1 Detecting Biosignatures of an Evolving Earth-like Atmosphere via New Worlds Observer Julia DeMarines University of Colorado newworlds.colorado.edu AbGradCon 2008

2 Abstract extrasolar planets have been found –1 has been imaged New Worlds will be able to image and take spectroscopy of the atmospheres of extrasolar planets What would an Earth look like if viewed at different points in its history via NWO? Biosignatures (such as CH 4 and O 2 ) could be detected as early as ~1.0 Gyr after planets formation! This is useful because we will be looking at stars of all ages, this planets in different stages of evolution

3 Early life may have been Methanogens –Early organisms may have utilized methanogenisis as a metabolic process which produces CH 4 (Schindler and Kasting 2000, Walker 1977). –The major influence of methane on the atmosphere may have begun almost as soon as life originated more than 3.5 billion years ago (Kasting & Siefert 2002; Ueno et al. 2006; Canfield 2006). Methanogens are believed to have produced methane levels roughly 1000 times that of today. Most of the methane in our atmosphere is produced by biological activity –The primary sources of Methane in our atmosphere is biological (Watson et at. 1990), although a small amount of CH 4 is from volcanic outgassing at mid ocean ridges (Schindler and Kasting, 2000, Welhan 1988, Kasting and Brown, 1998). Life may have began as early as 3.9 billion years (Mojzsis et al. 1996), possibly even photosynthetic life, but any O 2 would have reacted with volcanic gases (Schindler and Kasting, 2000).

4 Planet Detection Methods Doppler shift Transit Gravitational Microlensing Direct imaging

5 New Worlds Observer

6 As of February 2008, New Worlds was selected for an Astrophysics Strategic Mission Concept Study by NASA –With the purpose of preparing for the decadal review Mission conceived by Dr. Webster Cash of CU Starshade: –Occulter that suppressed the light from the star so the light reflected from the small terrestrial planets are visiable Current parameters: –16 petal 50m starshade –4m diameter telescope (or greater) –Over a hundred really good target stars in 20 parsecs –Spectra graph in the visible wavelength

7 Planet Hunting Candidate Star Region

8 4m telescope10m telescope16m telescope Courtesy of Phil Oakley

9 Lenton et al A) no oxygen produced by biosphere B) oxygen produced, but absorbed in oceans and by seabed rock C) oxygen starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer.

10 Kaltenegger et al. 2007

11 The Data I chose to use the atmospheric compositions at six different points (or epochs) in Earths history Data from Kaltenegger et al Epoch Time ( G y r )N2CO2O2CH4 O3, N 2 O a n d t r a c e e l e m e n t s %10%0%0.00%0.10% %1%0%0.20%0.98% %1%0.02%0.70%0.28% 3298%1%0.20%0.40% %1%2%0.04%0.46% %0.04%21%0.00%0.96% Epoch Time (Gyr)N2CO2O2CH4 O3, N2O and trace elements %10%0%Trace0.10% %1%0%0.20%0.98% %1%0.02%0.70%0.28% 3298%1%0.20%0.40% %1%2%0.04%0.46% %0.04%21%Trace0.96%

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13 The Code In collaboration with Giada Arney and Phil Oakley, supervised by Web Cash, we generated codes that simulate planets atmospheres via NWO Used spectral signatures of Sun and planets –reflectance of Earth Modeled at 10 parsecs Added exo-zodiacal light – subtracted background

14 White dotted line – Spectrum from planet Green line – Actual spectrum Red line – Fit to methane line at.725 microns CH 4 Based on current amounts of CH4 in Jupiter ~ 0.3%

15 CH 4 band at 730nm Resolution 100 Time 10 6

16 CH 4 ?

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18 False Positives Venus-like planet –Losing water due to run away greenhouse –Hydrogen escapes over <10 7 years –O 2 could build up to bars before reacting with surface –Would occur just before the inner edge of the habitable zone

19 False Positives Mars-like planet –Too small to maintain volcanism and too cold to have liquid water –O 2 production from photodissociation of H 2 O –Lighter H 2 escapes atmosphere leaving O 2 –Would occur just beyond the outer edge of the habitable zone

20 False Positives Ice World –“Oxygen having a nonbiological origin can accumulate on a large ice-bound planet.” (Kasting, 1997; Des Marais, 1997) –Ice prevents it from being absorbed by surface rock –However, larger planets likely have volcanic exhalations with chemicals that reduce –Such gasses would remove nonbiological oxygen Des Marais et al. 2002

21 Conclusion We can see the Methane band at.725 microns at only 0.2% of the total atmosphere and the Oxygen band at.761 microns at >2% of the total atmosphere –This corresponds to being able to detect a biotic planet at a lower limit of ~1.0 billion years after formation! “There may be only a very small range of planetary conditions that might produce a false positive answer for oxygen.” (Des Marais et al. 2002)

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