Herschel spectroscopy: update

In november Herschel has been carrying out performance verification phase (PVP) observations using the PACS and SPIRE spectrometers. A Herschel update by ESA provides some fine examples of observational results for a variety of astronomical objects. Spectra from HIFI – fully operational again in january 2010 – have determined the presence of organic molecules in massive star forming regions in our own galaxy (Orion nebula and DR21). HIFI also revealed a strong water line for the comet Garradd. For a complete update see the ESA log on Herschel spectroscopy.

Star formation

Fig.1 The HIFI spectrum on DR21

The Orion nebula and DR21 regions are examples of massive star forming regions (Fig. 1) in our own galaxy, the Milky Way. Observations of regions of massive star formation reveal a rich inventory of organic molecules. These spectral lines give insight in the chemistry and physical conditions in this region. The HIFI spectrum on DR21 reveals the fingerprints of a number of key organic molecules (formaldehyde, carbon sulfide, the formyl ion, the ethynyl radical, the methyladyne radical; HCO+, CH, C2H, H2CO and CS).


In the everlasting cold and darkness of the outskirts of Solar system, comets move unseen in their orbits. Comets are "dirty snowballs" – collections of small dust grains held together by ice – that were formed some 4.6 billion years ago in cold, outer regions of the Solar system. They represent left-over material from the formation of the Solar system. For most of their lives, comets dwell far from the Sun and hence they represent a rather pristine record of the early conditions from when the Solar system and the planets were formed. Small perturbations in their orbit can propel comets inwards. When they approach the Sun, the increased heat releases water and other molecules from the frozen nucleus, allowing us to measure the composition and characteristics of the comet.

Fig. 2 The HIFI spectrum of the comet Garradd reveals a strong water line

The HIFI spectrum of the comet Garradd reveals a strong water line (Fig. 2). Planned HIFI studies will inter-compare the characteristics of water and volatile organic molecules released by different comets in the Solar system as they approach the Sun. Comets may have contributed greatly to the inventory of volatiles such as water on the Earth and other terrestrial planets.