Download The ExOoS Mission - Extraterrestrial Octopus on Steroids

Aarhus University
Stellar Astrophysics Centre
Nordre Ringgade 1
DK-8000 Aarhus C
November 22, 2014
Project Report
The ExOoS Mission - Extraterrestrial
Octopus on Steroids
Matthias Morbitzer & Carla Pérez
”Do there exist many worlds, or is there but a single world? This is one of the most
noble and exalted questions in the study of Nature.” -Albert the Great
Project Report SAC Summer School
The ExOoS Mission
Abstract
Are we alone? That is the great unanswered question of humanity since its early beginning. Advances in space exploration techniques, day to day findings of exo-planets
and recent discoveries in biology point that life might be out there, even intelligent life.
However, none of the approved space missions till now are specifically designed to search
for our living companions in the Universe. In the present work, we propose a mission
based on the principle of interferometry aimed to detect biosignatures on exo-planets
and, as a complement, create a physical map of the studied planets. Our mission is
called OCTO-JWST-TPF-I and it consists of 8 telescopes with a mirror size of 6.5 m
λ
and, taking into account the interferometry, with a resolution of 3 × 10−6 D
after the
James Webb Space Telescope (JWST), Transiting Exoplanet Survey Satellite (TESS)
and Plato missions. Based on the data of these missions, OCTO-JWST-TPF-I will target 5 planets in the habitable zone of different stellar systems. It is necessary to have a
high resolution spectrometer that allows the detection of life and the accurate measure
of physical planets properties. Our mission might answer the big question of ’are we
alone?’ and provide the first tomographic map of a planet.
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Contents
1 Introduction
4
2 Biosignatures
2.1 Detection of H2 O, O2 , O3 , CO2 , CH4 and
2.2 Detection of C2 H6 and CH3 Cl . . . . .
2.3 Red edge measurement . . . . . . . . . .
2.4 Detection of sodium and asphalt . . . .
N2 O
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3 Targets
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4 Techniques
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4.1 Planet Tomography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2 Determining the Planetary Rotational Period . . . . . . . . . . . . . . . . 16
4.3 Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5 The Instrument: OCTO-JWST-TPF-I
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5.1 Interferometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2 Mirrorsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6 Future Perspective and Alternative Ideas
6.1 Incorporation of more biosignatures . . . .
6.2 Increase in resolution: Gravitational lensing
6.3 Alternative Ideas . . . . . . . . . . . . . . .
6.3.1 Rouge Planets . . . . . . . . . . . .
6.3.2 Free-floating Life Forms . . . . . . .
7 Conclusion
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Project Report SAC Summer School
The ExOoS Mission
1 Introduction
Astrobiology is one of the fields with the fastest development in the last years (Harrison
et al. 2013; Seager et al. 2012). Advances in molecular techniques and technology have
allowed the detection and the study of living organisms and their traces in environments
traditionally unconceivable to host life (Harrison et al. 2013). Life is a common phenomenon on earth, having been detected in almost any kind of environment; from acidic
lakes such as Rio tinto in Spain, to the atmosphere or the deep earth (Harrison et al.
2013). This fact, linked to the day-to-day increasing discovery of iso-planets, raises the
need of searching for life in the outer space and the probability to succeed on it (Schneider et al. 2010; Seager et al. 2012).
Future spaces missions such as TESS, PLATO and JWST will focus in the search and
study of iso-planets, confirm current candidates, find new ones in further systems and
determine their physical properties (Ricker et al. 2009). However, none of these missions
are designed to specifically look for life. The main focus in the searching of extraterrestial life is the detection of biosignatures, defined as any substance (e.g. an element,
isotope, molecule) or phenomenon that provides scientific evidence of past or present
life (Steele et al. 2006). When there is access to samples, as in the case of meteorites,
biosignatures can rate from special geological features or precipitates to even fossils that
resemble living forms on earth (McKay et al. 1996; Martel et al. 2012). However, in
the most common case of remote sensing, in which the planet is observed through the
distance, biosignatures are mainly confined to gaseous byproducts of metabolism (eg.
oxygen, methane, nitrous oxide) and/or biological features in the surface of the planet
(eg. Plant Canopy) (Schneider et al. 2010; Seager et al. 2012; Rugheimer et al. 2013).
Currently remote sensing relays mainly in spectroscopy, which allows the determination
of numerous planets characteristics without the costly need of direct imaging. Spectrometry have already succeed in the remote detection of biosignatures, as in the case of
the Hubble mission, which detected methane (CH4 ) and carbon dioxide (CO2 ) on the
GJ-1214 b iso-planets atmosphere (Kreidberg et al. 2014). Moreover, modelling studies
suggest the feasibility of detecting another biosignatures, such as sulphur and chloride
compounds from the secondary metabolism (Segura et al. 2005; Domagal-Goldman et
al. 2011; Rugheimer et al. 2013). With the incoming advances in space exploration
technics, the detections power as well as the range of biosignatures that we will be able
to detect will broaden (Schneider et al. 2010). Therefore, being life an extended phenomenon on earth and having the power to detect its traces through spectrometry, it
emerges the need of having a high resolution spectrometer in the space for the detection
of biosignatures on planets from the habitable zone.
The discarded TPF and Darwin missions were proposed to cover this need. The idea
was to send numerous spacecraft telescopes such as to create by interferometry a high
resolution spectrometer (Des Marais et al. 2002). The missions were aimed to detect
water (H2 O) as well as resolve the absorption profile of the metabolic gases oxygen (O2 ),
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ozone (O3 ), CH4 and CO2 (Des Marais et al. 2002). In the present work, we proposed
a modification of the TPF and Darwin original missions. Specifically, we propose new
planet targets, based on the data collected from Kepler and futures missions such as
TESS, as well as the detection of a broader range of biosignatures, not only gaseous but
also in the surface of the targeted planets. Aditionally, as we would have higher resolution, we also propose to accurately determine the planet rotational period and even to
map it by tomography.
In the next sections we will portray the design of our mission. We will first focus on
explaining the biosignatures that we aim to detect and the planet characteristics that we
aim to determine. Then, we will focus on the technical specifications necessary to achieve
our goals. Finally, we will go through several suggestions for future improvements and
alternative ideas about other projects.
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2 Biosignatures
We will detect biosignatures and/or combination of biosignatures following the criteria
of (1) do not naturally exist in the planetary atmosphere at ambient temperatures and
pressures, (2) are not produced and/or rapidly destroyed by photochemistry, (3) are
not created by natural abiotic processes, (4) have a strong spectral signature. Being
these criteria in agreement with Saeger et al. (2012). In parallel, we will check for the
presence of water in the planet. Water is not considered a biosignature, as it is not
produced by biotic process; however it is traditionally assumed to be essential for life
(Shapiro and Schulze-Makuch 2009). As biosignatures; we proposed to detect gases from
the primary metabolism: O2 , CO2 , CH4 and nitrous oxide (N2 O), but also -as a noveltywe propose to incorporate gases from the secondary metabolism: ethane (C2 H6 ) -as an
indirect measure of sulphur compounds- and methyl chloride (CH3 Cl). Along with the
detection of O2 we propose to detect O3 , which forms under the accumulation of O2
in the atmosphere and allows more robust results. In addition, we suggest checking for
the red edge effect as a surface biosignature, which would occur if earth-like plants are
present. Finally, we propose the detection of biosignatures associated with intelligent
life: sodium (N a+ ) and asphalt because street lights of citys and roads emit sodium
light while streets and buildings reflect the asphalt absorbtion spectrum. A summary of
the different biosignatures and the chemical reactions from which they are produced are
shown in table 1.
2.1 Detection of H2 O, O2 , O3 , CO2 , CH4 and N2 O
For the detection of these gases we need to look at the main visible and the infrared
spectra, in the interval from 0.5 to 25 µm approximately. Water does not present a
strong spectral signature, but with enough resolution it is possible to detect its peak at
6.3 µm (figure 1).
Oxygen is the most robust biosignature, at least on earth, properly fulfilling the outlined
criteria for good biosignatures (Seager et al. 2012). Oxygen is a ’unique’ biosignature
as it only derives from the biological process of photosynthesis. Moreover, under this
process it accumulates in great quantity in the atmosphere where it remains stable for
a long time. Finally, it present a strong spectral signature, showing 2 peaks in the
visible (0.69 and 0.63 µm), several in the infrared (0.76, 1.06, 1.27 and 1.58 µm) plus a
continuum range between 6-7 µm (figure 1). As an indirect measure of O2 , we will also
measure O3 , which present clearer spectral features with two peaks at 3.3 and 4.74 µm
(figure 1). Although the presence of oxygen is a strong indication of life, it is important
to take into account the levels of water. High levels of oxygen associated with saturation
levels of vapour water in the atmosphere would not be an indication of life but of an
abiotic runaway greenhouse process. In this process water is highly evaporated from
the oceans and it accumulates in the atmosphere where it is photodissociated in H and
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Biosignature
O2
CO 2
CH4
N2 O
C2 H6
CH3Cl
Red edge
N a+
Asphalt
The ExOoS Mission
Biotic production process
Oxygenic photosynthesis
H2 O + CO → Hydrocarbons + O
Respiration
CH2 O + O → CO2 + H2 O
Methanogenesis
Hydrocarbons + CO2 → CH4 + H2 O
H2 + CO2 → CH4 + H2 O
Nitrate reduction
N O3− → N O2− → N O → N2 O → N2
Sulfate and sulfur reduction
Sulphur compunds
→ CH3 compounds → C2 H6
Hydrocarbon synthesis
CH3 Cl + Cl → HCl + Cl
Earth-like deciduous plants reflectivity
between 0.7 and 1 µm
Human-like artifitial lighting
Human-like roads
Abiotic process production
Present in the atmosphere
Volcanism
Inorganic CH4 production
CH4 → CH3 → C2 H6
Table 1: Biosignatures proposed and their production process.
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The ExOoS Mission
O2 , leading to the observed O2 build-up. On contrary, high levels of O2 associated with
very low levels of H2 O would be observed in dry, CO2 -rich planets in which there are
few geochemical sinks for O2 and thus O2 accumulates in the atmosphere (Seager et al.
2012).
N2 O is considered also a reliable biosignature as it comes from bacteria denitrification
(Seager et al. 2012). However it has a very weak spectroscopic signature which, besides,
overlaps with the water absorption profile. In addition, recent works argue that it can
be produced by nonbiological processes (Samarkin et al. 2010). In this case, spectral
peaks can be observed at 2.9, 4.1 and 4.5 µm (figure 1).
CO2 and CH4 comes from the aerobic respiration, however they are not unique biosignatures as they are also produced in geological and photochemistry reactions. CO2 gas
present several absorption peaks at 1.4, 1.6, 2.0, 2.7 and 4.3 µm (figure 1). CH4 is produced by methanogenic bacteria but it can also come from volcanism. In this case, the
absorption peaks are present at 1.7, 2.2 and 3.3 µm (figure 1).
2.2 Detection of C2 H6 and CH3 Cl
Sulphur compounds come from the anaerobic sulfate-reducing metabolism, which is
widespread in the marine environments of our planet. However, sulphur compounds
(e.g H2 S) have been discarded as biosignatures as a large quantity of them comes from
abiotic processes (e.g volcanism) and they do not present a strong spectral signature
(Domagal-Goldman et al. 2011; Seager et al. 2012). Interestingly, in a recent modelling
study conducted by Domagal-Goldman et al. (2011), the authors propose the comparison of C2 H6 and CH4 levels as an indirect indication of organic sulphur compounds
production. In several simulations they observed that an increase in organic sulphur
compounds was associated to a high increase of C2 H6 up to detectable levels across
interstellar distances. C2 H6 indirectly derives from organic sulphur compounds but it
also derives from CH4 , which can have a biological or non-biological origin. Thus, a high
C2 H6
CH4 ratio would be an indication of organic sulphur compounds production. The detection of C2 H6 would be achieved through its spectral signature between 11 and 13 µm
(figure 2).
Methyl chloride is produced in the hydrocarbon biosynthesis and has also been recently
propose as a potential biosignature (Segura et al. 2005; Rugheimer et al. 2013). In this
case, methyl chloride is a unique biosignature as oxygen and nitrous oxide, but it has a
very week spectral signature, extending from 3 to 4 µm (figure 3).
2.3 Red edge measurement
This potential surface biosignature was first proposed by Seager et al. (2005). The
’red edge’ is the increase in leaf reflectance in between 0.7 and 1 µm that appears in
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Project Report SAC Summer School
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Figure 1: The high resolution spectra of the major atmospheric gases (by Sokolok, 2008)
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The ExOoS Mission
Figure 2: Absorbtion cross sections for the gases included in the spectral model of DomagalGoldman et al. (2011). It is marked the spectral signature for C2 H6 in the interval
10-15 µm.
Figure 3: Relative absorbtion of CH3 Cl derived from the model of Rugheimer et al. (2013).
the deciduous plants spectrum. This increase is due to chlorophyll, which absorbs at
ultraviolet and visible wavelengths, thus reflecting at near-IR wavelengths (figure 4).
Currently, the ’red edge’ measurement is used in remote sensing to study the state, type
and distribution of the different plant species on earth’s surface. In the study of Seager
et al. (2005), the authors states that the TPF and the Darwin missions would be able
to detect this signature. Furthermore, the leaf reflectance spectrum shows a bump at
0.5 µm, also due to the absorption spectral range of the chlorophyll, and several water
absorption bands (figure 4). With enough resolution, it would also possible to measure
these spectral signatures.
2.4 Detection of sodium and asphalt
Street lamps and a great part of other artificial lighting systems are made of sodium. It
could be that hypothetical developed civilizations in other planets were using lighting
sources similar to ours. Sodium is a common element on earth, thus its sole detection
would not be a biosignature. However, an increment on the sodium signal or a shift in
its distribution on the planet from the day to the night-time could be a sign of artificial
lighting. An important problem to take into account is that the artificial lights might
be made from another material or, as it happened on earth with the development of
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Project Report SAC Summer School
The ExOoS Mission
Figure 4: Increase in the refelcetance between 0.7 and 1 µm. It is also noticeable the chlorophyl
bump at 0.5 µm. (Seager et al 2005)
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Figure 5: Absorbtion spectrum of sodium.
leds, the material might have changed even when it was sodium in the first place. In
any case, we think that it would be really interesting to track the sodium spectrum
changes. The spectra signature of sodium present two peaks very close to each other; at
5.890 and 5.986 µm (figure 5). To distinguish between these two peaks we would need
a resolution of at least 10−3 , which is a very high value for remote sensing. However,
advances in technology and the use of interferometry might allow reaching this resolution. Moreover, under this resolution it would be possible to resolve the spectra of the
biosignatures proposed above and asphalt. Asphalt would be another interesting marker
for extraterrestrial intelligence, in this case surface signature of earth-like developed civilizations. Roads on Earth are made of this material and there are even studies of the
type of asphalt and/or their age based on their different spectral signatures (e.g Herold
and Roberts 2005). In this case, the spectral signature extends from 10.7 to 11.24 µm
with two peaks, from 11.97 to 12.34 µm also with two peaks and from 12.7 to 13.25 µm
with one peak (figure 6). An important issue is that due to the detection distance these
peaks would be probably lost, although the high resolution required for the detection of
the sodium might be sufficient to detect them.
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The ExOoS Mission
Figure 6: Absorbtion signature of asphalt. (Chang 1998)
3 Targets
To search for biomarkers, the ExOoS Mission will target 5 different stars for 3 years
each. The three year coverage provides three cycles in the planets seasons for a planet
with a one year periode and increases the overall photon count to get a better signal to
noise ratio.
The targets will be selected very carefully to get the highest chance for the mission to
find life. Therefore the planet and the star have both to full fill certain criteria. First of
all, the planet has to orbit its star in the habitable zone. The habitable zone is defined
as the area in which water can occur in liquid stable form on planet surfaces. Therefore,
this area must receive a stellar photon flux such as this flux provides enough energy for
water molecules not to freeze out and, at the same time, this energy is low enough so the
surface water does not boil away and the planet can have a water vapour atmosphere.
The second criterion is the size of the star. The spectral type has to be a early K-star
at least, preferably a G-star. This is why for smaller stars the habitable zone is much
closer to the star. However, for close distances the tidal interactions between the star
and the planet become strong. Therefore, for later stars, the planets in the habitable
zone get tidally locked. Since we want to map the planet and use its rotation, we need
a non tidal locked planet.
Furthermore the star should not be too big. Because of the technique to measure the
planetary day night cycle, we need a slow rotating star compared to the planetary
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rotation. Larger stars usually have smaller rotational periods, so basically we want the
star to be as small as possible, where the lower border is defined as the one in which the
planet gets tidally locked.
To illustrate the range of targets which full fill these criteria, the mass of the star is
plotted against the distance of the planet. (See figure 7) The yellow area resembles the
habitable zone, while the dashed line marks the border of the zone where the planet
gets tidally locked. The targets and their basic parameters will be determined by next
decades space telescopes such as the JWST, TESS or Plato.
Figure 7: The stellar mass in solar masses versus the planets distance from the star.
The border for tidal lock and the habitable zone are marked.
( from
http://www.daviddarling.info/encyclopedia/H/habzone.html)
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Figure 8: The planet spins around its axis. The stellar light is reflected from the planets surface
while the spectrum depends on the surface and atmospheric features.
4 Techniques
4.1 Planet Tomography
Once the rotational period is determined by fitting, the planet can be “mapped“. The
technique used here is called planet tomography. While the planet spins around its own
axis the telescope sees the same side reflecting the stars’ light after every period. This
means that spectral features like oceans or landmasses with or without vegetation will
be visible depending on the observation time. Phase folded with right period we get a
infra red spectra and a visible light spectra. See figure 8.
The goal is to ”map“ the planet in 1-D with a precision ∆l of
∆l =
1h
Pplanet
2πrplanet
(1)
in geographical latitude. This precision depends strongly on the data gathered. In principle every precision lower than ∆l can be achieved by binning. This will increase the
signal to noise ratio although we have to take into account that the map will become
less accurate.
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Figure 9: The fictional planet surface consitst of 50% water and 50% rocky material. This should
change the spectrum of the planet, depending on the visible side. For positions near the
transit the reflecting area becomes smaller.
To illustrate the influence of the surface features we create a fictional planet. One side
is covered with an ocean, the other side is a barren rocky world (See fig. 9). When the
planet spins around its axis, we can see the spectrum of a water world to slowly change
into the spectrum of a barren planet. Depending on the position of the planet with
respect to its star the reflecting area can become very small, thus the spectrum would
change faster.
If the data are binned in the right order one can get information not only about the surface features but also about seasonal changes or the weather. In general, for example,
clouds can have a huge impact on the spectrum because they can drastically change the
planets albedo.
4.2 Determining the Planetary Rotational Period
To achieve the goal of mapping the planet, the Telescope has to add up many measurements, because the number of photons it receives from the planet is very low. To add
up the correct time sections, the spectra will be phase folded with the planets rotational
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Figure 10: One side of the planet reflects red shifted light, the other reflects blue shifted light. The
rotational period measurement is finished after half a year.
period. But getting the period is a very difficult task, too.
When the observer sees the planet at the greatest distance in respect to the star, one sees
exactly the half of a disk. The stars’ reflected light from this disk shows a red shift or a
blue shift depending on the rotational velocity of the planet. (See figure 10) When we
meassure the doppler shift at this particular position and then we meassure again half
a year latter, we can obtain the rotational velocity and the direction of the rotation of
the planet. With the data of the rotation and the planet radius we can then determine
the period of the day night cycle.
∆λ
v
=
λ
c
ω =v×r
(2)
(3)
Resolving for ω gives us
∆λcr
.
(4)
λ
The difficulty in the procedure is the ultra high resolution, which is needed to resolve
the Doppler shift of the planets surface. If we assume the planet has a rotational speed
of 1000 m/s, the Resolution needed would be
ω=
R=
v
1000
=
≈ 10−6 .
c
3 × 108
(5)
This broadening applies to the already broadened spectral lines of the stellar light due
to the rotation of the star. Because of that, the target planets must orbit slow rotating
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stars compared with their own rotation. To get very sharp lines, the determination of
the period will be done with the stellar spectrum reflected by the planet.
4.3 Problem
The technique of planet tomography has a weakness. If the observed planets rotational
axis is tilted by a high inclination and the axis lies near the line of sight, the observer
would always look at the same side of the planet and only seasonal changes can be observed. Such a planet can be found in our solar system. Neptune has an inclination of
its rotational axis of 97.77◦ . This example shows that such a inclination can exist, so
this can be a serious problem for the mission. As soon as this is noticed the target might
be changed to a backup target.
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5 The Instrument: OCTO-JWST-TPF-I
A space mission with the ambitious goal of mapping a planet, tough the mapping is done
in an unusal way, has to fullfill certain requirements. These requirements come from the
large distance to the observed system and the fact that a planet is very faint compared
to its star.
5.1 Interferometry
Getting photons from the planet is a very difficult task because of the huge distance
from the sun to the host star and the small distance of the planet to its star. When
just imaged with an ordinary telescope, the planet would vanish in the light of its host,
because the star is much brighter. In order to get rid of the stellar light we choose the
mission to be an interferometry mission. Therefore the distance between two interfering
telescopes is set by the geometrical properties of the observed system.
The Kepler data suggest that the nearest earth like planet will be round about 10 parsec
away from us. Assuming that the observed star is a G-star like the sun, the orbital
distance of the planet to the star would be 1 AU.
The detection resolution would be
λ
R=
(6)
b
where R is the distance between the planet and the star divided by the distance of the
sun to the star, λ is the observed wavelength and b is the baseline of the interferometer.
5.2 Mirrorsize
The number of photons arriving to the OCTO-JWST-TPF-I can be calculated with the
Planck function
2hc2
Bλ (T ) =
(7)
hc
λkB T
5
λ e
−1
where λ is the observed wavelength, h the planck constant, c the speed of light and T
the temperature of the observed object.
We assume that the planet will emit light in the infra red with the black body temperature of 300 K and that it will reflect the stellar light with an albedo of 0.184, which is
the half of the earth. This number is assumed because we expect the planet to reflect
just with one half of its visible disc and 0.367 is the albedo of the full earth. Therefore,
the reflected light contains the black body radiation of the stellar light as well. We also
assume the star to be sun like, so it emits at a temperature of 5778 K. The total amount
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of energy emitted per second, square centimetre, Hertz and steradiant can be calculated
by
2
rplanet
2
Btot = Bλ (300K) + Bλ (5778K) ×
× 0.185 × 10−4 4πrsun
.
(8)
4(1AU )2
2
The factor of 10−4 4πrsun
is due to the size of the star since the Planck function assumes
a black body with a surface of 1 cm2 .
Furthermore we assume the planet to be of the same size as the earth and so it has a
radius of 6371 km.
Now we resolve the equation
c
nh = Btot (λ)
(9)
λ
for n within the observed wavelength range from 200 nm to 25 µm in steps of 1 nm and
get the photon number n. For black bodys the signal to noise ratio is calculated with
√
S
= n.
N
(10)
Now, with a ratio for the mirror size and the surface of a sphere around the star with
an radius of 10 parsec, we can calculate the number of photons arriving to the telescope.
The result is that only several tens of photons will be detectable within a wavelength
range of 1 nm and a time interval of several hours, which shows the need of using an interferometer to distinguish between planetary and stellar photons. Then it is possible to
build up a good spectrum with a high signal to noise ratio during many hours. Another
advantage of an interferometric space telescope is the increased photon collecting area
due to the multiple mirrors.
Because the JWST will fly soon and the OCTO-JWST-TPF-I will fly after it, we decided
to select the mirror of the JWST as a model. With its 6.5 m mirror the interferometer
will be able to detect enough photons from a planet to get a signal to noise ratio better
than 15 at the infra red spectrum and a signal to noise ratio better then 10 at the visible
spectrum. This would be for an interferometer consisting of eight units in which each
unit has a JWST mirror mounted. These units would target to planets orbiting its stars
at 1 AU and at a distance of 10 parsec far away from to the sun.
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6 Future Perspective and Alternative Ideas
6.1 Incorporation of more biosignatures
An interesting idea is spectropolarimetry, consisting of detecting the polarization changes
of the reflected light from iso-planets when it crosses the atmosphere (Sterzik et al. 2012).
The changes are associated with the surface characteristics and the gaseous composition
of the atmosphere of the planet. The detection of these changes would add valuable
information about the different biosignatures to the information already obtained from
the absorption spectrum. For example, this technique has been applied on Earth, being
possible to detect the plant coverage. With a longer integration time in the observation
of the targeted planets it might be possible to apply this technique in the space. Also,
with higher spectroscopy resolution we could try to detect isotopic fragmentation on
essential elements such as carbon (C) and nitrogen (N ). Isotopic fragmentation occurs
when there is a significant higher abundance of one isotope over the others from the same
element, and it is usually associated with biological activity. For example, N 1 5 and N 1 4
are both stable isotopes. However, N 1 4 is preferably fixed and produced by organisms
and thus its abundance is higher. In this regard, recent studies on earth (e.g Elmore and
Craine 2011) applies remote detection of N 1 5 and N 1 4 to estimate broad plant coverage
distribution. Finally, it could be interesting to incorporate the detection of gamma rays
as another biosignature of human-like developed civilizations. High radiation of gamma
rays would appears in nuclear contamined worlds, due to a nuclear war probably followed
by a total destruction of the civilization. In fact, nuclear destruction is a parameter that
appears indirectly in Drake’s equation
N = R∗ fp ne fl fi fc L,
(11)
where fi is the number of intelligent life forms in the milky way. If we find worlds with
high gamma radiation, we could estimate how common planetary wars are in the galaxy
and how long the average lifetime L of a civilisation is.
6.2 Increase in resolution: Gravitational lensing
To get a very high magnification of signals Frank Drake came up with the idea of using
the sun as a gravitational lens in 1988 at a IAU conference. We wanted to take a step
further. The idea is to put the OCTO-JWST-TPF-I into the focal sphere of the sun, so
we could observe planetary surface features in detail. This idea did not made it to the
main topic because of the horrendous cost to send a spacecraft (or multiple space crafts)
to the orbit of approximately 550 AU around the sun.
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6.3 Alternative Ideas
We came up with some additional ideas about planning a mission for exoplanetary
research. Some of them are worth to mention within this report.
6.3.1 Rouge Planets
Simulations show that planet migration of gas giants can kick out very easily smaller
terrestrial planets. With a high chance of getting kicked out the planets have to float
around in the interstellar space until they are captured by a star. Such a planet would
emit light corresponding to its temperature. To look for them the idea is to observe a
very empty region of the sky and to search for infra red light. Since several programs
failed to find Dyson spheres, we did not decide to do this project.
6.3.2 Free-floating Life Forms
When life is generated everywhere, where it can be generated, why not in interstellar
molecular clouds?Maybe the energy produced in a contracting cloud can be enough for
life to emerge and be mantained. But without any idea about how to measure or to find
such lifeforms, this idea was rejected very early.
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7 Conclusion
In conclusion the project is planned after the next great generation of space telescopes.
This includes the James Webb Space Telescope and PLATO. We assume the OCTOJWST-TPF-I to be build in the early 2030s. It is designed to find a valid proof of existing
life on exoplanets via biomarkers and to get the first ”map” of an extrasolar planet.
Therefore the mission uses the new technique of planet tomography, where the rotation
of the planet is used to get time resolved spectra of a planet. The technique was never
used before and yet no mission is designed to use it in the future. Additionally this is
a chance to test the often simulated atmospheres of exoplanets. So with the results of
this mission the great question ”Are we alone?” might possibly and finally be answered
after thousands of years of wondering.
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