Download Lecture #27: The Next 100 Years

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Transcript
The Next 25(?) Years
Future Missions to Search for
Extra-solar Planets and Life
The census so far
As of December 3rd: 268
extrasolar planets
Almost exclusively “Hot
Jupiters” in elliptical orbits:
only 3 with the possibility of
a habitable terrestrial planet
So far, no extrasolar Earths...
but we haven't really looked We can see
this!
that hard
But we want
this!
Limited by search size...
Imagine, if you shrunk our solar system
to a little larger than a quarter:
Our whole Solar
System
Our Milky Way Galaxy
would be this big
would be the size of
the United States.
From: http://planetquest.jpl.nasa.gov/Navigator/material/sim_material.cfm
And the neighborhood
where we’ve found new
planets would only be
the size of Manhattan.
You can even see some of the stars
that have planets in the night sky…
From:
…if you know where to look
From:
Limited by ground-based
technique...
Doppler “wobble” is
limited by our spectral
resolution (we can
already see shifts of
only ~100 mph)
Earth's atmosphere
causes stars to
“twinkle” when viewed
from the ground, so
this limits imaging
methods
The Goal:
To find planets capable of supporting life or even
find extra-solar life!
Recap: We need...
Larger search area
New technique
to find terrestrial planets in the habitable zone of
their stars!
It’s all about location, location, location!
A New Technique...
The ultimate goal is to directly image an
extrasolar Earth
But right now we're pretty far from that.
Prof. Close's work:
A New Technique...
The ultimate goal is to directly image an
extrasolar Earth
But right now we're pretty far from that. But
we can (just) image super Jupiters
New results (1 year old)
from Keck & Gemini
telescopes
The Next Step
Kepler (NASA)
COROT (ESA)
Kepler: A Larger Search Area
Kepler
Field of View
100,000 stars!
Sensitive to extrasolar
“Earths” around stars
like our Sun 3000
light-years away
2/3 of systems surveyed will
be binaries...
A New Technique
Transits (from
space)
Earth would lower the Sun's brightness by only
1/10,000 for up to 13 hours. We're limited by:
Orientation
The intrinsic variability of stars
Orientation
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Orbit (AU)
0.39
0.72
1
1.52
5.2
9.5
19.2
30.1
Transit Depth (%) Probability (%)
0.0012
1.19
0.0076
0.65
0.0084
0.47
0.0024
0.31
1.01
0.089
0.75
0.049
0.135
0.024
0.127
0.015
12% of the time we detect Earth or Venus... we detect both of them.
Stellar Variability
• Stars vary, but on
different timescales
• We need to see a
planet transit
several times to
know it's real: it will
take 4 transits
(years) to detect
an “Earth”
We will see only about 0.5%!! of Earth-like
planets transit in front of their stars!
Kepler specs
Will look at 100,000 stars in 4 years!
95 mega pixels!! (Your digital camera has ~
4-5 and these CCDs need to be much
higher quality)
Expects to find ~ 50 Earth-like planets!
Obviously depends on how many Earth-like
solar systems actually form, but if they are
there we WILL see them!
More on Kepler
http://www.bridgewater.edu/~rbowman/ISAW/Transit-1.html
SIM (NASA) & Darwin (ESA)
2015 ???
Space Interferometry specs
Looks for planets by detecting the wobble of star
due to planet, BUT by directly measuring the
movement of the star as opposed to just looking
at the change in the wavelength emitted by the
star
To detect Earth-size planets with this it needs and
accuracy of 1 microarcsecond 1 * 10-6
arcseconds which is like seeing a nickel at the
distance of the Moon!
SIM will look at the nearest ~100 stars to look for
planets of ~ few Earth masses!
Terrestrial Planet Finder 2020 ???
Will find terrestrial size planets:
by astrometry (detecting the wobble of the
host star directly)
also imaging them directly by
coronagraphy (meaning blocking out the
light of the central star to observe fainter
objects around it)
TPF will survey 250 of the closest stars as a
follow up for Kepler and SIM
So by sometime this century we will almost
certainly have a real image of a terrestrial
planet…..
But if we find terrestrial planets how do we
detect life?
This is not as easy as it might sound….
We can look for things that are common in
Earth’s atmosphere like Oxygen, Methane,
CO2
But Venus, Earth and even Mars look pretty
similar in a spectrum…..and yet they are
very different planets
After TPF?
Life Finder Mission? Human manned observatory
on the Moon or somewhere in space to look for
signatures like chlorophyll
And if we find signatures of Life
Planet Imager? To get more information about a
planet with life we would require a large number
of telescopes working together as to give a total
observing area around 350km!!