poorly explored territory. This instrument performed brilliantly during in-flight testing.
Because Herschel has a limited life span, the first batch of results papers, 152 in all, covering the first few months of science operations, were published in a dedicated volume (518) of Astronomy and Astrophysics, and it is this collection that has rocketed these three papers on the observatory to the top of the table.
Highlights of Herschel’s early science include a look in the submillimeter band at the Great Observatories Origins Deep Survey, a window to the distant universe that has now been observed by many telescopes. Another surprise is high-resolution spectral scan of the Orion nebula has revealed water and a rich variety of organics in great detail. As a result it will now be possible to develop a deeper understanding of interstellar chemistry and to see how the chemical elements are recycled through the ISM and into regions of star formation.
The papers citing our top three are just a glimpse at the rich harvest that Herschel will yield. Herschel expands a huge scientific agenda of understanding how structure arises in the universe, and how the universe has evolved.
Dr. Simon Mitton is a science writer and Fellow of St. Edmund’s College, University of Cambridge.
Related information:
Speical Topic of Planetary Exploration, May 2011.
What's Hot in Physics | |||
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Rank | Paper |
Cites This Period Nov-Dec 10 |
Rank Last Period Sep-Oct 10 |
1 | G.L. Pilbratt, et al., "Herschel Space Observatory. An ESI facility for far-infrared and submillimetre astronomy," Astron. & Astrophys., 518: No. L1, July-August 2010. [ESA, Noordwijk, Netherlands; ESA, Madrid, Spain; ESA, Darmstadt, Germany] *646GQ | 191 | † |
2 | A. Poglitsch, et al., "The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory," Astron. & Astrophys., 518: No. L2, July-August 2010. [20 institutions worldwide] *646GQ | 117 | † |
3 | M.J. Griffin, et al., "The Herschel-SPIRE instrument and its in-flight performance," Astron. & Astrophys., 518: No. L3, July/August 2010. [36 institutions worldwide] *646GQ | 106 | † |
4 | E. Komatsu, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Cosmological interpretation," Astrophys. J. Suppl. Ser., 180(2): 330-76, February 2009. [14 institutions worldwide] *406EI | 105 | 1 |
5 | S.H. Park, et al., "Bulk heterojunction solar cells with internal quantum efficiency approaching 100%," Nature Photonics, 3(5): 297-302, May 2009. [U. Calif., Santa Barbara; Gwangju Inst. Sci. & Tech., S. Korea; U. Laval, Quebec City, Canada] *447UY | 65 | 3 |
6 | K.N. Abazajian, et al., "The Seventh Data Release of the Sloan Digital Sky Survey," Astrophys. J. Suppl. Ser., 182(2): 543-58, June 2009. [110 institutions worldwide] *448UE | 50 | 5 |
7 | J. Dunkley, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Likelihoods and parameters from the WMAP data," Astrophys. J. Suppl. Ser., 180(2): 306-29, February 2009. [14 U.S. and Canadian institutions] *406EI | 47 | 4 |
8 | O. Adriani, et al., "An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV," Nature, 458(7238): 607-9, 2 April 2009. [17 institutions worldwide] *427RK | 39 | 9 |
9 | H.Y. Chen, et al., "Polymer solar cells with enhanced open-circuit voltage and efficiency," Nature Photonics, 3(11): 649-53, November 2009. [Solarmer Energy, Inc., El Monte, CA; U. Calif., Los Angeles; U. Chicago, IL] *526PG | 36 | 9 |
10 | W.B. Atwood, et al., "The Large Area Telescope on the Fermi Gamma-Ray Space Telescope mission," Astrophys. J., 697(2): 1071-1102, 1 June 2009. [57 institutions worldwide] *446YT | 22 | † |
SOURCE: Thomson Reuters Hot Papers Database. Read the Legend. |