An update from MESSENGER

In February of this year, I wrote an entry about the MESSENGER spacecraft, NASA's recent expedition aimed at learning more about the planet Mercury. Despite being relatively close to us in the solar system (a few scant planets away), we know relatively little about this rocky planet. MESSENGER is an attempt to answer some long-standing questions about the planet, including (if you remember from my previous post) what half of the planet even looks like! I figured it was about time to give you an update on what MESSENGER's been up recently.

Some of the latest news to come from the MESSENGER mission concerns the origin of Mercury's magnetic field. The question of what exactly is a magnetic field opens the door to a big area of physics called electricity and magnetism. I'm not going to go into a lot of detail about magnetism - at least, not right now. I will tell you that a magnetic field is a a field that permeates space and exerts a magnetic force on moving electrical charges and magnets (otherwise known as magnetic dipoles). Earth (as I'm sure you know) has a magnetic field; this fact gives us north and south. There does not appear to be a simple answer for why Earth has a magnetic field. It seems that it has something to do with our rotation. We believe this because the planet Venus, though it has a similar iron core to Earth's, has a different rotation pattern and has no magnetic field itself. Earth's rotation may generate something called a dynamo effect, causing the fluid iron in the core of our planet to circulate. At the same time, convection occurs, drawing the hottest part of the molten iron away from the center of the planet towards the surface. This combination of rotation and convection generates electric currents, which in turn generates and sustains our magnetic field.

Now, while it's long been known that Mercury has a magnetic field (though it is about 100 times weaker than our own), why it does so has been a mystery. Scientists had believed that Mercury's iron core was thought to have cooled long ago; a lack of fluidity in the core would make it incapable of generating a dynamo effect. But it turns out that Mercury's core is not as quiet as they once believed. The latest news from MESSENGER seems to indicate that a combination of volcanic activity and fluidity in Mercury's core is responsible for the generation of this magnetic field.

Of course, as is always the case in science, as soon as one question is answered, another is posed. The question now is not "why does Mercury have a magnetic field," but "why is Mercury's core still molten?" For the answer to that one, however, it looks like we'll have to wait for more data from MESSENGER, and another announcement from NASA.

In the meantime, here are a few other facts about Mercury that NASA has announced from the latest data from the spacecraft:
1. Mercury appears to have active volcanic vents around something called the Caloris basin, This is one of the solar system's largest and youngest impact basin - a basin formed by an impact with an asteroid or comet during the first billion years in the history of the solar system.
2. The planet has shrunk in on itself more than anyone had ever expected - in fact, the planet seems to have shrunk one-third more than anyone predicted
3. The magnetosphere around Mercury is more complex than scientists had predicted. The magnetosphere (a kind of bubble around the planet that contains atomic and molecular particles) contains more complex particles than had been expected, given how close it is to the sun. In fact, many of the particles themselves originate from the planet, and are not carried there by solar wind.

MESSENGER is supposed to make another flyby of the planet in October, so I'm sure that more news about Mercury will be coming shortly. Until then, if you want to see a really interesting picture from the latest set of data, check out picture of the Caloris basin on the MESSENGER website at:
http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=193

Octopus - up close and personal

I wanted to write a quick post about a topic I've written on before - octopus. In May, I wrote an entry about the intelligence of octopus (and I don't know about you, but some of what I learned certainly surprised me!). Well, my husband and I recently came home from a vacation in Hawaii. We both love to snorkel and scuba dive, and though we weren't able to do any scuba diving this trip, we did get in some great snorkeling. And this time we saw something we've never seen before while in the ocean - an octopus.

Now, we strongly suspect that there are octopus all over the areas where we often snorkel. The rocks and coral have so many cracks and fissures that there are ample hiding places for them. There are also significant numbers of moray eels in the area, and octopus are a tasty snack for a moray (if it can catch one, that is). And finally, we've heard other people say they've seen octopus around there before. So we knew that they were there. But we've never seen one before.

I think there are 2 main reasons for this. First, octopus are nocturnal, and we always snorkel during the day. And second, octopus are really, really, really good at hiding - especially when it comes to camouflage! An octopus sitting motionless in a crevice looks just like a rock - brown and bumpy. Put that "rock" 10 feet below the surface of the water, and a snorkeler swimming over the top of it will never see it.

However, this year we were extremely fortunate. We managed to see an octopus as it was moving to a new hidey-hole. It was fairly easy to see it when it was in motion; moreover, once it was settled into its new spot, we knew where to look for it, and were able to watch it quite easily. It was pretty big, maybe 2 feet long from the head to the tips of the arms, much longer than I ever expected to see in the wild. And perhaps the coolest thing about it was the way that it would rapidly change colors when one of us swam close to it. It would instantly switch from rock-brown to dark red, then fade back to brown when we backed off. I think that means we were spooking it a little bit!

We saw quite a few other interesting sea creatures while snorkeling this year, as well, including both the largest and the smallest moray eels we've ever seen (the largest being probably close to 4 feet long, and the smallest being only several inches), and a huge devil scorpionfish. This has to be one of the uglier fish I've ever seen. They sit on the bottom of the ocean, disguising themselves as rocks. They kind of look like a fishy equivalent of a gargoyle, actually - lumpy, brown, and extremely grumpy looking. And while you don't want to touch these guys (yes, they are poisonous), being able to find one is actually quite a treat. (Can you see the face of this one on the right-hand side of the picture, with a fin in the bottom left corner?)

I'm sure there were all kinds of interesting creatures in the ocean where we were snorkeling that we never even saw. But I think we were very fortunate to find the things that we did! Of course, the next time we go, I'll be on the lookout for even bigger and better things.