Date: August 17th, 2012
Title: Probing the Almost Nothingness
Podcaster: Bob Hirshon
Organization: American Association for the Advancement of Science (AAAS)
Link: www.aaas.org
Description: The exosphere of Mercury has lots and lots of empty space, populated by a few atoms and ions. AAAS Science Update host Bob Hirshon spoke with MESSENGER scientist Ron Vervack, at the Johns Hopkin Applied Physics Laboratory, about the remarkable amount of knowledge to be gained from this rarified environment.
Bio: Bob Hirshon is Program Director for Technology and Learning at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 25th year, Science Update is heard on over 300 commercial stations nationwide. Hirshon also heads up Kinetic City, including the Peabody Award winning children’s radio drama, McGraw-Hill book series and Codie Award winning website and education program. He oversees the Science NetLinks project for K-12 science teachers, part of the Verizon Foundation Thinkfinity partnership. Hirshon is a Computerworld/ Smithsonian Hero for a New Millennium laureate.
Today’s Sponsor: This episode of 365 Days of Astronomy is sponsored by The Education and Outreach team for the MESSENGER mission to planet Mercury. Follow the mission as the spacecraft helps to unlock the secrets of the inner solar system at www.messenger-education.org
Additional sponsorship for this episode of 365 days of astronomy was provided by iTelescope.net – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.
Transcript:
Welcome to the 365 Days of Astronomy Podcast. I’m Bob Hirshon from the American Association for the Advancement of Science. You may know me from roles in such radio shows as Science Update, Kinetic City Super Crew, and as Bob the Science Slob on The Absolutely Mindy show on Sirius/XM radio’s Kids’ Place Live.
Or not.
If matter were musical notes, the surface of the planet Mercury, or any other solid planet, would sound something like this:
(Rock power chords)
The exosphere, on the other hand, would sound more like this:
(New age ethereal, occasional note)
Ron Vervack, senior research scientist at the Johns Hopkins Applied Physics Laboratory, says that sometimes it’s a big advantage to be able to examine atoms in isolation, instead of all bunched together. And he says that the atoms in Mercury’s exosphere are so sparse that even if you gathered them all up, you could pack and ship them via standard UPS ground delivery.
Vervack:
We’ve often talked about as a team making an estimate of, okay, if we took all of the atoms that are currently in the exosphere and shoved them into a box, how big would big would the box be? Would it be the size of a refrigerator? Would it be the size of a truck? We’re not talking about things that would be much bigger than something of that scale, if you compress it down to the type of density we have at Earth’s surface. So it’s not a lot of material, but it’s very informative.
Hirshon:
Vervack is on the Science Team of the MESSENGER Mission to planet Mercury. The MESSENGER spacecraft is now in orbit around Mercury and has several instruments designed to examine and analyze the planet’s surface. Vervack says that surprisingly, looking at what’s going on hundreds of kilometers above the surface can make that job easier.
Vervack:
All of the material in the exosphere has as its ultimate origin on the surface of the planet. So you’re going to learn something about the composition of the surface, we look at what are known as emission lines, so the atoms give off wavelengths—ah, they give off light at a particular wavelength, it’s a very diagnostic wavelength, we know exactly what species things are coming from, so we can learn about the composition of the surface by what’s coming off of it. And in some ways this is extremely complimentary to what you get from the surface instruments, because they can tell sometimes that it might be this or that, and can’t distinguish against it, we might be able to provide a clue on that.
Hirshon:
Not only can this tell you something about the composition of the surface, but also a lot about what processes are going on there. Vercack says the exosphere is in constant flux, with some atoms getting added from the surface, others leaking out into space, and still others carried back to the surface.
Vervack:
The exosphere has to constantly be replenished. It is, as I say, when stuff comes off it either falls back or escapes from the system, and that happens on the time scale of minutes to days. So if we weren’t constantly regenerating the exosphere, it would just go away. So you really want to understand how it’s regenerating.
Hirshon:
Atoms are sent up to the exosphere in three primary ways: one is from sunlight hitting the surface. Photons either warm the materials up and boil them off, or break the bonds of loosely held atoms. Vervack says interactions with sunlight are known as “cool processes.”
Vervack:
They take very low energy, so they’ll affect certain species more than they will others. One species in particular that that’ll affect is sodium, which is the same sodium that you will see in the sodium vapor lamps on Earth: that nice kind of amber yellowish color, that’s the emission line that we’re seeing at Mercury. And it’s the strongest emission in Mercury by far.
Hirshon:
The other two interactions are called hot, or high-energy processes. They include charged particles hitting the surface, and also micrometeoroid impacts.
Vervack:
Tiny little dust particles, not big things—and they are just constantly hitting the surface and knocking material off; also charged particles, either coming in from the Sun in the solar wind, or from the magnetosphere itself: Mercury has this very vigorous and dynamic magnetosphere that sends particles back to the surface. Those can get into the surface, break bonds, and these are both energetic processes, so they’ll launch material to much higher altitudes. And they, we thought, were the primary sources of calcium and magnesium, which are the other two really easily seen emission lines that we study on a regular basis.
Hirshon:
But in one of many mysteries that Mercury has served up, that hasn’t been the case.
Vervack:
If you think, going in, that it’s meteoroid impacts, the dust in the solar system, that’s hitting the surface and knocking stuff off, or if it’s the charged particles from the sun and the magnetosphere knocking stuff off, you would expect to see certain uniformity or particular places where the charged particles come in, sort of like what are known as the magnetospheric cusps, the equivalent on Mercury of where the aurora would be on Earth. It’s a totally different process, but you have aurora at northern latitudes, southern latitudes, you would expect to see similar types of enhancement. We didn’t see that. What we saw with calcium in the flybys, and we continue to see it all of the time in orbit, is that calcium seems to be coming off of the surface near the dawn terminator. So basically in the early morning that’s where the calcium density in the exosphere is the highest. And that’s surprising, because you, there’s no reason to expect an energetic process to be so focused at the terminator like that. So that was our first surprise, “wow, so it’s not behaving.”
Hirshon:
Just as weird is that magnesium, which normally would follow calcium, isn’t pairing up with calcium at the dawn terminator. It’s sort of doing its own thing.
Vervack:
Calcium and magnesium are thought to be very similar in terms of the ways they would be knocked off the surface. Clearly, something is affecting calcium and not affecting magnesium in the same way.
Then just more recently, we discovered that magnesium has a different behavior than we expected. It’s showing some enhancements at different portions of the exosphere, different so-called local times, where… local time is basically 6 in the morning, 8 in the morning, noon. And we’re seeing enhancements at different local times.
Hirshon:
You might think all these misbehaving elements would be disconcerting to Vervack and his colleagues, and you’d be right. But it’s also kind of exciting.
Vervack:
One of the things we may learn from all of this unusual behavior in the exosphere is it may point to processes, for example, that are new, and the wonderful thing about Mercury is that it’s really a nice laboratory. You have this rocky surface with a very vigorous and dynamic magnetosphere because it’s so close to the sun and interacts so strongly with the solar wind. So we’re learning things about magnetospheric processes that we aren’t, that are new, even though we’ve had a lot of magnetospheric spacecraft at Earth, studying our magnetosphere, it’s very different at Mercury, so they’re learning things, in turn that leads to models of how the charged particles come down to the surface, which may tell us something about what we’re seeing. So we’re learning about processes we already know are there, but we’re learning new things about the way they work. That’s one thing. And you can take that to any planet that has a magnetosphere and say, okay, maybe this explains something at Jupiter that we didn’t understand before. So in that case, it’s kind of nice—it informs things other than just studying Mercury for Mercury’s sake. And, again, it may uncover a new process that we didn’t think was important at all. That’s always exciting because, hey, we never even considered this and there it is. So that’s neat.
Hirshon:
Or maybe there are no new processes going on, just strange concentrations of elements on the surface. And that also would be interesting. You may recall that in an earlier podcast, I reported on the discovery of “hollows” on Mercury: strange patterns of pits, where it looks like something boiled or evaporated away. Maybe the anomalous behavior in the exosphere is a clue.
Vervack:
We may find that, perhaps this is material that’s in the “hollows” that geologists talk about. We don’t know that, we haven’t seen those sort of tight correlations with the features. That’s something we’re hoping to do in the future, but if it is something like that, then it points to, Okay, these are magnesium rich or if, in the case of calcium over on the dawn side, you know, these are calcium rich things. They may not be able to figure that out other than from the information that we can provide. So we may learn something about the material—very localized material—on Mercury which can then point to something about how those particular materials came to be in place, whether it’s volcanism or some other process. So everything’s tied together. The space environment could be influencing us, it almost certainly is, but it could be influencing us in ways that we don’t even understand. That could point to you know, ways that the surface itself is chemically arranged, and that can point to the geology people, who can then take that and run with it in terms of how Mercury came to be in its present state on the surface. So there’s a lot of feedback. That’s what’s so nice about the MESSENGER mission is that all the teams really have to talk to one another to put the big picture together.
Hirshon:
So there you have it: the incredibly high proportion of information per unit mass of Mercury’s exosphere. If you have questions, comments, observations, anecdotes, jokes, rants, witticisms, poems, songs, secret messages, haiku, anagrams, opinions, suggestions or anything else you’d like to share, please click the comment box. Thanks for listening. For the 365 Days of Astronomy podcast, I’m Bob Hirshon.
End of podcast:
365 Days of Astronomy
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