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History of the Search for Extrasolar Earthlike Planets

 

There has always been the question “are we alone?” floating through the minds of scholars and ordinary people alike. This question for centuries has driven humans to look towards the heavens for the answers which we seek most. The universe is a vast, open space with many light-years to cover--so is there another “earth” floating around in a similar system?

 

 

Within the search for extrasolar planets, astronomers are looking for other planets that could be considered “earth-like” in terms of temperature, size, and mass (Seager).  The problem has not been finding extrasolar planets in general, the problem is finding Earth-like extrasolar planets. For example, about 182 extrasolar giant planets have been found orbiting around a star similar to our sun, even some of them have multiple giant extrasolar planets. (Seager)

At first, finding extrasolar planets was quite impossible due to the star’s luminosity to that of the planet orbiting around it, the star would just blur out the planet. Until about 15 years ago, the luminosity was a problem, but scientific advances has allowed us to examine these planets that orbit quite close to their respective stars.

The first extrasolar planet was discovered in 1992 by finding deviations in the usually regular pulse of the pulsar PSR1257+12 (scitizen.com) . The deviations in the pulse led scientists to infer the presence of three planets, probably not containing life because of a pulsar being a dead star thus making it near impossible for planets to sustain life. 

When these planets were first discovered they were thought to be the cores of planets which survived the supernova explosion which formed the pulsar, luckily recent studies have shown these planets most likely formed after the explosion when the pulsar dragged in material which was originally cast out by the supernova (extrasolar.net). The three planets have been dubbed a, b , and c (PSR1257+12a would refer to the closest planet to the pulsar, etc). These three planets seem to rotate on the same plane as their parent star PSR1257+12’s rotation, as shown in the figure below.

 

 

Even with the discovery of the planets, there is not much possibility for life on them. Besides orbiting a dead star, the planets are subject to intense radiation being sent out by the pulsar thus making the surfaces uninhabitable.

 

This was an exciting discovery but still no planets had yet been discovered which orbited a star like our sun (hydrogen-burning). This was until 1995 when the first exoplanet was found to be orbiting a main sequence star like that of our own sun. The star was named 51 Pegasi B and was discovered by “precise radial velocity measurements” (scitizen.com). This “precise radial velocity measurements” is described by scitizens.com as “as the planet orbits the star, it induces a small periodic motion of the star (both the planet and the star circle around the center of mass of the system, which is slighlty offset from the star center). The radial component of this periodic motion can be measured as a shift of the entire stellar spectra towards the blue when the star approaches and towards the red as the star recedes (Doppler shift effect)."  Using this technique is how almost all of the currently known exoplanets have been discovered (scitizen.com).

 

  

51 Peg b is “a massive Jupiter-like planet orbiting at only 0.05 Aus from its sun, far closer than Mercury.”  However, if you would remember the theories we learned in class, how could a Jupiter-like planet be orbiting so close to a star?  According to extrasolar.net “Light was shed on the puzzle of the Hot Jupiters when simulations of protoplanetary disks showed that gas giants like Jupiter could migrate inward towards their stars, either due to drag against disk material or by gravitational perturbations with the disk. Tidal forces and disk clearing near the star would tend to park such migrating planets at orbital distances quite similar to those of the Hot Jupiters. It would appear that 51 Pegasi b and its kin originally formed far from their stars but spiraled inward to their current orbits.” So this might explain how the Jupiter-like planet is surviving so close to its parent star, but we don’t know is how long it will be able to survive there. An artist’s rendering of what 51 Peg b might look like is shown above, the dark grey color is possible due to the amount of sodium gas in the planet (extrasolar.net)

 

 

So far none of the extrasolar planets discovered are Earth-sized.  Most are many times the mass of Jupiter and lack the characteristics to support life as we know it. Many techniques are being developed to find these earth-like extrasolar planets so hopefully in the future we can learn more about planets such as ours.

 

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