MSSL Planetary Science News
- Mars Advanced Summer School, China
- New Planetary Group Website Launched
- Cassini CAPS Team Meeting: Glacier National Park, Montana
- Workshop on future observations and study of Uranus
- Joint meeting of the European Planetology Network and Division of Planetary Sciences of the American Astronomical Society in Nantes, France
- 4th ExoMars Science Working Team Meeting, ESTEC, The Netherlands
- ScienceWatch interview with Prof. Andrew Coates
- Dr. Adam Masters wins the Robert Boyd Award for Outstanding Scientific Achievement
- Planetary Group attends the 2011 Fall meeting of the American Geophysical Union in San Francisco
- Dione's thin oxygen exosphere
- Dr. Gethyn Lewis attends a meeting of the Spacecraft Plasma Interaction Network
- Planetary group attends the RAS National Astronomy Meeting in Manchester
- Comet studies in the planetary group catch media attention at the RAS National Astronomy Meeting
- Planetary group scientists attend Cassini Magnetospheric and Plasma Science Meeting
- Selection of JUICE mission to Jupiter and Ganymede by ESA
- Planetary science group hosts Cassini CAPS Team Meeting 43
- Dr. Chris Arridge awarded a Royal Society University Research Fellowship
- Rover Trial
- Research Images Competition
- Kimberley Birkett awarded 2013 Outstanding Student Paper Award (OSPA) at the AGU Fall Meeting
- ExoMars landing sites narrowed down – and PanCam appears on BBC News
- Planetary Space Weather
- Venus is slowly losing its atmosphere
- Titan's atmosphere even more Earth-like than previously thought
- Planetary group student organises Sample Space Science Week at MSSL for sixth formers
- Ions from Comet 67P – early Rosetta results and increasing activity
- Cassini mission provides insight into Saturn
- UCL's ExoMars PanCam kit one step closer to Mars
- Saturn and Enceladus produce the same amount of plasma
- Giotto at Halley: 30 years ago!
- Solar storms trigger Jupiter's 'Northern Light'
- Liftoff to Mars!
- Strong 'electric wind' strips planets of oceans and atmospheres
Titan's atmosphere even more Earth-like than previously thought
18 June 2015
Scientists at UCL have observed how a widespread polar wind is driving gas from the atmosphere of Saturn’s moon Titan. The team analysed data gathered over seven years by the NASA/ESA Cassini probe, and found that the interactions between Titan’s atmosphere, and the solar magnetic field and radiation, create a wind of hydrocarbons and nitriles being blown away from the top of its atmosphere into space. This is very similar to the wind observed coming from the Earth’s polar regions.
Titan is a remarkable object in the Solar System. Like Earth and Venus, and unlike any other moon, it has a rocky surface and a thick atmosphere. It is the only object in the Solar System aside from the Earth to have rivers, rainfall and seas. It is bigger than the planet Mercury.
Thanks to these unique features, Titan has been studied more than any moon other than Earth’s, including numerous fly-bys by the Cassini probe, as well as the Huygens lander which touched down in 2004. On board Cassini is an instrument partly designed at UCL, the Cassini Plasma Spectrometer (CAPS), which was used in this study.
“Titan’s atmosphere is made up mainly of nitrogen and methane, with 50% higher pressure at its surface than on Earth,” said Andrew Coates (UCL Mullard Space Science Laboratory), who led the study. “Data from CAPS proved a few years ago that the top of Titan’s atmosphere is losing about seven tonnes of hydrocarbons and nitriles every day, but didn’t explain why this was happening. Our new study provides evidence for why this is happening.”
Hydrocarbons are a category of molecules that includes methane, as well as other familiar substances including petrol, natural gas and bitumen. Nitriles are molecules with nitrogen and carbon tightly bound together .
The new research, published today in the journal Geophysical Research Letters, explains that this atmospheric loss is driven by a polar wind powered by an interaction between sunlight, the solar magnetic field and the molecules present in the upper atmosphere.
“Although Titan is ten times further from the Sun than Earth is, its upper atmosphere is still bathed in light,” says Coates. “When the light hits molecules in Titan’s ionosphere, it ejects negatively charged electrons out of the hydrocarbon and nitrile molecules, leaving a positively charged particle behind. These electrons, known as photoelectrons, have a very specific energy of 24.1 electronvolts, which means they can be traced by the CAPS instrument, and easily distinguished from other electrons, as they propagate through the surrounding magnetic field.”
Unike Earth, Titan has no magnetic field of its own, but is surrounded by Saturn’s rapidly rotating magnetic field, which drapes forming a comet-like tail around the moon. In 23 fly-bys which passed through Titan’s ionosphere or its magnetic tail, CAPS detected measurable quantities of these photoelectrons up to 6.8 Titan radii away from the moon, because they can easily travel along the magnetic field lines.
The team found that these negatively-charged photoelectrons, spread throughout Titan’s ionosphere and the tail, set up an electrical field. The electrical field, in turn, is strong enough to pull the positively charged hydrocarbon and nitrile particles from the atmosphere throughout the sunlit portion of the atmosphere, setting up the widespread ‘polar wind’ that scientists have observed there.
This phenomenon has only been observed on Earth before, in
the polar regions where Earth’s magnetic field is open and oxygen ions can
escape. As Titan lacks its own magnetic field the same thing can occur over
wider regions, not just near the poles. A similarly widespread ‘polar wind’ is
strongly suspected to exist both on Mars and Venus – the two planets in the
Solar System which are most Earth-like. It gives further evidence of how Titan,
despite its location in orbit around a gas giant in the outer Solar System, is
one of the most Earth-like objects ever studied.
Image credit: MSSL/UCL
Page last modified on 18 jun 15 15:37