How many different ways could we get to Alpha
Centauri Bb, and how long would it take?
“Bb.” “Bb.” Where do we come up with this
stuff?
Alpha Centauri is a binary star system,
like many in our galaxy, and to distinguish between the two stars we assign
them capitol ‘A’ and ‘B’. These denote
the larger and smaller stars in a double star system respectively. Alpha Centauri ‘B’ is therefore the smallest
of the binary pair. At their closest approach they are separated by just 11.2
AU, similar to the distance between the Sun and Saturn, and at their furthest
they stretch out to the orbit of Pluto at around 36 AU.
This system, however, is special. Not only
is Alpha Centauri AB the closest star system to our own, it is also the closest
planetary system as well. In November this year an article was published in
Nature reporting the discovery of an Earth-mass planet orbiting Alpha Centauri
B. Alpha Centauri Bb, or α Cen Bb, was
discovered using the radial velocity method to be 1.13 times the mass of the
Earth in an orbit of just 3.5 days orbiting its star at a distance similar to
that of Mercury. The exoplanet community has adopted a lowercase ‘b’ to name
the ever-growing population of planets in our galaxy, and hence the slightly
awkward names.
So as Alpha Centauri is the closest
planetary system to us, and although the planet would sadly not be habitable,
what would it take to get there?
The system is a meager 4.09 light years
away; that means that it takes the light leaving the star 4.09 years to reach
us here on Earth. Therefore if we were able to travel at the speed of light in
just over 4 years we could be vacationing on a not so comfortably warm world.
But most of us drive or take a plane to get to our holiday destinations. How
long would it take then?
If we were to drive in a car at an average
of 60 mph traffic permitting and without having to stop for gas in just 46
million years we could be there. That is almost as long since the dinosaurs
were wiped out. What about a plane then, a Boeing 747 has a cruising speed of
570 mph cutting your travel time down to just 5 million years only twice the
time it took our genus, Homo, to evolve on the Earth.
Let’s be more realistic now, what about a
rocket how fast could that make us go?
Conventional rockets are funnily enough
designed to go only as far as they need to and that then dictates the speed at
which they travel to get there. Perhaps the easiest destination from the earth
would be to the International Space Station in low Earth orbit. To get there
you would need a rocket that travels at a minimum of 17,000 mph, although this
would bring your trip to Alpha Centauri down to a more imaginable 170,000 years
we are still not quite within the realms of the plausible. What we really want
to know is what it would take to leave the solar system and the gravitational
grasp of the Sun. For that we require more fuel, the only problem is that with
more fuel comes more mass and this does not follow a nice smooth relationship.
The more mass we add soon out ways the effect it has on the speeds we can reach
and the reasonable distances we can then travel. A solar escape rocket like
those used for the Voyager missions needs to be travelling at over 36,000 mph.
Voyager 1 and 2 were launched in the 70’s and have barely made a dent in the 10
trillion miles to Alpha Centauri, negating the fact that they would have to
stop on the way and ask for directions.
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| Solar Probe+ |
Though Voyager 1 and 2 are among the
fastest manmade objects we have launched out into the solar system another type
satellite has gravity on its side and beats them hands down. Helios II currently
holds the tile of ‘fastest man-made object’ traveling at an astounding 160,000
mph; that means that in one hour it could circumnavigate the Earth six and a
half times. This, however, will be surpassed by another solar probe, which will
reach speeds of 200 km/s with the help of the Suns gravitational pull, that’s
nearly 450,000 mph, and is brilliantly named Solar Probe Plus. At this speed it
would only take 6,400 years to reach Alpha Centauri an admittedly enormous
stretch of time but significantly smaller than the 46 million years we started
off with.
In all honesty the most realistic speed we
would need to accomplish in order to make it to the system within a lifetime of
a standard space crew would be one-tenth the speed of light. Light can travel 300
million meters in one second one-tenth of this is the equivalent of 68 million
miles per hour, over 150 times the speed of Solar Probe+. At that speed we would get there in just 40
years and a mission to Mars will look like a walk in the park.
Alpha Centauri Bb is just the closest in a
myriad of stellar systems out there to explore. So get on it engineers and
build us a ship we have places to go a planets to see.
MORE...
Check out the discovery article in Nature of Alpha Centauri Bb
Also look at this great post about the fastest spacecraft we've ever built
