This Day In Space - August 17


By KD Martin


Phobos and Stickney Crater, ultra-res  ↔

August 17, 1877 - Phobos   Asaph Hall discovers the Martian moon Phobos using the US Naval Observatory refractor (then the world's largest refractor) in Washington, D.C.  Phobos is a chunk of blackish carbonaceous chondrite rock some 17 miles long by 12 miles wide. Its most striking feature is a giant depression, Stickney Crater, which is about a half a mile across.  Hall has two craters named for him, one on the Moon and one on Phobos.

Faint dust rings produced by Phobos and Deimos have long been predicted but attempts to observe these rings have, to date, failed.  Recent images from Mars Global Surveyor indicate that Phobos is covered with a layer of fine-grained regolith at least 100 metres thick; it is believed to have been created by impacts from other bodies, but it is not known how the material stuck to an object with almost no gravity.


Asaph Hall   ↔

Over a hundred years before the moons' discovery, in 1877, British writer and satirist Jonathan Swift "predicted" their existence in the book we now know as "Gulliver's Travels." There is no way Swift could have known the moons were real yet he described Phobos' orbital period as 10 hours (very close to the real figure of 7.6) and Deimos' as 21.5 (close to the real 30.2).

Both seem to be very lucky guesses.  Since Earth had 1 moon and Jupiter 4 (that were known), Swift and Voltaire both predicted Mars would have 2 moons.

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Carl Sagan   ↔

August 17, 1962 - Carl Sagan    At a lunar exploration conference, Dr. Carl Sagan warns a panel of scientists of the need for sterilization of lunar spacecraft and decontamination of Apollo crewmen, pointing out that previous satellites like Lunik II and Ranger IV probably had deposited terrestrial microorganisms on the moon.  Dr. Sagan also points out the possibility that lunar microorganisms might be brought back to earth where they could multiply explosively.  Fortunately, no lunar organisms were detected on the return of any Apollo mission.

It will take a return lunar mission to determine whether or not any Earth microorganisms have managed to survive the harsh lunar conditions near and/or on the equipment and satellites left on the Moon.

Amazing, isn't it?  Current theory is that both Phobos and Deimos are captured asteroids, possibly from the asteroid belt.

Look at those striation marks on the west side of the moon.  Almost as if Phobos and some other asteroid just grazed each other.  No theories yet as to their formation.

http://www.universetoday.com/guide-to-space/mars/mars-moon-phobos/