His talk focused on who planets are defined and classified. As we gear up for this summer’s IAU General Assembly, many folks are wondering if (hoping really) they will clarify what is and is not a planet.

As a starting point he explained that the discussion originated from the IAU trying to sort our who had the responsibility of naming Michael Brown’s then new discovery of an object that is bigger than Pluto. Should the small body committee name it? Should the planet committee name it? Or…? Well, clearly someone had to decide what a planet is and is not.

The criteria that was landed on and voted on, however, aren’t the most sensible. Here they are:
1) A celestial body that is in orbit around the Sun (but this precludes exosolar planets from being “planets”)
2) Has sufficient mass so that it assumes a round hydrostatic equilibrium configuration (this means it’s bigger than the asteroid Juno, and most Moons count)
3) It has cleared the neighborhood around its orbit (Ummmm – there is random stuff in the orbits of *all* the planets.)

Let’s look at this last criteria a bit more closely within our modern understanding of the solar system. Prior to 1992 we didn’t have evidence there was a Kuiper Belt and we didn’t have evidence of other planets. Our understanding of planets was based on our own 8 planets + Pluto. Once we started realizing the dynamic range of planets (and stars) are very different, we needed to reconsider everything.

Mass is an easy criteria to consider. Can an object know it is large? The answer is simply yes. Once an object gets large enough gravity makes it round. Period. This is a good starting criteria for “Could be a planet.” Keep lumping on mass and eventually they start burning stuff in their cores. That would define the “Could be a star” boundary.

But mass does not effect the other criteria. An object of a given mass doesn’t always orbit the Sun (look at Ganymede and Titan – both very planet-like moons).

What it takes to clear an orbit via either scattering or accretion also depends on the size of the star and how far an object is from the object it orbits. In our solar system, if you stuck the Earth out at 40 AU (Pluto’s mean distance) it could not clear its orbit! It would fail the “What’s a planet?” criteria for the exact same reason as Pluto! In general, as the mass of the star goes up, planets must grow, and as planets move further from the star, they must be bigger to clear their orbits. (For those into the numbers, for a planet to clear it’s orbit it must have a mass where M_planet > ~G^(-3/4)T_system M_star^(1/4) a_planet^(9/4) )

Why is it do hard to define a planet? Well, the problem comes with finding a starting point and finding consensus. Today’s criteria aren’t really based on anything that describes the geophysics of the object. A brown dwarf star could get classified as a planet! As we rethink our definitions, Stern encourages us to each find our own way of looking at this problem and to look at intrinsic characteristics that distinguish planets based on their physical properties. If you look out at the largest Kuiper Belt objects (Pluto and its roughly same size friends, all of which are over 800 km in diameter) you find a set of objects that are all like the terrestrial worlds in terms of similar formation, sometimes have atmospheres, sometimes having moons, and otherwise looking and acting very different from their asteroidal cousins.

People tried very hard to get Stern to make a recommendation on what should and should not be a planet. He gave us two bits of advice: Make up our own minds, and do not let the “Well if there are too many planets my kid won’t remember all their names” issue bias us (after all, we have more than 12 states in the union).

So go forth and think. And tell your local IAU representative what you think should make a planet.

Okay, so that last one is an exaggeration. As far as I know, human babies and the CMB have nothing in common. The remark about the Oort Cloud, however, may not always be as far fetched as it sounds. A group of scientists working at the Harvard-Smithsonian Center for Astrophysics, and lead by David Babich, have theorized a new technique for determining the mass distribution in the Oort cloud using distortions in the Cosmic Microwave Background.

According to the theories of Babich and his team, if you observe the light of the CMB through the Oort cloud, the intensity you detect is related to both how much CMB light is blocked by Oort cloud objects (which are so small and so far away that you can look through them the way you look though a cloud of fine dust), and to how much light the Oort cloud objects emit at the color being observed (in this case, the dust you are looking though is made of glow in the dark paint). If the Oort cloud isn’t symmetrical, any distortions may be visible as anisotropies in the light of the CMB.

The key to understanding this result is understanding that warm objects give off light in a variety of colors. The hotter an object is, the shorter the wavelength of the light – the bluer the light. The colder an object, the longer or redder the light will be. Humans, for instance, give off the most light in infrared. That doesn’t mean we give off all our light in any one specific wavelength of infrared. Rather, we give off most of our light in one shade of color, but there is light of a variety of colors coming from our warm bodies, even in the darkest of rooms (although some colors, like green, aren’t emitted in numbers enough higher than zero to matter).

The CMB is basically a perfect black body with a temperature of 2.728 Kelvin. It is located at essentially infinity in all direction. It is a perfect background light. This team theorizes that objects in the Oort Cloud should have temperatures related to their distances, such that an object at 1000 AU would have a temperature of 8.5 K and nearer objects would be hotter while farther objects are colder (think of the temperatures of rocks illuminated by a camp fire. The same physics describes the heat of the rocks and of the objects in the Oort Cloud. These temperatures are very similar, and the same technology that can be used to detect the CMB will also detect the heat signature of Oort cloud objects.

So, while the 2.728 K CMB and 8.5 K Oort cloud objects both emit microwave light, the light doesn’t peak at the exact same color, although there is overlap. Despite the amazing precision that WMAP and other missions have already mapped the CMB, their accuracies weren’t sufficient to test this theory, but this is something that future missions, like Planck, may be able to. Any distortions in the Oort cloud that are found will point to past encounters with stars. As our Solar System passes near other stars on its orbit through the galaxy, the Oort cloud gets distorted and these distortions trigger long period comets.

Good theories, in my mind, are defined as theories come in to forms. There are those, relativity, that put existing observations together in a new way that leads to deeper understanding and understanding of previous mysteries, while also making predictions. There are also good theories that look at the universe and apply existing knowledge to predict future discoveries we can’t get to through more common means. This set of papers falls in that second category. This isn’t theory for the sake of pretty math – this is theory that defines how to build a better mouse trap.

Locally, COROT (vaguely rhymes with Inspector Perot), obtained first light today (image above, credit CNES 2006 – D. Ducros). This orbital observatory will dedicate it self to the search for rocky worlds around other stars. A product of the European Space Agency, COROT will study nearby stars with its 30cm telescope, looking for slight changes in brightness indicative of planetary transits. The images it takes will also be useful for asteroseismology, the study of how stars bump and wiggle in reaction to chemical and thermal processes deep beneath their surfaces. Pre-launch calculations predict that every 150 days (the time COROT will spend studying one area of the sky), COROT could discover 10-40 rocky planets and tens of gas giants. Since the first published discoveries of an extrasolar planet around a pulsar in 1992, and around a normal star in 1995, astronomers have only discovered 209 extrasolar worlds. With COROT, that number could double in as little as 1 year.

A little farther out, the STEREO spacecraft (left, credit: NASA/Johns Hopkins University Applied Physics Laboratory) are swinging past the moon on their way to their final orbital homes ahead of and behind the Earth. From these positions they will produce three dimensional images of the Sun in much the same way that your two eyes are able to give you a three-dimensional view of the world around you.

Out near Jupiter, the New Horizons (right, credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)) mission is zooming toward its first major science target. While zipping past our solar system’s largest gas giant, New Horizons will test its instruments. New Horizons images will be the first close ups on Jupiter since the Galileo spacecraft ended its life by plunging into Jupiter’s atmosphere on Sept 21, 2003 (I’m personally looking forward to seeing what New Horizons can learn about Red Spot Junior.)

Somewhere out past Mars, Stardust is waiting to learn if NASA will let it visit more comets. Launched in 1999, this little capsule that could imaged asteroid Annefrank in November 2002 , investigated comet Wild 2 in Jan 2004, and returned to Earth a sample of comet and interplanetary dust in January 2006.

Also on the go are Mars Express, Venus Express, Rosetta, SOHO, XMM-Newton, Integral, Hubble, Spitzer, Cassini, Voyager I, Voyager II, Spirit, Oppurtunity, and many many more space craft. In recent decades NASA and ESA have demonstrated over and over that while they have their moments of bad luck and stupidity (Mars Polar Lander, anyone?), they can very successfully get to objects all over the solar system and explore them in ways that both bring home good science and get the public interested in space.

At the same time, the private sector is getting in on the space gig as well. SpaceX is readying to test their Falcon 1. Virgin Galactic has a business plan and has partnered with Scaled Composited (the guys behind SpaceShipOne, GlobalFlyer and nospaces in names) to get everyday men and famous dudes into space starting sometime in the next couple years. Bigelow Aerospace has inflated modules on orbit and is aiming to start launching hotel pieces late this year. Along side these companies are roughly two dozen competitors, all aimed at making a buck off of space. Today, the sky isn’t a limit for companies seeking to get people and goods farther, faster and cheaper.

In my ideal fantasy universe, each agency and company is able to thrive doing what it does best. In the case of space, NASA and ESA and their international government run space agency brethren use tax dollars to explore with robots and probes, doing the science that serves to excite and inspire, but that doesn’t exactly do much to raise anyone’s financial bottom line. At the same time, the I dream of seeing some of the two dozen plus commercial space corporations becoming tomorrows PanAm and TWA or UPS and FedEx as they compete to get people and goods everywhere. In this perfect fantasy world, Mars gets explored by man, but it is paid for in the same commercial spirit that the Dutch and British East Indian Trade Companies paid to explore the Earth’s ocean’s.

But today’s space reality is far from my personal fantasy. Today, NASA’s space science budget is getting raped by the manned space program. With congress announcing that budgets will be flat in this first quarter of 2007, NASA Administrator Michael Griffin has said he will be compensating for a half-billion dollar funding hole by taking money from programs he believes are low priority to fund the International Space Station and Orion crew exploration vehicle programs. So far, money has been cut from weather and climate research budgets, and a lot of people are holding their breath as they wait to see what space exploration programs get put on hold and/or canceled.

So, here is my question for the people who figure out how NASA dollars should be calculated. When was the last time a press release from the International Space Station (ISS) took someone’s breath away the same way Cassini images so often do? When was the last time science results from the ISS made people think life the way the results of finding evidence on Mars so often do? What exactly has the ISS done for anyone lately? Our failure to be on time and on budget has got to be annoying our international collaborators. I’m not really sure what we’re learning, and I try to stay up to date on this stuff. I do think we need to replace the shuttle, but before we go building heavy-lift, Moon and Mars heading vehicles, shouldn’t we be asking, what do we need people doing in space? The Mars Rovers have demonstrated that we can reprogram robots to do new things from great distances. People are great construction workers. We can repair things really really well. Having the ability to go into orbit, grab a satellite and fix or update it is really useful. I can totally get behind that type of a project. But, we can’t take a person and put it in a parking orbit like we did with Stardust, and spend a few months trying to figure out what to do next.

But NASA is gearing up to make fewer StarDusts and to spend my tax dollars putting people on Mars. I don’t like this, so what can I do? Well, I can sign petitions, like the one put together by the Planetary Society, and I can write my congressional representatives. And I can ask you to think about what you feel NASA, ESA, or any other tax dollar spending space agency should be doing, and once informed, write to let the people spending your tax dollars know what you think they should be doing.

Space is the last great frontier, and while I don’t advocate filling it with garbage, I like to thinking that we are slowly decorating our corner of the universe with bits of science gleaning flying metal bits.