Space Forum / Space Science / July 2008

Simply put, science is doing its job in a logical fashion.

We're exploring the nearest planetary body that's even moderately
convenient. (read realistic)

The moon has no atmosphere, and is tough to deal with, that way.  Radiation
and temperature are extreme.
We'll go there anyway, just because it's close.

Venus is closer than Mars, but with +800 degree temperatures in an
atmosphere 90 times as dense, and laden with sulphuric acid,
also tough to take.

We will cover this ground (Mars) until we can get elsewhere!

On 05/27/2008 10:48 AM, aj531@ncf.ca wrote to All:

-> We're exploring the nearest planetary body that's even moderately
-> convenient. (read realistic)

Titan is a pretty good option, too. It's a long way away, but, as the
Huygens probe showed, it's easy to land on. Just a parachute works fine.
And, although it's very cold, conditions there aren't dreadful.
Nuclear-powered landers should be able to survive for long periods.

And it's *very* interesting.

                                dow

-> Obviously, Ceres is the best candidate after Mars. Rocket-assisted
-> landing is a breeze there, and the presence of a surrounding asteroid
-> field makes it the most radiation-shielded planetary body in the
-> neighborhood.

-> Navigation could pose problems, however, due to the many large
-> intervening chunks of matter.
 
Go out and look at the sky, along the ecliptic. Do you see anything
looking like the milky way? Do you see anything at all, different from
the sky in other directions?
 
Sure, there are a lot of asteroids in the belt between Mars and
Jupiter, but there's also a lot of empty space. Spacecraft going to
Jupiter and beyond go through the belt with no problems. The chance of
colliding with an asteroid is very small. But, also, the radiation
shielding provided by the asteroids is negligible.
 
Ceres is probably as boring as the moon, but a lot further away.
 
                    dow

-> Ceres might be boring like the moon, but it's composition is worlds
-> apart from the lunar mantle-blob that lights our night sky. The
-> physical features on the next worldlet out from Mars might be far more
-> Earthlike than anything resembling our moon -- or even dusty Mars.
 
Earthlike? Ceres is far too small to have an atmosphere, or liquid
water on the surface. Unlike some satellites such as Europa or
Enceladus, Ceres is not tidally heated, so water can't exist in the
interior, either. Almost certainly, Ceres is as dead as the moon, and
not very different in composition either.
 
I forget its name, but there is a spacecraft on its way to fly past
Ceres and a few other bodies in the asteroid belt. If it shows Ceres
to be anything other than a cratered wilderness, I'll be very
surprised.
 
                           dow

-> I'm guessing that Ceres still has its original mixture of minerals and
-> ices; unlike our moon (which had an unusual origin, less accretion
-> than conglomeration), or Mars which -- imo -- burned off its great
-> salt lake in a furious bout of magmaphreatism.

-> So, if Ceres does contain a frozen lake of water ice, some areas
-> should appear less cratered. Features formed by glacial erosion could
-> also exist. That big reflective spot might be a snow-capped peak,
-> unfettered by gravity and carved by ice into a magnificent
-> Matterhorn.
 
Why should only the peak be snow-capped? With no atmosphere to impose a
temperature gradient, ice would be no more or less likely to exist at
high altitudes than low ones.
 
But, I suspect, the existence of ice anywhere on or in Ceres is
unlikely. The temperature is high enough that ice would sublime away
quite quickly, and there is insufficient gravity to hold the vapour and
allow it to re-condense.
 
We'll see, but I'm not at all optimistic.
 
                    dow

Life on Mars needs to be rad-hard, and otherwise tough as nails.

Next should be Venus, or at least that of our once upon a time icy
moon.

If time and money are not a problem, then perhaps IO.

Brad Guth Brad_Guth Brad.Guth BradGuth

-> Ceres is at best almost as bad off as Mars, if not worse.

-> Does Ceres have thorium?

-> Does Ceres have salt?
 
Worse, I'd guess.
 
The important questions are not whether thorium or salt exist in Ceres.
They're whether thorium *ores* or deposits of rock-salt exist, from
which the thorium or salt could be extracted reasonably easily.
 
On the earth, ores are formed in the liquid state, when materials
precipitate out of solution in water, or from molten rock. But there
can never have been oceans on Ceres, so ores (or rock salt) could not
have been formed that way. And, although impacts must have melted rock
locally and briefly, it's doubtful that there would have been time for
minerals to be separately deposited before the rock solidified.
 
So I'm doubtful that there are workable deposits of thorium ore (or
other metal ores) or rock salt on Ceres.
 
                      dow

On 07/07/2008 8:58 AM, pmunnsub@pearce-neptune.demon.co.uk wrote to All:

-> Leafing through alt.sci.planetary, I read David Williams's message of
-> Tue, 27 May 2008:
->
-> >Titan is a pretty good option, too. It's a long way away, but, as the
-> >Huygens probe showed, it's easy to land on. Just a parachute works fine.
-> >And, although it's very cold, conditions there aren't dreadful.
-> >Nuclear-powered landers should be able to survive for long periods.
->
-> Titan missions will probably continue for some time to be significantly
-> cheaper when Jupiter is conveniently aligned for gravity assist (once
-> every 20 years).  This would suggest a mission arriving in the 2020's,
-> and I'm very confident such will be proposed, with that once-in-20-years
-> opportunity being a big part of the rationale.
-> --
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It doesn't take very much more rocket power to reach Saturn directly than
via Jupiter. It would be slower, but not 20 years slower. I'd guess the
total journey would take between 15 and 20 years, as opposed to 10 or 12
years via Jupiter. So it might not be worth waiting for the
once-in-20-years alignment of the planets. Just shoot for Saturn, or Titan,
directly.

                              dow