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The Planetary Society WeblogGuest Blogger: Rosaly LopesSeptember 4-10, 2006
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Rosaly Lopes is Lead Scientist for Geophysics and Planetary Geosciences at the Jet Propulsion Laboratory and an investigation scientist on the Cassini Titan RADAR mapper team. Her main research interests concern volcanoes in the solar system, especially on Earth and Io. She recently published The Volcano Adventure Guide, an adventurous tourist's guidebook to the safe exploration of Earth's diverse volcanoes. |
The Pluto Controversy
It is my pleasure to be this week's guest blogger, a totally new experience for me. I will start by briefly introducing myself. I am a planetary scientist working at JPL, currently Investigation Scientist for the Cassini RADAR instrument and very excited about exploring Titan. My expertise is in planetary geology and volcanology, and many of you know me because of my work on Io and participation on the Galileo mission. (If you want further details about my background, see my personal website -- you can also listen to a couple of interviews on Planetary Radio.
I will start by commenting on what is still the hot topic of the week, or month, or even year. No, it is not a major discovery. It is dear little old Pluto, demoted from planet status. I am not taking sides on this debate, but I am sure hearing a lot about it.
I am a member of the IAU's Nomenclature Committee, so I hear about the issue from my IAU colleagues, who naturally defend the IAU's decision. I am a collaborator on the New Horizons mission to Pluto, so I hear the point of view of other scientists on this mission, many of whom don't agree with the "demotion". I am a member of the Division for Planetary Sciences of the AAS, and my colleagues there also comment on the issue and even started a petition to re-instate Pluto as a planet. Plus there are ad-hoc email lists about the issue, and I seem to have ended up on several of those. There are colleagues from South America (Brazil is my native country) and Europe (I lived in England and Italy) who also have strong opinions to share. All over the world, the Pluto issue is at the forefront of planetary science discussions.
The most interesting aspect to me is how big an issue this has become. We planetary scientists have seen, over the years, our budgets slashed and our missions cancelled, yet never have I heard so much debate and complaining in the community. Pluto, a fascinating world who surely doesn't care what it is called, is now at the center of a major controversy, with pro-Pluto and anti-Pluto camps debating its planetary status with no end in sight. This problem is not new, it seems to arise whenever we try to fit Nature into neat categories.
 A View from Pluto's Moon An artist's conception of the view from one of Pluto's new moons showing Pluto, Charon, and the other small moon. Credit: NASA, ESA, G. Bacon |
Can a compromise be reached that will satisfy both camps? So far, the best
compromise I have heard came from an email from the National Science Teachers
Association. It said "Pluto is a dwarf planet. It is still a planet, you don't need to take
it off your wall". This is not quite what the IAU meant by its definition,
but perhaps the teachers have already worked out a compromise, ahead of us
scientists. When you explain science to kids, you have to simplify concepts.
How many members of the general public understand the concept of a body clearing
its neighborhood?
Perhaps the best thing about this hot issue is that now everyone knows about
Pluto, even if they don't know whether it is a planet or not. You can now get
a paraphernalia of Pluto products in the internet. Comedians are having more
fun with Pluto than they had even with the Hubble (remember those days?). My
Sunday paper had a hilarious essay by George Waters, "Pluto, we hardly knew ye".
It seems that we will now have only 11 days of Christmas, as the Three French
Hens walked out in solidarity with Pluto. But Waters says not to worry, Congress
has hired replacements, the Three Freedom Hens. It is nice to know that Congress
has come to the rescue once again.
Planetary Names: How do we come up with them?
Yesterday's blog brought a question from a friend of mine: Who is going to name the other "dwarf planets" beyond Pluto? Since I am on the IAU's Nomenclature Committee, I thought I would take today's blog to talk about naming things. It is actually quite a fascinating process that people everywhere seem to want to know about. Why is one of Io's volcanoes called Loki (the Nordic trickster god) while on Titan we have Ganesa (the Hindu god of good fortune)? Who decides what should be named?
There are two groups who name objects and features in the Solar System. One is the IAU's Working Group for Planetary System Nomenclature (WGPSN, the one I am part of) and the other is the Committee on Small Body Nomenclature (CSBN). The WGPSN names features on planets, satellites, and asteroids, as well as planets and satellites (though so far the IAU has never named a planet). The CSBN names all the non-satellite small bodies. It is not yet clear which group will name the new dwarf planets; probably both groups will work together, in consultation with the discoverer(s).
Both group's websites are worth browsing. Want to know if a crater is named after your hometown? Consult the WGPSN's Gazetteer. Has an asteroid been named after an astronomer you know? Look it up in the CSBN website. The general public can suggest names for the name bank. I know that the WGPSN has taken suggestions from the public, but they must conform to the themes. We maintain a database of potential names for planetary features, which must all fit within a theme for that body. For example, eruptive centers on Io are named after mythological deities that are related to fire, Sun, or thunder (Loki, for example, is a Norse blacksmith as well as the trickster god).
 Loki erupts on Io's limb This Voyager 1 image of Io shows the active volcanic plume of Loki on the limb. A heart-shaped feature southeast of Loki consists of fallout deposits from the active plume Pele. The images that make up this mosaic were taken from an average distance of approximately 490,000 kilometers (340,000 miles).Credit: NASA / JPL |
How does the WGPSN choose what to name? When images are first obtained of the
surface of a planet or satellite, a theme for naming features is chosen and a
few important features are named. Later, as higher resolution images and maps
become available, additional features are named at the request of investigators
mapping or describing specific surfaces, features, or geologic formations.
Anyone may suggest that a specific name be considered by a task group,
but there is no guarantee that the name will be approved. If the members
of the task group agree that the name is appropriate, it can be retained
for use when there is a request from a member of the scientific community
that a specific feature be named. Names successfully reviewed by a task
group are submitted to the WGPSN. Upon successful review by the members
of the WGPSN, names are considered provisionally approved and can be used
on maps and in publications as long as the provisional status is clearly
stated. Provisional names are then presented for adoption to IAU Division
III at the IAU General Assembly, which meets once every three years. A
name is not considered to be official -- that is, "adopted"-- until after
the IAU General Assembly.
The next IAU General Assembly will take place in my home city, Rio de Janeiro, in August 2009. I will be there for sure, and hope that the Pluto controversy has been laid to rest by then!
Io, Still a Mystery Moon
The Galileo spacecraft may be long gone, observing time for Io may be limited, but this very strange moon still holds our interest. However, there has been a hiatus on the acquisition of new spacecraft data. The last Io observations made by Galileo were obtained in early 2002, while the eagerly anticipated New Horizons observations during its Jupiter fly-by will not happen until February of next year. In the meantime, there has been new analysis and interpretations of Galileo data and new telescopic data, both ground-based and from the Hubble Space Telescope. Papers continue to be published (Alex Blackwell picked up on a couple in the For Members forum), and a book summarizing our knowledge after the Galileo mission is in press. Forgive me for advertising my own book, but Iophiles everywhere will want to see this one, as its 12 chapters are written by top Io researchers, summarizing what we know about Io from its formation and interior to its atmosphere and torus. "Io After Galileo" will be published by Springer-Praxis in early 2007. Unfortunately, research-level books tend to have small print runs and therefore be expensive. Get your Library to buy a copy!
 Jupiter's Moon Io Swirls of brightly colored sulfur-rich surface deposits make volcanically active Io one of the most colorful places in the solar system. Scale: 2005.00 meters per pixel. Created: 12 December 1995. Credit: NASA/JPL/DLR |
Being chief editor of this book was an excellent way to gain insight into how much we don't know about Io. From the inside out, Io keeps its mysteries. Galileo data showed that Io has a large core, but its composition is not known. There are now better constraints on the heat flow, but more accurate measurements over time are needed to understand how tidal heating works in the Jovian system. We know that Io has very tall mountains, but their origin is uncertain, as is the thickness of the lithosphere that supports them. Temperature measurements of Io's active volcanoes from Galileo suggested very high temperatures -- higher than basaltic lavas can be -- but the composition of Io's lavas is still unknown. We think the lavas are silicate lavas (similar to those on Earth). Sulfur volcanism was suggested by Carl Sagan and others from Voyager data, but we are still not sure if sulfur volcanism exist on Io at all. A lot needs to be learned about how volcanic eruptions work on Io, from lava lakes to plumes, and these may give us important clues about how volcanic eruptions work in other environments, including Earth. Io's atmosphere and torus have their own mysteries. We do not know if the atmosphere is mainly supplied by volcanic venting or sublimation of Sun-warmed sulfur dioxide frost. And we still don't understand how variations in volcanic activity controls the supply of plasma to the torus. There is much more we don't know, but what we do know we tried to include in our book.
 Eruption at Tvashtar Catena, Io The Galileo spacecraft caught Io in the act of an active volcanic eruption on February 22, 2000. Tvashtar Catena is a chain of calderas, collapse pits formed by volcanic eruptions. The active site of the eruption is visible on the left edge of the image, where infrared imaging sees the glow of a hot lava flow more than 60 kilometers (40 miles) long. This picture is about 250 kilometers (about 155 miles) across. North is toward the top and illumination from the Sun is from the west (left). Credit: NASA / JPL |
Will New Horizons help us understand Io better? Yes, but the brief fly-by cannot
answer all these questions. I am sure that New Horizon's instruments, though
designed for distant Pluto, will return invaluable data and show us what Io looks
like years after Galileo. Will surface changes be evident? Will we find new plumes
and hot spots? I'm betting we will.
Io's activity is so intense and variable that the way to understand this very strange world is to have constant monitoring with a dedicated mission that can last months if not years. This is extremely hard to do, because of the very high radiation environment around Io (a human would get 4,000 times the lethal dose in one day). This environment is not healthy to spacecraft either. Will we have a dedicated Io mission one day? I'm sure the answer is yes, but it won't be anytime soon. If I am lucky, they will bring me out of retirement for it. In the meantime, I hope that we catch glimpses of Io as spacecraft bound elsewhere fly by, and that another mission to the Jupiter system spends some of its precious resources giving us new views of this most strange world.
Titan, the Strangest Moon
Yesterday I talked about Io, which is, by any standards, a pretty exotic moon. Since the Galileo mission ended and I joined the Cassini Radar Team, my focus has shifted to Titan, which arguably is the strangest moon in the solar system. Yesterday, September 7, Cassini flew by Titan again. We acquired more Synthetic Aperture Radar (SAR) images using the Titan Radar Mapper. It is a small data set this time, as the flyby was not dedicated to our instrument. However, any Titan data is precious data and we eagerly wait for the downlink and processing.
Radar has covered less than 10% of Titan's surface so far, and showed us different geologic features each time. Each flyby so far has had a different flavor and some surprises. The Ta flyby (October 2004), our first, showed a young surface with no craters and several tell-tale volcanic features. The largest, named Ganesa, is a large dome or shield about 180 kilometers in diameter. Being a volcanologist, I was ecstatic. Although we have not seen so far any evidence that there is active volcanism currently going on, the features we saw tell us that volcanism is (or was) a major process on Titan. More recently, during the T19 fly-by, we found calderas, many of which contained lakes.
 Possible Titan lakes and drainage channels In this segment of the July 22, 2006 RADAR swath on Titan, very dark features are possible lakes; some, less dark features could be lakebeds that are now dried up. The darkest lake-like feature near the top of this image appears to have a thin drainage channel emptying into it from the east. It may even be possible that this channel connects the lake feature to one of the possible dried-up features to its southeast. However, the channel disappears into the background noise of the RADAR data, so evidence that the two features are connected is not conclusive. Credit: NASA / JPL |
Titan's volcanism is radically different from Io's or Earth's --
we call it cryovolcanism or ice volcanism. The magma is not molten rock
but liquid water coming from below the frozen surface, most likely mixed
with other components such as ammonia. Cryovolcanism exists on other strange
moons in the solar system, most notably Enceladus and Triton,
where cryovolcanic activity is still going on. Surprisingly, these exotic
icy mixtures can produce surface features very similar to those formed
by "real" lava, because the viscosity of mixtures such as ammonia-water,
and ammonia-water-methanol, are similar to those of silicate lavas.
Studying Titan's geology is challenging and totally fascinating. The Cassini orbiter and the Huygens probe have shown us that Titan's geology is remarkably similar to Earth's. Titan has volcanoes, impact craters, rivers, mountains, lakes, and fields of dunes. However, when looked at in detail, Titan and Earth are not at all similar. The difference between silicate volcanism and cryovolcanism is not the only one. While water carves river valleys on Earth, the liquid on Titan is likely to be methane. The lakes that the SAR images showed in the T19 flyby are not water but likely methane or ethane. Methane may also come down in the form of rain and we know from that methane is present in clouds near the south pole. Rivers of methane may carve dendritic channels such as those seen in several radar passes, particularly T13 (over the bright Xanadu region). Titan, like Earth, appears to have few impact craters, suggesting that the surface is young and dynamic. Best of all, Titan has just begun to yield its secrets. No doubt many more will be revealed in the next few years. The Cassini mission is scheduled to last until at least mid-2008, making a total of 44 fly-bys of Titan. We are already planning a two-year extended mission, where more Titan fly-bys are a priority. I look forward to staying in touch with Planetary Society members and telling you more about this strangest of moons.
 Cassini RADAR coverage on Titan as of April 2006 Credit: NASA / JPL |
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