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MESSENGER’s Day in the Sun

We rarely talk about the inner planets here, and even Mars gets short shrift. That’s because I decided at the outset that because there were so many excellent sites covering planetary exploration — and especially Mars — my only focus within our Solar System would be on the outer planets and, of course, what lies beyond them. But the MESSENGER mission is simply too fascinating to ignore, the first mission to Mercury since Mariner 10 way back in 1974, and beyond that, one of its project scientists is a man I deeply respect, Ralph McNutt (JHU/APL), who in addition to his MESSENGER duties also serves as one of the consultants for the Project Icarus starship design.

In fact, McNutt’s work in regions both near and far from the Sun is voluminous. For MESSENGER, he will be analyzing the planet’s surface composition using data from the spacecraft’s X-Ray Spectrometer and Gamma-Ray and Neutron Spectrometer instruments. But he’s also a co-investigator for the New Horizons mission to Pluto/Charon, works with the Cassini team on the Ion Neutral Mass Spectrometer investigation, acts as a science team member for the Voyager probes, and is actively involved in interstellar probe design, as witness his work on the Innovative Interstellar Explorer mission, a near-term precursor probe to 200 AU.

Image: This high-resolution mosaic of NAC images shows Mercury as it appeared to MESSENGER as the spacecraft departed the planet after the mission’s second flyby of Mercury. This mosaic resembles one of the first images received back at Earth following that flyby, an image that showed for the first time the spectacular rays of Hokusai crater extending great distances across Mercury’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

MESSENGER is set to achieve Mercury orbit after a 4.7 billion mile trip that has included fully fifteen trips around the Sun and six planetary flybys. Orbital insertion should be around 0100 UTC on the 18th, marking the first time a spacecraft has orbited the planet. It’s been a long journey not only in miles but in time since MESSENGER launched more than six and a half years ago. Ahead is a year-long science mission as MESSENGER orbits the barren world in an orbit that closes to within 200 kilometers of the planet’s surface. Says APL’s Eric Finnegan:

“For the first two weeks of orbit, we’ll be focused on ensuring that the spacecraft systems are all working well in Mercury’s harsh thermal environment. Starting on March 23 the instruments will be turned on and checked out, and on April 4 the science phase of the mission will begin and the first orbital science data from Mercury will be returned.”

Remember that Mariner 10’s images of Mercury’s surface were made during three flyby maneuvers in 1974 and 1975, but the spacecraft could only send us pictures of one side of the planet. MESSENGER has been filling in the gaps through its own flybys, and now we’ll complete the picture. What’s exciting isn’t just the thrill of making a full study of a little-examined world, but knowing that the more we learn about the geological history, surface composition and other salient facts about Mercury, the more we learn about rocky planets in general, knowledge which we’ll apply as we try to make sense out of the smaller worlds we find around other stars.

Coping with heat will be a major issue for this mission, which is why the spacecraft’s instruments are shielded against the reflection from the planet’s surface. Thermal issues have consequences for the spacecraft’s orbit as well, says Ann Sprague (University of Arizona):

“The spacecraft is going to go very fast, traveling around the planet every 12 hours. The orbit is highly elliptical to allow the spacecraft to cool down. We couldn’t do this with a circular orbit, like around Mars. Everything would just overheat. MESSENGER must swoop in, keeping its sunshade pointed toward the Sun, and then it has to swing out far into space so it can cool down.”

We have much to learn, including the question of whether frozen water may be found beneath dust layers in the permanently shadowed crater bottoms at the poles, the nature of the planet’s exosphere (a thin region of atoms and ions generated by charged particles from the solar wind striking the surface and interacting with elements there), and the question of Mercury’s magnetic field. The planet is small enough (not much larger than the Moon) that it should have solidifed to the core, as this UA news release points out. But the presence of a magnetic field tells us that there may be molten material inside, generating a field MESSENGER will examine closely.

All of this reminds me that Mariner 10’s Mercury travels had ramifications in unexpected ways. Flaking paint from the spacecraft’s high-gain antenna caused problems with its navigation sensors and a disturbed star tracker caused the spacecraft to roll, venting critical attitude control gas. The control team at the Jet Propulsion Laboratory was able to use Mariner 10’s solar panels to adjust the spacecraft’s attitude, an early and striking demonstration of the power of solar photons. These days we’re just entering the era of the solar sail, but it’s worth recalling that the concept was demonstrated much earlier, and in this case, in entirely unanticipated ways.


Comments on this entry are closed.

  • ljk March 16, 2011, 9:31

    For those who want to know all about the Mariner 10 mission to Mercury, check out this NASA book from 1978 on the subject online here:


  • ljk March 16, 2011, 9:34

    FYI, Mercury very likely has a molten core:


  • bigdan201 March 16, 2011, 10:13

    This is a fascinating mission! I’ve been hearing about MESSENGER for awhile, so it’s nice to see things underway.

    I’ve read that Mercury has a magnetic field, but this should help specify its strength and other properties. This should, in turn, give clearer answers to how helpful it would be for future activity on Mercury.

    Although this planet is often overlooked, I’ve never forgotten its potential. Solar power is plentiful there, and there may be significant natural resources to be mined. The fact that it has mars-like gravity is also encouraging. The polar regions could be home to permanent outposts.

    However, there are many challenges, such as extreme temperatures and its depth in the suns gravity well. Hopefully, MESSENGER will give us more information on Mercury and its potential.

    I was interested to see that MESSENGER took a “family portrait” of 6 of the planets, in the tradition of Voyager: http://en.wikipedia.org/wiki/Family_Portrait_(MESSENGER)

  • Greg March 16, 2011, 11:22

    What materials make up Mercury? I wonder if the thermoelectric effect has anything to do with the magnetic field detected? With it’s extremely hot and extremely cold sides, I can’t imagine a better place to occur.
    With that said, it would be an ideal place to use thermal energy and beam it back to Earth. That’s just the engineer in me talking, but the power that can be harnessed I’m sure could easily launch a star-wisp or laser sail to 100’s if not 1000’s of miles a second.

  • James M Essig March 16, 2011, 16:56

    Hi Folks;

    I am happy to hear of the Innovative Interstellar Explorer mission research. 200 AU is a profound distance in comparison to current assets all ready in operation. This is 30 billion kilometers or 1/333 of a light year and roughly 0.1% of the distance to Alpha Centauri. It was just a few decades ago when the distance fraction of our furthest space craft with respect to Alpha Centauri had a few additional zeros to the left of the decimal point. This is indeed progress.

    Popular Science Magazine had a recent article about human travel prospects to other star systems, and the general opinions expressed by the scientists and engineers interviewed is that humans will reach the stars at some point. The article featured an interview with Marc Millis among other visionary intellects.

    If anyone would like more detailed information about the article, I can provide it. I would need to find my copy of the subject issue. As always, Popular Science included some whimsically beautiful illustrations within the article.

  • Enzo March 16, 2011, 17:00

    A Mercury orbiter was long overdue and an important mission, but two ?
    I really question ESA judgment of sending a second, however better it might be, mission to Mercury given the current poor funding conditions.
    I mean, with the third effective cancellation of an Europa orbiter, the cancellation of SIM and all the rest, it’s not if they were short of more interesting targets.
    Absolutely depressing.

  • Phil March 16, 2011, 19:16

    Here’s to finding more about the putative but fascinating polar volatile deposits too, as per an Icarus paper about the latest Arecibo results from last year: 10.1016/j.icarus.2010.08.007.

    Obviously they are in the polar dark, so I guess that rules out visual detection, but maybe neutron counting?


  • Volucris March 16, 2011, 20:38

    I must agree, ESA ought to rather pick different targets than NASA missions, unless it can really get there first.
    Of coming ESA missions I think Gaia seems most interesting (Hipparcos follow-up in grand scale). Origins Billion Star Survey was a similar proposal, and Russians had plans also, but I guess they left it to ESA, no sense to send 3 missions to do almost the same thing.

  • Scott G March 16, 2011, 21:40

    Mercury and Jupiter are current visible in the evening sky together. This article (“See Mercury at Sunset” — http://www.physorg.com/news/2011-03-mercury-sunset.html ) provides a chart showing their relative positions from March 13 – March 16.

    Hopefully you’ll still be able to see them together for another few days. If not, here’s an amazing pic of the two planets taken on March 13 (referenced in the same article — http://cdn.physorg.com/newman/gfx/news/hires/2011/pete-lawrence1.jpg ). Jupiter’s on the right, Mercury on the left. There’s something fascinating about seeing these two together.

  • Scott G March 16, 2011, 21:44

    ***Correction*** in the image I just posted, Jupiter is on the LEFT, and Mercury is on the RIGHT.

  • Enzo March 16, 2011, 22:43


    I believe that this is down to the fact that ESA seems to take longer than NASA to decide on a mission but, once selected, it sticks to it no matter what. This has its merits.
    In the case of Mercury it hasn’t worked very well.
    However, in the case of Gaia, it has. I remember reading about Gaia in 1997. It slowly made it through the ESA approving process and it is soon to be launched. NASA in the meantime came up with SIM, a higher precision mission (but maybe less comprehensive, especially SIM-lite, not sure).
    Unfortunately SIM did not survive the uncertain funding process.
    So, sticking to it, no matter what sometimes works.

    ESA has also terrible PR. They launched COROT before Kepler. Granted, COROT is not Kepler, but, by not releasing candidate planets it has been totally eclipsed.
    I also remember the RADAR mission on Mars express : no information for years. The first time I saw something that resembled a MARSIS result was basically at the same time SHARAD on Mars Reconnaissance Orbiter (launched much later) was publishing images.

  • Rob Henry March 17, 2011, 3:17

    Ljk, I find it intriguing that there is significant direct evidence for a liquid core of Mercury. If Mercury has a large nickel iron core and thin mantel, as is the traditional explanation for its density, then low mass is not the only, or even the most significant reason for implying that its core is solid. Metal conducts heat far more rapidly than rock, so Mercury’s should have cooled several times quicker than a more typical planet of its mass. Additionally most of the inventory of primordial radionuclides co-fractionate with the mantel, most of which has been thought to be blown off by early impact(s). I know that Kenneth Goettel calculated that our current physical data on Mercury could allow its core to contain up to 17.5% sulphur, even though that seems like a ridiculously high volatiles content for such an inner planet. The question then should probably be: could such a S content increase the insulating properties of the core sufficiently to allow it to remain liquid to this day?

  • ljk March 17, 2011, 9:43

    I distinctly remember ESA’s coverage of the day that Huygens landed on Titan in January of 2005. It felt like they spent more time showing various managers congratulating and thanking each other than displaying any images or data from the lander, which they did sparingly and only many hours later. We had to rely on some college kids to download the first surface images from the University of Arizona database to see them on the same day.

    Good luck, MESSENGER. Make Mariner 10 proud! Mercury may seem not as interesting as other worlds in our Sol system, but it may turn out to be one of the keys to getting ourselves established in space with its mineral wealth and our first probes to the stars with its proximity to the Sun, as commenters have said in this blog thread.

  • Eniac March 20, 2011, 1:48

    I believe Mercury is also interesting from a SETI point of view, as it could be a favored spot for self-replicating mechanical probes to hang out. Lots of sunlight, lots of metal, just what a self-replicating machine needs. Of course, they would have been designed to stay low profile, or else the planet would have been eaten long ago.

  • Todd March 20, 2011, 6:21

    I’m hesitant to criticize the BepiColombo mission. Sure, it would be nice to have follow-ups at Jupiter and Saturn every nine years. Personally, I’d like to see a Uranus orbiter, which at the risk of uttering heresy, if it weren’t for Voyager 2, might be on the way already.

    First, Mercury is a substantial world, enough to have geological and geophysical interest that one orbiter and a flyby won’t satisfy. It would be one thing if ESA/JAXA were sending an orbiter to Eros. The BC mission profile looks interesting enough to merit benefit of the doubt. Mercury may not have permafrost, but I suspect ESA mission scientists in 2020 will have more to do than yawn and say, “Another day, another crater.”

    Two, ESA/JAXA have yet to mount a mission to the outer solar system, except as a piggyback to Cassini. If they have the technology for powering a functional mission of more than seven years, maybe they need to prove it. With their launch capabilities, they’re looking at a Galileo or Cassini-style inner system cruise, a five-year minimum but probably seven. A Europa orbiter would require at least two years at Jupiter of a Messenger-style approach for orbit.

    What’s really too bad is that the Americans couldn’t bridge the technological divide to replace the cancelled ESA Mercury lander. That would have been a great fasterbettercheaper mission.

  • ljk May 6, 2011, 12:30

    Alan Shepard and MESSENGER Stamps Unveiled at Kennedy Space Center Ceremony

    by Ken Kremer on May 5, 2011

    KENNEDY SPACE CENTER – 50 Years ago this week, Alan B. Shepard became the first American to be launched into space. Shepard blasted off on May 5, 1961 from Cape Canaveral, Florida. NASA and the US Postal Service honored Shepard’s historic achievement today (May 4) at an Official First-Day-of-Issue dedication ceremony at NASA’s Kennedy Space Center in Florida.

    Alan Shepard was one of the seven Project Mercury astronauts – who will be collectively known for all eternity as – “The Original 7”.

    The US Postal Service simultaneously released two new 44 cent Forever Stamps at today’s commemoration, which bookend two historic space achievements – Shepard’s inaugural manned spaceflight aboard the Mercury capsule and NASA’s unmanned MESSENGER mission which recently became the first probe from Earth to achieve orbit about the Planet Mercury.

    Full article here:


  • ljk November 1, 2011, 9:03


    Hydrogen Geysers And Metallic Iron Could Explain Puzzling Hollows on Mercury

    The strange features spotted by the MESSENGER spacecraft may be caused by hydrogen venting from the planet’s interior, says planetary geologist

    kfc 10/31/2011

    You can be forgiven for thinking that the Solar System’s innermost planet is a perennial disappointment. Mercury has always appeared a dead, crater-scarred ball of rock with little of interest for the discerning astronomer.

    And yet, last week the planet surprised everybody by presenting planetary geologists with a conundrum. The MESSENGER spacecraft, currently in orbit about Mercury, sent back images of strange features on the surface that defy explanation.

    The pictures have generated more than a little fuss. The hollows are irregularly shaped, shallow, rimless depressions which have have formed in craters, indicating that they must be relatively recent additions to the landscape. They are also strangely bright, indicating that they are covered in a highly reflective material.

    That means the surface of Mercury must be active in some way. The question is: how?

    Today, Marvin Herndon, an independent scientist based in San Diego, gives us his idea. He points out that if, during the planet’s formation, the pressures and temperatures were high enough for iron to become liquid, then it ought to have absorbed large amounts of hydrogen.

    As the liquid solidifies, this hydrogen would be released and escape through the surface of the planet. The result would be hydrogen geysers that erupt from time to time on the planet’s surface.

    These hydrogen geysers could certainly have caused the rimless depressions that MESSENGER sees, says Herndon, a self-proclaimed maverick in the world of planetary geology.

    What’s more, hydrogen would react with various substances as it passes through the planet’s crust. One possible reaction is the reduction of iron sulphide to metallic iron. Iron sulphide is common on the surface of Mercury.

    It is this light dusting of metallic iron that gives the depressions their high reflectivity, says Herndon.

    Interesting idea.

    Ref: http://arxiv.org/abs/1110.5796: Explanation for Observed Evidence of Geologically Recent Volatile-Related Activity on Mercury’s Surface

  • ljk February 1, 2013, 16:25

    Do we finally have a piece of the planet Mercury?


    To quote:

    The new Moroccan find is now officially known as Northwest Africa 7325. Ralew sent samples to the laboratory of Anthony Irving (University of Washington), well known for his expertise with unusual meteorites from the Moon, Mars, and elsewhere.Once cut open, the stones revealed interiors full of a stunning emerald-green silicate mineral infused with chromium. The crystals were relatively large and obvious, suggesting that the magma from which they solidified cooled slowly. Irving and his team found lots of magnesium and calcium in the suite of silicate mineral, but even more important is what didn’t find: they contain virtually no iron.

    Irving, who’ll present his team’s findings at a planetary-science conference next month, is trying to keep his enthusiasm in check. “NWA 7325 is tantalizing, and certainly more consistent with the Messenger results than either angrites or aubrites,” he explains, “but we need a [spacecraft-returned sample] for ‘ground truth’.”