Comments on: Steller Cartography

By: Anonymous

Anonymous — Mon, 01 Dec 2008 05:29:42 +0000

“Sirius is a binary system containing one star that’s thought to be too hot for life (Sirius A) and a white dwarf (Sirius B) that’s far too cool. White dwarves are even cooler than red dwarves. This binary system is 8.58 light years away.”

Nearly right – white dwarves are actually hotter than red ones.

By: Ywns

Ywns — Thu, 18 Oct 2007 22:02:03 +0000

If you haven’t seen it, you might want to look in libraries for _Habitable Planets for Man_. I was introduced to it at age 10 or so by a scifi-writer relative. It is a study funded, I believe, by the Rand Corp., to determine the qualities needed for habitable planets. Joe Haldeman reviews it favorably at the Amazon link below. High-gravity planets are likely to be very poor in metals near the surface! Colonists beware. And just how large does a body have to be to escape tidal lock? Dang, I think I’ll re-read it.

One of the things I valued it for as a geeky young thing was the great star names, my favorites always being the rhyming Sigma Draconis and Delta Pavonis.

http://www.amazon.com/Habitable-Planets-Man-Stephen-Dole/dp/0444000925

Nice blog you’ve got. I wandered in off a search for Tau Ceti images.

By: Karl Hallowell

Karl Hallowell — Fri, 03 Feb 2006 23:21:02 +0000

I see that your primitive culture has finally discovered 3D star maps. You might find this technology useful.

By: Stephen Gordon

Stephen Gordon — Wed, 01 Feb 2006 20:10:37 +0000

Paul:

I think you’re right because an asteroid would continue to pick up speed as it falls toward the star it is orbiting – eccentrically.

The closer the earth-like planet has to be to its star to be habitable, the faster a potential impactor would be moving. I buy that.

By: Paul F. Dietz

Paul F. Dietz — Wed, 01 Feb 2006 17:13:09 +0000

Yes, it would have more energy, which presumably would make it more damaging.

The energy does depend on whether the asteroid is coming or going, but for a given encounter geometry the relative speed scales as I indicated (since the velocities of the planet and the impactor both increase as M^-3/8, and the energy as the square of that.)

By: Stephen Gordon

Stephen Gordon — Wed, 01 Feb 2006 08:04:10 +0000

Paul:

So, you’re saying that an asteriod impact within the habitable zone of a dimmer star would have more energy and would, therefore, be more lethal than an asteriod impact in the habitable zone of our own Sun. Right?

I suppose it would depend on whether the asteriod hit you coming or going, wouldn’t it?

By: Paul F. Dietz

Paul F. Dietz — Tue, 31 Jan 2006 22:26:12 +0000

Another important thing that happens around small stars is increased impact energy.

The luminosity of a main sequence star of mass M goes as about M^3.5, so for planets in the habitable zone the energy of the orbit around the star goes as M^-.75. Smaller stars will therefore have habitable planets in more energetic orbits. Asteroid and comet impact energy will scale proportionally to the energy of the orbit (assuming this energy is much greater than the escape energy of the planet itself, as it should be in this case.)