Transcript Slides - Durham University

Martin Ward
Our Solar System –
unique or ubiquitous?
A "planet" is defined as a celestial body that (a) is in orbit around the
Sun, (b) has sufficient mass for its self-gravity to overcome rigid body
forces so that it assumes a hydrostatic equilibrium (nearly round)
shape, and (c) has cleared the neighbourhood around its orbit.
Mars
The Surface of Titan, (moon of Saturn)
Observational evidence for
existence of other solar systems
Hubble Space
Telescope
observations of
Orion Nebula
(local stellar
nursery) – can see
protoplanetary
discs around
protostars
The clearing of a debris disc by a
large “Jupiter like” planet
Detecting extra-solar planets
Several techniques in use:
I. Velocity shifts (so-called Doppler wobble)
II. Transits (eclipses)
III. Gravitational micro-lensing
IV. Pulsar timing
V. Direct imaging
As of April 2008 we know of 287 extra-solar planets –
vast majority from method I, ~10% from method II
and 4 from gravitational lensing (Pulsars ?)
The Velocity Shift, Method I
Earth = 0.1 m/s
Jupiter = 12.4 m/s
Neptune = 0.3 m/s
What type of solar systems do we find?
The Transit, Method II
Gravitational Micro-lensing
Showing type of planet detected by microlensing
Pulsar Planets?
Highly accurate periodic signal, modified by the presence of a planet.
However, this will not be a normal planet because of supernova explosion
Can we “see” an extrasolar planet?
Early suggestions of life on other planets…
Giordano Bruno
1548-1600
…claiming the existence of the plurality of worlds
Where could we live?
The Goldilocks constraint
• What are the necessary conditions for life
to emerge and flourish?
• We assume require a terrestrial planet
• This planet must support liquid water
• For this we require conditions that are
neither too hot nor too cold, but just right…
Galactic Habitable Zone
Too close to centre high stellar density
increases planetary
system disruption; AGN,
SN and GRBs sterilise
planets
Too distant from centre low metallicity - insufficient
heavy elements for
terrestrial planets to form
Galactic Habitable Zone
Temperature of planets
• For life: require liquid water at surface of
planet - temperature of the planet is critical
Consider example
of Earth: heat
energy in from
Sun balanced by
Earth’s thermal
emission
Our solar system’s Habitable Zone
• Putting Earth/Sun values into equilibrium
temperature equation gives TEarth = 255 K
minus18ºC !
or
• But actual mean surface temperature of Earth at
~ 15ºC (fortunately for us…)
• We are saved by the - greenhouse effect
Greenhouse effect can be
critical for life
• Earth has mild effect (difference ~ 33 K)
• Venus is in Sun’s HZ - but surface
temperature of ~740 K!
– Difference: runaway greenhouse effect
– Earth has not suffered this (due to lower
carbon cycling via plate tectonics)
Properties of planet lying in HZ
• Inner and outer radius of Habitable Zones
varies with the type of star
Interferometry and extra-solar
planet studies
• Can gain improve resolution by
using two or more separate
telescopes as an interferometer
- d is the separation of the
telescopes
• Limit then from “wobble” of
Earth’s atmosphere (seeing)
• Ground-based telescopes used
as interferometers e.g. Keck,
VLT
VLT
Keck
Space missions NASA: Kepler
kepler.nasa.gov
• ~ 1m telescope
• Quite small field of
view
• Monitors 100000
stars for 4 years
• Will detect at least
50 Earth-like
systems
Launch: Feb 2009
Space Missions ESA: Darwin
Nulling Interferometry
Vital signs for Life
Atmospheric changes
imprint distinct spectral
signatures - this could be
used to identify
inhabited planets
So… what’s the relevance of all this for
Durham University ?
Theory
Question: is the moon important for the
evolution of life?
Question: how do big planets get so
close to their stars?
Modeling of protoplanetary discs
Observations
we build
advanced
instruments
Durham
in Space!
Thomas Wright of Durham
An Original Theory, or New Hypothesis of
the Universe, 1750
Durham University Observatory