  Here is some sample Python code that uses the PyVista library to create a 3D visualization of the solar system:
```
import pyvista as pv

# Load models of the planets
earth = pv.read("earth.obj")
mars = pv.read("mars.obj")
jupiter = pv.read("jupiter.obj")
saturn = pv.read("saturn.obj")
uranus = pv.read("uranus.obj")
neptune = pv.read("neptune.obj")

# Apply textures to the planets
earth.texture = "earth_texture.jpg"
mars.texture = "mars_texture.jpg"
jupiter.texture = "jupiter_texture.jpg"
saturn.texture = "saturn_texture.jpg"
uranus.texture = "uranus_texture.jpg"
neptune.texture = "neptune_texture.jpg"

# Position the planets in a 3D space
earth.position = [0, 0, 0]
mars.position = [100, 0, 0]
jupiter.position = [200, 0, 0]
saturn.position = [300, 0, 0]
uranus.position = [400, 0, 0]
neptune.position = [500, 0, 0]

# Create a light source to simulate the sun
sun = pv.LightSource(position=[100, 100, 100], color=[1, 1, 1])

# Add the planets and light source to a plotter
plotter = pv.Plotter()
plotter.add_mesh(earth, color="blue")
plotter.add_mesh(mars, color="red")
plotter.add_mesh(jupiter, color="yellow")
plotter.add_mesh(saturn, color="green")
plotter.add_mesh(uranus, color="purple")
plotter.add_mesh(neptune, color="orange")
plotter.add_light_source(sun)

# Create subplots for individual planets
earth_subplot = plotter.add_subplot(earth, title="Earth")
mars_subplot = plotter.add_subplot(mars, title="Mars")
jupiter_subplot = plotter.add_subplot(jupiter, title="Jupiter")
saturn_subplot = plotter.add_subplot(saturn, title="Saturn")
uranus_subplot = plotter.add_subplot(uranus, title="Uranus")
neptune_subplot = plotter.add_subplot(neptune, title="Neptune")

# Create a visualization of Venus with and without its atmosphere
venus = pv.read("venus.obj")
venus_atmosphere = pv.read("venus_atmosphere.obj")
venus_subplot = plotter.add_subplot(venus, title="Venus")
venus_atmosphere_subplot = plotter.add_subplot(venus_atmosphere, title="Venus with Atmosphere")

# Show the plotter
plotter.show()
```
This code uses the PyVista library to load models of the planets, apply textures to them, and position them in a 3D space. It also creates a light source to simulate the sun and adds it to the plotter. The code then creates subplots for individual planets and a visualization of Venus with and without its atmosphere. Finally, the code shows the plotter using the `show()` method.