Transcript Planetary Science

The Heavy Elements in Planets
• Where did they come from?
– Heavy element fusion in massive stars
– Supernova explosions
• Why are they not all at the centre?
– It’s likely that many heavy elements are in the
planet cores
– Some are not
• Recycled in magma, ejected in volcanism
• Fixed in the solid crust
© Colin Frayn, 2008
www.frayn.net
Cooling Planets
• Are the planets radiating heat too quickly?
– Incoming heat flux from sun is less than heat radiation
from planet
– Net cooling effect
• Jupiter
– Heat loss is very slow
• It is still radiating heat from its formation
• Saturn
– Heat loss is slightly too fast
• Heat is gained from gravitational energy of helium
precipitation
• An unusually low upper atmospheric abundance of Helium
is observed
– This gives strength to the theory
© Colin Frayn, 2008
www.frayn.net
Saturn’s Rings
• How did they form?
– Probably from the disintegration of a satellite
(moon) or comet
• How old are they?
– It was believed that they were 100 million
years old
– New observations from Cassini suggest that
they are much older
• Particle ‘recycling’ gives impression of young ring age
• Rings could be the same age as the solar system
• They may be debris from the planet’s formation
– Even if they were young, it’s not a problem!
© Colin Frayn, 2008
www.frayn.net
Recession of the Moon
• The moon is receding (moving away) at a rate of
3.8cm per year
– This is no problem for the age of the Earth-Moon system
– Often much faster (incorrect) rates are claimed
• Also, the rate of recession is much faster now
than it has been
– Observation of tidally laminated sediments shows us the
moon’s orbital period over evolutionary time
– Mean recession rate of 2.16 cm/yr over the last 650 Myr
– Between 2.5Gyr and 650Myr, mean rate was 1.27 cm/yr
© Colin Frayn, 2008
www.frayn.net
The Earth’s Magnetic Field
• Earth’s magnetic field strength is falling
– If you follow backwards in time, it would have been too
high a few thousad years ago
• This is based on:
– Obsolete models of the Earth’s interior
• The Earth’s magnetic field is generated by a dynamo effect
• It is not a simple, decaying field
– Incorrect (or unsupported) extrapolation from data
• There’s insufficient evidence to fit an exponential decay
– Incorrect assumptions about the cause of the reduction
• It is periodic, not monotonical decay
• Magnetic reversals regularly occur
© Colin Frayn, 2008
www.frayn.net
Moon Dust
• Why is there not more lunar dust?
– How much should we expect?
• Hans Pettersson, February 1960, Scientific American
• Claimed an upper estimate of 39,000 t/d of dust falling on
Earth
– Some creationists still use this massively incorrect figure
today!
• Overestimated by a factor of 1,000!
– Correct value (30-40 t/d) known since 1972 (Dohnanyi)
– How much dust did NASA expect?
• Very little:
“In 1965, a conference was held on the nature of the lunar surface. The
basic conclusion of this conference was that both from the optical
properties of the scattering of sunlight observed from the Earth, and
from the early Ranger photographs, there was no evidence for an
extensive dust layer.” S. Shore, 1984
© Colin Frayn, 2008
www.frayn.net
The Vapour Canopy
• A vapour canopy above the Earth
– How could this avoid gravity?
• The Meissner Effect
– Sometimes incorrectly spelled ‘Mysner’
– This is irrelecant:
• It only applies to superconductors!
– i.e. not the Earth
• Water would condense and fall as rain
– It couldn’t remain up there for 1,500 years!
© Colin Frayn, 2008
www.frayn.net