Transcript Document

AGA 0316 AULA 16
Buscando a vida fora da Terra:
Além do Sistema Solar
Extrasolar planets
• Extrasolar planets=Exoplanets= planets
around stars other then the Sun
• Planets are the environments for the origin
and evolution of life.
• Giordano Bruno: “There are countless suns
and earths all rotating around their suns in
exactly the same way as the seven planets of
our system..” (1584)
• First confirmed planet – 51 Pegasi on
October 1995 by Mayor and Queloz (1995)
Which type of star?
Exoplanets
(Oct 2013: ~ 1040 DESCOBERTOS)
Hertzsprung-Russell
(HR) Diagram
http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_1ai.html
Prospects for finding habitable
planets
• Best candidates are F, G, and early K-type
stars, i.e., stars not too different from the
Sun
• Early-type stars (blue stars)
– High UV fluxes
– Short main sequence lifetimes
• Late-type stars (red dwarfs) – M-class
– Tidal locking
– Lots of flares
59 planets
11 planets
9 systems
1 multiple
1 planet
8 planets
7 systems
1 multiple
321 planets
274 systems
33 multiples
7 planets
4 systems
2 multiple
Extra-Solar Planets Catalog (http://exoplanet.eu/catalog.php). Last update: 30/05/2009
How to detect exoplanets?
1) Direct detection
2) Astrometry
3) Microlensing
4) Velocitometry
5) Transits
9
Methods for detection of Exoplanets
1) Astrometry: changing on spatial star
position  exoplanet detection
Inconclusive and marginal.
2) Direct (imaging) detection: only for BIG
and sufficiently distant planets: weak
contrast
Contrast Star-Planet:
> 100,000,000 for a Jupiter-like planet in
the Visible
~ 100,000 for a Jupiter-like planet in the IR
 interferometric/coronagraphic
techniques
10
Direct detection: planet around star Fomalhaut (25 l-y from
the Sun)
11
Other examples of direct detection
Beta Pic
AB Pic
Hubble image of possible
exoplanet TMR-1C (NASA)
12
Four planets around HR 7899 (Palomar)
13
Methods for the detection of exoplanets
3) Gravitational
effect)
microlensing (Einstein
Planet
OB05390
Some dozens
exoplanets
discovered with
this method
(Mpl ~Atm)
14
Methods for the detection of exoplanets
4) Velocitometry: stellar radial velocity
variations 
 presence of unseen body
Many hundred
exoplanets
discovered by this
method
Radial velocity variations + Kepler's 3rd law  Mpl ;
Porb
15
PROBLEM with the velocitometry method
Described by Newton's law:
F = G x Mstar x Mplanet
distância2
►► BIAS: detected mainly planets
more massives & nearer to their hosts
stars
16
Detection by velocitometry method: the system of Gliese
581
Discovery of 3 planets:
April, 2007(Udry et al.)
2009-2012: discovery of
other planets, not all
confirmed yet
Planet
Mass
Period Distance
Gliese
581b
15
MEarth
5,4 d
6 millions km
Gliese
581c
5 MTerra
13 d
11 millions
km

Udry et al: planet d at ZH?
17
?
GLIESE 581 PLANETARY
SYSTEM?
No atmosphere
18
Methods for the detection of exoplanets
5) Transit method: detection of the tiny eclipse
caused by the passage (transit) of a planet in front
of its star.
 Rpl ; Porb
Transit of
VENUS
June 6, 2012
19
Method of planetary Transits
20
d
d  Rpl2 ⁄ Rstar2
CoRoT star
Porb = interval between 2
eclipses
21
Satellites observing transits
CoRoT
KEPLER
Europe + Brazil
NASA
22
KEPLER and CoRoT
have found tens of
multiplanetary systems
The moment of the eclipse by
one planet is perturbed by the
presence of other planet(s)
23
The launch of CoRoT (Dec 26th, 2006)
(launch no. 1735 of SOYUZ without a failure)
24
Exoplanets: methods of detection
25
The Habitable Zone (HZ)
Definition: region around a star where the
temperature on the surface of an eventual
planet or moon can afford the
presence of liquid water.
Conditions: the position and width of the HZ
depends on the presence and composition of
the atmosphere (greenhouse effect - GE).
On EARTH: GE raises temperature by ~32 °C
26
Exoplanets & Astrobiology
The Habitable Zone (HZ): liquid water
27
Outra possibilidade interessante:
Rocky Moon orbiting a Jupiter in HZ
There are many Jupiters
discovered in HZ
Planets and Astrobiology
Most favorable cases: F-G-K stars
(similar to the Sun): stability and
evolution time
Hot (blue) stars: too much UV radiation
and
short MS
evolution time
Cold (red dwarf) stars: energetic
explosions (flares) and tidal lock
problem.
29
THE EXOPLANET ZOO
Number of planets in the Milky Way: ~
400 billion
Number of Earth-like planets in the
Milky Way: ~ 100 billion
30
NUPESC Ago 2012
31
The KEPLER + CoRoT legacy (www.seti-setr.org)
Period ~20hs
Mass  7 MEarth
CoRoT 7-b, the first planet discovered with Earth-like density
33
34
35
36

 = CoRoT 7b
NUPESC Ago 2012
37
How Will We Know A Planet
Supports Life?
Look for
evidence of
oxygen
Analyze the
reflected light
from the planet to
see if the planet
has an
atmosphere
Look for liquid
water
Look for signs
of biological
activity
(methane)
And Rule Out Other Explanations?
17
NIMS Data for the Earth (from Galileo)
(‘A’ band)
Sagan et al. (1993)*
*But credit Toby Owen for
pointing this out (1980)
NIMS data in
the near-IR
• Simultaneous presence
of O2 and a reduced
gas (CH4 or N2O) is
the best evidence for
life
*Credit
Joshua Lederburg
and James Lovelock for
the idea (1964)
Sagan et al. (1993)*
Wavelength
Thermal IR
spectra
Source:
R. Hanel, Goddard
Space Flight Center
Possibility of remote detection of life
Explore the contrast star/planet in thermal IR (Des Marais et al. 2002, Segura et al. 2003)
Window at 8-12 μ m: Tsurface
Porto de Melo et al., Astrobiology, 2006
H2O
6.3 μm +
12 μm band
> 106
CH4
7.7 μm
O3
9.6 μm
CO2
15 μm
Darwin
(ESA)
2022?
Darwin summary
•
•
ESA’s Darwin mission
may eventually be able to locate Earth-sized planets
around other stars and take either visible or thermal-IR
spectra of their atmospheres
• O2 (or O3) and CH4 have absorption bands in both
wavelength regions that may be used as potential
indicators of extraterrestrial life
But,
• We need other bio-indicators for reduced, early-Earth type
atmospheres
An Integrated Program of Planet Finding
(NASA)
KEPLER
Science
Navigator
Survey of distant
stars for Earths
Program
Optical signs of
habitable worlds
KECK
TPF-C
Survey of nearby
stars for dust and
giant planets
LBTI
1
Delayed
3 yrs
SIM
Masses and
orbits of large
terrestrial
planets
Overcost
PLANET DETECTION
• Nearby giant planets
• Young, hot Jupiter's
2005
Mid-infrared signs
of habitable worlds
TPF-I
approved
2010
PLANET CHARACTERIZATION
• Planet chemistry in visible and
infrared
• Presence of water
• Radius
• Surface gravity and temperature
• Atmospheric conditions
• Biomarkers
•Young Jupiters
•Transit Follow-up
•Debris Disks
2015
Cancelled
ARE THERE OTHER
HABITABLE WORLDS?
JWST
ARE THERE OTHER
SOLAR SYSTEMS LIKE
OUR OWN?
Cancelled
2020
2025
OUTRAS MISSÕES PROGRAMADAS PARA
2020-2030 SOBRE EXOPLANETAS (NASA,
ESA)
PLATO (ESA), ECHO (ESA), TESS, SIM, JWST
ALMA (Atacama Large Milimmeter Array),
MATISSE (espectro-interferômetro, IV), etc...