APOD: Enhanced Color Caloris (2015 Mar 05)

[APOD Robot]

Enhanced Color Caloris

Explanation: The sprawling Caloris basin on Mercury is one of the solar system's largest impact basins, created during the early history of the solar system by the impact of a large asteroid-sized body. The multi-featured, fractured basin spans about 1,500 kilometers in this enhanced color mosaic based on image data from the Mercury-orbiting MESSENGER spacecraft. Mercury's youngest large impact basin, Caloris was subsequently filled in by lavas that appear orange in the mosaic. Craters made after the flooding have excavated material from beneath the surface lavas. Seen as contrasting blue hues, they likely offer a glimpse of the original basin floor material. Analysis of these craters suggests the thickness of the covering volcanic lava to be 2.5-3.5 kilometers. Orange splotches around the basin's perimeter are thought to be volcanic vents.

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[Nitpicker]

Beautiful. Thanks APOD.

[Guest]

Since the Earth suffered the Late Heavy Bombardment, around 3.8 billion years ago, can we also distinguish the
signature of the sudden uptick of the LHB on Mercury, or any other planet for that matter? Also, why are there
many fairly straight lines emanating from very near the Caloris Basin's center? Rebound effects after the impact?

[starsurfer]

Wonderful and magical image of the only planet visible to the naked eye that I've not seen in the sky yet. Before I read the description, I thought it was the Moon!

[Tszabeau]

I ain't never licked no cane toad... but I shore could use one, right about now.

[Visual_Astronomer]

Wonderful and magical image of the only planet visible to the naked eye that I've not seen in the sky yet. Before I read the description, I thought it was the Moon!

Mercury is elusive (mercurial) - you must have an unobstructed horizon, favorable weather, and know just when to look.

[Joe Stieber]

Wonderful and magical image of the only planet visible to the naked eye that I've not seen in the sky yet...

Does that mean you've not seen Mercury at all, or just not naked eye? It might also imply that you've seen Uranus naked eye, which I think is generally more difficult than seeing Mercury naked eye. Recently, Mercury was really easy to see without optical aid because of its proximity to bright Venus, as illustrated by the APOD of January 15, 2015. An unaided sighting of Uranus requires a reasonably dark sky (certainly outside the suburbs at least) and a knowledge of which faint speck is the one you're looking for. (I have experience in this area since I regularly spot Mercury and Uranus, with and without optical aid -- it's something of a sport for me.)

[Chris Peterson]

Wonderful and magical image of the only planet visible to the naked eye that I've not seen in the sky yet. Before I read the description, I thought it was the Moon!

Mercury is elusive (mercurial) - you must have an unobstructed horizon, favorable weather, and know just when to look.

Nevertheless, it's an easy target for nearly everybody for several days, several times a year.

[MarkBour]

. . . Also, why are there many fairly straight lines emanating from very near the Caloris Basin's center? Rebound effects after the impact?

Those lines are very interesting. They do not all emanate from the center of the crater. The crater has been named Apollodorus, and the overall feature the Pantheon Fossae (http://en.wikipedia.org/wiki/Pantheon_Fossae). In that article, it is said they are perhaps extensional faults. To me, the pattern looks a lot like the shatter-pattern of a windshield when hit with sufficient force (http://images-2.drive.com.au/2011/01/13 ... -420x0.jpg). I wonder if it is possible that the dried lava basin acted as a unit when an impact formed Apollodorus, transmitting shocks and shearing along those lines. Of course, it's always wild speculation with me.

[CharlesE]

Why are virtually all of the craters circular. Would not a larger fraction be somewhat elliptical as objects hit at an angle?

Thanks for any answers.

[Chris Peterson]

Why are virtually all of the craters circular. Would not a larger fraction be somewhat elliptical as objects hit at an angle?

Thanks for any answers.

Hypervelocity impacts nearly always produce circular craters, except sometimes for very shallow strike angles (just a few degrees from horizontal).

[kellogg]

Beautiful!

I've always found Caloris Basin formation to be fascinating.
Right now, I'm writing a webcomic about a similar event on Venus.

Scott Kellogg

[starsurfer]

Wonderful and magical image of the only planet visible to the naked eye that I've not seen in the sky yet...

Does that mean you've not seen Mercury at all, or just not naked eye? It might also imply that you've seen Uranus naked eye, which I think is generally more difficult than seeing Mercury naked eye. Recently, Mercury was really easy to see without optical aid because of its proximity to bright Venus, as illustrated by the APOD of January 15, 2015. An unaided sighting of Uranus requires a reasonably dark sky (certainly outside the suburbs at least) and a knowledge of which faint speck is the one you're looking for. (I have experience in this area since I regularly spot Mercury and Uranus, with and without optical aid -- it's something of a sport for me.)

I've not seen Mercury in the sky with or without any equipment. Also generally Uranus is too faint to be visible with the naked eye and can only be seen with a telescope and maybe binoculars.

[Joe Stieber]

I've not seen Mercury in the sky with or without any equipment. Also generally Uranus is too faint to be visible with the naked eye and can only be seen with a telescope and maybe binoculars.

Uranus runs around magnitude 5.8 to 5.9, so it's an easy binocular object; in fact, I've been spotting it with binoculars in recent days as Venus closed in on it (despite my suburban location, a relatively low altitude and residual twilight). Granted, it appears star-like in binoculars, but with a pale, non-stellar bluish color. One does need a telescope to resolve it as a disc. That magnitude also puts it within the nominal 6th magnitude limit for naked-eye visibility (although some experienced observers can see well beyond that nominal limit). I've seen Uranus a number of times naked eye and make it a point to do so every year in the months around opposition, usually from the New Jersey Pinelands, which are relatively dark, but hardly a true dark-sky location.

[DavidLeodis]

When I click on links in the explanation and credits to APODs their blue colour then changes to red, presumably to indicate that I have already clicked on that link. Oddly however with this and yesterday's APOD the next but then unclicked link then also changes to red and when I click on that link the next link and so on then changes to red! I'm . It is of no real concern but I'm curious why it has just started to happen, or are others not getting that to happen?

[geckzilla]

When I click on links in the explanation and credits to APODs their blue colour then changes to red, presumably to indicate that I have already clicked on that link. Oddly however with this and yesterday's APOD the next but then unclicked link then also changes to red and when I click on that link the next link and so on then changes to red! I'm . It is of no real concern but I'm curious why it has just started to happen, or are others not getting that to happen?

I couldn't quite follow your explanation. The links turn that purplish color as a browser function, though. It's not something APOD tells them to do. If you've visited a particular link then it will always be that purplish color.

[DavidLeodis]

When I click on links in the explanation and credits to APODs their blue colour then changes to red, presumably to indicate that I have already clicked on that link. Oddly however with this and yesterday's APOD the next but then unclicked link then also changes to red and when I click on that link the next link and so on then changes to red! I'm . It is of no real concern but I'm curious why it has just started to happen, or are others not getting that to happen?

I couldn't quite follow your explanation. The links turn that purplish color as a browser function, though. It's not something APOD tells them to do. If you've visited a particular link then it will always be that purplish color.

Hi geckzilla.

I have obviously not made it clear what seems to suddenly be happening. When I click on a blue link (normally the first one in an explanation) its colour changes to red as usual but the immediately following link which should still be blue as turned to red even before I click on that link. When I click on that now red link the immediately following blue link has already turned to red, and so on. Unless I've been very unobservant all these years I'm sure that has never happened before as links were always blue until I clicked on them.

[geckzilla]

I'd say you've got something funky going on at your end. Either a misbehaving browser add-on / extension or some kind of malware. It doesn't happen to me.

[DavidLeodis]

I'd say you've got something funky going on at your end. Either a misbehaving browser add-on / extension or some kind of malware. It doesn't happen to me.

Hi geckzilla.

I'm not sure if it was malware but you are right in that "something funky" was going on. I had very recently installed the Ghostery browser extension (on the recommendation of a reliable computer magazine) that enabled me to stop sources collecting my browsing habits. Realising that the links colour change irritation had only happened since I installed Ghostery I have now uninstalled that and the 'problem' seems to have cleared up as only links that I have clicked on now become red.

[Chris Peterson]

I'm not sure if it was malware but you are right in that "something funky" was going on. I had very recently installed the Ghostery browser extension (on the recommendation of a reliable computer magazine) that enabled me to stop sources collecting my browsing habits. Realising that the links colour change irritation had only happened since I installed Ghostery I have now uninstalled that and the 'problem' seems to have cleared up as only links that I have clicked on now become red.

I run Ghostery (inside Firefox) and have never had that problem. I also block Google Analytics, which is the only script that APOD or Asterisk tries to run.