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Why Not Visit

All of the methods we've described for detecting exoplanets involve observations from Earth, or from Earth-orbiting telescopes. You might ask, "Why not go there and check? Why not send a space probe to that star, to see for certain whether or not there is a planet?"

The reason we don't discuss such approaches is that, with our current level of technology, travel to another solar system is exceptionally difficult and time-consuming. The most imposing difficulty is the sheer distance involved. The Mars Rover Curiosity traveled for more than seven months to get to one of our closest neighboring planets, within our own solar system. Other solar systems are far more distant.

The fastest long-distance space probe launched so far is still the venerable Voyager 1, moving at 17 kilometers per second and slowly leaving the outer edges of our solar system. It was moving faster when it was launched, but gravity from the sun has been continuously pulling Voyager backward since that day. Many probes are faster, but they are typically moving toward the sun rather than away from it. Solar Probe Plus, to be launched in 2018, will have a blistering speed of 200 kilometers per second as it approaches and studies the sun. At this speed one can travel around the Earth in less than four minutes.

Solar Probe Plus would not be able to retain all of that speed if it traveled away from the sun, but let's imagine that it could. How long would it take to get to the nearest star, Proxima Centauri? At 4.24 light years distance, Proxima Centauri is not currently known for certain to have planets, but it is still our closest neighbor in space.

Click this link for a diagram that shows the scale of our solar system with the moon as a single pixel. Be warned - it takes a long time to scroll through.

The frame below shows you a diagram with our solar system and the distance to Proxima Centauri, and just past it to Alpha Centauri. The entire diagram above - our entire solar system, with all our planets - fits inside the tiny blue circle on the left-hand side of the diagram below. To find Alpha Centauri, scroll very, very, very far to the right.

Constructing a probe that will last long enough to cover this distance is a huge challenge. Contact with a single micrometeorite could destroy the entire probe, and interstellar radiation could cause degradation in the probe's more delicate components. Constructing a transmitter that can broadcast a signal over such an immense distance is also difficult. Long-distance transmitters are typically large and require substantial power, and the probe must be as small as possible so that it can be launched with less fuel.

Speaking of fuel, slowing the probe down when it arrives will require nearly as much fuel as launching it in the first place. We would like to have our first contact with another civilization be peaceful, not a 200 km/s multi-ton bullet.

For these reasons and more, there have been no probes launched toward nearby stars, and there are unlikely to be any in the near future. For now, we will continue to improve our telescopes and observational techniques, and learn as much as we can about exoplanets from our home planet.

Солнечная система и ее тайны