MESSENGER's third tryst with Mercury

By Phil Plait | October 8, 2009 10:00 am

Last week, the MESSENGER spacecraft passed the solar system’s smallest planet for the third and final time; when they next meet it won’t be some quick fling, it’ll be for a long term relationship.

Several gorgeous images were returned from the spacecraft, but this one is my favorite so far:


This is a large impact basin about 260 km (160 miles) across. It’s never been seen before! Only one other spacecraft has visited Mercury before — Mariner 10 in 1974 — and its orbit was such that it never did see many parts of the planet. MESSENGER was in the right place at the right time to snap this picture.

Note that it’s a double ringed crater. It’s not quite clear why these features form. It may be due to the forces generated upon impact, when a shock wave travels through the rock and rebounds inside the crater, or it may be from subsequent volcanic flows. Double rings are only seen in large impact events, so that must have something to do with it. You can also see concentric troughs or cracks in the crater middle. Those are due to the stretching of the crater floor after the impact.

messenger_brightspotOther images of Mercury from this third pass are just as cool: a bright splash around a double crater (seen here; most likely lighter material under the surface blasted out on impact), a crater with an elongated pit in its floor that makes it a pretty good smiley face, and a lovely shot of the northern limb of the planet spattered with craters.

I imagine they’ll release a handful more images over the next few days, but that’ll be it for the most part until March 2011, when MESSENGER meets up with Mercury one last time, settling into orbit… and then we’ll see lots more images. Lots and lots more… and they’ll be even higher resolution than these. What wonders will we see then?


Comments (18)

  1. Wow, there’s a face on Mercury too? Comparing the Martian and Mercurian faces, I think the Mercurians are more friendly.

    Also, I submit “Hermean” as the name of an inhabitant of Mercury, rather than “Mercurian”. Since there likely aren’t any, I’ll vote as proxy for them. “Aye”.

  2. Mark

    It appears from the image that Hermeans only have one eye. I wonder how that affects their depth perception?

  3. Adrian Lopez

    It’s amazing how Mercury looks so much like our Moon. It’s almost as if they used the same movie set!

    I’m just kidding, of course… but it does look a lot like the Moon.

  4. Bruce

    You say concentric rings happen for large impacts, but the crater upper-left of the big one also has concentric rings, and it’s much smaller.
    Is there a threshhold below which we don’t expect concentric rings?

  5. Very cool and relevant. :) Although, I can’t help but note nothing about the new diffuse ring around Saturn. Even a squishy squid had a post about it! ūüėõ

  6. This is objectively awesome. I heart the space program. It would be cool if maybe the people in control of MESSENGER could swing that camera around and take a picture of Earth, like they did with Voyager…if the spacecraft has that ability.

  7. Rift

    This is just so cool… Ever since I was a kid, there have been blank spots on the map of Mercury, and now they are being filled in!

    Yeah, I might comment a lot on your non-astronomy posts, Phil, but this things like this is why your Blog is my favorite.

  8. Carolyn Ernst

    Although the exact physics behind the formation of double-ringed impact craters is an ongoing field of study, it is widely accepted that they form as a result of the impact itself. In some cases, subsequent volcanism does occur; however, this does not cause the formation of the inner ring. In the case of this basin, the center surface is smooth and may represents a subsequent infill of volcanic material unrelated to the inner ring.

    When craters get to a critical size (the exact size depends on the planet in question), they start to exhibit central peaks, like the crater to the upper left of the basin in your first image (the one referred to by Bruce’s comment at 11:08). As craters get even bigger, they reach another critical size where they begin to form an interior central ring instead of a central peak (called peak-ring or double-ring basins). The largest basins have multiple rings (called multi-ring basins), though the extra rings in these cases exist outside of the original crater rim and likely form as the result of post-impact collapse.

    Regarding the second picture of the “bright splash”, the depression central to the bright area is not an impact crater. It is an irregular depression, which may have formed through volcanic processes. The bright material would have been expelled volcanically from the subsurface, not excavated by an impact.

    Great blog, glad to see MESSENGER coverage!

  9. sylva333

    Dear Mark,
    I think you may have been a little confused, the Mercurian (Hermean) pictured here is saluting the Flying Spaghetti Monster by wearing an eye-patch.


  10. mike burkhart

    I agree photos of Mercury do look simular to photos of the moon . Now we need to land a probe on mercury its the only iner planet that no probe (US OR RUSIAN) has landed on I like to see a view from the surface

  11. OrionHntr

    Kewl pics, mate. I rotated the smiley face and have that as my wallpaper. BTW…does this mean the Comedian was also an astronaut?

  12. DGKnipfer

    Cool Pics.

    You do know that PZ scooped you on the latest Saturn findings, right? What’s up with that BA? Squid boy is horning in on your turf.

  13. Jess Tauber

    I’ve heard that Mercury has a much thinner crust than the other rocky planets- how far down is it supposed to be before you hit metal? Miner’s paradise?

    Jess Tauber

  14. American Voyager

    Amazing! I was beginning to loose hope that we would ever see the “other” side of Mercury. It seemed like everyone had lost interest. now in a quick two years, all the blanks are pretty much filled in. They were worth the wait!

  15. Gonzo

    Man, Phil, I don’t comment enough on the photos you post but they are always awe-inspiring things of beauty. They quite often make my day. Thanks.

  16. mike burkhart

    One more thing Mercury is a problem its so close to the sun that its hard to see in the sky it only appers shortly before the sun rises or after the sun sets and then only for a short time I’ve only seen mercury a few times myslef the only advice I can give is to look for a bright star in the east shortly before the sun rises (you might confuse it with venus venus is brighter)or in the west after the sun sets . a star chart planspher or astronomy sofware can help some online star charts show the positions of the planets and are updated daly

  17. PLutonium being from Pluto

    Thankyou BA!

    I was hoping we’d hear something about this from you & glad to see this here.

    Belated thanks. :-)

    PS. I still can’t post on here from my home computer. Sigh. :-(

    @ 13. Jess Tauber Says:

    I’ve heard that Mercury has a much thinner crust than the other rocky planets- how far down is it supposed to be before you hit metal? Miner’s paradise?

    Probably not as much as some iron & mineral rich asteroids but perhaps yeah.

    My understanding is that Mercury is especially dense and this indicates its lost mostof its outer layers in a major impact – maybe the one that formed the Caloris basin? If memory serves about two-thirds or 70 % of the planet is made of its iron-nickel core. It’d be a pretty hostile environment for mining although I guess ideal for solar power!

    I can certainly see Mercury being colonised after Mars and the asteroids and ahead of the more distant planets and more hostile (understatement!) Venus.

    @ 16 mike burkhart :

    Mercury is a problem its so close to the sun that its hard to see in the sky it only appers shortly before the sun rises or after the sun sets and then only for a short time I’ve only seen mercury a few times myslef

    Well according to a possibly apocryphal but also quite plausible story the great Copernicus (the guy who first realised the Earth goes round our Sun not vice-versa) *Never* saw Mercury in his whole life so you’re doing better than him! ūüėČ

    (In that regard anyhow.)

    – aka StevoR

  18. We have to say, I get pleasure from reading this web page. Maybe you could let me know how I can subscribing with it.


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