As of 1.0 stable, the Threat Level of a planet is directly related to the planetary biome of planet, not the character. The biome of a planet can be identified by the highlighted keywords in its description, while their threat level is identified by the "Threat" keyword.
- Tier 1 - Low - Iron - Barren1, Asteroid Field, Lush
- Tier 2 - Moderate - Tungsten - Desert, Forest
- Tier 3 - Risky - Titanium - Ocean, Snow, Dry Grassland
- Tier 4 - Dangerous - Durasteel - Mutated, Jungle, Toxic
- Tier 5 - Extreme - Aegisalt, Ferozium, Violium - Frozen, Dark, Frigid Ocean
- Tier 6 - Inconceivable - Solarium - Magma, Volcanic, Scotched
1 Barren planets do not have any ores on them
2 All planets also have coal, copper, silver, gold, core fragment and diamond ores. These are not used as the primary material for most weapons and armor.
All enemies receive a damage multiplier based on the thread level of the planet they're on, so the same enemy species on a Scotched planet (Inconceivable threat) will do significantly more damage than one on a Lush planet (Low threat). Higher threat level planets will also require more EPP upgrades as their environments are less hospitable.
Planets with higher threat level contains higher tiered ores, inclusive of all lower tiered once - eg. a Mutated planet (Dangerous threat) will have Iron, Tungsten, Titanium and Durasteel ore. In general, you need the previous tier's armor and weaponry to explore planets of the next threat level, thus creating a natural progression system, not unlike that of Terraria.
According to currently available sources, farming is not affected by any external factors (soil type, rainfall, biome, temperature etc.). The only factor that affects plant growth is the growth rate of the particular crop. Toxic Tops require roughly 280 growth cycles, whereas Wheat only requires 27 cycles (a growth cycle represents the interval at which the game calculates growth, and is 20 seconds).
Taken from the Starbound Wikia site: http://starbound.wikia.com/wiki/Farming
Obviously, as the game is still in beta, there is room for this to change.
Best Answer
Once you've bookmarked a teleporter you can teleport to it as well as use it to teleport to other bookmarked locations or party members the same way as you would from your ship.
Once a flag is bookmarked you can teleport to it from any teleporter, but once you are there you can not teleport out.
Edit: It's worth noting that there is a difference between casual and normal in that you can only beam to ship from near the surface on normal. So if you are building under ground you cannot easily get anywhere else on normal mode (making teleporters more valuable).