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The Planetary Society WeblogGuest Blogger: Jim BellAugust 21 - 27 , 2006
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Jim Bell, an associate professor in the Cornell University Astronomy Department, is the lead scientist for the Pancam color imaging system on the Spirit and Opportunity rovers and is also a member of The Planetary Society's Board of Directors. This fall, he is publishing a pictorial history of the rover missions titled Postcards from Mars. His research interests focus on the geology, chemistry, and mineralogy of planets, asteroids, and comets. When not taking pictures on Mars, Jim enjoys woodworking, gardening, and playing as much baseball as possible in the short Upstate New York summers. |
What's in a Name?
All last week I was agonizing about what I could "blog" about while covering for Emily Lakdawalla this week. It's an awesome responsibility, but I was nervous because I've never blogged before and I didn't want to let Emily down (hell hath no fury like a mother scorned). Then, like manna from heaven, the International Astronomical Union rained bloggable bits all over me.
Unless you've been living on some other celestial orb recently, you've no doubt heard all the ballyhoo about the IAU's efforts to redefine the term "planet." The proposal, worked on for years by a committee of astronomers, scholars, and artists, came out in newspapers and websites (and even blogs!) all over the world this past week and made a big splash because, if it is approved, we will suddenly live in a solar system with 12 "planets" (and perhaps more), instead of our familiar 9.
The Greek's came up with the term planetes or "wanderer" for the five objects besides the Sun and Moon that they could see move through the constellations with their naked eyes. When Uranus and Neptune were discovered later by telescopes and found to be much, much larger than Earth, calling those two "planets" made a lot of sense. Then Ceres and Vesta and a host of other objects were found between Mars and Jupiter. Small, starlike... "asteroid" seemed to fit, though formally the IAU and others adopted the term "minor planets."
OK, planets big, asteroids small. No problem. Then, of course, Clyde Tombaugh found Pluto orbiting way way out there past Neptune and the debate became sticky. People began to ask, is Pluto, smallish and in an oddly-tilted orbit different from anything else then know, a planet? Now we know that Pluto is just the easiest-detectable representative of a large population of similar distant, icy objects, variously known as Kuiper belt objects or trans-Neptunian objects. I think that the long hiatus between the discovery of Pluto in 1930 and the discoveries in the 1990s of Pluto's numerous similar cousins provided the opportunity for the public to get comfortable referring to Pluto as a "planet". It was just one more, after all -- an odd duck, but part of the family.
Reactions to the IAU's proposal to formally, quantitatively define the term "planet" are all over the map. Some scientists think it makes sense, others think it's crazy. The media seem mostly amused by the idea. Many people in the general public that I've talked with about this are just plain confused, however. When I've brought up the topic on airplanes, in cafeteria lines, or around the breakfast table, I hear the same kinds of questions: "Why do we need more planets?" "Don't astronomers have better things to do?" "How can Pluto's moon be a planet?"
My own reaction is one of mild frustration, because parts of the definition just don't seem to make sense for our solar system. For example, if the IAU's definition is adopted in voting this week, the (former) asteroid Ceres and (former) moon Charon will both become planets. Both are smaller than, for example, Jupiter's moon Ganymede and Saturn's moon Titan. How can little Ceres be called a majestic planet but already-majestic Titan not be?
Parts of the proposed definition -- like requiring the object to be large enough to have become spherical and to not be a star -- make some scientific sense and are, for the most part, quantifiable. But the part of the definition requiring that the object not be a satellite of a planet seems arbitrary to me. Why not? Would a rogue planet that gets captured by another planet suddenly cease to be a planet? And why Pluto's moon Charon doesn't qualify as a satellite of a planet but instead would be part of a "double planet" system may make sense to orbital dynamicists comfortable with terms like "barycenter", but it's really, really hard to explain to regular people, especially kids.
To be fair to the IAU, coming up with a definition of an ambiguous term like "planet" is really a no-win situation. Is it a crocodile, or an alligator? A donkey or a mule? Planet-hunter Dave Jewitt has compared it to telling the difference between a ship and a boat. None of those words matter if you're bitten, kicked, or sinking fast, however. It's just a word, and words can be fuzzy. Why try to rein it in? I'm surprised the IAU decided to take this debate on, and I'm even more surprised that a committee of scientists and others could come to an agreement about this. Perhaps the old adage about any press being good press was on peoples' minds. If so, it was a good call -- there certainly has been a lot of press!
Ultimately, some people are lumpers, and some are dividers. When it comes to planets, I'm a lumper, perhaps to the extreme. I like our nine common planets, and this view of our solar system family has become ingrained in our culture. But I also think of our Moon as a planet in its own right, with a fascinating geologic and internal history. I lump Jupiter's giant moons into the planet category, and the big ones around Saturn, Uranus, and Neptune, too, as they have been shaped by their own internal forces and either evolved or continue to evolve since the time they were born. By my own personal (perhaps naive and nonscientific) reckoning, we live in a solar system with 25 or so planets, some big, some small, some gassy, some rocky, some orbiting others, and some on their own. Even with them and millions of asteroids and perhaps billions of comets there's still plenty of room for more planets. Bring 'em on! "Planet" is in the eye of the beholder.
For more information about this new "planet" definition, Amir Alexander has a story up on The Planetary Society's site and Wikipedia has great summary of this topic.
We Need Global Warming
We really do! Be patient and you'll see why...
Like many members of The Planetary Society, I've followed closely the studies and the debates about the nature of global warming during the 20th, and now 21st, centuries. There seems to be little debate that Earth's average temperature is rising, by something like a degree or two over the last century. And there seems to be little debate that the average amount of CO2 in Earth's atmosphere has increased over the same time period. These are the measurements, and they appear solid. What's controversial is whether or not human activity is responsible for the CO2 rise and especially the temperature increase, or whether this is just part of the natural cycles of climate change that Earth goes through all on its own.
 Antarctic Ice Sheet Today, Earth science missions such as NASA's Gravity Recovery and Climate Experiments (GRACE) are taking sensitive measurements of our planet's gravity and climate to monitor changes in the oceans, ice sheets, atmosphere, and land. Recent analyses of GRACE data indicate that the Antarctic ice sheet may have lost mass equivalent to between 19 and 40 trillion gallons of water. This photo of Antarctica's Riiser-Larsen ice shelf was taken in December 1995. Credit: NASA / GRACE / DLR / Ben Holt Sr. |
Has the Earth's climate changed in the past? Yes, dramatically. Will it
change in the future? Absolutely, and again, dramatically. Ice ages and warm
spells come and go over thousands of year timescales because of slow oscillations
in Earth's orbital parameters. Other effects, like large impacts, episodes
of extensive volcanism, and perhaps even changes in the Sun, are also thought
to be responsible. None of these involve us, and these things were going on
long before we were here. So what's all the fuss? Does the Earth even care
that we are here?
For two reasons, I believe the answer is yes, we are influencing the Earth's climate. First, it is logical and reasonable to believe that our technological society is responsible for the increase in CO2 in our atmosphere. Burning of enormous amounts of fossil fuels and massive deforestation have been facts of life since the beginning of the industrial revolution a few hundred years ago. And second, given the physics of CO2, the only way the atmosphere can react to that CO2 increase is to absorb more incoming and outgoing energy, and thus to heat up. It's more complicated in the details, of course, but the net result on average can only be warming -- just how much warming is the coin of the realm.
Here's the part that I find fascinating. We need global warming. Really,
we do. What I mean is that if you do the calculation of balancing the amount
of energy that Earth receives from sunlight with the amount of heat that Earth
radiates back into space, then, if the atmosphere had no effect, the Earth's
average temperature would be about -17°C, or about 0°F. In other words, Earth would be a frozen ice ball. But wait! The Earth's average temperature is actually about +18°C, a difference of about 35°C from what it "should" be. That temperature difference -- that "global warming" effect
-- comes from our atmosphere. CO2 and water and other gases in our
atmosphere trap some of the heat that would normally escape (the "greenhouse effect"),
and warm the planet. Global warming makes our planet an ocean world. Global
warming enables life as we know it to exist on the surface. We need global
warming. Just not too much...
Part of the reason we study the other planets is to try to understand how our own planet works. Both Mars and Venus have atmospheres also, and it turns out they also have global warming. The CO2-rich
atmosphere of Venus is nearly 90 times thicker than Earth's, and so its global
warming effect has gone berserk, warming the surface by more than 500°C
above what it would be otherwise. The CO2-rich atmosphere of Mars,
though, is about 90 times thinner than Earth's, and so its greenhouse effect
only warms the surface by about 5°C -- not enough to take the planet out
of its current deep freeze. There's lots of evidence that the Martian atmosphere
used to be thicker in the past, though, and that global warming on Mars may
have brought the average temperature above freezing and allowed liquid water
(and perhaps life?) to exist stably on the surface for long periods of time.
It's an active area of planetary science research, and the models used to study
the atmosphere of Mars, and of Venus, Titan, and other worlds out there with
atmospheres, are constantly influencing models of our own planet's atmosphere,
and vice versa. The better we get at matching what we see on the diverse worlds
around us, the better we seem to get at modeling and predicting our own climate.
 First images from Venus Express VIRTIS These false-color views of the south pole of Venus were captured as part of a single observation by the VIRTIS imaging spectrometer on April 12, 2006, shortly after Venus Express' orbit insertion. The left half is a day-side view composed of ultraviolet and infrared images and shows swirling clouds at an altitude of 70 to 80 kilometers above the surface. The right half shows heat being emanated from the surface on Venus' night side. Wispy, opaque clouds at an atltitude of about 50 kilometers block the thermal energy from escaping Venus, so the image is in effect a backlit view of the 50-kilometer-altitude clouds. At the south pole is a vortex with particularly thick cloud cover. Credit: ESA / INAF-IASF, Rome, Italy, and Observatoire de Paris, France |
What the models show is that our climate is part of an incredibly delicate, and
perhaps even tenuous, system that involves the atmosphere and the surface (land
and ocean) absorbing, reflecting, and storing energy from the Sun. Small changes
in the balance of one element versus another in the system can result in large
energy, and thus climate, fluctuations. The kicker is that the system is slow
to react compared to the timescales of political lifetimes or even actual human
lifetimes. If we are conducting a grand, unintentional experiment in climate
change, and if it somehow goes awry, it may be our children or grandchildren
who have to live with the results.
It's a frightening prospect. Maybe it's not going to happen; maybe Earth
doesn't really care about us puny little humans and our comings and goings.
But think about the risk and the implications if that's wrong. Isn't it
worth seriously contemplating alternate ways to generate electricity, heat
and cool our homes, and move us and our goods around the planet in ways
that we know won't add to this risk? I think so. And I think the way to
start is one person, one family, one company at a time, educating themselves
about the issues and trying to lessen their potential negative impact.
I believe the momentum is already swinging this way, in fact, perhaps spurred
by the environmental movement during the last 30 years, or perhaps by the
more recent possibility of $5/gallon gasoline in the U.S. Whatever the
impetus, individual actions are the key if there is any hope to, as my
friend Bill Nye likes to say, "Change the World!" Or at
least, keep the one we've got.
I can't remember what my day job used to be like
I have one of the coolest jobs in the world. Every morning when I come in to work, I start up my computer and download brand new pictures from Mars, taken by cameras on the Spirit and Opportunity rovers that my colleagues and I from Cornell, JPL, and other institutions around the world helped to build and continue to operate. Pictures from Mars, taken just a few hours (or minutes!) ago. Incredible. I look at the Sun shining out my office window and it reminds me of the motto that we put on each rover's calibration target or MarsDial: "Two Worlds, One Sun."
 The 10,000th image of the MarsDial from Spirit As of sol 701 of its mission, Spirit had acquired 10,000 separate images of its MarsDial. The 10,000th image was taken through a green filter (it is combined with two others to create this RGB composite). The MarsDial is pinkish with dust, but numerous "cleaning events" have whisked away most of the dust that has accumulated over the course of the mission. Credit: NASA / JPL / Cornell |
There are more than 60 active robotic and human space exploration missions
going on right now (check
out the list at NASA). This means that there are some amazing spacecraft
operations adventures happening around the world every day. In my little corner
of the world in Upstate New York, people in our group are working on data and
operations planning for Cassini, Hubble
Space Telescope (HST), Spitzer, MESSENGER, Deep
Impact, and of course the Mars Armada: Mars
Global Surveyor (MGS), Mars
Odyssey, the rovers Spirit
and Opportunity, Mars
Reconnaissance Orbiter, and now, the 2009 rover, Mars Science Laboratory
(MSL). My research lately involves working with HST, Odyssey, and MGS data,
and helping to plan for MSL, but it's the rovers that have taken up almost
all of my research time for the past three years. In fact, I was remarking
to some friends the other day that I can't remember what my day-to-day research
work was like before the rovers. What did I do with all the free time I must
have had?
It's remarkable to think about all of the complex work and the technology that is required to run a spacecraft mission. Our experience with the rovers, helping to operate the
Pancam color cameras from the Cornell campus every day (except weekends and holidays, which we get off but the rovers and some JPL and Deep Space Network folks don't), provides a glimpse into that complex, very specialized world.
The rovers are commanded from JPL, and so the spacecraft engineering team in Pasadena sets the schedule and pace. The Pancam group's rover
planning day typically starts with a kickoff meeting via video- and tele-conference
around 10:00 or 11:00 a.m. east coast time, or first thing in the morning in
L.A. The engineers assess the health of the rovers and estimate how much power
and downlink data volume and time for science observations will be available
that day, and the scientists make an assessment of how things went "yesterday" on
Mars.
We're not on "Mars time" any more like we were early in the mission, so the rover's day or "sol" on
Mars, which is 40 minutes longer than an Earth day, slowly drifts through different
parts of the day in L.A. Sometimes the start of a new day's planning session
will be many hours after yesterday's data get beamed back from Mars, and so
everyone has plenty of time to look through the images and other measurements
in order to suggest new activities. Sometimes the data are literally arriving
at the start of the kickoff meeting, however, and we are scrambling to react
to the latest findings. It can be hectic, but it can also be very valuable
to have this kind of flexibility in the mission. It also helps keep us all
excited about the exploration aspect of these missions: many times we won't
know what we're going to be doing that day with a rover until we see the results
from yesterday.
Next we convene a virtual gathering of scientists and engineers from around
the world involved in each mission to come to a consensus on what specific
activities to do with the rover that next sol. This is called the Science Operations
Working Group or SOWG meeting. It's a give-and-take among scientists and engineers
to fill every moment of rover time on Mars with useful science or necessary
engineering, rover maintenance, or driving activities, and to cram as much
information as possible into the available downlink. It's also a give-and-take
between us different scientists -- geologists, mineralogists, atmospheric scientists,
others -- lobbying for specific observations or campaigns. Fortunately, we
all get along quite well on our team, and these "bit battles" are usually quite
cordial. The SOWG meeting usually takes about an hour, and when we've outlined
a basic plan for that day that fills all the available resources and which
the engineers and mission managers agree is doable and does not compromise
the health and safety of the rovers (or the team!), then the meeting is adjourned.
For much of the rover team, that's the end of the day, and the next step is
waiting for the data to come down to start the cycle again the next day.
For those of us responsible for the instrument operations, however, that's
really just the beginning. I like to describe what comes out of the SOWG as
sort of an index card version of the rover's next sol, with one pithy line
of text describing every activity (Drive, Deploy Arm, Acquire Panorama, etc.).
Our job at Cornell is to take every line on the index card that says "Pancam" and
to expand it into the detailed instructions that point the cameras and acquire
the images, and then to send those instructions to JPL so that they can be
converted into spacecraft language and transmitted to the rovers by the engineering
team. There are similar groups around the world (in Flagstaff, Phoenix, Manhattan,
Germany, Canada, and Pasadena) doing the same thing for other instruments and
systems on the rover. It's a great example of truly distributed spacecraft
operations.
 Opportunity panorama: "Burns Cliff," sols 287-294 Opportunity scrambled slowly across the steeply sloped wall of Endurance Crater to reach "Burns Cliff," a vertical pile of finely layered rocks that was irresistible to the rover sceintists. From this precarious position it captured a 7-color panorama from sols 287 to 294 (November 13 to 20, 2004). The bulging appearance of the wall is due to Spirit's very close position to it; in reality the view spans about 180 degrees and the wall is gently concave. For the full-resolution image, visit the Pancam website. Credit: NASA / JPL / Cornell |
This part of the job for Pancam can take anywhere from an hour to eight hours,
depending on the complexity of the sol being planned (or, on Fridays, the three
sols being planned to cover Saturday, Sunday, and Monday on Earth). Most of the
Pancam work is being done by a dedicated staff of Payload
Uplink Leads (PULs), and they are supported by programmers, documentarians,
graduate student and staff image analysts, and a
gang of Cornell undergraduates who calibrate the Pancam images every day. Sometimes the PULs work until 7 or 8 p.m. east coast time to finish the job, delivering the camera instructions to JPL for validation and integration with the activities from other instruments.
It's painstaking work being done by some of the most intelligent, dedicated,
and meticulous people that I have ever worked with, but I know they appreciate
the rewards: having the privilege and quiet pride of being the "cameramen" behind
the incredible color pictures being shot by Spirit and Opportunity. As I've
described in a coffee table book I've got coming out in November called
"Postcards from Mars", once in a while in this process we have the luxury
of thinking like real photographers when designing an imaging sequence or processing
the data afterwards. That is, we can sometimes think about things like the
lighting, framing, depth of field, and color balance -- things that landscape
photographers think about all the time. The amazing longevity of the rovers,
the unexpectedly large amount of downlinked data that we've been able to send
back from Mars, and the flexibility of our instruments and mission operations
scheme have all combined to allow us to be, in a sense, the first "photographers" on
the Red Planet.
This is how the Mars rovers' distributed operations process works today. Originally, for the first few months after we landed on Mars, this whole process was done at JPL and it used to take more than 12 to 15 hours sometimes to complete from start to finish. Now that the team has become so adept at this after more than 1850 combined sols on Mars (and no one knows how many more) and the software tools have been refined and optimized, a typical sol's planning cycle might take more like 6 to 9 hours, and some days that might include 2 or 3 sols of activity rather than just 1. The rover team has made spectacular scientific discoveries during the past two and a half years, and has settled into a now-familiar routine (as if operating rovers on Mars could ever be routine) of continued exploration and discovery. We have become engrossed with and consumed by Mars. Maybe that's why I can't remember what my normal day job used to be like...
Giving Away the Data
When I was a graduate student studying planetary science in the 1980s, there were very few active space missions to the planets. The Viking Orbiters and Landers had finished their work at Mars. The Soviet Union had sent orbiters and probes/landers to Venus and were turning their sights back to Mars and Phobos. They and the Europeans and the Japanese were sending probes to rendezvous with Halley's comet. The U.S. Halley observational space mission, and indeed most of the American space exploration program, was crippled with the loss of the space shuttle Challenger and her crew in 1986 (also delaying the shuttle-launched Galileo mission to Jupiter, which wasn't launched until three years later). It was a difficult and "data lean" time for space exploration. It was no wonder my thesis research was based on telescopic observations, rather than space mission data.
I had been lucky enough as a student to be invited to participate in the Voyager 2 encounters of Uranus in 1986 and Neptune in 1989 (the former, as an undergrad at Caltech by my research supervisor Ed Danielson, and the latter, as a grad student at University of Hawaii by one of my mentors, Fraser Fanale). "Participate" is a generous term. I was really just a gopher -- running errands, making copies, going on late-night pizza runs for science team members -- but it was still an incredible thrill just being there and watching the images come down, one by one, as each planet got bigger and bigger in the windshield. Of course, there was no "internet"; a small number of people were the only ones to see all the images as they came in, and the media were given hardcopies of some of the greatest hits for the newspapers and the evening news.
 Crescent Uranus This view of Uranus was recorded by Voyager 2 on January 25, l986, as the spacecraft left the planet behind and set forth on the cruise to Neptune. Voyager was 1 million kilometers (about 600,000 miles) from Uranus when it acquired this wide-angle view. The picture -- a color composite of blue, green and orange frames -- has a resolution of 140 kilometers (90 miles) per pixel. Credit: NASA / JPL |
For me, it was an amazing and inspiring experience to be part of, even just
as an observer. However, I also experienced for the first time some much less
inspirational and sometimes downright depressing examples of human behavior
and team/media interactions. As a naïve young student, I was not prepared
to see scientists be greedy, secretive, angry, and just plain nasty about access
to, sharing of, and publication of, their data. Many team members had worked
for years (some, decades) helping to get the mission approved, then built,
tested, and launched, and then it had taken 7 and 10 years to get to Uranus
and Neptune, respectively. It was a long wait during this data-lean time. There
were historic discoveries and first-authored Science and Nature papers ripe
for the picking in those images, and new Ph.D. theses waiting to be born. Some
people felt a sense of personal ownership of the data, which was embargoed
for public release as "proprietary" by NASA. Using "someone else's" data
for a publication or even showing a certain picture to a member of the media
without permission could get a person in a lot of trouble. To be fair, most
of the people that I met on the Voyager team were not like this (quite the
contrary, in fact), but still the bad apples gave the whole experience a sort
of sour aftertaste. I vowed to remember and learn from this experience. There
must be a better way.
Well, I grew up, graduated, and before I knew it found myself in charge
of the high-tech Pancam color cameras on two rovers being sent to Mars.
Remembering my Voyager experience, I had a talk one day with rover science
team leader and Cornell colleague Steve Squyres about the whole issue of "sharing the data." I had strong opinions about what we should do with the Pancam images, and I was bracing for a possible fight with Steve about my proposal. However, Steve told me that he had had a somewhat similar experience to mine on a different mission early in his career, and it had left him with a similar bad aftertaste. It turned out we were on the same page. We both wanted to give all the images away, sharing them in as close to "real time" as
we possibly could. No restrictions, embargoes, or proprietary data periods.
Happily, most of the rest of the rover science team felt similarly.
It was actually a bit challenging working with the JPL team to implement this. Many peoples' first reaction was sort of disbelief, based on previous mission experience and the expectation that we would probably want to horde the data close to our chests, slowly leaking out a greatest hits image here and there but saving the best for press conferences or splashy science papers. No, we said, what we want is that when the images are decoded at JPL from the radio signals the rovers send from Mars, a computer program should automatically generate a JPEG version of every image, and then post those immediately on a publicly-accessible web site. Well, that's exactly what they did at http://marsrovers.jpl.nasa.gov/gallery/all/spirit.html
and http://marsrovers.jpl.nasa.gov/gallery/all/opportunity.html
The JPL folks tell us that millions of people, from around the world, have
been accessing and downloading these and other images that we've posted on
the rover's main web
site,
and we post "near real time" color images from the Pancams on our own Cornell
site. Spectacular!
The Mars rovers aren't the only space missions sharing their images like this. The Cassini orbiter imaging team is doing it too with images of Saturn and its moons. Both the rovers and Cassini have expanded on the data-sharing efforts of previous investigations and teams, like the prolific Mars Global Surveyor Mars Orbiter Camera team
at Malin Space Science Systems, who have been posting a spectacular "Picture of the Day" (with
a caption!) from Mars for years, and, previously, the Near Earth Asteroid Rendezvous Multispectral Imager team, who posted an asteroid 433 Eros Image of the Day from 2000 to 2002. Maybe this is a new trend: Share all your pictures. I think it's unfortunate that some missions, like the Hubble Space Telescope and the European Mars Express orbiter, don't share all their data as quickly. Heck, it's (partly) my tax dollars at work, too... Maybe they can be talked into joining the fun.
 Saturn and Tethys Tethys floats above Saturn's rings. The rings cast wispy shadows across Saturn's northern hemisphere. Created on June 10, 2005. Credit: NASA / JPL / Space Science Institute |
Some of our colleagues think we're fools to be posting all the rover images online in real time ("You're giving your data away!"). It is true that we have been "scooped" a few times on scientific papers or media stories by some scientists who use these instant images to get a quick result in press. It's not the worst thing in the world, and anyway we're collecting the data for everyone, not just ourselves. Indeed, getting scooped by a colleague now and again is a small price to pay to allow so many others-kids, teachers, bloggers and other space enthusiasts, laypeople, even members of Congress -- to be able to follow along in near-real-time and to be a part of this amazing, continuing (today is Spirit sol 939, Opportunity sol 919) Martian adventure. I feel that all of us involved in space exploration are privileged to have been entrusted with taxpayer dollars to do the best possible science. We have an obligation to share both our successes and failures openly and honestly with the general public.
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