Author: tcavalie

The Herschel Space Observatory (Pilbratt et al. 2010) was launched on May 14th, 2009, to study the Universe in the submillimeter wavelength range. It carried three instruments: the Heterodyne Instrument for the Far-Infrared (HIFI ; de Graauw et al., 2010), the Photodetector Array Camera and Spectrometer (PACS ; Poglitsch et al., 2010), and the Spectral and Photometric Iaging Receiver (SPIRE ; Griffin et al., 2010).

The Herschel Guaranteed Time Key Program “Water and related chemistry in the Solar System” (PI: P. Hartogh, MPS, Germany), also known as “HssO” (Herschel Solar System Observations), proposes to determine the origin, the distribution and evolution of water and its isotopes in the atmospheres of Mars, the outer planets and Titan, and the comets (Hartogh et al. 2009).

 

The D/H ratio has been measured in the atmospheres of the giant planets and some comets to constrain the composition of the primordial ices of the Solar System (Feuchtgruber et al. 2013, Lis et al. 2013, Bockelée-Morvan et al. 2012, Hartogh et al. 2011). The water cycle of Mars is studied by monitoring the vertical profile of this species. Retrieving the vertical profile of water in giant planet stratospheres is key in assessing the type and magnitude of their external oxygen sources.

I have been involved in the preparation and execution of the HssO program since 2005. I am responsible for the science theme “Spatial distribution of water in Jupiter and Saturn”. In 2009-2010, I participated in the calibration activities of the HIFI Instrument Control Center (Roelfsema, et al., 2012)

HssO official website: https://www2.mps.mpg.de/projects/herschel/HssO/

Reference: Hartogh et al. 2009, Planetary and Space Science 57, 1596-1606.

Related posts:
The cometary water of Jupiter
A water torus discovered around Saturn
An external source of CO for Uranus

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A major discovery of the Infrared Space Observatory (ISO) was the detection of water vapor in the stratospheres of the giant planets and Titan (Feuchtgruber et al. 1997, Coustenis et al. 1998). It implies the existence of external sources of oxygen, as water condenses at the tropopauses of these planets and can therefore not come from their tropospheres.

This supply of oxygen material that manifests itself not only through water, but also carbon monoxide and carbon dioxide, has several possible sources:

• Interplanetary dust particles (IDP) produced by collisions of asteroids and by the activity of comets (Prather 1978, Landgraf et al. 2002)
• Icy rings and satellites (Strobel and Yung 1979, Prangé et al. 2006)
• Impact of Shoemaker-Levy 9 (SL9) type comets (Lellouch et al. 1995).

It is important to assess the relative magnitude of each of these sources to better understand the production of dust at high heliocentric distances (Kidger et al. 2003, Moses and Poppe 2017), the ionisation and/or transport of solid and gaseous material from rings and satellites to the upper atmospheres (Connerney 1986, Cassidy and Johnson 2010, Moore et al. 2015), and the frequency of comet impacts in the outer Solar System (Zahnle et al. 2003).

With Herschel, Odin and the JCMT, I have obtained new evidence regarding the origin of oxygen species in the stratospheres of giant planets.

Relevant posts:
The cometary water of Jupiter
An external source of CO for Uranus
Detection of a water torus around Saturn at the orbital distance of Enceladus
Is carbon monoxide of cometary origin in Saturn?

While observing Saturn’s water with Herschel in June 2009 with the goal of determining its origin, the HssO Team detected a cold water vapor torus orbiting around Saturn. This torus was absorbing Saturn’s emission because of a favorable observation geometry. It was Saturn’s equinox and Herschel was crossing Saturn’s ring plane. The analysis of the data shows that the torus is located at the orbital distance of Enceladus, one of Saturn’s small icy moons.

 

Observations of water in Saturn with SWAS in 1999 (top) and Herschel in 2009 (bottom). The observation geometry of Saturn and the Enceladus water torus is also displayed. Taken from Hartogh et al. (2011).

 

 

 

Interestingly, and a few years back, the Cassini mission had detected water geysers at the South Pole of Enceladus (Porco et al. 2006, Hansen et al. 2006, Waite et al. 2006). Cassidy and Johnson (2010) predict that a significant fraction of this water eventually rains into Saturn’s atmosphere. Additional observations of Saturn are required to assess whether this model is correct.

 

The geysers of Enceladus (credits: NASA)

 

 

 

 

Reference: Hartogh et al. 2011, Astronomy and Astrophysics 532, L2.

ESA press releases: click here for a short version, or here for a detailed version.

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