The search for life on planets orbiting other stars will dominate astronomy for the remainder of this century (unless an incredible space phenomenon that was utterly unimagined pops up).
By the beginning of the next century scientists will be planning on how to travel to other worlds to see alien life forms up close. This will at last provide incontrovertible evidence for astrobiology on a muticellular level.
By 2110 we will have mapped the surfaces of the nearest exoplanets to see oceans, storms, continents, and volcanoes. There will be photometric and spectroscopic evidence for forests and savannahs. We will have also catalog numerous satellite companions.
Once convinced a planet is inhabited (which may not satisfy all scientific skeptics), there will be endless wonder and speculation about the type of creatures that are living there. Imagine beholding the interworking of an entire alien biosphere.
But it would take a telescope with the effective diameter of the sun to actually take photographs of something the size of an elephant strolling on an exoplanet only 4.3 light-years away. (In fact the sun could be used as a gravitational lens to amplify the image of a planet, but that would not come close to providing the needed magnification.)
In a recent paper Helmut Lammer of the Austrian Academy of Sciences, Space Research Institute, predicts that there will be a big hiatus in significant exoplanet research until we can send robotic probes to physically travel to these worlds and come face to face with whatever lives there.
Just surviving the encounter would be problematic. We’d be plopping artificially intelligent entities down in the middle of an extraterrestrial Serengeti — as dramatized in the Discovery Channel program "Alien Planet."
But surviving the flight to these worlds could be even more perilous. Lammer and Ian Crawford of the University of London recently debated the dangers in several Internet postings.
There isn’t enough room here to discuss the various propulsion schemes for accelerating a craft to at least 1/10th the speed of light. Suffice to say that 22nd century technology is so unpredictable that the exercise is as pointless as asking Lewis and Clake to imagine how they might travel from St. Louis to the Pacific Coast in three hours.
But a cold hard physics fact is that something hurting though space at 18,000 miles a second could be torn up by a collision with the tiniest speck of dust imaginable. Hitting a dust mote-sized particle would impart the same kinetic energy as slamming head on into a speeding freight train. All it would take is one direct hit to knock out the entire vehicle and demolish a trillion-dollar mission.
But this debate too could be a moot point in the 22nd century. First, the vehicle would have to have a very small cross section and rely heavily on nanotechnology for miniaturization. Imagine a payload the shape and size of a torpedo.
Secondly, the probe could have an active radar or lidar defense that targets debris and uses lasers to vaporize the dust particles. The mini-starship might project a cloud of co-moving particles in front of it to fragment dust through collision. Physical shielding is impractical because of the huge weight penalty of dragging along a beryllium bumper. However, cosmic rays from the particle collisions could be shielded by a 3-foot thick water bag.
There may be even more exotic "bumpers" developed by space-faring extraterrestrial civilizations. And these might be detectable as an odd manifestation of cosmic rays from an unseen object with a high proper motion.
Lammer says that it will likely take a monumental discovery for governments to come up with the motivation and cash for funding the mother of all engineering projects. For example, imagine the wonder at detecting spectral features that cannot not explained by complex organic chemistry, like laser emissions. Or maybe finding excessive chlorofluorocarbons (if the aliens all use hairspray).
I predict that an impetus will be the discovery of a habitable planet around the nearest pair of stars: Alpha and Beta Centauri. This will greatly catalyze exoplanet research. Hurtling across space at 1/10 the speed of light, the starship would get to Alpha Centauri within the lifetime of its builders.
The expense and enormity of interstellar travel might compel extraterrestrial civilizations to say home and instead transmit images and information about their biology in the hopes of finding interstellar pen pals. Imagine receiving a Wikipedia Galactica with volumes of information detailing their biosphere.
In any event we will likely undertake interstellar travel in the next century. Therefore why hasn’t any alien probe come by to visit us? This is probably an indirect argument that no advanced civilization lives on Alpha Centauri, otherwise we should have seen manifestations of their technology visiting the solar system.
Or, maybe, interstellar robots have already stopped by.