Difference between revisions of "June 23, 2004"

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=Concentric Craters=
 
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      <td><h2 align="left">Concentric Craters</h2></td>
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      <td><h2 align="right">June 23, 2004</h2></td>
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      <td><div align="center" span class="main_sm">Image Credit:  [mailto:cwood@observingthesky.org" class="one Chuck Wood]  &amp; [http://www.lpi.usra.edu/research/lunar_orbiter/" class="one Luna Orbiter IV] </div></td>
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  <p class="story" align="center"><b>Concentric Craters</b></p>
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  <p class="story" align="left">The nearside of the Moon contains more than 11,000 craters larger than 3.5 km wide. Virtually all of them are standard impact craters, mostly small, ranging from very fresh to quite degraded.
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  There are a handful of oddball craters and one of the weirdest and least studied are concentric craters. These are small craters - on average 8 km in diameter, that contain an inner ring approximately half the crater width.
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  The most famous concentric crater is Hesiodus A on the south shore of Mare Nubium. According to a paper I published in 1978 (see link) Hesiodus A is 14.9 km wide, 1.7 km deep impact crater, surrounded by a faint ejecta blanket.
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  Inside Hesiodus A is a 6 km wide donut-like ring. back in 1978 I cataloged 51 concentric craters and 70% looked similar to Hesiodus A.  It is strongly unlikely that these bulls-eye crater within crater structures formed by
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  two unrelated chance impacts. A number of the craters are located near domes and rilles, and 70% occur on the margins of maria. These spatial relations suggested to me that the inner rings were volcanic in origin. Perhaps an
 +
  effusive flow of relatively viscous magma from fractures at the edge of the crater's floors built up the inner rings. Today, this interpretation is not very compelling to me as it was 26 years ago. But, suggestions that the
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  rings are some sort of wall slump features within normal impact craters is also unbuttressed by any significant evidence. I don't know how to interpret concentric craters - do you?
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<p class"story"><b>Related Links:</b><br>
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  [http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1978LPI.....9.1264W  Lunar Concentric Craters 1978 Paper] 
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  </p>
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  <p class"story"> <b>Tomorrow's LPOD:</b> Gambart Environs</p>
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      <td><p align="center" class="main_titles"><b>Author & Editor:</b><br>
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          [mailto:chuck@observingthesky.org Charles A. Wood]</p>
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        <p align="center" class="main_titles"><b>Technical Consultant:</b><br>
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            [mailto:anthony@perseus.gr Anthony Ayiomamitis]</p>
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        <p align="center" class="main_titles"><b>[mailto:webmaster@entropysponge.com Contact Webmaster]</b></p>
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        <p align="center" class="main_titles"><b>A service of:</b><br>
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            <a class="one" href="http://www.observingthesky.org/">ObservingTheSky.Org</a></p>
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        <p align="center" class="main_titles"><b>Visit these other PODs:</b> <br>
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          <a class="one" href="http://antwrp.gsfc.nasa.gov/apod/astropix.html">Astronomy</a> | <a class="one" href="http://www.msss.com/">Mars</a> | <a class="one" href="http://epod.usra.edu/">Earth</a></p></td>
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Revision as of 15:40, 4 January 2015

Concentric Craters

Concentric Craters

June 23, 2004
<IMG SRC="images/LPOD-2004-06-23.jpeg" NAME="main_image" width="441" height="424" border="0">
Image Credit: " class="one Chuck Wood & " class="one Luna Orbiter IV

Concentric Craters

The nearside of the Moon contains more than 11,000 craters larger than 3.5 km wide. Virtually all of them are standard impact craters, mostly small, ranging from very fresh to quite degraded. There are a handful of oddball craters and one of the weirdest and least studied are concentric craters. These are small craters - on average 8 km in diameter, that contain an inner ring approximately half the crater width. The most famous concentric crater is Hesiodus A on the south shore of Mare Nubium. According to a paper I published in 1978 (see link) Hesiodus A is 14.9 km wide, 1.7 km deep impact crater, surrounded by a faint ejecta blanket. Inside Hesiodus A is a 6 km wide donut-like ring. back in 1978 I cataloged 51 concentric craters and 70% looked similar to Hesiodus A. It is strongly unlikely that these bulls-eye crater within crater structures formed by two unrelated chance impacts. A number of the craters are located near domes and rilles, and 70% occur on the margins of maria. These spatial relations suggested to me that the inner rings were volcanic in origin. Perhaps an effusive flow of relatively viscous magma from fractures at the edge of the crater's floors built up the inner rings. Today, this interpretation is not very compelling to me as it was 26 years ago. But, suggestions that the rings are some sort of wall slump features within normal impact craters is also unbuttressed by any significant evidence. I don't know how to interpret concentric craters - do you?

Related Links:
Lunar Concentric Craters 1978 Paper

Tomorrow's LPOD: Gambart Environs

<img src="../../../MainPage/spacer.gif" width="640" height="1">

Author & Editor:
Charles A. Wood

Technical Consultant:
Anthony Ayiomamitis

Contact Webmaster

A service of:
<a class="one" href="http://www.observingthesky.org/">ObservingTheSky.Org</a>

Visit these other PODs:
<a class="one" href="http://antwrp.gsfc.nasa.gov/apod/astropix.html">Astronomy</a> | <a class="one" href="http://www.msss.com/">Mars</a> | <a class="one" href="http://epod.usra.edu/">Earth</a>

 


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