Friday, May 1, 2015 12:00am -0400

How MESSENGER Reshaped Our Understanding of The Solar System

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MESSENGER Spacecraft and Mercury MESSENGER Spacecraft and Mercury NASA
Good day, everyone,
I haven't sent much out partly because I have been so so SO busy with the MESSENGER and New Horizons missions that I haven't had much time to do any sky stuff. But as of yesterday the bulk of my MESSENGER duties was brought to a final close as the spacecraft slammed into the surface of Mercury at over 8700 miles/hour. More on that in a moment.

For upcoming night sky stuff, last year this month there was a lot of hype and talk about the new Camalopardid meteor shower - which ended up fizzling. I haven't seen anything mentioned about it since. But there's still stuff to turn your eyes upward to see!
Currently in the evening skies, high to the west you might have noticed a really brilliant starlike object. That would be Venus. It is about as high in the sky after sunset as it will be this year. For the next few days, however, if you have a clear, low western horizon, you might be able to pick out Mercury peeking through the dimming twilight below and to the left of Venus. It reaches its highest point this Saturday, and then will drop from view again by the 13th. 
Almost directly overhead will be Jupiter. If you have access to a telescope, even a small one, this is something to check out, as you'll be able to see up to four of its moons, and perhaps some of the cloud bands. Over the course of the coming weeks Jupiter and Venus will be getting closer to each other in the sky.
Before the end of the month, Saturn will start to rise at sunset in the southeast, and be visible all night long. Although it is not as bright as Jupiter and Venus, it'll be that yellowish starlike object not far from the constellation Scorpio.
Turning from the night sky for a bit, yesterday we said a fond farewell to the MESSENGER spacecraft. You may have heard about this in the news, if you had not seen posts on Facebook or someplace else. I saw this morning that Al Rokker mentioned it on the Weather Channel, however, he said, "NASA expected it to crash on Mercury. I don't know why.". Anyone here who followed my Facebook posts will know (and if you didn't, the short answer is the tug of the Sun's gravity, Mercury's gravity, and to a lesser extent the solar wind, all made the orbit inherently unstable, which we knew going in, and after 4 years of orbital operations, we eventually ran out of fuel to keep the orbit from deteriorating). 
As I type this, it's been 7 hours since the MESSENGER spacecraft went on the other side of the planet Mercury (as seen from Earth) one final time, it's altitude over the surface of the planet plummeting like mad. At 3:26:02 pm EDT today, MESSENGER plowed into the lithosphere of Mercury at 3.91 kilometers/second (or 8747 miles/hour). There was not much left but a 16-meter (52 feet) diameter crater, and debris. 
This happened 7 hours ago (though more like 8 when I finish this. Since that moment a lot has happened. There was a celebratory wake in the Mission Ops Center at work, many, many faces of people who had worked on MESSENGER at some point along it's journey came by, there was laughter, there was conversation, but there was melancholy sadness, too, though you couldn't easily see it. Meanwhile, I've had time to reflect on the mission, and the past 8-1/2 years since I joined it.
MESSENGER was launched on August 3, 2004. I was still working on Hubble at the time (but wouldn't be for much longer). I remember a year later getting an email from Karl Whittenburg saying how they just shot the Goddard Spaceflight Center with the laser on MESSENGER. I didn't really fully understand what he was talking about. Up to that point my life had been wholly wrapped up in doing Hubble stuff. What was this MESSENGER thing? Some spacecraft going to Mercury. Why bother going to Mercury?? I mean, it's just a dead, barren, rocky world of very little interest, right? 
I could not have been more wrong.
October 2006. I had been working on the FUSE mission, a satellite that was dying (it had lost 3 of its 4 reaction wheels, and its gyros were going on the lam; we were steering the satellite using the magnetometers, of all things!), for a little more than a year. Then I got a call from my friend Noam Izenberg, asking if I would be interested in joining MESSENGER. I vaguely recalled Karl's email about the spacecraft, and decided this was a good opportunity to learn something new.
I not have made a better move. 
Mercury 640x318
 November 2006 the MESSENGER team welcomed me aboard, and over the intervening 8-1/2 years, it's been I think the most fulfilling mission I have been on. I've gotten to do things I never thought I could, I was allowed to explore methods and procedures that hadn't been developed or laid out, I was allowed to be involved in more than just one small aspect of the mission, got to go places - no, *encouraged* to go places! - I never thought I would get to, and I got to meet an incredible number of supremely interesting, cool, and helpful people, both in the mission operations and on the science side (sorry to say, I did not have much of this experience with the science side of the house when I was on Hubble). I even got to meet and periodically chat with the principle investigator of the mission, Sean Solomon. (Heck, he even knows me by name.) MESSENGER's science team was incredibly forthcoming with what they were working on, and *wanted* to share it with us in mission ops. That was so cool. I got to learn so much more about this little world than I would have ever otherwise.
No matter how much you like your job, everyone has days in which they just don't want to go in to work. After 8-1/2 years on MESSENGER, I can count those days on one hand. It's just been *that* cool to work on.
MESSENGER has revolutionized our understanding of the planet Mercury, and by extension forced planetary geologists to rethink (again) how our solar system came to be. MESSENGER has discovered on this barren lump of rock so MUCH it's difficult to list it all. It discovered that Mercury's exosphere has seasons. It discovered that Mercury has shrunk. It discovered that the spinning iron core giving rise to its global magnetic field is offset northward inside the planet by several hundred kilometers or more from the center. It discovered that there are vast deposits of water ice at the poles. It revealed an entirely *new* geologic feature that the science team named "hollows" because we had no other word for them (they've never been seen on any other body in the solar system). MESSENGER has shown us that Mercury is not at all boring, but a vastly geologically complex world. What we've learned from this mission is but the tip of the iceberg to the secrets Mercury still holds. 
MESSENGER also holds an enormous number of "firsts" in space exploration. First and obviously, it was the first to orbit our innermost planet, Mercury. Additionally, it was the first spacecraft to employ the technique of solar sailing (also called fire sailing). It was the first to operate so close to the Sun (and survive with 99% of it's functionality still intact at the end). It was the first to use the cold helium gas pressurant as a propulsion source after it depleted the reservoir of hydrazine that was used to periodically maintain it's orbit. The list goes on.
8-1/2 years ago I joined along in this adventure to Mercury, but now the mission is over. Thanking all the people who have been involved, it's been one of the best journeys I've had the pleasure to experience. 
The associated image (above) is a first/last of Mercury from MESSENGER. The very first image we took during the first of three flybys in 2008, and the last image we took and downlinked before the end today. The resolution of the first image (left) is 2.7 kilometers/pixel. The resolution of the second image (right) is several orders of magnitude better, at 2.1 *meters* per pixel. More info here: HERE.
Goodbye, MESSENGER. It's been quite a trip, and I'll never forget. But now it's time to move on to New Horizons, and the innermost object of the Kuiper Belt - Pluto!
Mk (Mark 'Indy' Kochte)
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