Date: February 10, 2012
Title: 365 (More) Days of MESSENGER
Podcaster: Bob Hirshon
Organization: American Association for the Advancement of Science (AAAS)
Links: www.aaas.org
Description: The MESSENGER mission to planet Mercury has nearly completed its primary mission: a year of data-gathering while in orbit around Mercury. Now Science Update host Bob Hirshon speaks to MESSENGER Project Scientist Ralph McNutt about the newly approved extended mission that adds an additional year of orbital observations, and what the scientists hope to learn.
Bio: Bob Hirshon is Senior Project Director at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 24th 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.
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.
Transcript:
Hirshon:
Welcome to the 365 Days of Astronomy Podcast. I’m Bob Hirshon, host of the AAAS radio show and podcast Science Update. [clip from that podcast]. Remember that? Well, it’s hard to believe but it’s been nearly a year since MESSENGER became the first spacecraft to go into orbit around the planet Mercury. According to MESSENGER project scientist Ralph McNutt, one reason the time has flown is that MESSENGER has been having so much fun.
McNutt:
We’ve taken over 81,000 images now, and multiple different color filters. We’ve covered over 99% of the planet both at a little bit better than one kilometer per pixel in color, that’s eight different color filters, and we have a monochrome base map covering over 99% of the planet at better than 170 meters per pixel. And we’ve covered now more than 80% of the planet with a stereo-based map in monochrome. So, we’re really getting for the first time, a real close look at Mercury including all the various features: what was apparently a large amount of volcanism in the planet’s past, all sorts of features that are suggestive of how the planet evolved.
Hirshon:
You might think that with that mountain of data, the MESSENGER science team would be completely satisfied. But you would be wrong. The team requested an extended mission for the spacecraft for an additional year, and in November, NASA granted the request. This week, at the 25th meeting of the MESSENGER science team, the scientists are discussing exactly what they’ll do for the additional year.
McNutt:
The upcoming observations are going to be very similar in some respects to what we’ve been doing first year, but also very different in another aspect. We are actually going to be changing the orbital period from 12 hours down to 8 hours. So we’ll have more passes across the planet, slightly faster, being in a slightly warmer environment overall, because the instruments won’t have as much of a chance to cool off. But what this will do is enable for us to concentrate really on some of the details, and be able to look at targets at very much higher spatial resolutions. And basically drawing upon a lot of the discoveries that were made when we were making observations during the primary mission.
Hirshon:
During the primary mission, the team learned a lot about the origin of Mercury, and ruled out some earlier theories for its relatively large iron core. For example, the high concentrations of volatile compounds on the surface ruled out the theory that the planet had been whacked by another celestial body early in its life, knocking off the outer layers. Such a catastrophe would have eliminated those volatiles. The team also confirmed volcanic origins for Mercury’s vast plains. They discovered mysterious new surface features called “hollows.” And they found that the planet’s magnetosphere and exosphere are far more dynamic and, well, mercurial than was expected. These surprises led to new research questions for the team, and at their meeting this week, they discussed how they can use MESSENGER’s suite of instruments to answer them.
McNutt:
For example, we’re going to be running the magnetometer at its high rate of data accumulation all the time now in the extended mission. One of the things we have learned is that not only does Mercury have a magnetosphere, it is incredibly dynamic on time scales a lot shorter than we originally thought. And part of trying to tease out some of the physics behind that activity, we need to be able to look at really the highest data resolution available, which we’ve had in pieces during the main mission, but we’ll be getting that continuously.
Hirshon:
The new tighter orbit will also give them more opportunities to conduct high resolution imaging of unusual features found during the primary mission phase.
McNutt:
For example, one of the interesting features which was reported on by Dave Blewett and co-authors in an issue of Science magazine, special coverage of Science that came out the end of last year, was on the so called “hollows,” which are depressions in some of the craters. They look for all the world like that they have somehow been hollowed out from relatively recent activity, of geologic activity of some sort, and whether that those are related to the volatile content of the crust or not is something we still don’t know. And one of the things we’ll be doing in the extended mission is taking a much closer look at those.
Hirshon:
They’ll also continue to wrestle with a question posed for the primary mission but still not definitively answered: is there water ice on the floors of craters near Mercury’s poles?
McNutt:
We’ve got a neutron spectrometer on board which can look at the possibilities—this has been done both at Mars and at the Moon—of high concentrations of hydrogen. Now hydrogen is certainly not some element that’s going to be loose on the surface of Mercury, but nonetheless it can certainly be bound in a matrix of all sorts of different hydrogenous, or hydrogen-bearing materials, and of course one of those would be in the form of water ice. And the question was actually raised many years ago, because of radar measurements that were made by John Harmon and others of Mercury, and they found that there were anomalously large radar reflections in some of the craters near both the north pole and the south pole of the planet. One of the things we have been doing on MESSENGER is taking a very close look—working with John—of exactly where that those deposits are and how they are situated with respect to the craters that we’re seeing in imaging. And one of the things that we have been able to confirm is that indeed where those deposits are seen—or those reflections, signatures, are seen—are consistent with regions near Mercury’s north pole that are indeed—and south pole—that are indeed in permanent shadow. So at least it’s consistent with the fact that these could be cold traps where that water ice could be contained. The reason for thinking it might be water ice is because that the radar reflection looks a lot like the radar reflections that you get off of the Galileon satellites in the Jovian system. And of course there we know that on Europa and Ganyemede and Callista we’re looking at radar coming off of water ice. So what MESSENGER will hopefully be able to do is to get us a better number, or get us a number, on much hydrogen-containing material there is and that will be a smoking gun for thinking that we’re really maybe looking at water ice in permanently shadowed craters. That’s still being worked on.
Hirshon:
So it’s fortunate that both MESSENGER and the International Year of Astronomy have been given an additional 365 days. We’ll be keeping up with new findings from MESSENGER as the extended mission progresses. For the 365 Days of Astronomy Podcast, I’m Bob Hirshon.
End of podcast:
365 Days of Astronomy
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