Andrew Coates on the Plasma Environments of the Planets
Special Topic of Planetary Exploration Interview, November 2011
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The scientific goal of ASPERA is to study the escape of the Mars and Venus atmosphere, and the related plasma processes. Mars and Venus lack a dipole magnetic field, unlike the Earth, though Mars has magnetic "anomalies." There have been a number of important advances in this area given the Mars Express and Venus Express data.
At Mars, the effect of the magnetic anomalies, regions of crustal magnetization left over from when Mars had a dipole magnetic field 3.8 billion years ago, has been something I've been investigating with the help of Ph.D. students. We have also been studying ionospheric photoelectrons at both Mars and Venus, and making comparisons with Titan. We think they may play a long-term role in atmospheric escape at these objects.
Over the last few years we have learned a good deal about both Mars and Venus. At Mars, many of the highlights are to do with water at Mars, either as seen in surface minerals e.g. clays, under the surface in ice form or escaping to space. Overall this helps us build up a picture of what Mars was like between its formation 4.6 billion years ago and now. In particular we know that a huge change happened 3.8-4 billion years ago. Before this time, Mars had water on the surface at least episodically, had large-scale activity and volcanism, had a warmer climate than now, and had a magnetic field.
What would you personally most like to discover through these investigations and missions?
It's difficult to predict what one might find. What we are interested in is exploring, and in looking at physical and chemical processes on other planets as well as our own. The processes that affect the origin and evolution of the solar system are really fascinating.
Some of our key discoveries have been serendipitous—like heavy negative ions at Titan which nobody had predicted. It's a tribute to the instrument team that the CAPS-ELS instrument works well enough to not only study the electrons in Saturn's magnetosphere that it was designed for, but also unexpected populations like negative ions at Titan and charged ice nanograins at Enceladus.
"The processes that affect the origin and evolution of the solar system are really fascinating."
But it is certainly clear that a number of places in the solar system, including Mars, Titan, Enceladus, and Europa have at least some of the ingredients for life. If our research helps to contribute to mankind's knowledge of the solar system and the Universe, this is a fantastic motivation. And the possibility for past or even present life elsewhere, while not all-encompassing, is an important enough topic to help drive scientific space exploration.
How has the field as a whole changed over the years?
Planetary science has always inspired the public—witness the moon landings, the Voyager flybys, the Cassini mission and Mars surface exploration. One way in which things have changed is how interested the public are in what we do. We have a fabulous story to tell and I firmly believe we owe it to our funders—the taxpayers—to explain what we do.
Also, planetary science has become more international over the years. ESA's entry into this was with Giotto 25 years ago. Cassini-Huygens was an excellent example of international collaboration. Mars Express, Venus Express, and Rosetta have continued the European involvement and lead in key areas. We hope ExoMars-C will continue and further internationalize Mars exploration.
Where do you hope to see this research go in the next decade?
The exploration of the Saturn system is planned to continue until 2017 with the Cassini orbiter. Many exciting phases of the mission remain, where we are looking at seasonal affects as Saturn heads towards Northern summer, eventually providing some overlap with Galileo. The Solstice mission includes further exciting flybys, and the phase late in the mission with orbits near the rings, the first in-situ exploration of Saturn's ionosphere and the plunge into Saturn.
For future outer planets work we hope for further exploration of Jupiter's satellites Ganymede and Europa by the European JUICE (Jupiter Icy Moons Explorer) in 2022 and/or international missions. Those moons with their subsurface oceans have a fascinating interaction with their plasma and particle environments, forming weak atmospheres as do Rhea and Saturn's rings. It would also be great to follow up on our heavy ion discoveries at Titan with a mission to Titan and perhaps Enceladus. It would be important to follow those large particles at Titan, the haze particles, from their birth in the ionosphere as they float through the atmosphere as tholins, to the surface.
Cometary exploration will be revolutionized by Rosetta, which will orbit comet Churyumov-Gerasimenko at about 3 AU, deploy its lander and fly with the comet as activity develops. This will be a fascinating plasma environment as well as a first detailed study of a Jupiter family comet.
At Mars, with ExoMars-C in 2018 we have a great chance to probe the third dimension at Mars—under the surface—for the first time. This will be a key step in understanding the habitability of Mars.
As always we will find many new things—but also pose many more questions for the next generation of space scientists.
Stephen Hawking has stated that he believes the long-term future of the human race is in space. Do you agree with him—why or why not?
Personally I think that this is our planet where we belong. But sending robotic probes to explore and find out about our place in the Universe is one of our most important and inspiring endeavors. Technology development means we can do this in more and more capable ways, at a small fraction of the cost of human exploration. Particularly at present, we need to live within the financial and technological constraints, and to do our best exploration with robots. I don't think we need to go ourselves—but at some point, we might have to.
Andrew J. Coates
Mullard Space Science Laboratory
University College London
Dorking, Surrey, UK
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ANDREW J. COATES'S MOST CURRENT MOST-CITED PAPER IN ESSENTIAL SCIENCE INDICATORS:
Young DT, et al., “Cassini plasma spectrometer investigation,” Space Sci. Rev. 114(1-4): 1-112, 2004 with 147 cites. Source: Essential Science Indicators from Clarivate.
KEYWORDS: PLANETARY EXPLORATION, HALLEY’S COMET, PLASMA, DUST TAIL, AMPTE, GIOTTO, ARTIFICIAL COMET, ROSETTA, PLASMA INTERACTION, UNMAGNETIZED OBJECTS, COMETS, TITAN, ENCELADUS, VENUS, MARS, PLANETARY MAGNETOSPHERES, PLASMA INSTRUMENTS, CASSINI, SATURN, CLUSTER, MARS EXPRESS, VENUS EXPRESS, PLANETARY SURFACES, STEREO CAMERA, PANCAM, EXOMARS ROVER, CASSINI CAPS, ELS, RING ATMOSPHERE, IONOSPHERE, HEAVY NEGATIVE IONS, WATER CLUSTER IONS, RHEA, COROTATION SPEEDS, PROTONS, ELECTRONS, ION SPECTRA, DIPOLE MAGNETIC FIELD, IONOSPHERIC PHOTOELECTRONS, ATMOSPHERIC ESCAPE, WATER, MARS HISTORY, GANYMEDE, EUROPA, EUROPEAN JUICE, CHURYUMOV-GERASIMENKO COMET.
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