How can we detect life on extrasolar planets?

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Table of Contents

Abstract
Introduction
The habitable zone
Methods of Detecting Extrasolar Life and Their Limitations
Proposed solutions for extrasolar life detection
Conclusion
Works Cited

Abstract

Extrasolar planets are planets that are found outside the solar system. Mathematical probability shows that some of these planets may contain life. However, this needs to be proven using credible scientific evidence. The current scientific methods to search for extrasolar life heavily depend on telescopes. The available telescopes however are not big enough to provide the necessary precision needed to detect signs of life on extrasolar planets. By February 2010, no signs of extrasolar life had been detected.

Introduction

The increased detection of extrasolar planets has led to a lot of optimism on the existence of extrasolar life (Bekwith, pp 1). It has acted as an incentive to search for life in other galaxies. Extrasolar planets are planets found outside the earth’s solar system and extrasolar life is therefore the life found on such planets.

The possibility of having extrasolar life is just hypothetical and no scientifically credible proof has been put forward. In fiction, life on other planets is shown to exist and this has led to a lot speculation from majority of human beings. Stories of disappearances, unidentified flying objects (UFOs) and mysterious green organisms find their way into public media.

Detecting life on extrasolar planets is not an easy task. It has many limitations and major technological advancements are still required. This research shows that the current techniques and available equipment cannot detect extrasolar life. However, plans by space exploration bodies are promising to shed more light on the issue in the coming few decades. This will revolutionize the current scientific and religious believes.

The habitable zone

Searching for signs of life cannot be done haphazardly; a target approach must be employed. A home for the life must be detected (which is the planet) and signs of life on that home are searched.The planets are commonly detected using indirect methods (astrometry, radial velocity or Doppler method, circumstellar disks, pulsar timing, eclipsing binary, and gravitational microlensing) and direct imaging (“Space science”).

Life in these planets can take many different guises and this makes the basis of their detection quite complex. It is therefore logical to first search for signs of life that are similar to those on earth. The habitable zone is the region occupied by a planet that is similar to that occupied by earth in relation to the sun.

Searching for signs of life on all detected planets is not feasible. A criterion is needed to determine the candidates that can possibly support life. Life as we know it can only occur within a certain zone around the mother star (a main sequence star), the habitable zone.

It is important because around this region, the temperatures are around 273K and 373K (Beckwith), which is necessary but not sufficient for the support of earth like life. At these temperatures, water is in a liquid phase. The temperatures are determined by the distance of the planet from the star, which gives the planet warmth. After detection of the planet, it is analyzed for signs of life.

Methods of Detecting Extrasolar Life and Their Limitations

In the solar system, scientists detect life using direct and indirect methods. In the direct methods, the scientists search for forms of life on the planet by direct imaging. Direct observation of the extrasolar planets is difficult due to their low light reflection and proximity to their stars, which are brighter than the planets (Beckwith, pp 2).

The star light therefore creates a glare that washes out the planets light. Another direct method is the monitoring of radio frequencies in space by organizations such as SETI (search for extra-terrestrial intelligence). This method has been used in the search for intelligent life.

Monitoring for radio signals from other extraterrestrial civilizations is not a very promising method due to the great distances between earth and the extrasolar planets. The nearest extrasolar planet is 10.5 light-years from earth. Radio communications between such distances would take too long. This is further limited by the fact that the life on such planets must be intelligent life that is using the same radio signals for communication.

Therefore, these direct methods are more productive for planets that are in the earth’s solar system such as Jupiter, mars and Venus. For planets outside the solar system, they are not very efficient and application of indirect methods is necessitated.

The most productive indirect methods involve telescopic analysis of the extrasolar planets’ atmospheres for the basic molecules of life (methane, oxygen, carbon dioxide, and water). These compounds were detected in the atmospheres of two extrasolar planets. However, the physical conditions of the planets cannot support life for they are hot gases. In the current search for life on extrasolar planets, ‘life’ refers to carbon based organic life whose survival depends on water (Beckwith).

For a planet to support this kind of life, it must meet two main conditions: it must lie within the habitable zone of its solar system (where the water is in liquid form) and it must retain an atmosphere (it is rocky). Mathematically, there is a high probability of existence of such planets within the habitable zone but detecting them remains to be done (Bell, para 6). This is because, the resolution of the current generation of telescopes is not high enough to detect and analyze planets near a star and those similar to earth in size.

Many extrasolar planets have been detected with Doppler method being the most productive technique. However, the extrasolar planets detected using Doppler method do not fall within the habitable region of the main sequence stars.

They are mainly large gaseous planets that cannot support life although two of them were found to contain compounds that are some of the ‘markers’ of life; these were water, methane and carbon dioxide. All these planets apart from twenty-five of them are 10 times the size of earth with most of them being larger than Jupiter, the largest planet in the solar system. This further clarifies that technologies developed so far are unable to detect smaller planets.

Large planets are most likely to be gaseous and therefore their surface temperatures are too high to support life, as we know it (Kleefman). Apart from the Doppler method, other indirect methods have also detected huge planets with the same characteristics; they are not rocky and therefore cannot support life.

The slightly more than twenty-five Earth like masses and solids already detected are not within a habitable zone of their stars. They were detected when using pulsar-timing method and they have been found to be orbiting pulsars. Pulsars provide even more extreme conditions for life. They are radio sources that regularly emit very short bursts of signals; they are highly magnetic and there is no likelihood of a habitable zone (Kleefman).

The other planets of smaller sizes that have been detected are known as ‘brown dwarfs’. They are of low temperatures and luminosity and do not become hot enough in the core to cause thermonuclear reactions. They therefore are not actual planets but stars that were not completely formed. These objects cannot support life. Even if chemicals needed for life are detected in these planets, life cannot exist on them and they probably were formed from other processes.

Even if a planet within the habitable zone were detected, detection of life on it would still be constrained. The actual methods for detecting signs of life in extrasolar planets have limitations too. The most promising method involves analysis of the atmosphere of the planets for signatures of chemicals necessary for life (Beckwith).

It is based on the fact that on earth, the chemical components of its atmosphere have been altered by life; therefore, the proof of life on earth can be detected from afar in the spectral signatures of molecules such as oxygen, water vapor, methane, and carbon dioxide. By employing this fact, the atmospheres of extrasolar planets are analyzed for spectral signatures of the above-mentioned molecules. The analysis is done using large telescopes.

The limitation of this method is that the planet must be abundant in life forms for the molecules to be detected by the current telescopes. The large number of life forms would be able to cause detectable changes in the atmospheric composition. This is especially possible for higher forms of life.

If low numbers of simple life forms exist, changes in the atmospheric composition would be minimal and therefore, detection would be minimal too. The precision of the current detection methods needs to be improved a great deal before such forms of life can be detected.

Microlensing is a more accurate method for detecting planets that may fall within the habitable zone, but it also has limitations. The occurrence of micro-lensing events is very rare and for that reason, detection of such planets may never be achieved (Kerins, para.3). Another problem is that even if the micro-lensing event occurs, there is only one chance for recording data. If the chance is lost, data is never recorded.

Proposed solutions for extrasolar life detection

It has been proposed that the use of direct methods may also be possible to detect signs of life on extrasolar. This may be achieved by use of well-designed searches for life forms of microbial nature (Knuckle).

This could be based on remote sensing techniques to search for signatures of compounds associated with life such as chlorophyll and other photosynthetic compounds; conversely, such observations would require to be done through strong, interfering absorptions and scattering radiances. The precision of such observations would be low due to the current resolution and signal to noise ratio constraints. This means that direct observation of extrasolar planets is still impossible at the current generation of telescopes.

The current propositions to build huge telescopes for space exploration are promising to eliminate such constraints. The building of a huge telescope named OWL (OverWhelmingly Large) is expected to revolutionize astronomy (“OWL”). It is proposed to have a diameter of between 60 and 100 meters.

This gigantic telescope will be able to detect an object that is 1500 times fainter than the faintest object observed currently. The telescope and others proposed to have 8 meters diameter will make it possible to characterize more extrasolar planets but until then, extrasolar life remains a mystery.

Conclusion

The search for life beyond earth started over 50 years ago. It has been marred by controversies from scientists, religious leaders, media and the common person. It is important therefore to review critically the available information to determine what the truth is about life in the extrasolar planets.

This paper looked at the current techniques employed in detecting life on extrasolar planets. Their productivity so far and possible future improvements was also reviewed. The detection of life on extrasolar planets depends on ability to detect extrasolar planets themselves so techniques to detect these planets were briefly discussed.

Not all extrasolar planets can support life. In fact, only a small proportion of extrasolar planets can support life, as we know it. These planets must lie within the habitable zones of their stars and must also be rocky. So far, no such planets have been detected and therefore, no extrasolar life has ever been detected.

Although compounds necessary for life (methane, carbon dioxide and water were found on two extrasolar planets, no life form can exist on the planets’ conditions. Scientists have discovered that these compounds were probably formed through other processes.

The available techniques of detecting life on planets beyond the solar system are not up to the test. The distance between Earth and those planets is too great for the available equipment. The technologies are also not able to remove interferences that increase the signal to noise ratio in life detection processes.

The precision of our current detection technologies need to be increased a great deal before we can detect extrasolar life. However, if telescopes like OWL are built, useful data may be obtained in the near future. Until then, likelihood of life outside our solar system remains an open question.

Works Cited

Beckwith, Steven W. Detecting life bearing extrasolar planets with space telescopes 2^nd Ed. California: university of California press. 2008.

Kerins, Eamonn. “Microlensing.” The university of Manchester. 2008. Web.

Kleefman, Mark. “Could life exist on discovered extrasolar planets?” Life on other planets. 1997. Web.

Knuckle, Roger “Possibilities of detection of microbial life on extrasolar planets”. Pubmed new and noteworthy. U.S. national library of medicine. 2003. Web.

“Owl- a future milestone in astronomy”. Eso telescopes division. European southern observatory. 2006. Web.

“Space science-how to find an extrasolar planet.” Feature. European space agency. 2007. Web.

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