"""create planets table

Revision ID: 1234567890ab
Revises: 
Create Date: 2023-05-25 10:00:00.000000

"""
from alembic import op
import sqlalchemy as sa
from sqlalchemy.sql import func

# revision identifiers, used by Alembic
revision = '1234567890ab'
down_revision = None
branch_labels = None
depends_on = None


def upgrade():
    # Create planets table
    op.create_table(
        'planets',
        sa.Column('id', sa.Integer, primary_key=True, index=True),
        sa.Column('name', sa.String, unique=True, nullable=False),
        sa.Column('description', sa.String, nullable=True),
        sa.Column('diameter', sa.Integer, nullable=False),
        sa.Column('mass', sa.Integer, nullable=False),
        sa.Column('distance_from_sun', sa.Integer, nullable=False),
        sa.Column('created_at', sa.Integer, default=func.now()),
        sa.Column('updated_at', sa.Integer, default=func.now())
    )


def downgrade():
    # Drop planets table
    op.drop_table('planets')
```

This Alembic migration script creates a new table named 'planets' with the following columns:

- `id` (Integer, Primary Key, Indexed)
- `name` (String, Unique, Not Nullable)
- `description` (String, Nullable)
- `diameter` (Integer, Not Nullable)
- `mass` (Integer, Not Nullable)
- `distance_from_sun` (Integer, Not Nullable)
- `created_at` (Integer, Default value from `func.now()`)
- `updated_at` (Integer, Default value from `func.now()`)

The `upgrade()` function creates the table using the `op.create_table()` operation, while the `downgrade()` function drops the table using `op.drop_table()`.

Note that the revision ID, revision identifiers, and create date are included as comments at the top of the script.