Earth - (1685) Toro Asteroid Resonance

The asteroid (1685) Toro is in an 8:5 resonance with earth. This simply means that it makes 8 rotations about the sun in the same time as the earth makes 5 rotations.

The orbital elements of (1685) Toro show that its daily mean motion n = 0.61646079 deg /day

Thus its rotational period is 360 deg / (0.61646079 deg /day) * (1 yr/365.25 days)= 1.60 yr

5 rotations of Toro takes 2919.894 days or 8.0 years, the same time as 8 earth rotations.

(1685) Toro is also in an 13:5 resonance with Venus, but Earth predominates with a stronger restoration force to its orbit.

The synodic period of Venus is 224.70069 days
5 rotations of Toro takes 2919.894 days or 13 Venus rotations.

From orbital elements for Toro

a 1.3673061 AU
e 0.4358292

perihelion distance q = a - ae = a(1 - e) = 0.7713942 AU
aphelion distance Q = a + ae = a(1 + e) = 1.9632180 AU

a_Mars 1.52371034 AU
a_EM Barycenter 1.00000261 AU
a_Venus 0.72333566 AU

As Toro orbits the sun, it crosses the orbits of Earth and Mars, passing near the orbit of Venus at its perihelion. Over long periods of time Venus, Earth, and Mars will influence its orbit perturbing it as the asteroid approaches and receeds to and from each planet with tidal forces that affect th asteroid's angular momentum and causes its orbit to osculate. This causes precession in its longitude of perihelion. Its orbit librates (or oscillates) with respect to Earth and Venus. The effect of earth's gravity provides an impulsive force on its orbit during every close encounter which stabilizes the resonance with Earth. Encounters with Venus and Mars will disturb this until it encounters Earth again. This is like the earth's pull on the pendulum in a grandfather clock.

Other small perturbing solar system bodies usually considered in perturbation calculations include: Ceres, Pallas, Vesta, which are the most massive asteroids.

Perturbed orbital elements for an object like Toro will only be valid near the Epoch they are calculated for.

Toro is an Apollo type NEO with Earth MOID = 0.0504725 AU
Tholen spectral type: S
SMASSII spectral type: S
Absolute magnitude H: 14.23
Geometric albedo: 0.31
Diameter: 3.4 km
Rotation period: 10.196 h
Color index B-V: 0.880 mag
Color index U-B: 0.470 mag
Discovered 1948-Jul-17 by Wirtanen, C. A. at Mount Hamilton
T_jup = 4.716

Perihelion T: 2455025.524942745145 (2009-Jul-13.02494275)

Since this object's Earth MOID is greater than 0.05 AU, it is NOT classified as a Potentially hazardous Asteroid (PHA).
Its last encounter with earth was 2008-Jan-24 16:03 at a nominal distance of 0.19634 AU.
Its next encounter with Earth is at 2012-Jul-28 22:16 at a nominal distance of 0.3017 AU.
It has an impact probability of 0. This object has been well observed over 60 years which includes radar observations. It just passed its perihelion on July 13, 2009. Currently it is at magnitude 18.0, slowly fading, in the early morning sky at RA: 13 07 39.3 DEC: -14 44 47

References:

Minor Planet Ephemeris Service: http://scully.cfa.harvard.edu/~cgi/MPEph2

JPL Small-Body Database Browser:
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1685;orb=0;cov=0;log=0;cad=0#elem

Alfvén, Hannes; Arrhenius, Gustaf; SP-345: Evolution of the Solar System, Scientific and Technical Information Office, NASA, Washington, D.C., 1976: http://history.nasa.gov/SP-345/ch8.htm

http://history.nasa.gov/SP-345/ch8.htm

Hazards due to Comets and Asteroids (1994), Ed. T. Gehrels, pp.540-543

EAR-A-5-DDR-TAXONOMY-V4.1

Venus Fact Sheet:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
Mars fact Sheet:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
Earth Fact Sheet:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

The Sylacauga Meteorite

About 1 PM CST on November 30, 1954, Elizabeth Hodges of Sylacauga, Alabama, was slightly injured from bruising, when an 8 1/2-pound meteorite crashed through the roof of her house, smashed a wooden radio cabinet, and then hit her hand and hip as she lay dozing on her couch. She was bruised. She was pictured in the December 13, 1954, issue of Life magazine showing her bruised hip. Media reports at the time indicated people from Georgia, Alabama, and Mississippi reported seeing a bright fireball in the afternoon sky. Witnesses heard three explosions near the time Hodges was struck. She was the first person to ever have been struck by a meteorite. An Air Force pilot from Maxwell Air Force Base flying at high altitude witnessed the fireball. Witnesses on the ground reported a black mushrooming cloud with a narrow cork screw tail at the bottom.

The grapefruit sized object (approximately 5 inches by 7 inches) became known as the Sylacauga or Hodges Meteorite. It is classified as an Ordinary Chondrite H-type, a common form of stony meteorite linked to S-type asteroids. It was found to cause a deflection on a magnetic compass needle.

The event created a national media frenzy, an investigation by the U.S. Air Force, and a dispute over ownership. Wishing to avoid continued media controversy, she donated it to the Alabama Museum of Natural History located in Smith Hall on 6th Avenue near the Quad on the University of Alabama campus in Tuscaloosa.

The largest fragment which hit Ms Hodges is known as the Hodges fragment. A second 3.75 pound (4 inch x 4 inch x 5 inch) fragment was found a day later on December 1, 1954 by J. K. McKinney in the middle of a dirt road near his farm and is known as the McKinney fragment. McKinney was driving a mule-drawn wagon with a load of firewood near his farm a few miles away. His mules reacted to the dark object on the road and he got out of his wagon to look at the strange rock and kick it off the road out of the way. The McKinney fragment is on display at the Smithsonian Institution in Washington, D.C. It is believed there might be a third fragment, but none has been found.


References:

http://en.wikipedia.org/wiki/Sylacauga_(meteorite)

Swindel, G. W.; Jones, W. B.; The Sylacauga, Talladega County, Alabama, Aerolite (CN=0863,332); Meteoritics, volume 1, number 2, page 125. (1954):
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1954Metic...1..125S&db_key=AST

Hodges Meteorite Strike (Sylacauga Aerolite):
http://www.encyclopediaofalabama.org/face/Article.jsp?id=h-1280

A star fell on Sylacauga '54 meteorite struck home, woman, changed lives, by M.J. Ellington
http://legacy.decaturdaily.com/decaturdaily/news/061130/meteorite.shtml

My Top 10 Favorite Display Pieces in the Meteorite Exhibit at the Smithsonian' s National Museum of Natural History:
http://www.meteorite-times.com/Back_Links/2003/August/Accretion_Desk.htm

It Came From Outer Space
http://www.americanheritage.com/articles/web/20051130-meteorite-alabama-smithsonian-space-race-cold-war.shtml

UA Museum to Observe 50th Anniversary of Hodges Meteorite
http://uanews.ua.edu/anews2004/nov04/meteorite112404.htm

Alabama Museum of Natural History
http://www.ua.edu/academic/museums/history/wordpress/

Image links:


Looking up at the hole in the ceiling - 1

Looking up at the hole in the ceiling - 2

Ms Hodges holding the meteorite

Basic Asteroid Spectral Types

There are three major asteroid spectral types: C, S, M (carbonacious, stony, metal) and U for unclassified  others. This is based on early study using polarimetry, radiometry, and spectrophotometry by Clark R. Chapman, David Morrison, and Ben Zellner for ~100 asteroids published in 1975 and further refined by Bowell et al 1978 and others (see taxonomy data in PDS).  In this C-S-M taxonomy, most asteroids are either C-type or S-type.

• C: Carbonaceous
• S: Stony or silicate or silicaceous
• M: Metallic
• U: Undetermined or rare

C-type

• 76%
• Most common
• Extremely dark (albedo 0.03)
• Similar to carbonaceous chondrite meteorites
• Approximately the same chemical composition as the Sun minus hydrogen, helium and other volatiles
• Predominate the main belt, especially the outer half of the main belt between 2.77 and 3.0 AU
• Largest C-type asteroids include (1) Ceres, (2) Pallas, (10) Hygiea, (511) Davida

S-type:

• 16%
• Relatively bright (albedo 0.10 - 0.22);
• Metallic nickel-iron mixed with iron- and magnesium-silicates.
• Predominate the inner main belt
• Many S-type objects have diameters of 100–200 km
• Examples: (15) Eunomia, (3) Juno

M-type

• 5% - Most of the rest
• Third most common asteroid type.
• Bright (albedo 0.10-0.18)
• Pure nickel-iron or mixed with small amounts of stone
• Examples: (16) Psyche, (21) Lutetia, (22) Kalliope, (216) Kleopatra

U-type

• 3%
• For unclassified or rare such as E-type or enstatite achondrites
• Examples (4) Vesta, (1566) Icarus, (162) Laurentia, (267) Tirza

References:

C. R. Chapman, D. Morrison, and B. Zellner Surface properties of asteroids: A synthesis of polarimetry, radiometry, and spectrophotometry, Icarus, Vol. 25, pp. 104 (1975)
http://adsabs.harvard.edu/abs/1975Icar...25..104C

http://www.observeasteroids.com/images/spectra2.gif

http://www.psi.edu/pds/archive/asteroids.html

The Asteroids, Chapman, C. R.; Williams, J. G.; Hartmann, W. K.; Annual review of astronomy and astrophysics. Volume 16. (A79-14551 03-88) Palo Alto, Calif., Annual Reviews, Inc., 1978, p. 33-75
 http://adsabs.harvard.edu/abs/1978ARA%26A..16...33C

Bowell, E.; Chapman, C. R.; Gradie, J. C.; Morrison, D.; Zellner, B., Taxonomy of Asteroids Icarus vol. 35, Sept. 1978, p. 313-335: http://adsabs.harvard.edu/abs/1978Icar...35..313B

Neese, C., Ed., Asteroid Taxonomy. EAR-A-5-DDR-TAXONOMY-V5.0. NASA Planetary Data System, 2005 : http://www.psi.edu/pds/resource/taxonomy.html

Other classifications:

• Tholen classification: Tholen, D. J. 1989.  Asteroid taxonomic classifcations.  In  Asteroids II (R. P. Binzel, T. Gehrels, and M. S. Matthews, Eds.),  pp. 1139-1150.  Univ. of Arizona Press, Tucson.  [THOLEN1989]  
• SMASS classification: S. J. Bus, F. Vilas, and M. A. Barucci Visible-wavelength spectroscopy of asteroids in Asteroids III, pp. 169, University of Arizona Press (2002)
• Barucci, M. A., M. T. Capria, A. Coradini, and M. Fulchignoni 1987. Classification of asteroids using G-mode analysis.  Icarus 72, 304-324. [BARUCCIETAL1987] 
• Tedesco, E. F., J. G. Williams, D. L. Matson, G. J. Veeder, J. C.Gradie, and L. A. Lebofsky 1989.  A three-parameter asteroid taxonomy.  Astron. J. 97, 580-606. [TEDESCOETAL1989]                  
• Howell, E. S., E. Merenyi, and L. A. Lebofsky 1994. Classification of asteroid spectra using a neural network.  J. Geophys. Res. 99, 10847-10865. [HOWELLETAL1994]                       
• Xu, S., R. P. Binzel, T. H. Burbine, S. J. Bus 1995.  Small main-belt asteroid spectroscopic survey: Initial Results. Icarus 115, 1-35. [XUETAL1995]                                                                                        
• Bus, S.J. and R.P. Binzel 2002.  Phase II of the small main-belt asteroid spectroscopic survey:  A feature-based taxonomy.  Icarus 158, 146-177. [BUSETAL2002]                                                                  
• Lazzaro, D., C.A. Angeli, J.M. Carvano, T. Mothe-Diniz, R. Duffard,   and M. Florczak, S3OS2: The visible spectroscopic survey of 820 asteroids, Icarus 172, 179-220, 2004. [LAZARROETAL2004]"