Venus Earth’s Twin?

1. VenusEarth’s Twin? Very SimilarVery Different

3. Physical Properties Earth Venus Mass 100% 81.5% x 1024 kg 5.97 4.87 Radius 100% 94.9% kilometers 6378 6052 Density 100% 95.1% kg/m3 5515 5243

5. Where’s the Magnetic Field? • With a similar size and similar density, we can conjecture that Venus’ interior should be very similar to earth. • Then why is there no planet-wide magnetic field? (at least not stronger than 10-5 as strong as the earth’s magnetic field.)

6. No Magnetic Field • Several missions to Venus, from the 1962 Mariner 2 to Pioneer Venus Orbiter in 1979-1981 carried magnetometers. Orbital passes as low as 150 km did not detect any internally-generated magnetic field.

7. No Magnetic Field (3) • The best idea right now is that the core of Venus has somehow developed differently than the core of the earth. • There is evidence that the core has been hot fairly recently on geologic time scales (last 500 million years.)

8. Not even the rocks will tell • While igneous rocks usually record the magnetic field that permeates them when they cool, the rocks on Venus are above the Curie temperature, and have lost all traces of whatever magnetic field Venus may once have had.

9. Normal Orbit, Abnormal Rotation • Average distance from the sun: 108.2 million km (0.72 A.U.) • Perihelion: 107.5 million km. • Aphelion: 108.9 million km. • Orbit eccentricity: 0.0067 (very circular) • Orbital period: 225 days

10. Normal Orbit, Abnormal Rotation • Inclination of orbit to ecliptic: 3.4o • Occasional transit across face of sun • June 6, 2012 is next.

14. Abnormal Rotation • Venus rotates in a retrograde fashion, from E to W. It’s north pole is tipped over 177o. • Venus takes 243 days to rotate on its axis, 18 days longer than it takes to orbit the sun! • A solar day on Venus would be 117 earth days long.

16. The link below opens to a QuickTime movie ofVenus’ rotation compared to the Earth’s: http://www.solarviews.com/cap/earth/earthven.htm How did Venus acquire this retrograde rotation, or was it formed this way? Could the slow rotation contribute to the lack ofmagnetic field?

17. Venus’ Interior • Without a magnetic field, we know very little about Venus’ interior. • Widespread volcanism and extensive lava flows indicate that the interior was molten as recently as ½ billion years ago.

19. Surface Conditions • Surface Temperature 464oC (~870oF) • Surprisingly, the temperature varies by less than 10oC from day to night. • Surface Gravity: 8.9 m/s2 (0.90 G) • Albedo: 0.65 How does it stay so hot?

21. Venus Atmosphere • Venus’ atmospheric pressure is 92,000 millibars or over 90x greater than earth’s. • The atmosphere is so dense that each cubic meter has a mass of 65 kg.

22. Atmospheric Composition • 96.5% CO2 • (The total mass of CO2 on Venus is the same mass as on the Earth. On Venus, almost all the CO2 is in the atmosphere; on Earth, it’s in the rocks!) • 3.5% N2

23. Atmospheric Composition (2) • Traces of SO2, Ar, CO, He, Ne. • What’s missing? H2O vapor levels are only about 20 parts per million (20 mg per kilogram of atmosphere.) • On earth, the atmosphere can contain as much as 5000 mg of water vapor per kilogram of atmosphere. • Without water, the CO2 can’t be removed from the atmosphere.

24. Runaway Greenhouse Effect • CO2 is a greenhouse gas, trapping or re-absorbing infrared radiation that would otherwise remove surface heat to space. • Venus represents what would happen if the CO2 in our limestone rocks were to be released into our atmosphere. • It’s a terminal, but stable condition.

25. Cloud layers 20 km thick.

26. Surface Features • Venus has high elevation regions (terra & regio) resembling continents, and low elevation planitia resembling ocean floors. • Are these true continents, “floating” on top of the mantle? • Faulting is extensive, but tectonic plate boundaries are difficult to find.

27. Surface Features • Ishtar Terra – north polar “continent” • Maxwell Montes, Mt. Maxwell • Aphrodite Terra – equitorial “continent” • Alpha Regio • Beta Regio

29. Maxwell Montes – similar in height &extent to Himalayas

30. “Blob” or Hot-Spot Tectonics • Rather than plate tectonics, Venus appears to have many mantle hot spots (upwelling mantle currents or plumes). • What might this mean about the crust of Venus?

32. On earth, mantle plumes couple with plate movements to make island chains. What would be formed without the plate movement?

33. Coronaeor Arachnoids • Enormous circular structures with raised rims and lowered floors. • resemble volcanic calderas. • have a sunken “moat” just inside the rim

36. Ridge Belts

37. Tesserae or “Mosaic Tiles” • Extremely complex cross-faulted region. • Compression forces from 2 directions causes “wrinkles” in several directions. • Ridges are cut by faulting.

39. Complex Faulting

40. Of course…volcanos Maat Mons

42. What’s Missing? Craters • Venus has few craters. Craters tend to be larger than 5 km in diameter. Why? • Venus has few craters for 2 reasons: • lava flows have covered many • small meteors have difficulty making it to the surface.

44. CraterAurelia

45. Missions to Venus • Venera 1 – 16. Russian series of orbiters and landers. • Venera 7was the first spacecraft to land on the surface of another planet, December 15, 1970. It radioed back data for only 23 minutes before the heat and pressure destroyed it.

47. US Missions • Mariner 5 & 10 (same mission to Mercury) • Pioneer Venus 1 & 2 • Pioneer Venus 1 was the first spacecraft to use radar to map another planet. Operated from 1978 until 1992.

49. US Missions • Magellan • spent 1990 through 1994 in orbit, mapping Venus with radar. • Mapped 98% of Venus’s surface at a resolution of 300 meters. • Was launched from the Space Shuttle Atlantis is 1989.