Tuesday, August 7, 2012

Nearest Exoplanet to Earth

We are living in an unprecedented time in human history because only in the last couple of decades has it become possible to study planets outside of our solar system. Considering that only a millennium or so ago even the concept of a world beyond our solar system did not exist in the human consciousness, the ability to peer into these other worlds is truly remarkable. Of the currently known exoplanets, fast approaching 1000 in number, what is the closest one to Earth? What is it like? How long would it take for a spacecraft to get there? How long would it take for a radio signal sent by a hypothetical life-form from that planet to reach us?

As it happens, the exoplanet that is the nearest to Earth and our solar system has held the record since the year 2000. Unfortunately it has a rather clinical name, eps Eridani b. The planet has a mass of approximately 1.5 times that of Jupiter (or nearly 500 times the mass of Earth), although there is a large margin of error on this. Even though there is no information on the size of the planet, it is not likely to be Earthlike because the lower bound on its mass is still more than 300 times that of Earth. Such a massive planet that is more like the size of Earth has not been found so far.

The nearest exoplanet to Earth, eps Eridani b, is at a distance of 10.44 light years, which is more than 60,000 billion miles (nearly 100,000 billion kilometers). It would take light 10.44 years to travel between the exoplanet and Earth. At speeds that are currently achievable, say 20,000 miles per hour (about 32,000 km per hour), the travel time is 350,000 years. This may seem depressing, but considering that the nearest star to Earth (Proxima Centauri) is at a distance of 4.2 light years from Earth, we are lucky to have found an exoplanet so close (no planets have been found around Proxima Centauri). Clearly we are not likely to witness human space travel to our nearest neighbor exoplanet in our lifetimes. Will it be possible in the near-term future, within hundreds of human generations, say? Although it is impossible to predict, contemplate the achievements of the human intellect and spirit: it has hardly been more than a century since humans first made powered flying machines, and in just half a century humans have walked on the moon, and sent probes beyond the solar system, with another one on its way to Pluto right now.

So, does our nearest exoplanet neighbor support life, or even perhaps the seeds of life? So far it has not been possible to detect molecular signatures from the planet and it is not possible to directly image the planet (the latter is true for the majority of exoplanets). SETI-type activities naturally pay special attention to worlds that are closest to us, but nothing definitive has turned up from radio-signal searches of extraterrestrial intelligence in any system. On the other hand, the possibility of eps Eridani b supporting seeds of life has not been ruled out.

Finally, it's worth mentioning that a second planet in the eps Eridani system has been suspected for years but definitive proof remains elusive because the signals that have provided tentative evidence are complex, carrying many ambiguities that have to be disentangled. Such disentanglement often does not lead to a unique and definitive interpretation of the data but future improvements in instrumentation might give less ambiguous results.

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