Phobos and Deimos

The satellite of Mars were named Phobos and Deimos, (Fear and Panic) who were sons and arm bearers of Ares, the God of war in Greek mythology. (Aerology is the study of Mars). The names for the satellites were suggested by a science master at Eton, Henry Madan (50 years later his grand niece Venetia Burney coined the name Pluto!). In Homer's Iliad, Ares while preparing for a raid, ordered Phobos and Deimos to harness his horses and himself got into shining armour".
Phobos is about 10,000 km from Mars and about 25 km across.

Questions:
1. As seen from the Martian surface, how bright would you expect Phobos to be as compared to the brightness of Moon as seen from earth? As compared to Venus as seen from Mars?
Ans: 1/60, 12.



2. Deimos, the smaller satellite is 24,000 km from Mars and about 15 km in diameter. How bright would it appear from the Martian surface as compared to Venus in our sky?
Ans: 1.3.

3. How long would a solar eclipse by Phobos as seen from Mars last? How many times does it eclipses the Sun in a year?
Ans: 25 s.

4. How long would Deimos take to transit the Sun (as seen from Mars)?
Ans: 100 s.

5. Phobos may crash on the surface of Mars in about hundred million years. Explain. How much energy would you expect to be released in such an impact?
Ans: 1 Exp(23) J.
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Numerology:

The total number of goals scored in WC 2010 is 145. This is an interesting number as 1! + 4! + 5! = 145. Apparently there is only one other (larger) number that has this property. Can you guess the number? Hint : read up on factorion.
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Image courtesy:

1. http://amoz.trip0d.eu/10052407/phobos-and-deimos/
2. http://www.absoluteastronomy.com/topics/Mars%27_natural_satellites