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evilbill
2010-Jan-02, 06:37 AM
So I was reading the http://www.bautforum.com/life-space/97916-why-still-there-no-alien-contact-8.html#post1650900 thread and this post triggered a question:

When will the Voyager 1 count as an interstellar probe? So I did a couple of back of the envelope calculations:

Voyager 1 velocity: 17 m/s
Distance to nearest star: 4.2 light years
1 light year = 9.46 10^15 meters
Time to get to nearest star system 74 Million years

And that's even assuming it is "aimed" there.

So I'd say it's pretty optimistic to send it with a message. Then again, the universe has lot of time. Does anyone know of any good resources where this was discussed before? (and if anyone can confirm or correct my calculations, I'd appreciate it.)

01101001
2010-Jan-02, 06:44 AM
Does anyone know of any good resources where this was discussed before?

By "this" do you mean the definition of "interstellar"?

NASA has some background on the interstellar mission: Voyager - Interstellar Mission (http://voyager.jpl.nasa.gov/mission/interstellar.html).

I'd say it takes an interstellar probe to do an interstellar mission.

The exact point where a craft enters interstellar space probably depends on who you ask, but the heliopause is probably one popular border, maybe in 2015 for Voyager 1.

It's a little like trying to define exactly when you are in a rural area when you take a road trip between cities.

Tensor
2010-Jan-02, 02:38 PM
It's not aimed there. The Heavens Above Satellites Escaping the Solar System page (http://www.heavens-above.com/solar-escape.asp?lat=0&lng=0&loc=Unspecified&alt=0&tz=CET) has the specifics for each of the five satellites that are escaping from the solar system. With the Declination, Right Ascension. and the tilt to the solar system plane (Ecliptic Latitude), you should be able to find the nearest star to those coordinates and figure the time to that star.

Romanus
2010-Jan-02, 04:28 PM
Whoa there, Tiger--the Voyagers aren't *that* slow. Voyager 1 is going 3.6 AUs per year, and a light-year is 63,241 AUs; I figure ~17,600 years for one light-year. Thus, about 75,000 years to reach Alpha Centauri.

The real bogus in all this isn't the distance, though; it's the fact that all these spacecraft have become independent objects in interstellar space moving relative to other independent objects. I've fancied figuring out where New Horizons is "going", what stellar near-encounters are in its future, but have so far been thwarted because it's not enough to know where it's going*, but how other stars are moving in relation to it as opposed to just the Sun (toward, away, tangentially), a fairly daunting task when you think about it.

*Pluto will make a roughly equilateral triangle with Xi1 and Xi2 Sagitarii on July 15, 2015.