The ‘Why’ of Interstellar Flight

From the standpoint of pure research, one of the arguments for not going to nearby stars is that by the time we develop the needed technologies, we’ll have no need to make the journey. After all, we’ll soon be able to learn vast amounts about nearby worlds from space-based telescopes, not to mention planned Earth-side instruments like the European Extremely Large Telescope, a 42-meter powerhouse 100 more sensitive than the best of today’s optical telescopes. Putting observatories on the far side of the Moon is another way we’ll see deeper than ever before.

Extend space research out fifty years, a hundred, and you have to reckon with capabilities we can only dream about today. Webster Cash (University of Colorado) has been championing one Sun-shade design (there are others) that in its fullest deployment could give us views of an exoplanet as if we were no more than a hundred kilometers away. Or consider the fusion of new propulsion technologies with space-based observatories that can tap the Sun’s gravitational focus. This would open up the galaxy for the detailed exploration of countless planetary systems, with the potential for exoplanet finds as far away as Andromeda.

An Earth-based Perspective

All this is given relevance (and perspective) by the upcoming launch of Kepler, which will look for transiting planets down to terrestrial size. And as I was pondering these issues, there came the news of not one but two ground-based detections of exoplanet atmospheres. Six hundred images of the hot Jupiter OGLE-TR-56b, from the ESO’s Very Large Telescope and Carnegie’s Magellan-Baade instrument in Chile, produced the first result. This one is quite a catch, the planet being some 5,000 light years away in the direction of galactic center. Listen to Mercedes López-Morales (Carnegie Institution) on last summer’s work:

“Others have tried to detect planetary atmospheres from Earth, but to no avail… The successful recipe is a planet that emits a lot of heat and has little to no wind in its atmosphere. Plus it has to be a clear, calm night on Earth to measure accurately the differences in thermal emissions when the planet is eclipsed as it goes behind the star. Only about one of every 3,000 photons from the star comes from the planet. This eclipse allows us to separate the emissions of the planet from those of the star. The magic moments came on July 2nd…”

In the same issue of Astronomy & Astrophysics comes news of the measurement of thermal emissions in the near-infrared from TrES-3b, another hot Jupiter studied from the ground. This work is out of the University of Leiden in the Netherlands, again relying on accurate information about the planetary transit that allows the strength of the planet’s light to be measured. The instruments involved were the William Herschel Telescope (WHT) on La Palma (Canary Islands, Spain) and the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea in Hawaii.

Given this early work on exoplanetary atmospheres from Earth, where will we be in fifty years? And if, let’s say in a century, we find ourselves with the capability of studying distant planetary systems in exquisite detail, will we still have the motivation to build ships to make the journey to them? From a planetary security perspective, we can theoretically safeguard our species by expanding out in our own system with space-based habitats and possibly terraforming as options. The question then remains: What is it that drives the push to interstellar flight?

Philosophy and Realism

Many answers suggest themselves, and I’m not inclined to wax philosophical here. I think a realistic answer is that as we expand into the Solar System and build the infrastructure to support human populations in space, we will inevitably develop the tools that make further explorations possible, including propulsion technologies to get us to the Oort Cloud and beyond. Human history tells me that there is always a portion of the population that is willing to get on a cramped ship and go to the other side of nowhere for reasons that vary from the pure exploratory impulse to the need to escape political or religious persecution.

And my guess is that at some point interstellar flight will begin in much the same way. Protecting the species by spreading into the cosmos is a laudable goal, but it couples neatly with this exploratory imperative that has shown up in the behavior of our ancestors and shows no signs of abating now. Indeed, a universal exploratory urge is part of the puzzle noted by Fermi’s paradox — ‘Where are they’ indeed, for we would expect anyone with the capability of making an interstellar journey to set about the task. That’s because we know deep down that that is exactly what we would do — will do — assuming we survive our technological coming of age and can develop the engines to make it happen.