Planet cracker

[lexington]

I wonder where he got those numbers from.

[jason taylor]

Originally Posted by lexington

I wonder where he got those numbers from.

He is an agent of The Shadows. Don't you know?

[lwcamp]

Originally Posted by lexington

I wonder where he got those numbers from.

Why do you think they are called planetary nebulae?

Luke

[lexington]

Originally Posted by lwcamp

Why do you think they are called planetary nebulae?

Luke

Because they eventually coalesce into planets? I'm honestly not clear on the naming.

[lwcamp]

Originally Posted by lexington

Because they eventually coalesce into planets? I'm honestly not clear on the naming.

Ah, well in real life, a planetary nebula is a shell of gas spat off by a dying star. They were called that because old time astronomers (but not so old they didn't have telescopes) could see them as a faint disk. Since planets also had a visible disk, it reminded the astronomers of planets, hence the name.

As a joke, they are called planetary nebulae because Winch Chung (the Atomic Rockets guy) blew up planets into clouds of gas to experiment with how much energy it would take to cause various levels of disruption.

Luke

[lexington]

Originally Posted by lwcamp

Ah, well in real life, a planetary nebula is a shell of gas spat off by a dying star. They were called that because old time astronomers (but not so old they didn't have telescopes) could see them as a faint disk. Since planets also had a visible disk, it reminded the astronomers of planets, hence the name.

As a joke, they are called planetary nebulae because Winch Chung (the Atomic Rockets guy) blew up planets into clouds of gas to experiment with how much energy it would take to cause various levels of disruption.

Luke

lol, okay I see. I suppose I can jus e-mail him and find out where the numbers came from.

[lwcamp]

Originally Posted by lexington

lol, okay I see. I suppose I can jus e-mail him and find out where the numbers came from.

Oh, you were being serious. In that case, the values for boiling or evaporating the oceans likely come from knowing the mass of the ocean and the specific heat and heat of vaporization of water. It takes 4180 J to raise the temperature of 1 kg of water by 1 degree C. So if the average temperature of the ocean is 10 C, for example, then for every kg of ocean water it takes (100 C - 10 C) * 4180 J to raise it to boiling. Once you have it at boiling temperature, it takes 2,257,000 J/kg to boil the water into steam. This is assuming the water is pure - salt and other stuff will affect these values a bit, but not by all that much.

The rest probably comes from knowing the mass of the atmosphere, oceans, and crust and figuring the work needed to take than mass from the planets surface to far enough away that it is no longer under the influence of the earth's gravity. Since the escape velocity on earth is 11.2 km/s, 1 kg of mass shot off the earth with enough speed to escape from the earth would have a kinetic energy of 63 MJ. This gives the energy per kilogram needed to gravitationally unbind something from our planet - assuming you are not lifting so much off the planet that the mass of the planet significantly changes. So multiply the mass of the oceans in kg by 63 MJ to get the energy to blast all the oceans on earth off the planet so hard they will not come back.

Luke

[Not another shrubbery]

Originally Posted by lwcamp

Just for reference, in the thread that you link to the relativistic spacecraft would have a kinetic energy of 3.6E22 J (if I did the math right). From the ever useful Atomic Rocket boom table
http://www.projectrho.com/rocket/rocket3x1.html , about 1/6 of the way down the page
that's about an order of magnitude less energy than the Chicxulub event that ended the dinosaurs. It would cause a lot of consternation to the people living there, but would not really damage an earth-like planet.

Handy little site... Bookmarked, and thanks for the link!