Planetary Geology – Part 4

1. Planetary Geology – Part 4

2. Comets Comets are created of matter left over from the formation of the Solar System Comets are composed of ices (water, ammonia, methane, carbon dioxide and carbon monoxide) that hold together pieces of silicate rock and dust

3. Comets Most comets are in extremely elongated orbits (long period orbits) and can take thousands and even up to millions of years to complete one revolution around the Sun

4. Comets A few comets, like periodic Comet Halley, are trapped in the inner Solar System in short period orbits that only take dozens to hundreds of year to complete

5. Comets As a comet approaches the Sun, solar energy begins to vaporize the ices, first forming a coma of ionized gases around the comet Then, as the comet gets close to the Sun, it may form a tail of streaming gases and dust that is easily seen from Earth

6. Comets The solar wind pushes the ionized gases away from the comet and radiation pressure pushes the dust Sometimes, the escaping gas and dust form two separate tails

7. Comets Both the solar wind and the radiation pressure causes the comet’s tail to point away from the Sun

8. Oort Cloud In 1950, the Dutch astronomer Jan Oort proposed that comets originate in a great sphere, extending 1.5 light years in distance beyond the Sun Oort predicted that there could be millions of comets The latest estimates are in the billions and perhaps in the trillions

9. Sun Grazers It is not unusual for the orbit of a comet to bring it extremely close to the Sun These are referred to as sun grazer comets On occasion, they may crash into the sun The NASA spacecraft called SOHO, the Solar & Heliospheric Observatory, has photographed several sun grazers

10. Comet Shoemaker-Levy In July 1994, periodic Comet Shoemaker-Levy passed too close to Jupiter The comet went into orbit around Jupiter, fragmented into pieces and crashed into the planet

11. Comet Hartley 2 On November 4, 2010, NASA’s EPOXI mission spacecraft successfully photographed Comet Hartley 2, from as close as 435 miles During the encounter, the spacecraft and comet zoomed past each other at a speed of 27,560 miles per hour Here is what it looked like in real time http://www.youtube.com/watch?v=YS40HsFcLeA

12. Comet Hartley 2 Comet Hartley 2 is composed of rock rubble and ices Left is the spacecraft view and below is the view from Earth using a telescope

13. Titus-Bode Law In 1772, Johann Bode proposed the hypothesis that the average distance of the planets from the Sun follows a simple mathematical rule Other, such as Johann Titus also proposed the same hypothesis This became known as Bode’s Law or as the Titus-Bode Law What makes Bode’s Law of interest, was the prediction by Johann Bode that there was a planet missing between Mars and Jupiter

14. A Missing Planet? In 1800, astronomers in Europe decided to conduct a coordinated search for this “missing planet,” but before the search got underway... On January 1, 1801, the Italian Catholic Priest and astronomer, Giuseppe Piazzi, discovered the missing planet, which he named Ceres Ferdinandea(this was later shortened to Ceres) The missing planet was exactly where it was predicted to be, between Mars and Jupiter

15. But Wait, There is More! The “planet” Pallas was discovered in 1802 The “planet” Juno was discovered in 1804 The “planet” Vesta was discovered in 1807

16. Asteroid Belt Today, we know that hundreds of thousand of small planetesimals, called asteroids, orbit between Mars and Jupiter in a region that is called the Asteroid Belt They are composed of silicate rock and some metals, such as iron and nickel

17. Ceres Ceres, the first asteroid that was discovered, turned out to be the largest, with a diameter of about 950 kilometers (590 miles) It is a sphere and therefore is now classified as a dwarf planet

18. The Dawn Mission On September 27, 2007, NASA launched the Dawn spacecraft mission to Vesta and Ceres Dawn arrived at Vesta in July 2011 and orbited the asteroid until September 2012 Dawn is now flying onto Ceres and will orbit the asteroid between February 2015 and July 2015

19. The Dawn Mission Vesta is the second largest known asteroid, having a diameter of 530 kilometers (330 miles), but it is much smaller than the Earth’s Moon

20. The Dawn Mission The “oblate spheroid” appearance of Vesta is clearly evident in this imager (i.e., it is shaped like a smashed ball)

21. The Dawn Mission More than a billion years ago, two giant craters were formed at Vesta’s south pole when smaller asteroids crashed into Vesta These impacts flatten the shape of Vesta

22. The Dawn Mission The peak at the center of the basin (arrow) is about 180 kilometers (110 miles) wide and is 22 kilometers (14 miles) high This is the second highest known mountain in our Solar System

23. Asteroid Belt Spacecraft have visited several asteroids Most asteroids are potato-shaped or very irregular-shaped, and all are heavily cratered Only a few exceed more than several kilometers (a few miles) in diameter

24. Asteroid Belt The asteroid Ida is a good example of a potato-shaped asteroid, with dimension of 54×24×15 kilometers in length, width and height It has a moon called Dactyl, which is only 1.4 kilometers in diameter and orbits Ida every 1.54 days at an average distance of 108 kilometers

25. Near-Earth Objects Near-Earth Objects (NEOs) are asteroids and large meteoroids whose orbits bring them close to Earth's orbit, and which may therefore pose a collision danger As of November 17, 2010, 7439 NEOs have been discovered It is expected that thousands more will be discovered

26. Near-Earth Objects Most NEOs are not large, typically being less than a kilometer in diameter The smallest known is only 3-4 meters (10-13 feet) in size

27. Near-Earth Objects Eros is a large potato-shaped (33×13×13 kilometers) NEO asteroid that orbits half-way between Earth and Mars that was studied for over a year by the NASA Near spacecraft This animated GIF image shows Eros rotating below the orbiting spacecraft Note all of the craters

28. Near-Earth Objects The Japan Aerospace Exploration Agency (JAXA) successfully send the Hayabusa spacecraft to an NEO called Itokawa and returned a small sample of “rocky dust” collected from the asteroids surface This is only the second object, besides the Moon, from which samples have been returned to Earth Itokawa is best described as a pile of loose rubble with an overall length of 545 meters (1775 feet)

29. Near-Earth Objects About 1000 of the known NEOs have been classified as Potentially Hazardous Asteroids because their orbit brings them close enough for Earth for a possible impact Near misses are fairly common events

30. Near-Earth Objects 2004 FH is a near-Earth asteroid that was discovered on March 15, 2004 by NASA The object is roughly 30 meters (100 feet) in diameter and passed just 43,000 km (26,000 miles) above the Earth's surface on March 18, 2004

31. Near-Earth Objects (CNN 9/8/2010) – “A small asteroid passed within the moon's distance from the Earth on Wednesday morning, and another will do likewise later in the day ... Near-Earth asteroid 2010 RX30, which is estimated to be 32 to 65 feet in diameter, passed within 154,000 miles of Earth at 5:51 a.m. ET Wednesday ... The second object, 2010 RF12, estimated to be 20 to 46 feet in diameter, will pass within 49,088 miles of Earth at 5:12 pm ET.”

32. Near-Earth Objects What would be the effects caused by an asteroid or comet that smashed into Earth?

33. Life on Earth It is estimated that there are at least two million different species of living organisms on Earth, ranging from bacteria to birds to homo sapiens

34. Life on Earth Some argue that considering the ocean depths are all but unexplored, there may as many as 15 million species on Earth or even 50 million

35. Life on Earth Since the first inception of life on Earth, more than 3 billion years ago, it has been estimated that there have been about two billion species have lived on our planet Therefore, 99.8% of all species are now extinct Many, but nowhere near most, of these species left some evidence in the fossil record

36. Extinction Marine fossils are generally used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land animals Based on the marine fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years

37. Mass Extinction? However, the extinction of the dinosaurs so significantly exceeded the back ground rate, that it is referred to as a mass extinction

38. Mass Extinction Amass extinctionis defined as a sharp decrease in the number of species in a relatively short period of time Mass extinctions affect most major taxonomic groups present at the time, dinosaurs, reptiles, amphibians, fish, invertebrates and other simpler life forms

39. Mass Extinction Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction rate Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty

40. Mass Extinction There are 5 big mass extinctions, which are widely agreed upon as the most significant: Ordovician-Silurian Devonian-Mississippian Permian-Triassic Triassic-Jurassic Cretaceous-Tertiary Note that each extinction is so great that it marks the end of one geologic period and the start of a new

41. Mass Extinction We will briefly look at two of these mass extinctions The “PTr” or Permian-Triassic mass extinction occurred about 251 million years ago The “KT” or Cretaceous-Tertiary mass extinction occurred about 65 million years ago (this is the one that has caught the public’s fancy, since it marks the end of the dinosaurs)

42. Permian-Triassic Extinction Based upon the fossil record, the PTr is the greatest extinction to have ever occurred 53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species became extinction All together 95% of all living animals on Earth died off

43. Cretaceous-Tertiary Extinction About 50% of all species became extinct The KT extinction was rather uneven, some groups of organisms became extinct, some suffered heavy losses and some appear to have got off relatively lightly This extinction has great significance for humans because it ended the reign of the dinosaurs and opened the way for mammals to become the dominant land vertebrates

44. Why? How can a species, that so dominated the Earth, so suddenly disappear?

45. Impact It is now commonly thought that the aftermath of a major impact by an asteroid or comet on Earth is the primary cause of mass extinctions

46. Impact Craters on the Earth? Long after impact craters were accepted as being very common on the Moon, there was bitter controversy over whether impact craters also occurred on Earth All craters of unknown origin were classified as “cryptovolcanic structures”

47. Impact Craters on the Earth Eugene Shoemaker studied Barringer Crater, Arizona from 1957 to 1960 and proved that it was an impact crater (the key was his discovery of high pressure quartz)

48. Impact Craters on the Earth Geologists have now found 185 confirmed and 655 suspected impacts sites on Earth

49. Impact Craters on the Earth Botsumtwi Impact Crater, Ghana Tenoumer Impact Crater, Mauritania

50. Tunguska Event At 7:17am, June 30, 1908 in Tunguska, Russia, there was a tremendous explosion in the atmosphere equivalent to a nuclear bomb Shock waves knocked nearby residents off their feet and broke windows