Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 September 27 
Posted on 09/27/2003 5:21:53 AM PDT by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 September 27
Explanation: "Safe!" In September 1967 (during regular season play), the Surveyor 5 lander actually slid several feet while making a successful soft landing on the Moon's Mare Tranquillitatis. Equipped with television cameras and soil sampling experiments, the US Surveyor spacecraft were intended to determine if the lunar surface at chosen locations was safe for the planned Apollo landings. Surveyor 5 touched down on the inside edge of a small crater inclined at about 20 degrees. Its footpad slipped and dug the trench visible in the picture. Covered with dusty lunar soil, the footpad is about 20 inches in diameter.
1959
Luna 1 - Jan 2, 1959 - Flyby
Pioneer 4 - Mar 3, 1959 - Flyby Luna 2 - Sep 12, 1959 - Impact Luna 3 - Oct 4, 1959 - Probe 1960 1961 Ranger 1 - Aug 23, 1961 - Attempted Test Flight Ranger 2 - Nov 18, 1961 - Attempted Test Flight 1962 Ranger 3 - Jan 26, 1962 - Attempted Impact Ranger 4 - Apr 23, 1962 - Impact Ranger 5 - Oct 18, 1962 - Attempted Impact 1963 Luna 4 - Apr 2, 1963 - Flyby 1964 Ranger 6 - Jan 30, 1964 - Impact Ranger 7 - Jul 28, 1964 - Impact 1965 Ranger 8 - Feb 17, 1965 - Impact Ranger 9 - Mar 21, 1965 - Impact Luna 5 - May 9, 1965 - Impact Luna 6 - Jun 8, 1965 - Attempted Lander Zond 3 - Jul 18, 1965 - Flyby Luna 7 - Oct 4, 1965 - Impact Luna 8 - Dec 3, 1965 - Impact 1966 Luna 9 - Jan 31, 1966 - Lander Luna 10 - Mar 31, 1966 - Orbiter Surveyor 1 - May 30, 1966 - Lander Lunar Orbiter 1 - Aug 10, 1966 - Orbiter Luna 11 - Aug 24, 1966 - Orbiter Surveyor 2 - Sep 20, 1966 - Attempted Lander Luna 12 - Oct 22, 1966 - Orbiter Lunar Orbiter 2 - Nov 6, 1966 - Orbiter Luna 13 - Dec 21, 1966 - Lander 1967 Lunar Orbiter 3 - Feb 4, 1967 - Orbiter Surveyor 3 - Apr 17, 1967 - Lander Lunar Orbiter 4 - May 8, 1967 - Orbiter Surveyor 4 - Jul 14, 1967 - Attempted Lander Lunar Orbiter 5 - Aug 1, 1967 - Orbiter Surveyor 5 - Sep 8, 1967 - Lander Surveyor 6 - Nov 7, 1967 - Lander 1968 Surveyor 7 - Jan 7, 1968 - Lander Luna 14 - Apr 7, 1968 - Orbiter Zond 5 - Sep 15, 1968 - Return Probe Zond 6 - Nov 10, 1968 - Return Probe Apollo 8 - Dec 21, 1968 - Crewed Orbiter 1969 Apollo 10 - May 18, 1969 - Orbiter Luna 15 - Jul 13, 1969 - Orbiter Apollo 11 - Jul 16, 1969 - Crewed Landing Zond 7 - Aug 7, 1969 - Return Probe Apollo 12 - Nov 14, 1969 - Crewed Landing 1970 Apollo 13 - Apr 11, 1970 - Crewed Landing (aborted) Luna 16 - Sep 12, 1970 - Sample Return Zond 8 - Oct 20, 1970 - Return Probe Luna 17 - Nov 10, 1970 - Rover 1971 Apollo 14 - Jan 31, 1971 - Crewed Landing Apollo 15 - Jul 26, 1971 - Crewed Landing Luna 18 - Sep 2, 1971 - Impact Luna 19 - Sep 28, 1971 - Orbiter 1972 Luna 20 - Feb 14, 1972 - Sample Return Apollo 16 - Apr 16, 1972 - Crewed Landing Apollo 17 - Dec 7, 1972 - Crewed Landing 1973 Luna 21 - Jan 8, 1973 - Rover 1974 Luna 22 - Jun 2, 1974 - Orbiter Luna 23 - Oct 28, 1974 - Lander 1975 1976 Luna 24 - Aug 14, 1976 - Sample Return 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990
Hiten - Jan 24, 1990 - Flyby and Orbiter 1991 1992 1993 1994 Clementine - Jan 25, 1994 - Orbiter 1995 1996 1997 AsiaSat 3/HGS-1 - Dec 24, 1997 - Lunar Flyby 1998 Lunar Prospector - 7Jan 7, 1998 - Orbiter 1999 2000 2001 2002 2003
SMART 1 - Sep 2003 - Lunar Orbiter 2004 Lunar-A - Aug 2004 - Orbiter and Penetrators 2005 Selene - Dec 2005 - Lunar Orbiter
Hubble uncovers Uranus' smallest moons yet seen
SPACE TELESCOPE SCIENCE INSTITUTE NEWS RELEASE
Posted: September 25, 2003
Astronomers have discovered two of the smallest moons yet found around Uranus. The new moons, uncovered by NASA's Hubble Space Telescope, are about 8 to 10 miles across (12 to 16 km) -- about the size of San Francisco.
The two moons are so faint they eluded detection by the Voyager 2 spacecraft, which discovered 10 small satellites when it flew by the gas giant planet in 1986. The newly detected moons are orbiting even closer to the planet than the five major Uranian satellites, which are several hundred miles wide. The two new satellites are the first inner moons of Uranus discovered from an Earth-based telescope in more than 50 years. The International Astronomical Union (IAU) will announce the finding today. The Hubble telescope observations also helped astronomers confirm the discovery of another tiny moon that had originally been spotted in Voyager pictures.
 The arrow in the frame at right points to one of two newly discovered moons, among the smallest moons yet found around Uranus. The arrow in the frame at left points to a rediscovered moon orbiting 750 miles away from the moon Belinda. Credit: NASA, M. Showalter (Stanford University/NASA Ames Research Center), J. Lissauer (NASA Ames Research Center) |
The newly discovered moons are temporarily designated as S/2003 U 1 and S/2003 U 2 until the IAU formally approves their discovery. S/2003 U 1 is the larger of the two moons, measuring 10 miles (16 km) across. The Hubble telescope spotted this moon orbiting between the moons Puck, the largest satellite found by Voyager, and Miranda, the innermost of the five largest Uranian satellites. Astronomers previously thought this region was empty space. S/2003 U 1 is 60,600 miles (97,700 km) away from Uranus, whirling around the giant planet in 22 hours and 9 minutes.
The smallest Uranian moon yet found, S/2003 U 2, is 8 miles (12 km) wide. Its orbital path is just 200 to 450 miles (300 to 700 km) from the moon Belinda. S/2003 U 2 is 46,400 miles (74,800 km) away from Uranus and circles the planet in 14 hours and 50 minutes. The tiny moon is part of a densely crowded field of 11 other moons, all discovered from pictures taken by the Voyager spacecraft.
"The inner swarm of 13 satellites is unlike any other system of planetary moons," says co-investigator Jack Lissauer. "The larger moons must be gravitationally perturbing the smaller moons. The region is so crowded that these moons could be gravitationally unstable. So, we are trying to understand how the moons can coexist with each other."
One idea is that some of the moons are young and formed through collisions with wayward comets. For example, the Hubble telescope spotted two small moons orbiting very close to the moon Belinda. One of them is the newly detected moon, S/2003 U 2, which is traveling inside Belinda's orbit. The other, designated S/1986 U 10, was found in 1999 by astronomer Erich Karkoschka of the University of Arizona, who uncovered the satellite in Voyager pictures. But the finding required confirmation by an Earth-based telescope. This is the first time this moon has been seen since Voyager snapped a picture of it. S/1986 U 10 is 750 miles (1,200 km) away from Belinda.
"Not all of Uranus's satellites formed over 4 billion years ago when the planet formed," Lissauer says. "The two small moons orbiting close to Belinda, for example, probably were once part of Belinda. They broke off when a comet smashed into Belinda."
The astronomers hope to refine the orbits of the newly discovered moons with further observations. "The orbits will show how the moons interact with one another, perhaps showing how such a crowded system of satellites can be stabilized," Showalter explains. "This could provide further insight into how the moon system formed. Refining their orbits also could reveal whether these moons have any special role in confining or 'shepherding' Uranus's 10 narrow rings."
Astronomers stretched the limit of Hubble's ACS to find the tiny satellites. "These moons are 40 million times fainter than Uranus," Showalter says. "The moons are at 25th magnitude and Uranus is at sixth magnitude. They are blacker than asphalt, if their composition is like the other small, inner moons. So they don't reflect much light. Even with the sensitivity and high resolution of Hubble's ACS, we had to overexpose the images of Uranus to pinpoint the moons."
The newly detected moons, when approved by the IAU, will bring the Uranian satellite total to 24. Uranus ranks third in the number of IAU-certified moons behind Jupiter (38) and Saturn (30). Excluding the outer moons that travel in elongated orbits and are probably captured asteroids, Uranus holds the record for the most satellites with 18 in its inner system. All of them have nearly circular orbits. Saturn is second with 17.
The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).
Below is a lunar sample with caption. You can see that the regolith "sticks" to itself. Static charges? Shape and/or size of the dust grains?
This is a close-up view of Apollo 12 lunar sample no. 12025, called Core Sample 1, and collected on the lunar surface, about 225 meters below the point where the Apollo 12 Lunar Module touched down. This core sample and others collected on the Apollo 12 mission differ from those collected by the Apollo 11 crewmen in the Sea of Tranquility in that the Apollo 12 core samples have easily recognizable stratigraphy and two coherent crust-like layers. This sample has dominantly fine-grained texture.
Also the lunar regolith surface is a VERY fine powder. It's easier to leave an impression in cornstarch than it is to leave an impression in sand.
Below is a breakdown of the grain sizes in a sample of lunar soil courtesy of Apollo 11:
| Grain Size (mm) | %Weight |
| 10 - 4 | 1.67 |
| 4 - 2 | 2.39 |
| 2 - 1 | 3.20 |
| 1 - 0.5 | 4.01 |
| 0.5 - 0.25 | 7.72 |
| 0.25 - 0.15 | 8.23 |
| 0.15 - 0.090 | 11.51 |
| 0.090 - 0.075 | 4.01 |
| 0.075 - 0.045 | 12.40 |
| 0.045 - 0.020 | 18.02 |
| less then 0.020 | 26.85 |
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