[ExI] Life must be everywhere!

Tomasz Rola rtomek at ceti.pl
Sat Apr 14 21:00:16 UTC 2012

> On Sat, 14 Apr 2012, BillK wrote:

> > 2012/4/14 Tomaz Kristan wrote: The velocity of the Pioneer probes was 
> > several tens of km per second.
> > The escape velocity from the distance of Earth's orbit out of the 
> > Solar system is about 17 km/s.
> >
> > Virtually everybody should know that. Especially people discussing 
> > here.

Knowing is silver but learning is golden :-).

> :)  Escape velocity depends on what you are escaping from.

> in the Solar System, to escape from the Milky Way's gravity:  >= 525 km/s

> Pioneer was 'just' escaping from the solar system.

> To leave planet Earth, an escape velocity of 11.2 km/s (approx. 40,320
> km/h, or 25,000 mph) is required; however, a speed of 42.1 km/s is
> required to escape the Sun's gravity (and exit the Solar System) from
> the same position.

Yup, you guys are right. I misread the table from the very same wikipage. 
The right one is on the right.

Trying to go there by another means:

[4]> (defconstant +Big-G+ 6.67384L-11 "m^3 * kg^-1 * s^-2")
[5]> (defconstant +M-Sun+ 1.9891L30 "kg")
[6]> (defconstant +r-Sun-Earth+ 1.496L11 "m")

[9]> (defun Vesc (m r) (sqrt (/ (* 2 +Big-G+ m) r)))

[10]> (Vesc +m-sun+ +r-sun-earth+)

That's in m/s - success! 42 km/s!!

Applying this to the impact calculator doesn't change much, however. A 1km 
piece of ice falling down at 42km/s is going to burn me alive anyway.

Ten times slower speed required only means ten times longer exposure to 
life killing factors.

The escape velocity gets lower and lower, the farther from the Sun we talk 
about. If we assume total mass of Solar System to be 2 Sun mass and agree 
it ends at the biggest proposed distance for Oort cloud (~ 1.87 ly), we 

[11]> (defconstant +LYear+ 9.461L15 "m")

[12]> (Vesc (* 2 +m-sun+) (* 1.87 +lyear+))

Again, in m/s - a speed comparable to fastest cars. So, whatever gets this 
far is likely to be able to get away from the Sun, either directly or as 
side effect of relatively benign asteroid clashes.

So, it seems that indeed a big number of rocks can travel between the 
stars. The problem is, can they sustain life for a very long time periods.
Millions years, maybe billions. Everything can happen during such journey. 

Again, I don't think a natural panspermia is very likely to occur. And if 
it does, then it's on a very limited scale. Still, a nice idea to think 

Tomasz Rola

** A C programmer asked whether computer had Buddha's nature.      **
** As the answer, master did "rm -rif" on the programmer's home    **
** directory. And then the C programmer became enlightened...      **
**                                                                 **
** Tomasz Rola          mailto:tomasz_rola at bigfoot.com             **

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