71 Awesome Deimos Facts – The Second Moon of Mars

Mars – the red planet has its own natural satellites. The person who discovered the moons almost gave up. Thanks to his wife’s inspiration, he continued his search and ended up finding two natural satellites of the planet.

In this article on Deimos facts, we are going to learn about the second moon of the red planet. In case you want to learn about the first moon, follow this link.

Now, without further ado, let us begin with our list of 71 Deimos facts. Are you ready?

Deimos Facts: Basic Tidbits | 1-20

1. Deimos is the smaller of the two moons of Mars. The other moon is known as Phobos.

2. Deimos is also the outermost most of Mars.

3. There is a systematic designation for Deimos and it is also known by the name Mars II.

4. The closest that this moon can get to Mars is 23,455.5 kilometers.

5. The farthest that this moon can get away from Mars is 23,470.9 kilometers.

6. It takes 1.263 Earth days or 30.312 Earth hours to complete one revolution around Mars.

7. The overall dimension of Deimos is 15 x 12.2 x 11 kilometers.

8. The mean radius of the moon is 3.9 miles or 6.2 kilometers.

9. The total surface area of this natural satellite of Mars is 495.1548 square kilometers.

10. The total volume of the moon is 999.78 cubic kilometers.

11. The mean density of the object is 1.471±0.166 g/cm3.

12. The gravity on the surface of the moon is 0.003 m/s2.

13. The escape velocity of Deimos 5.556 m/s.

14. The temperature of the celestial object is ≈ 233 Kelvin.

15. We mentioned the farthest and the closest distance of the moon from Mars. Take a careful look at the two numbers. They indicate that the orbit of the moon is almost circular.

16. Deimos itself is non-spherical and it is about 56% the size of Phobos.

17. The apparent magnitude of Deimos is 12.89.

The apparent magnitude is the brightness of any astronomical object when viewed from Earth. The lower this number, the brighter it is. Put is other words, the lower the number (that is, lower the apparent magnitude of any celestial object), the brighter it is. For instance, our Sun has an apparent magnitude of -26.7.

18. The mass of Deimos is 1,476,188,406,600,740 kg.

19. Deimos is 1027.6 times smaller than Earth.

20. The mean orbit velocity of Deimos is 4,864.8 km/h.

Composition and Surface | 21-29

21. The moon is made of rock. The rock is very rich in carbonaceous material.

22. The surface of Deimos is cratered. However, the surface of the moon as a whole appears smoother compared to the surface of Phobos.

23. The reason why the surface of Deimos looks smoother is that the craters are partially filled with regolith.

Regolith is a loose layer of superficial deposits. It is made of broken rocks, dust, soil and other similar material.

24. The regolith that covers the craters is very porous. According to radar estimates, the regolith has a density of only 1.471 g/cm3.

25. There are only two geological features on Deimos that humans have assigned names.

26. Both the features are nothing other than craters. One is known as Voltaire and the other is known as Swift.

27. The craters are named after writers who, before the Deimos and Phobos were discovered, predicted the existence of two moons of Mars.

28. Swift is named after the writer Jonathan Swift, an Irish writer. The crater has a diameter of 1 kilometer and the name was approved in 1973.

29. Voltaire on the other hand is named after a French writer named Voltaire. This name was also approved in 1973. The diameter of the Voltaire crater is 1.9 kilometers.

Discovery and Naming | 30-37

30. Deimos was discovered by Asaph Hall III – an American astronomer.

31. He made the discovery on August 12, 1877 at around 7:48 UTC.

32. Asaph Hall made the discovery at the United States Naval Observatory located in Washington D.C.

33. 6 days later he went on to discover Phobos at around 9:14 GMT.

34. The discoveries made by Asaph were not accidental. He was deliberately looking for Martian moons.

35. Deimos has been named after a character in Greek Mythology. That character was called Deimos and he represented ‘dread.’

36. It was Henry Madan who proposed the names of the two moons of Mars. He proposed the names with different spellings – Deimus and Phobus.

37. Henry Madan was a Science Master at Eton and he took the names from Iliad’s Book XV. In the book, Ares (Roman counterpart is Mars) summoned Fear (Phobos) and Dread (Deimos).

Deimos Facts: The Origin of Deimos | 38-44

38. Whether it comes to Deimos or Phobos, the origin of either of the Martian moon is not known. There are several hypotheses that try to explain but they are all controversial.

39. The two major hypotheses that try to explain the origin of Deimos (and Phobos as well) are capture and accretion.

40. According to the capture hypothesis, the two moons were captured into the orbit of Mars from the asteroid belt that lies between Mars and Jupiter.

41. Possibly, the orbits of both Deimos and Phobos (according to the capture theory) were circularized by either tidal forces or by atmospheric drag.

42. While the capture of Deimos by atmospheric drag is a possibility, the other moon that is Phobos could not have been captured in such a way simply because of its size and because the atmosphere of Mars is too thin to apply braking.

43. The only way Phobos could have been captured by Mars was if Phobos was that if Phobos was a part of a binary asteroid that got separated because of tidal forces.

44. The alternative hypothesis put forward is accretion. Accretion is a process in which particles accumulate to form a massive object. So, accretion can lead to formation of both Deimos and Phobos in their current positions.

Deimos Facts: Fun Facts | 45-61

45. The orbit of Deimos is nearly circular. It is also close to the equatorial plane of Mars.

46. If you could stand on Mars and look at Deimos, the angular diameter of the moon would be no greater than 2.5 minutes.

Note: Angular diameter or angular size, apparent diameter or apparent size is basically an angular measurement that is used for describing how big a circle or a sphere will appear when someone looks at it from a given point.

47. To put in perspective, Deimos, when seen from Mars will appear to be 1/12th of the width of Moon (the natural satellite of Earth) when it is seen from Earth.

48. For anyone standing on Mars and looking at Deimos, the moon would actually look like a star to that person’s naked eyes.

49. When Deimos attains full-moon (that is when it is at its brightest), it will appear to be just as bright as Venus when it is seen from Earth.

50. Deimos rises in the east and sets in the west.

51. Because the orbit of Deimos is relatively close to that of Mars and because its orbit has a very small inclination to the equator of Mars, a person cannot see the moon if that person is standing at a Martian latitude of greater than 82.7°.

52. The orbit of Deimos is slowly getting larger. There are two reasons for this. First, Deimos is far enough from Mars and second, because of tidal acceleration (which is an effect of tidal force between a planet and its natural satellites).

53. Deimos will eventually escape the gravity of Mars.

54. If one looks at Deimos from Mars, it can be seen regularly passing in front of the Sun.

55. Deimos is way too small for creating a complete solar eclipse. It rather appears only as a small black dot that gradually moves across the Sun.

deimos facts
Public Domain, Link

56. Two Mars rovers named Opportunity and Spirit managed to photograph the transit of Deimos on March 4, 2004 and March 13, 2004 respectively.

57. Deimos is a pretty dark body and its surface material appears to have the composition as found on C-type asteroids that are usually found in the outer asteroid belt.

58. The craters that are found on Deimos are usually smaller than 1.6 miles or 2.5 kilometers in radius.

59. The moon does not have grooves and ridges that are found on Phobos.

60. There are no ejecta deposits on Deimos. This is probably because the ejecta escapes into space as the moon has low gravity.

What is ejecta? Did you know that when a meteorite strikes the surface of any astronomical object, the sheer force of the meteorite manages to throw out material from the crater it forms. The material that is thrown out is called ejecta and it then settles back on the surface around the crater.

deimos facts
Surface of Deimos | Public Domain, Link

61. The surface of Deimos has thick regolith deposits as we mentioned earlier. But, did you know that regolith deposit is nearly 100 meters or 328 feet deep? The regolith is formed by the meteorites that pulverized the surface of Deimos.

Deimos Facts: Exploration | 62-71

62. Several spacecrafts have managed to photograph Deimos from close vicinity. However, none of those spacecrafts were meant for Deimos. Their primary mission was always Mars.

63. No landings have ever been made on Deimos.

64. Soviet Union had a Phobos program under which two spacecrafts were sent. They were called Phobos 1 and Phobos 2.

65. The idea was that upon the success of Phobos 1, Phobos 2 wound head for Deimos.

66. Both Phobos 1 and Phobos 2 saw successful launch in 1988. However, Phobos 1 was lost when it was on its way to Mars.

67. Phobos 2 managed to send some data (including images) back to Earth but it too failed shortly before it was about to start its detailed examination of Phobos.

68. Under NASA Discovery Program, the Aladdin mission turned out as finalist in 1997 and 1998.

deimos facts
Phobos passing in front of Deimos Public Domain

69. Under Aladdin mission it was planned that both Phobos and Deimos would be visited and the probe would launch projectiles at the satellites.

70. The probe’s purpose would be to collect ejecta while the probe made a slow flyby at a speed of approximately 1 km/s. The samples would then be returned to Earth for a 3-year long study.

71. The estimated cost of the whole Aladdin mission was estimated at USD 247.7 million. Unfortunately, the MESSENGER mission was chosen to go to Mercury.

That concludes our article on Deimos facts. In case you think we have missed something, feel free to drop us a message.


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