Transcript ppt

Exoplanets
Or extra-solar planets have recently been
discovered. There are important to find to
help fill in the Drake Equation that
determines the probability of life existing
elsewhere in the universe.
What is a 'planet'?
A planet is an object that has a mass
between that of Pluto and the Deutriumburning limit (0.015 solar masses) that
forms in orbit around a star.
The formation of planetary systems
Finding Exoplanets
Finding exoplanets is tough because they are very dim
compared to the star that they orbit, and they are very
close.
Jupiter viewed from 5 pc away will just be separated
by 1 arcsecond and is just 0.000000001 times as
bright!
Therefore one away to detect the planet is by the
gravitational pull of a planet around the star it orbits.
As planets orbit a star they tug it causing the star to
wobble.
Bigger planets cause bigger
wobbles so we can generally
only observe the largest planets
using this technique.
The first exoplanet was
observed in 1994 by detecting a
wobble in the pulse of a pulsar!
The wobble can be seen directly in some nearby
stars by measuring the shift in the stars position in
the sky (astronometry) or be detecting a red-shift /
blue-shift wobble due to the Doppler effect (radial
velocity).
Like eclipsing binary star systems exoplanets
may be discovered by observing tiny dips in the
lightcurve of a star
Microlensing can also be used to spot
the existence of a planet around another
star
Nulling Interferometry
We could find much smaller planets,
and find out more about their nature if
we could directly detect the light from
them. One technique to do this is by
nulling interferometry which uses an
array of telescopes in space
separated by millions of miles to
improve the spatial resolution and
hence separate out the light of the
planet from the light of the star. It is
known as nulling interferometry
because by cancelling out lightwaves
from the star it blocks all of the star's
light allowing the planets light to be
detected.
From this we can observe its spectrum and hence see
what its atmosphere is made of and possibly detect the
presence of water – vital for life to exist.
So far we've found over
100 planets – mostly
Jupiter sized or bigger