The annual fall meeting of the American Geophysical Union is an overwhelmingly huge gathering of scientist from all over the world. This year, it’s clocked in at over 24,000 people, from disciplines as diverse as atmospheric science, to deep Earth processes, to planetary science. It is physically impossible to see everything. So, guess where I’ve been spending my time? To err on the side of exciting versus complete, I’ll give my impressions of what I’ve seen so far (Monday-Wednesday).
The surface of the Moon gets nailed daily by a hail of galactic and solar cosmic rays. These positive particles can get lodged some depth into the lunar regolith. If the rain versus discharge rate is high, then the potential difference across the top few millimeters can get so large that an actual spark will be produced. That spark could split regolith grains along grain boundaries and create smaller and smaller particles. This type of space weathering would tend to produce fine powder, kind of like what Neil Armstrong left his footprint in back in 1969. Really, this specific form of lunar gardening would be important in the permanently shadowed regions at the poles, since discharge rate is proportional to temperature. And, who would have thought that grains on the Moon could be sorted by a lunar magnetic field? Apparently, there are some magnetic field signatures measured in the crust, and a swirly sorting based on metallic iron content has been found which correlates with these fields. Nobody knows, yet, what produced the magnetic fields. It may take a manned mission back to the Moon to ultimately piece together whence the field.
We’ve had an orbiter zipping around Mars for ten years, and that orbiter is called Cassini. It still has some juice left, so they plan to modify the orbit over the next year or two to take it INSIDE the rings, and then between the rings and the planet. Imagine the detailed imagery we will get of both the ring material and the cloud structure of Saturn! Up to now, the detail in the rings has been incredible. We’ve seen shadows cast on the rings by larger particles and moonlets; we know that the albedo of the rings (e.g. the Cassini division) is caused mainly by particle size, not number; we know that huge storms can wrap around the planet, generate tons of lightning, and deplete the upper atmosphere of ammonia; we know that the moon Enceladus shoots out jets of salt water, implying both that there is a subsurface water ocean, and that that ocean is in contact with a rocky surface underneath. We also know that we don’t know what generates Saturn’s magnetic field. The dynamo theory doesn’t cut it, since it the field is almost perfectly aligned with the rotational axis. A corollary of this is that we still don’t know exactly what is the rotation period of the core. Then, we have the methane oceans of Titan, which are fed by sinuous rivers with dendritic tributaries that cut valleys into water ice bedrock. This moon may be a great target for human visitation, since it’s morphologically the most Earth-like body in the solar system. The lakes and oceans are found primarily on the northern hemisphere, though there are signs that liquid has filled areas of the southern hemisphere. It is likely that a Milankovitch-like effect moves the methane from hemisphere to hemisphere over the orbit of Saturn around the sun.
The MESSENGER probe is getting closer and closer to the surface of the tiny planet at its periapsis. So far, it’s gotten to within 25 kilometers of the surface, which now allows us to nab photos that show features only meters across, such as fluting within crater walls. We can see crustal fabrics that must be interpreted as young thrust fault scarps, which implies that the planet is contracting right now. The little planet has a huge magnetic field with no van Allen-type belts. There are transient energetic electron events which do not correlate with such events emitted from the sun, which implies that something in Mercury’s magnetosphere tail is accelerating electrons to ungodly speeds. We’ve also mapped the planet in magnesium and aluminum, and are building an ever more detailed map of sulfur and other elements. With MESSENGER as well as Cassini, the next two years will bring the probe closer and closer to the planet, which will lead to incredible detail and an inevitable impact. They say they’ve located an unforseen propellent in the craft that can extend its useful lifetime, though – they’re going to outgas the helium they’ve used to cool the instruments!
There was a Curiosity press conference, which I missed for some dumb reason. You can see the press release here. They reported a transient spike in methane detected in the atmosphere of Gale Crater, which indicates some local outgassing event. Otherwise, I haven’t been blown away by the Mars stuff I’ve seen this year, but there will be more later this week. There’s a ton of chlorine in the crust. There’s also some fluorine. These indicate outgassing from the crust and very little partial melting? Sorry, this stuff just didn’t float my boat. But, comets did.
Rosetta is orbiting comet Churyumov-Gerasimenko (“or comet 67P, for the cowards.” – Laurence Soderblom), and dropped its Philae lander to the comet’s surface in November. The lander bounced twice before coming to rest in some shadowed region of the comet’s surface. The shadowed region sucks on the one hand, because the lander’s solar panels are getting too little sunlight to power the craft. It’s great on the other hand, though, because when we turn Philae back on in January or February, it may survive the comet’s perihelion, which it hadn’t been designed to do. Also, the bounce allowed us to nail down the dynamical properties of Churyumov-Gerasimenko, and stuck us in a spot with a much larger variety of ice and dust grains than had been expected. The comet has already to begun to release gas from the neck region, and this gas contains water as well as heavier organics that weren’t expected. As a side note, all the comets that we’ve visited are shaped something like a duck, with a head, neck, and body. Either they’re all two objects stuck together, or the neck represents a rotational equator that has been eaten away by solar radiation. The jets that we’ve identified from Churyumov-Gerasimenko (I’m no coward) are coming from the neck region.
And last, but not least,
The New Horizons spacecraft will zip past the largest and most mooned Kuiper Belt object next Bastille Day (July 14). We don’t know what we will find. All we know for sure about this little guy we’ve learned from infrared spectra and occultations with its moon Charon, as seen by the Hubble Space Telescope. We don’t even know the exact size of Pluto beyond 30 km error bars. We know it has nitrogen and methane in its atmosphere. We know that some of that nitrogen is beta-nitrogen, which means the surface of Pluto gets above 36.5 Kelvins. There’s not a whole lot more besides models, though. About a billion observations are programmed into the spacecraft to be performed during its short flyby, including some observations of Pluto’s five moons.
And, that’s it for now. What, that’s not enough? Somebody in one of the sessions got up and stated something I brought up four years ago – We’re entering a period that would be excellent to get people into deep space, since the Sun is entering into an extended very quiet period, a period quieter than anything we’ve seen since Apollo.