Star Travel and the Interstellar Medium, particle effects
The interstellar medium - the coronal gas - forms a column between locations in space. The sun is 4 light years inside one edge of a 60 light-year-across Local Cloud with a density of 0.3 hydrogens per cubic centimeter, or 3e5 H/m³, encountering the sun as it moves towards Scorpio at 25 km/s. Around that cloud is the Local Bubble, 300 LY across with a density of 50 H/m³. A light year is 9.5e15 meters, so for the first 4 light years in one direction, and more than 50 LY in the opposite direction, we encounter a column of hydrogen atoms with a density of about 1e21 H/m²-LY. That is the density of a layer of liquid water 30 nm thick per light year. 100 light years, 3 micrometers.
These protons will implant themselves in the surface of any object passing through them. At a mere 25 km/s, the energy per proton is 3.6 electron volts - many will bounce off. Approaching the speed of light, the energy approaches multiples of the mass energy of the proton, 938 MeV/c². That will damage solid structure to the implant depth. The table below (from Janni 1966) shows stopping range in silicon extrapolated by gram density to glass and water - perhaps poorly.
The numbers below are estimates - real measurements needed!
Conditions in Local Cloud, 3e5 H/m³, 5e-22 kg/m³ as perceived from moving frame |
||||||||
speed |
v/c |
1\over{c²-v²} |
energy |
flux |
Stopping Range est mm |
Pressure |
|
|
m/s |
|
|
|
1/m2-s |
SiO₂ |
H₂O |
Pascals |
|
25k |
8e-5 |
1 |
4 eV |
8e9 |
|
|
|
|
30k |
1e-4 |
1 |
5 eV |
9e9 |
|
|
|
|
100k |
3.3e-4 |
1 |
50 eV |
3e10 |
1.1e-3 |
2.8e-3 |
|
|
300k |
1e-3 |
1 |
500 eV |
9e10 |
3.3e-3 |
8.5e-3 |
14μ |
|
1M |
3.3e-3 |
1 |
5 keV |
3e11 |
1.6e-2 |
4.1e-2 |
500μ |
|
1.4M |
5e-3 |
1 |
10 keV |
4e11 |
2.5e-2 |
6.5e-2 |
1.4m |
low energy ion implantation |
3M |
1e-2 |
1 |
50 keV |
9e11 |
0.08 |
0.2 |
14m |
low energy van Allen belt |
4.2M |
0.014 |
1 |
100 keV |
1.3e12 |
0.15 |
0.4 |
37m |
100 keV van Allen belt, 6000x more flux |
10M |
0.033 |
1 |
500 keV |
3e12 |
0.6 |
1.6 |
0.5 |
high energy ion implantation |
14M |
0.042 |
1 |
1 MeV |
4e12 |
1.2 |
3.1 |
1.4 |
1 MeV van Allen belt, 2e5 more flux |
30M |
0.10 |
1.01 |
5 MeV |
9e12 |
4.4 |
1.2 |
14 |
7 W/m2 particle power |
100M |
0.33 |
1.13 |
50 MeV |
3e13 |
37 |
95 |
570 |
|
200M |
0.67 |
1.80 |
380 MeV |
8e13 |
|
|
7K |
highest energy van Allen belt, 1e12 more flux |
250M |
0.83 |
3.28 |
500 MeV |
1.4e14 |
|
|
26K |
11 KW/m2 particle power |
