1 / 30

11a . Sun-Scorched Mercury

11a . Sun-Scorched Mercury. Earth-based observations of Mercury Mercury’s rotation & year Mariner 10 ’s images of Mercury Mercury’s interior. Mercury Data (Table 11-1). Mercury Data: Numbers. Diameter: 4,878.km 0.38 . Earth Mass: 3.3 . 10 23 kg 0.055 . Earth

amber
Download Presentation

11a . Sun-Scorched Mercury

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 11a. Sun-Scorched Mercury • Earth-based observations of Mercury • Mercury’s rotation & year • Mariner 10’s images of Mercury • Mercury’s interior

  2. Mercury Data (Table 11-1)

  3. Mercury Data: Numbers • Diameter: 4,878.km 0.38 . Earth • Mass: 3.3 . 1023 kg 0.055 . Earth • Density: 5.4 . water 0.99 . Earth • Orbit: 5.8 . 107 km 0.39 AU • Day: 58.65 days 58.65 . Earth • Year: 87.97 days 0.24 . Earth

  4. Mercury Data: Special Features • Mercury is the closest planet to the Sun • Mercury is the smallest terrestrial planet • Mercury has essentially no atmosphere • 3 sidereal days = 2 sidereal years • Mercury exhibits unique 3-to-2 spin-orbit coupling • Mercury is very heavily cratered • Mercury is a visual twin of the Moon except … • Mercury does not have any maria (i.e., “seas”) • Mercury’s interior is dominated by an iron core • 75% the diameter & 42% the volume • Mercury is very difficult to observe from Earth • Mercury is never >28° from the Sun • This third week of February 2013

  5. Earth-Based Observations of Mercury • Brighter than any star (at times) • Albedo is only 0.12, the same as weathered asphalt • Difficult to observe from Earth • Copernicus apparently never saw Mercury • Neither did I until April 2002 despite many attempts • Elongation maxima of Mercury • Maximum eastern elongation of 18° Evening sky • Maximum western elongation of 28° Morning sky • Elongation favorability of Mercury • Unfavorable Eastern & low angle to the horizon • Favorable Western & high angle to the horizon • Conjunctions Three inferior per year • Solar transits Crossing in front of the Sun • Aphelion in May & perihelion in November

  6. Transit of Mercury: 8 November 2006 2006 Transit

  7. Evening Morning Mercury’s Elongations

  8. Favorable & Unfavorable Elongations Western elongation Eastern elongation High-angle to horizon Low-angle to horizon Morning sky Evening sky

  9. Mercury’s Greatest Elongations Eastern (Evening)Western (Morning) Friday 26 October 2012Tuesday 4 December 2012 Saturday 16 February 2013Sunday 31 March 2013 Wednesday 12 June 2013 Tuesday 30 July 2013 Wednesday 9 October 2013 Monday 18 November 2013 Friday 31 January 2014 Friday 14 March 2014 Sunday 25 May 2014 Saturday 12 July 2014 Sunday 21 September 2014 Saturday 1 November 2014 Mercury Chaser's Calculator

  10. Mercury’s Rotation & Revolution • Determining Mercury’s axial rotation rate • 1880s Schiaparelli wrongly concludes 1-to-1 S.O.C. • Unable to see enough surface detail with his telescopes • 1962 Radio noise emitted from Mercury Passive • Sunlit side blackbody radiation curve ~623 K • Expected radiant temperature • Sunless side blackbody radiation curve ~103 K • Unexpected radiant temperature Too high! • Implied that Mercury has no permanent sunless side • 1965 Arecibo radio telescope Active • Transmitted 1 precise radio l to Mercury • Reflected radio signal analyzed for Doppler shift • Mercury’s left side Very small blue shift Approaching • Mercury’s right side Very smallredshift Receding       • Measured at very nearly 59 days • 2/3 of Mercury’s year • 3-to-2 spin-orbit coupling Unique in the Solar System

  11. Measuring Mercury’s Axial Rotation

  12. Mercury’s 3-to-2 Spin-Orbit Coupling

  13. Causes of 3-to-2 Spin-Orbit Coupling • Solid Sun tides distort Mercury into an ellipsoid • There is a tidal bulge on opposite sides of Mercury • Mercury is in a highly elliptical orbit • Mercury’s aphelion distance is ~ 1.52 x perihelion • The Sun’s gravitational force varies ~ 2.3 x • The Sun’s gravitational force cannot lock onto one side • The Sun’s gravitational force can lock onto one axis • Some effects • 1.00 Mercury day = 2.00 Mercury years • Occasional retrograde Sun motion in Mercury’s sky • Slow East -to-West sunset • Slow West-to-East sunrise • Slow East -to-West sunset

  14. Mariner 10 at Mercury (1974 & 1975)

  15. Mariner 10’s Images of Mercury • Only three passes of Mercury • Mariner 10 orbited the Sun, not Mercury • 1.00 Mariner 10 orbit every 2.00 Mercury years • March 29, 1974 ~704 km above Mercury • September 21, 1974 ~47,000 km above Mercury • March 16, 1975 ~327 km above Mercury • Same hemisphere toward the Sun each time • Mariner 10 obtained images approaching & leaving • Detailed mosaics of only one hemisphere

  16. Mercury & the Moon Compared

  17. Mercury’s Surface • Casually, Mercury looks much like the Moon • Mercury is heavily cratered but… • Crater density is not as high as on the Moon • Mercury has gray intercrater plains, not black maria • Mercury has long, irregular ridges & scarps • Probably shrinkage features as Mercury cooled • Most materials shrink as they solidify • The surface solidifies before the interior • When the interior solidifies, the surface gets compressed • Only ½ of Mercury’s surface was well-known • The Mariner 10 spacecraft went past three times • Precisely the same face toward the Sun both times

  18. Mercury & Moon: Subtle Differences Mercurian craters & plains Lunar highland craters

  19. Mercury’s Shrinkage Scarps (Cliffs)

  20. Mercury’s Caloris Basin • Very similar to the Moon’s Mare Orientale • Much larger than any other impact crater • Multi-ringed • Not flooded with lava • Jumbled terrain on opposite side of Mercury • Seismic wave energy focused by Mercury’s core • Similar to 17 October 1989 Loma Prieta earthquake • Seismic wave energy focused on San Francisco Bay area • Much stronger shaking than closer to the quake epicenter • Strong enough to fracture the surface • Chaotic hills ~100 to ~1,800 m high • Large smooth-floor crater superimposed on hills • Impact after formation of the Caloris Basin

  21. Mercury & Moon: Impact Basins Caloris BasinMare Orientale Mercury Moon

  22. The Caloris Basin: A Second Look http://en.wikipedia.org/wiki/File:Mercury_Double-Ring_Impact_Basin.png

  23. The Caloris Basin: A Third Look

  24. Mercury’s Interior • Dominated by a very large iron core • Mercury ~75% of diameter ~42% of volume • Earth ~55% of diameter ~17% of volume • Moon ~20% of diameter ~  1% of volume • Proposed causes • Too hot for condensation of low-densityminerals • Strong solar wind removed low-density materials • Head-on impact with a planetesimal • Computer simulations favor this hypothesis

  25. Planetary Interiors: Mercury & Earth

  26. Mercury Messenger Spacecraft

  27. Mercury’s de Graft Crater http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/EW1017384139G.3band.mapped.png

  28. Mercury’s Jumbled (Weird) Terrain http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/Caloris_antipode.jpg

  29. Mercury’s Formation: Head-On Impact

  30. Mercury seen from Earth Very bright yet very elusive Always close to Earth’s horizon Maximum E. & W. elongations Never more than 28° from the Sun Mercury’s unusual axial rotation 3-to-2 spin-orbit coupling Solid tides distort Mercury’s shape Radically changing solar gravity Mariner 10 at Mercury Made three passes Exactly 2 Mercurial years apart Imaged only one-half of its surface Result of 3-to-2 spin-orbit coupling Remarkably Moon-like surface Heavily cratered Caloris Basin & jumbled terrain Intercrater plains & no maria Ridges & scarps Mercury’s interior Completely core dominated Comparison with the Earth & Moon Probable head-on planetesimal impact Important Concepts

More Related