A Cloudy Day on Mars…

I’m working on a new show about Mars and thus have become a “sink” for Mars info. Humans have a record number of spacecraft at or on the planet right now, and getting images every few days or so from one or the other of them is like having a webcam on the red planet. The latest picture is something of a “weather report,” showing high, thin clouds that are pretty rare at the altitudes they’ve been found over the Martian surface.

Mars clouds as seen by Mars Pathfinder

What’s the scoop here? Back in 1997, the Mars Pathfinder rover snapped an image of wispy looking clouds at Mars. The big mystery was, since most clouds seemed to be closer to the Martian surface, what were these high fliers and how did they form?

Astronomers using the European Space Agency’s SPICAM instrument (an infrared spectrometer that measures what the clouds do to starlight as it passes through them) actually found a NEW layer of high, thin clouds at Mars. They seem to be made of carbon dioxide crystals that exist 80 to 100 kilometers (50 to 60 miles) up in the already thin carbon-dioxide atmosphere. You can read more details about the SPICAM findings here.

Why the interest in clouds? Although many images we see are of ground formations (craters, dunes, canyons, and volcanoes) on Mars, the atmosphere is an equally important component of the planet. Among other things, if you study the atmosphere for a long-enough time, you can build up a seasonal picture of change in the different atmospheric layers. It’s also important to know atmospheric density, since this affects the entry of spacecraft into the planet’s atmosphere.

I often wonder what future Mars explores will do with all this data we’re collecting today. Surely it will help refine their exploration routes and approaches. I wish we’d get there soon, so I can find out!

And Now, Cooler Heads Will Prevail…

or Not…

It seems the hoo-hah over Pluto and the newly-voted-upon definitions of “planet” and “dwarf planet” and “plutonians” (which reminds me of a race of science-fictional beings with green antennae wiggling around on their heads) is hardly over. Oh, at first glance, as I mentioned in previous entries, it seemed like a good way to finally get some definitions that make sense and help us figure out how to categorize things in the solar system.

Unfortunately, the new definitions don’t always help. If you apply some of the “rules” described in my previous entry, you could end up with some pretty ludicrous outcomes. Take, for example, the idea that a planet has to have “swept its orbit clean” dynamically. What, exactly, does that mean? Well, when a solar system forms, the larger pieces get glommed together (the technical term is “agglomerate”) from smaller pieces. The bigger agglomerations attract or sweep up the smaller pieces. Eventually a planet (or planet-like entity) forms out of these sweepings, leaving surrounding space reasonably clear of the planetary birth leftovers. While this is an important step in the creation of a planet, I’m not so sure it should be given as much weight as it has been in the IAU definition that was approved.

But, when you apply this “a planet sweeps up its surroundings” rule, you could get in trouble. Let’s say you discover a star that has a bunch of planets around it, and there’s one the size of Jupiter in the collection. Great, sounds like a planet, right? But, what if it’s surrounded by a huge ring of debris, larger than Saturn’s, and clearly the “stuff” hasn’t been swept up by the planet—yet. By strictly applying the definition, if it hasn’t cleaned up its environment, that bad boy ain’t a planet.

Of course, there’s the whole issue of whether that Jupiter-sized thing is in hydrostatic equilibrium and “roundish.” So, right there you have conflicting reasons to call it a planet—or not.

That’s just one example. People are discussing this whole thing. Planetary scientists like David Jewitt of the Institute for Astronomy in Hawai’i, are commenting on their web pages and publicly about the ramifications of the defnitions. More are coming up with other examples that provide tests of the system, and in some cases, point out how silly parts of the system are. Right there, it looks like cooler heads need to prevail over the small percentage of astronomers who took matters into their own hands at IAU and summarily rewrote definitions on the fly. Will cooler heads prevail? Good question, but in the meantime, we have been privileged to see “astronomers behaving badly” at the IAU (in the words of one of the attendees who was there for the discussion sessions and the vote). I think there’s some great street theater occurring in astronomy and planetary science circles, and that means this thing ain’t over yet.

Already there is a petition going around among some really well-known and respected planetary scientists denouncing the whole contretemps at IAU and refusing to use the new definitions. It may gather lots of steam, and that steam may come to a rather explosive head at the next IAU general congress in 2009.

Still, dissent means we should get a much better definition. And, as I keep saying, this can only serve to strengthen the science we do, and keep reminding us that the scientific process is not one of arbitrary standards and wishful thinking, no matter how badly some astronomers may behave at any given time.

Speaking of astronomers behaving badly, I am reading a really good book right now called Stargazer: The Life and Times of the Telescope. It’s written by Fred Watson, who is the astronomer-in-charge at Anglo-Australian Telescope in Siding Spring, Australia. Fred gave a talk at the International Planetarium Society meeting in Melbourne last month titled “Astronomers Behaving Badly,” in which he detailed some of the astronomical hijinks of past astronomers. He also explains these in great and amusing detail in his book. You also get a nice little introduction to the development of the telescope, which is sort of the whole point of the book. I wonder what Fred will write (providing he’s still around) in some future decade about the astronomer hijinks over Pluto?

Refining Plutonian Sense

Okay folks, the vote is in: Pluto is no longer a planet. Sort of. It’s in a new category called “Dwarf Planet” and is also the prototype of a category of objects in the solar system called “Trans-Neptunian Objects,” or TNOs for short. We’ve known about TNOs for a while, but today’s vote by the General Assembly of the International Astronomical Union made that category of objects official, along with the dwarf planets.

In addition, all the other small bodies of the solar system, comets, asteroids, etc., are now part of a class of objects called “Small Solar-system Bodies.”

So, I’ve noted already on CNN.com and other so-called “news sites” that the main story is that Pluto has been demoted. A little bit is being said about the fact that, with these newly ratified definitions, astronomers are codifying the exciting discoveries that have expanded and enriched our understanding of the solar system. It’s no longer just some planets, comets, and asteroids. There’s a whole frontier out there, populated with worlds we’re only just starting to explore. I wish somebody somewhere would make THAT the main news story, instead of the “bleeding lead” that Pluto is no longer a planet. It’s a dwarf planet, and that is a big story, too. One of the most valuable lessons to learn about science is that it grows as new data comes in. And so does our understanding of the cosmos.
For those of you who have been following the IAU news from home, here’s an excerpt from the press release about the whole vote. It is far more nuanced than any news reports you’re going to see.
IAU 2006 General Assembly: Result of the IAU Resolution votes 24-August-2006, Prague: The first half of the Closing Ceremony of the 2006 International Astronomical Union (IAU) General Assembly has just concluded. The results of the Resolution votes are outlined here.

It is official: The 26th General Assembly for the International Astronomical Union was an astounding success! More than 2500 astronomers participated in six Symposia, 17 Joint Discussions, seven Special Sessions and four Special Sessions. New science results were vigorously discussed, new international collaborations were initiated, plans for future facilities put forward and much more.

In addition to all the exciting astronomy discussed at the General Assembly, six IAU Resolutions were also passed at the Closing Ceremony of the General Assembly:

1. Resolution 1 for GA-XXVI : “Precession Theory and Definition of the Ecliptic”

2. Resolution 2 for GA-XXVI: “Supplement to the IAU 2000 Resolutions on reference systems”

3. Resolution 3 for GA-XXVI: “Re-definition of Barycentric Dynamical Time, TDB”

4. Resolution 4 for GA-XXVI: “Endorsement of the Washington Charter for Communicating Astronomy with the Public”

5. Resolution 5A: “Definition of ‘planet’ ”

6. Resolution 6A: “Definition of Pluto-class objects”

The IAU members gathered at the 2006 General Assembly agreed that a “planet” is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

This means that the Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called “dwarf planets” was also decided. It was agreed that “planets” and “dwarf planets” are two distinct classes of objects. The first members of the “dwarf planet” category are Ceres, Pluto and 2003 UB313 (temporary name). More “dwarf planets” are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate “dwarf planets” are listed on IAU’s “dwarf planet” watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.

The “dwarf planet” Pluto is recognised as an important proto-type of a new class of trans- Neptunian objects. The IAU will set up a process to name these objects.

Below are the planet definition Resolutions that were passed.

RESOLUTIONS

Resolution 5A is the principal definition for the IAU usage of “planet” and related terms.

Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype.

The IAU will set up a process to name these objects.

IAU Resolution: Definition of a “Planet” in the Solar System Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation “planets”.
The word “planet” originally described “wanderers” that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

RESOLUTION 5A

The IAU therefore resolves that “planets” and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A “planet”^1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape^2 , (c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.

(3) All other objects^3 except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.

IAU Resolution: Pluto

RESOLUTION 6A

The IAU further resolves:

Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.1

1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

2 An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.