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Asteroids, Comets
and Meteorites
← Eros: courtesy NASA
Comet McNaught in 2007 by Aberdeen Astronomical Society member Phil Hart, in Melbourne →
Perseid meteor shower courtesy NASA →
What is an Asteroid?
433 Eros ~ 30 km long
View from 50 km ~1.5×1.5 km
Asteroids discovered
Asteroid first discovered –
Ceres ( 914 km diam ) , now
a dwarf planet - in a
search for the ‘missing
Bode’s law planet’
between Mars and Jupiter
by Giuseppe Piazzi in 1801
Piazzi portrayed with Urania, the muse of Astronomy, announcing his discovery of Ceres
Asteroid facts
About 100 have diameters over 100 km Some reflect light well; others are black as coal Asteroids tumble as they orbit the Sun Estimate that 100, asteroids appear in stellar photographs
Gaspra, the first asteroid ever to be seen close-up ↓ Earth-crossing orbit of Apophis, discovered in 2004
Example Asteroids
Ida & Dactyl
Gaspra
Mathilde & Eros
Eros with close-up
Asteroid Lutetia, about 130 km long, photographed from just over 3000km away by ESA’s Rosetta probe on a flyby in July 2010 Lutetia Courtesy: ESA 2010 MPS for OSIRIS Team
Vesta
2 nd^ largest asteroid A surviving protoplanet ~530 km across Dry rocky surface with lava flows, over an iron- nickel core
Courtesy: NASA Dawn probeJuly 2011
Orbits of Asteroids
Well over 10,000 have computed orbits
Asteroid belt is between Mars and Jupiter Kirkwood gaps in the asteroid belt are caused by Jupiter’s periodic influence Most asteroids orbit close to the ecliptic Apollo asteroids (about 50 with diameters greater than 1 km) cross Earth’s orbit Trojan asteroids orbit in same orbit as Jupiter
Sun
Jupiter
60 o
LeadingTrojans TrailingTrojans
The Kirkwood Gaps
On a histogram of
number versus semi- major axis, there are gaps at a values where the asteroid period resonates with Jupiter’s period
Courtesy: www.ssd.jpl.nasa.gov
Aberdonia
Asteroids are named by
international agreement
One (5677) is named ‘Aberdonia’ after the University of Aberdeen, to mark the half millennium of our existence
30 th^ April 2008
Where are they now?
Public domain software lets you find out
Jupiter’s orbit
30 th^ April 2008
Perpendicular view
30 th^ April 2008
Corners include Jupiter’s orbit
Changing Direction of a
Comet tail
The fatter dust tail has the
combined orbital motion of
further out, slower speed matter,
and motion given by weak solar
radiation pressure
Thin ion tail is dominated by
very fast motion of solar wind
Fig. 10-
Courtesy: K & K
Kuiper Belt
Kuiper belt is an inner disk-like belt, 30 - 500 AU
from Sun, supplying shorter period comets
postulated in 1951 and attracting increasing attention the beginning of the rest of the solar system, beyond the planets, containing millions of objects a good many trans-Neptunian objects now discovered thought that inner Kuiper belt is much less populated than it used to be, thanks to influence of Neptune is the Kuiper belt the source of the Oort cloud?
Oort Cloud
Oort cloud is a thinly populated spherical shell
of cometary nuclei surrounding the solar system
between 10,000 (some say 1,000) and 100,000 AU
Oort cloud stretches about 1/3rd way to nearest star occasionally a comet is ejected → close to the Sun
P^2 = a^3 , Kepler’s 3rd law,
gives a period of 1× 106
years for a = 1 × 104 AU
Fig 10-
Courtesy: K & K
Stardust Mission
Stardust collected samples from the coma of comet Wild 2 additional samples of interstellar grains launched Feb 1999; intercept Jan 2004
Samples returned to Earth in Jan 2006
Nucleus of Wild 2, Jan 04
Rosetta II Mission
ESA’s mission to run with comet Churyumov- Gerasimenko for more than 1 year 10 years to intercept Lander for nucleus Mar 2004 ~ 2015
32m long solar array panel
One of the most ambitious of all space mission
Meteors -
appearance
Meteors are bright streaks of light in the sky
longer streaks are called meteor trails
Meteor showers come at
certain times of the year
from the same known parts
of the sky
e.g. Leonids ~Nov 17th
Fig 10-
Fig 10-
Meteors - cause
The cause of meteors is meteoroids, grains of
matter burning up in the atmosphere. An
estimated 1000 tons falls on the Earth daily
Material comes from asteroid collisions and
comet tails
e.g. Leonids are residue of material left by comet Temple Tuttle, which has a period of ~33 years Leonids are notable every 33 years sporadic meteors are on their own
Meteorites & Craters
Meteorites are pieces of rock that fall to earth stony - most meteorites (90%); Antarctica iron - usually with nickel; most commonly found stony/iron - a mixture! Most famous crater is ‘Meteor Crater’ near Flagstaff in Arizona. More than 1 km in diameter and 180 m deep, it resulted from a meteorite about 45 m across dinosaur extinction by a meteor 10 km across?
http://www.flagstaff.az.us/meteor/
UK impacts
The Silverpit structure about 20 km across 130 km offshore in the North Sea ~60 Myear old over 1 km below sea-bed The Ullapool impact reported in 2008 ~ 50 km across ~1.2 Gyear old (^) Silverpit seismic image, courtesy BP & PGL: http://en.wikipedia.org/wiki/Image:Silverpit_crater_seismic_map.jpg
Astrochemistry
Astrochemistry is flourishing with the
development of techniques that can analyze
meteorite particles ~1μm in size
the chemical memory of meteorites is potentially enormous. It represents a book in which is written the evolutionary history the Solar system, back in time to the interstellar material from which the Solar system condensed E crucial evidence is the relative abundance of different elements occurring together, and different isotopes of the same element
The Excitement of
Astrochemistry
The supernova that created the interstellar
material from which we are condensed created
solids in its expanding atmosphere
these included minerals, metals, hydrocarbons, icy aggregates when our Solar system was formed, the processes that led to the concentrations of elements we now find at different distances from the Sun were complex, resulting from both collapse and ejection from the protosun
