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?

Giordano Bruno …claiming the existence of the plurality of worlds Early suggestions of life on other planets…

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 T Earth = 255 K or minus18ºC ! 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 ~ 1m telescope Quite small field of view Monitors stars for 4 years Will detect at least 50 Earth-like systems kepler.nasa.gov 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