Whether a planet has an atmosphere or not depends on a number of factors: mass, temperature, composition of the crust, volcanic activity, and complex evolutionary processes.
rank the planets according to how well they retain their atmospheres, using the following criteria:
a. the planet that still maintains its primary atmosphere, ranks first.
b. the planet that lost its primary atmosphere but retains a dense secondary atmosphere, ranks second.
c. the planet that lost its primary atmosphere and retains a tenuous secondary atmosphere, ranks third.
d. the planet that retained neither its primary nor secondary atmospheres, ranks last.

Because its reliable.   there is no pollution  the chances of a radiation leak is low

When you go to ask a qustion there will be a picture of a paper clip looking thing and then it will pop up your files and you click on the imajes and then you up load it

Answer: a charge of -1.0  × 10⁻⁴ c must be placed  at x = 26 m.the sign of the charge will be the same sign as the  -4.0  µc charge.======electricstatic force between two point charges  is given by    where k is coulomb's constant,  8.99×10⁹  n·m²/c², q₁ and q₂ are the point charges, and r is the distance between the two point charges.assign positive to q₁let q₁ =  6.0 µc, q₂ = -4.0  µc, q₀ represent the charge at the origin, and q₃ represent this new charge to place.the charge at the origin q₀ would experience the following force f₀₁ from q₁, with r = 6.0 m (note that 1  µc = 10⁻⁶ c)    the force from q₂    the force from q₃    the net force on the origin charge, q₀, has to be zero for no electrostatic forcehaving an equation where k and q₀ can be divided out of the equation will allow us to solve for q₃    isolating:     a charge of -1.0  × 10⁻⁴ c must be placed  at x = 26 m.the sign of the charge will be the same as the  -4.0  µc charge