Yesterday I mentioned that we don’t know yet where New Horizons will ultimately end up on a map of the night sky like the ones used in a recent IEEE Spectrum article to illustrate the journeys of the Voyagers and Pioneers. We’ll know more once future encounters with Kuiper Belt objects are taken into account. But the thought of New Horizons reminds me that Jon Lomberg will be talking about the New Horizons Message Initiative, as well as the Galaxy Garden he has created in Hawaii, today at the Arthur C. Clarke Center at UC San Diego. The talk will be streamed live at: http://calit2.net/webcasting/jwplayer/index.php, with the webcast slated to begin at approximately 2045 EST, or 0145 UTC.
While both the Voyagers and the Pioneers carried artifacts representing humanity, New Horizons may have its message uploaded to the spacecraft’s memory, its collected images and perhaps sounds ‘crowdsourced’ from people around the world after the spacecraft’s encounter with Pluto/Charon. That, at least, is the plan, but we need your signature on the New Horizons petition to make it happen. The first 10,000 to sign will have their names uploaded to the spacecraft, assuming all goes well and NASA approval is forthcoming. Please help by signing. In backing the New Horizons Message Initiative, principal investigator Alan Stern has said that it will “inspire and engage people to think about SETI and New Horizons in new ways.”
Artifacts, whether in computer memory or physical form like Voyager’s Golden Record, are really about how we see ourselves and our place in the universe. On that score, it’s heartening to see the kind of article I talked about yesterday in IEEE Spectrum, discussing where our probes are heading. When the Voyagers finished their planetary flybys, many people thought their missions were over. But even beyond their continued delivery of data as they cross the heliopause, the Voyagers are now awakening a larger interest in what lies beyond the Solar System. Even if they take tens of thousands of years to come remotely close to another star, the fact is that they are still traveling, and we’re seeing our system in this broader context.
The primary Alpha Centauri stars — Centauri A and B — are about 4.35 light years away. Proxima Centauri is actually a bit closer, at 4.22 light years. It’s easy enough to work out, using Voyager’s 17.3 kilometers per second velocity, that it would take over 73,000 years to travel the 4.22 light years that separate us from Proxima, but as we saw yesterday, we have to do more than take distance into account. Motion is significant, and the Alpha Centauri stars (I am assuming Proxima Centauri is gravitationally bound to A and B, which seems likely) are moving with a mean radial velocity of 25.1 ± 0.3 km/s towards the Solar System.
We’re talking about long time frames, to be sure. In about 28,000 years, having moved into the constellation Hydra as seen from Earth, Alpha Centauri will close to 3.26 light years of the Solar System before beginning to move away. So while we can say that Voyager 1 would take 73,000 years to cross the 4.22 light years that currently separate us from Proxima Centauri, the question of how long it would take Voyager 1 to get to Alpha Centauri given the relative motion of each remains to be solved. I leave this exercise to those more mathematically inclined than myself, but hope one or more readers will share their results in the comments.
Image: A Hubble image of Proxima Centauri taken with the observatory’s Wide Field and Planetary Camera 2. Centauri A and B are out of the frame. Credit: ESA/Hubble & NASA.
We saw yesterday that both Voyagers are moving toward stars that are moving in our direction, Voyager 1 toward Gliese 445 and Voyager 2 toward Ross 248. When travel times are in the tens of thousands of years, it helps to be moving toward something that is coming even faster towards you, which is why Voyager 1 closes to 1.6 light years of Gl 445 in 40,000 years. But these are hardly the only stars moving in our direction. Barnard’s Star, which shows the largest known proper motion of any star relative to the Solar System, is approaching at around 140 kilometers per second. Its closest approach should be around 9800 AD, when it will close to 3.75 light years. By then, of course, Alpha Centauri will have moved even closer to the Sun.
When we talk about interstellar probes, we’re obviously hoping to move a good deal faster, but it’s interesting to realize that our motion through the galaxy sets up a wide variety of stellar encounters. Epsilon Indi, currently some 11.8 light years away, is moving at about 90 kilometers per second relative to the Sun, and will close to 10.6 light years in about 17,000 years, a distance roughly similar to Tau Ceti’s as it will be in the sky of 43,000 years from now.
And as I learned from Erik Anderson’s splendid Vistas of Many Worlds, the star Gliese 710 is one of the most interesting in terms of close encounters. It’s currently 64 light years away in the constellation Serpens, but give it 1.4 million years and Gl 710 will move within 50,000 AU. That’s clearly in our wheelhouse, for 50,000 AU is the realm of the Oort Cloud comets, and we can only imagine what effects the passage of a star this close to the Sun will have on disturbing the cometary cloud. If humans are around this far in the future, GL 710 will give us an interstellar destination right on our doorstep as it swings by on its galactic journey.