Can We Travel To That Exciting New Exoplanet?

An anonymous reader writes "The news last week that exoplanet Gliese 581g may be in the 'Goldilocks zone' and could therefore hold liquid water and alien life got everyone all excited, with good reason. A potentially habitable planet — and only 20 light years away! But to put things in perspective, here are a couple of estimates on what it would take to travel to Gliese 581g. One scientist puts the travel time at 180,000 years based on current space flight technology, while another explains that it could be quite quick if we build a matter-antimatter drive, and can figure out how to bring along 530 times as much mass in fuel as is contained in the ship and cargo itself."

Comments

Re:Nuclear pulse propulsion

[Xtense]

The theoretical speed for a momentum-limited, 100m orion craft would be 3,3% of the speed of light, so... no. No it wouldn't.

How about some past technology?

[Wonko the Sane]

Everyone is forgetting about Project Orion.

The biggest design above is the "super" Orion design; at 8 million tons, it could easily be a city.[6] In interviews, the designers contemplated the large ship as a possible interstellar ark. This extreme design could be built with materials and techniques that could be obtained in 1958 or were anticipated to be available shortly after. The practical upper limit is likely to be higher with modern materials.

...

Later studies indicate that the top cruise velocity that can theoretically be achieved by a thermonuclear Orion starship is about 8% to 10% of the speed of light (0.08-0.1c).[1] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by matter-antimatter pulse units would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light.

At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The late astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons.[10]

Re:Reality check

[MarcQuadra]

Right? The diameter of our solar system (Pluto's orbit) is about 80 AU. 80 AU is 0.0012 light years. This planet is 20 LY away. That means that it's about 1600 times as far as Pluto.

Remember, you need to bring along just as much fuel to slow down as you did to speed up. This is going to be a long, expensive, boring ride.

Re:I'd like a second opinion...

[Per Wigren]

18 days, 13 hours, 26 minutes and 24 seconds, captin.

Overly pedantic

[dreamchaser]

A man on a good horse can maybe cover 30 miles a day unless he wants to kill the horse. A man on foot maybe 20 if he's in top shape. My comment stands. Maybe I should have said "A dozen or few" but still, you're just being pedantic.

Re:Overly pedantic

[catbertscousin]

I was going to, but I needed Bronze Working first.

Re:Overly pedantic

[TheRaven64]

Man invented the bit (the thing that goes in a horse's mouth, connected to the reins), which was the technology that allows horses to be tamed and used for transport. This was invented approximately 5,000 years ago and set the maximum speed for humans to around twenty miles per hour (with short bursts up to 50) for almost all of the intervening time. The development of the steam locomotive, around 200 years ago, increased this speed to around 100 miles per hour. After that, the internal combustion engine and the jet made the leap to a few thousand miles per hour in under half a century. Solar sails and nuclear-powered ion drives push this maximum up even further. The rate of change of maximum speed for a human has been increasing a lot over the last few centuries.

Re:Overly pedantic

[GooberToo]

I think its funny how many people don't really understand what they are talking about.

Pragmatically, further back that a couple hundred years ago, people rarely traveled. Period. It was largely the aristocracy and wealthy and/or merchants who did the vast majority of traveling. A minority traveled father than twenty to forty miles; and that was typically a city trip for supplies. Its not like in the movies where everyone is constantly traveling around. Traveling to a new area frequently means months to years to become re-established. Its a big, life changing event.

Some exceptions are the military. On foot, on clear terrain, forty to fifty miles were expected. They could do more but would generally be useless for fighting if they did. On horse, with good terrain, calvary would expected to do roughly eighty miles. On rough terrain, a foot soldier was expected to do twenty miles. In heavy forest and/or mountains, snow, etc., ten miles is a good day. Now keep in mind, these guys had heavy equipment they had to carry too, not to mention supplies. And that's really the magic of it all. Having water and food is key. Sure, you *can* travel a much father distance, but being absolutely useless for the next couple of days, assuming you don't die, assuming supplies can catch up, doesn't do anyone any good whatsoever. And don't forget, most places didn't even have roads outside a city. That's one of the things that made Rome great after all.

There are some noteworthy exceptions, such as some of the African tribes who are legendary at running vast distances (example, Zulu) and going right into combat - and winning. But these guys carried only a shield, spear, and absolutely minimum of food and water, and even then, it was war. It was not an everyday event.

Going back to antiquities, it was exceedingly rare to ever travel outside of your valley - again, unless you were a merchant. Realistically, people did not travel. When they did travel, they rarely traveled father than twenty to thirty miles. Those that did travel farther than that, typically had a vocation which required it (merchant, navy, explorer) or a wallet to simply allow for it (summer, winter home). And even then, when they did travel, it was exceedingly rare to be great distances in a day. And of these, ships are the sole exception - until trains - and then cars and planes.

Re:A further shore....

[dasherjan]

We already have plenty of shores to explore in the solar system. They're just not as sexy as another earth type place. ;-)

Re:Our world

[Zenaku]

The planet is 4 times the mass of earth; so because of its gravity, I'd weigh 600 pounds

You are probably just trolling and I'm falling for it by correcting you, but just in case you actually think this. . .

No. Four times the mass does not imply that you would weigh 4 times as much unless the planet's radius is the same as the earth's. That is quite unlikely. A planet with 4 times as much mass as the earth is almost certainly going to be proportionally larger in volume as well. Gravity is proportional to mass, but inversely proportional to the square of the distance from the center of that mass. In the end, if the planet is made of the same sort of rocky material, it will have a similar density, and thus similar gravity.

Would it be exactly 1G? Probably not. Without knowing the planet's volume, we can't know exactly. But a number between .8G and 1.2G is much more likely than 4G.

Of course, I'm assuming that you weigh 150 pounds here on Earth. If you currently weigh 500 pounds, then I apologize. . . your estimated weight on this new world may have been fairly accurate after all. :)

Re:Nuclear pulse propulsion

[Mr. Slippery]

A vegan diet reduces the need to support non-human animal mass, but adds a requirement to be able to synthesize some vitamins and proteins.

No, it doesn't. Protein needs are easily met on a vegan diet; the only vitamin that can really be troublesome is B12, which is made by bacteria and so doesn't need to be synthesized.

Re:Our world

[FrangoAssado]

You're forgetting that the volume is proportional to the cube of the radius, while gravity is proportional to the inverse square of the radius. So, while gravity doesn't increase linearly with mass, it's not constant either:

4x mass -> 4x volume -> 4^(1/3)x radius -> 4/4^(2/3)x gravity

So, gravity would be increased about 1.6 times. You should apologize to him if he weighs 380 pounds, not 500. :)