Herschel/SPIRE image of Comet 103P/Hartley 2
This image shows comet 103P/Hartley 2 as viewed with the SPIRE instrument on board Herschel. The image was taken on 25 October 2010 at 250 microns, and covers a region of 1.7 arcminutes × 1.3 arcminutes. At the time the comet was 17.5 million km from the Herschel Space Observatory.
Herschel has obtained unique, sensitive far-infrared continuum images constraining the size of the large dust particles. This is the first time a comet has been imaged in this portion of the electromagnetic spectrum. The Sun symbol and arrow indicate the projected direction towards the Sun.
Spectroscopic data, acquired on the same occasion with the HIFI spectrometer on board Herschel, have revealed that comet 103P/Hartley 2 contains water with a similar deuterium-to-hydrogen ratio to that in Earth's oceans. This is the first evidence of a comet harbouring Earth-like water.