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View Full Version : Finding Alien Life via Spectroscopy - Dr. Isrealian



iquestor
2013-Sep-30, 01:27 AM
Recently in several threads discussing the possibility of finding alien biospheres using spectroscopy I have referenced Dr. Garik Isrealian's 2009 TED Talk (http://www.ted.com/talks/garik_israelian_what_s_inside_a_star.html)(first introduced to me by A. DIM) .

Since that was in 2009, I was wondering what progress we have made, and what Dr. Isrealian's thoughts were on the subject, in light of recent developments and the data returned by Kepler.

So, I emailed him and he was kind enough to answer my questions, the details are below:

Q: In the TED Talk you said you felt that we could possibly find alien life through spectroscopy in the next 15 or so years. Based on the data returned from Kepler, do you still feel that is possible?


A: Absolutely. NGST could get close , but we need a good instrument and camera.

Q: Do the data returned from the Kepler mission (and other planet finding missions or efforts) on earthlike worlds give us enough information to begin analyzing the spectra of their atmosphere once the technology to do so is in place?


A: Its hard to say. If we focus on Earth-twins around solar-twins, maybe not. But if we open the door wide, and look for other
systems in habitable zones, maybe we will have a chance. At least we know how to do it, and at least there are potential targets and
tools are there too. So i would say its a "question of time" to find not only biomarkers (biospheres around other planets), but also
markers which may indicate intelligent life (e.g. artificially produced spectral features in the atmospheres of planets, or in their
host stars).

Q: Are there any currently planned missions which could determine the presence of O2/O3, Ch4 and N2O in the atmosphere of an earthlike planet?


A: People are trying to detect more simple molecules like CO2 in transiting planets using ground spectrographs. However, sooner or
later we need to make this from space in the near infrared region of the spectra (this is where most of the molecules are found).
But for this, we need large mirrors in space, excellent infrared cameras and spectrographs. NGST* will have a near infrared spectrograph and will try to observe biomarkers. We keep fingers crossed ! I was in touch recently with John Mather (http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhonebookId=11051)and he is optimistic.

[* I assume he means the James Webb Space Telescope on which Dr. Mather is Senior Project Scientist]

Q: The Galileo Mission was able to analyze earthshine and determine life processes by seeing the spectra for these elements, and also directly for vegetation based on how chlorophyll works; If alien vegetation used some type of photosynthesis, would we be able to determine that via spectroscopy.


A: I think we can. Any spectral anomaly will be noticed. We know more or less what do we expect from normal earthshine (pr exo earthshine)
spectra. So any strange and new features, and spectral anomalies will be detected immediately. Again, i am very optimistic
about this strategy.

Noclevername
2013-Sep-30, 01:32 AM
I can see at least one major flaw in the idea: The method described detects anomalies. The only planet we know of in a habitable zone has life, so we know nothing about the exochemistry of non-biotic planets in habitable zones. So how would we know what is anomalous? You could get a lot of false positives that way.

iquestor
2013-Sep-30, 01:35 AM
I can see at least one major flaw in the idea: The method described detects anomalies. The only planet we know of in a habitable zone has life, so we know nothing about the exochemistry of non-biotic planets in habitable zones. So how would we know what is anomalous?

I think he is referring the the spectral lines we might find which doesnt fit with known molecules or elements, which, taking into account other factors we know about the target system, might indicate some type of photosynthetic processes. We see the same type of anomalies with earthshine which is caused by chloraphyll/photosynthetic plants.

Noclevername
2013-Sep-30, 01:41 AM
But how does the observer distinguish biological photosynthesis from a non-biological photo-reactive chemical?

ravens_cry
2013-Sep-30, 02:54 AM
But how does the observer distinguish biological photosynthesis from a non-biological photo-reactive chemical?
Finding a none biological free oxygen atmosphere would be still a very interesting discovery.

Noclevername
2013-Sep-30, 03:15 AM
Finding a none biological free oxygen atmosphere would be still a very interesting discovery.

I agree, it would.

However, there's several kinds of photosynthesis here on Earth, and not all of them produce free oxygen. For example, purple sulfur bacteria (http://en.wikipedia.org/wiki/Purple_sulfur_bacteria). All sorts of other chemical reactions may occur, especially in an alien environment. http://en.wikipedia.org/wiki/Photochemistry
http://en.wikipedia.org/wiki/Anoxygenic_photosynthesis

Selfsim
2013-Sep-30, 03:41 AM
On top of the issues raised in this thread, (http://cosmoquest.org/forum/showthread.php?146109-Drake-Equation-Revisited&p=2158087&highlight=isrealian#post2158087) I'd also like to know how he plans to distinguish the absoption spectra caused by an exo-planet's atmosphere, from other gas/debris clouds within, (or outside of), that exo-planet's system, which may also be co-incident along the line of sight?

There are also observation/integration time vs viewing window issues, which would either allow or not allow for detection of exo-atmospheres. Much of this is dependent on the occultation/transit time.

Selfsim
2013-Sep-30, 03:51 AM
The more I think about this technique, the more it becomes apparent that his prediction seems more dependent on an optimistic belief about the prevalence of exo-planets capable of exhibiting 'anomalous' spectra (of interest) from Earth's viewpoint, than on the actual viewing technology of say, the JWST, (or NGST).

iquestor
2013-Sep-30, 10:59 AM
The more I think about this technique, the more it becomes apparent that his prediction seems more dependent on an optimistic belief about the prevalence of exo-planets capable of exhibiting 'anomalous' spectra (of interest) from Earth's viewpoint, than on the actual viewing technology of say, the JWST, (or NGST).

I think he is optimistic, however he is also highly educated and has been working in spectroscopy for a very long time; perhaps he has reason to be optimistic? I hope so . I guess we can get some more answers IF JWST Launches in 2018.


There are also observation/integration time vs viewing window issues, which would either allow or not allow for detection of exo-atmospheres. Much of this is dependent on the occultation/transit time.

This is probably why he pointed out finding an 'earth twin around a solar twin' wasn't going to happen soon; transit times and windows are much smaller .

ravens_cry
2013-Sep-30, 01:35 PM
I agree, it would.

However, there's several kinds of photosynthesis here on Earth, and not all of them produce free oxygen. For example, purple sulfur bacteria (http://en.wikipedia.org/wiki/Purple_sulfur_bacteria). All sorts of other chemical reactions may occur, especially in an alien environment. http://en.wikipedia.org/wiki/Photochemistry
http://en.wikipedia.org/wiki/Anoxygenic_photosynthesis
So it's something to look at closer with our next generation or so of instruments and not a sure fire 'ding' for life.
Fair enough.
When we get the ability to construct things in space from raw material, we could have telescopes in space so large they would collapse on Earth and not survive launch.
What eyes we will have then!

iquestor
2013-Sep-30, 01:50 PM
So it's something to look at closer with our next generation or so of instruments and not a sure fire 'ding' for life.
Fair enough.
When we get the ability to construct things in space from raw material, we could have telescopes in space so large they would collapse on Earth and not survive launch.
What eyes we will have then!

I for one would rather see some Planet finding missions (with the discussed capabilities) launched even more than manned Mars missions.

ravens_cry
2013-Sep-30, 07:55 PM
I for one would rather see some Planet finding missions (with the discussed capabilities) launched even more than manned Mars missions.
The two are not mutually exclusive. A trip to Mars would be well served to use ISRU in my opinion. From that, admittedly, small beginning, we could get to a real manufacturing capability in space, and from there we could get space structures that are truly born in space, unfettered by gravity.

Selfsim
2013-Oct-01, 03:45 AM
So these guys have developed a theoretical model for studying what would happen to biomarkers in the remotely sensed spectra of Earth-like exo-planets, as a result of cloud cover:

"Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars" (http://www.aanda.org/articles/aa/abs/2013/01/aa19898-12/aa19898-12.html), M. Vasquez, F. Schreier etal. Jan 2013 A&A.

Its quite an interesting up-to-date read on the general topic of remote biosignature detection, but one section stood out for me:
The planet around the G-star could be considered as an Earth twin, whereas similarity to Earth conditions for F-, K-, and M-star planets could only be achieved by scaling the distance in order to assure similar incoming “solar” energy, thereby achieving moderate Earth-like surface conditions. However, upper atmospheric conditions are significantly different from Earth, such as for the lack of an inversion for the M-star planet or the high stratopause temperatures for the F-star planet. This restriction to Earth-like planets is in line with most papers investigating the spectral appearance of exoplanets and the detectability of biosignatures (see Sect. 1). Clearly it would be interesting to study radiative transfer for a much larger class of exoplanets. However, the actual state of numerous exoplanets discovered in recent years is likely to be way beyond our imagination, and defining atmospheric scenarios (using coupled radiation convection – chemistry models) required as input for radiative transfer modeling could easily become speculation.Nice to see some folk at least taking note of the most notable feature of all. (Which of course, also highlights the 'likely' futility of attempting to make predictions about what might lay ahead).

They also make the point that knowledge of atmospheric temperature profiles is essential for estimating the composition of an exo-atmosphere, and important for avoiding false negative detection of 'biomarkers'. They say that the CO2 bands however, allow temperature estimation from the upper stratosphere down to the troposphere, even in the presence of clouds.

Other 'biomarker' detection of: O3, N2O and CH4, depends on the cloud levels. (They assume the clouds are either liquid water, or water ice particle based only).

Interestingly, they also make the point that thus far, attempts at remote detection of exo-planet spectra (for HD 189733, HD 209458 and the super-Earth GJ1214b), have resulted in 'featurelessness'.

iquestor
2013-Oct-01, 12:51 PM
So these guys have developed a theoretical model for studying what would happen to biomarkers in the remotely sensed spectra of Earth-like exo-planets, as a result of cloud cover:

"Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars" (http://www.aanda.org/articles/aa/abs/2013/01/aa19898-12/aa19898-12.html), M. Vasquez, F. Schreier etal. Jan 2013 A&A.

Its quite an interesting up-to-date read on the general topic of remote biosignature detection, but one section stood out for me:Nice to see some folk at least taking note of the most notable feature of all. (Which of course, also highlights the 'likely' futility of attempting to make predictions about what might lay ahead).

They also make the point that knowledge of atmospheric temperature profiles is essential for estimating the composition of an exo-atmosphere, and important for avoiding false negative detection of 'biomarkers'. They say that the CO2 bands however, allow temperature estimation from the upper stratosphere down to the troposphere, even in the presence of clouds.

Other 'biomarker' detection of: O3, N2O and CH4, depends on the cloud levels. (They assume the clouds are either liquid water, or water ice particle based only).

Interestingly, they also make the point that thus far, attempts at remote detection of exo-planet spectra (for HD 189733, HD 209458 and the super-Earth GJ1214b), have resulted in 'featurelessness'.

Selfsim thanks for the link. Im looking forward to reading it on my lunch break :)