diff --git a/Rakefile b/Rakefile
new file mode 100644
index 00000000..f29f7c93
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,9 @@
+require 'rake/testtask'
+
+Rake::TestTask.new do |t|
+  t.libs = ["lib"]
+  t.warning = true
+  t.test_files = FileList['specs/*_spec.rb']
+end
+
+task default: :test
\ No newline at end of file
diff --git a/lib/main.rb b/lib/main.rb
new file mode 100644
index 00000000..98c5d9b4
--- /dev/null
+++ b/lib/main.rb
@@ -0,0 +1,112 @@
+require_relative "planet"
+require_relative "solar_system"
+
+require "awesome_print"
+require "colorize"
+
+SOLAR_SYSTEM = SolarSystem.new("Sol")
+
+# Optional: handling user entering bad command
+def handling_input(input)
+  possible_inputs = ["list planets", "planet details", "add planet", "find distance", "exit"]
+  until possible_inputs.any? { |word| word == input }
+    print "Invalid input.\nPlease enter \"list planets\", \"planet details\", \"add planet\", \"find distance\" or \"exit\": "
+    input = gets.chomp.downcase
+  end
+  return input
+end
+
+def existing_planets
+  earth = Planet.new("Earth", "blue-green", 5.972e24, 1.496e8, "it's the only planet known to support life")
+  SOLAR_SYSTEM.add_planet(earth)
+
+  venus = Planet.new("Venus", "yellow", 4.867e24, 67.3e6, "40 spacecraft have explored Venus")
+  SOLAR_SYSTEM.add_planet(venus)
+
+  mercury = Planet.new("Mercury", "blue", 3.285e23, 28.6e6, "kid-friendly")
+  SOLAR_SYSTEM.add_planet(mercury)
+
+  mars = Planet.new("Mars", "orange", 6.39e23, 141.7e6, "it has 2 moons")
+  SOLAR_SYSTEM.add_planet(mars)
+end
+
+def list_planets(input)
+  if input == "list planets"
+    list = SOLAR_SYSTEM.list_planets
+    puts list.colorize(:green)
+  end
+end
+
+def planet_details(input)
+  if input == "planet details"
+    puts "Which planet do you want to learn about? Choose one: Earth, Venus, Mercury, Mars"
+    planet_chosen = gets.chomp.downcase
+    # Optional: when user enters a planet that doesn't exist, raise an exception.
+    if !SOLAR_SYSTEM.planets.map { |planet| planet.name }.include?(planet_chosen.capitalize)
+      raise ArgumentError, "Planet entered is not in the list."
+    end
+    puts "\n"
+    puts SOLAR_SYSTEM.find_planet_by_name(planet_chosen).summary.colorize(:green)
+  end
+end
+
+def add_planet(input)
+  if input == "add planet"
+    puts "What is the planet's name?"
+    name = gets.chomp.capitalize
+    puts "What is its color?"
+    color = gets.chomp
+    puts "What is its mass(kg)?"
+    mass_kg = gets.chomp.to_f
+    # Optional: if user enters a bad value
+    until mass_kg > 0
+      puts "Mass must be a number greater than 0. Please enter again: "
+      mass_kg = gets.chomp.to_f
+    end
+    puts "What is its distance from the Sun in km?"
+    distance_from_sun_km = gets.chomp.to_f
+    # Optional: if the user enters a bad value
+    until distance_from_sun_km > 0
+      puts "Distance from the Sun must be a number greater than 0. Please enter again: "
+      distance_from_sun_km = gets.chomp.to_f
+    end
+    puts "What is its fun fact?"
+    fun_fact = gets.chomp
+
+    planet = Planet.new(name, color, mass_kg, distance_from_sun_km, fun_fact)
+    SOLAR_SYSTEM.add_planet(planet)
+    puts "#{name} has been added with the details below:".colorize(:green)
+    puts SOLAR_SYSTEM.find_planet_by_name(name).summary.colorize(:green)
+  end
+end
+
+def find_distance(input)
+  if input == "find distance"
+    puts "Enter first planet: "
+    planet_name1 = gets.chomp.downcase
+    puts "Enter second planet: "
+    planet_name2 = gets.chomp.downcase
+    puts "The distance is #{SOLAR_SYSTEM.distance_between(planet_name1, planet_name2)}".colorize(:green)
+  end
+end
+
+def main
+  existing_planets
+  puts "What would you like to do?"
+  print "Please enter \"list planets\", \"planet details\", \"add planet\", \"find distance\" or \"exit\": "
+  input = gets.chomp.downcase
+  input = handling_input(input)
+
+  until input == "exit"
+    list_planets(input)
+    planet_details(input)
+    add_planet(input)
+    find_distance(input) # OPTIONAL: Implement the optional distance_between method
+    puts "What would you like to do next?"
+    puts "Please enter \"list planets\", \"planet details\", \"add planet\", \"find distance\" or \"exit\": "
+    input = gets.chomp
+    input = handling_input(input)
+  end
+end
+
+main
diff --git a/lib/planet.rb b/lib/planet.rb
new file mode 100644
index 00000000..47e426bc
--- /dev/null
+++ b/lib/planet.rb
@@ -0,0 +1,16 @@
+class Planet
+  attr_reader :name, :color, :mass_kg, :distance_from_sun_km, :fun_fact
+
+  def initialize(name, color, mass_kg, distance_from_sun_km, fun_fact)
+    @name = name
+    @color = color
+    @mass_kg = mass_kg
+    @distance_from_sun_km = distance_from_sun_km
+    @fun_fact = fun_fact
+  end
+
+  # gets the details of the planet
+  def summary
+    return "#{name} is a/an #{color} planet. Its mass is #{mass_kg}kg, and it is #{distance_from_sun_km}km from the Sun. Fun fact: #{fun_fact}."
+  end
+end
diff --git a/lib/solar_system.rb b/lib/solar_system.rb
new file mode 100644
index 00000000..413bc0eb
--- /dev/null
+++ b/lib/solar_system.rb
@@ -0,0 +1,39 @@
+require_relative "planet"
+
+class SolarSystem
+  attr_reader :star_name, :planets #should keep? if so, need to add to spec
+
+  def initialize(star_name)
+    @star_name = star_name
+    @planets = []
+  end
+
+  def add_planet(planet)
+    raise ArgumentError, "Planet has to be an instance of Planet class" if !planet.is_a?(Planet)
+    raise ArgumentError, "Planet has already been added." if @planets.any? { |i| i.name.downcase == planet.name.downcase }
+    @planets.push(planet)
+  end
+
+  def list_planets
+    list = "\nPlanets orbitting #{@star_name}:\n"
+    @planets.each_with_index do |planet, index|
+      list = list + "#{index + 1}. #{planet.name}\n"
+    end
+    return list
+  end
+
+  def find_planet_by_name(name)
+    @planets.each do |planet|
+      return planet if (planet.name).downcase == name.downcase
+    end
+    # if the planet is not found, raise an exception
+    raise ArgumentError, "#{name} is not found."
+  end
+
+  # Optional: takes two planet names as parameters and returns the distance between them
+  def distance_between(planet_name1, planet_name2)
+    distance_planet1 = find_planet_by_name(planet_name1).distance_from_sun_km
+    distance_planet2 = find_planet_by_name(planet_name2).distance_from_sun_km
+    return (distance_planet1 - distance_planet2).abs
+  end
+end
diff --git a/specs/planet_spec.rb b/specs/planet_spec.rb
new file mode 100644
index 00000000..880d73c5
--- /dev/null
+++ b/specs/planet_spec.rb
@@ -0,0 +1,34 @@
+
+require "minitest/autorun"
+require "minitest/reporters"
+require "minitest/skip_dsl"
+
+require_relative "../lib/planet"
+
+# Get that nice colorized output
+Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
+
+describe "planet" do
+  describe "initialize" do
+    it "will create an instance of the class Planet with 5 parameters" do
+      new_planet = Planet.new("earth", "blue", 45, 67, "supports life")
+      expect(new_planet).must_be_instance_of Planet
+    end
+
+    it "will correctly read the parameters of the planet" do
+      new_planet = Planet.new("earth", "blue", 45, 67, "supports life")
+      expect(new_planet.name).must_equal "earth"
+      expect(new_planet.color).must_equal "blue"
+      expect(new_planet.mass_kg).must_equal 45
+      expect(new_planet.distance_from_sun_km).must_equal 67
+      expect(new_planet.fun_fact).must_equal "supports life"
+    end
+
+    describe "summary" do
+      it "will return a summary of the planet" do
+        new_planet = Planet.new("earth", "blue", 45, 67, "supports life")
+        expect(new_planet.summary).must_be_instance_of String
+      end
+    end
+  end
+end
diff --git a/specs/solar_system_spec.rb b/specs/solar_system_spec.rb
new file mode 100644
index 00000000..e9de1d86
--- /dev/null
+++ b/specs/solar_system_spec.rb
@@ -0,0 +1,65 @@
+require "minitest/autorun"
+require "minitest/reporters"
+
+require_relative "../lib/solar_system"
+
+# Get that nice colorized output
+Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
+
+describe "solar_system" do
+  describe "initialize method" do
+    new_sol = SolarSystem.new("New Sol")
+    it "will create an instance of the class SolarSystem with an empty array planets " do
+      expect(new_sol).must_be_instance_of SolarSystem
+      expect(new_sol.planets).must_equal []
+    end
+
+    it "will read the star name when initialized" do
+      expect(new_sol.star_name).must_equal "New Sol"
+    end
+  end
+
+  describe "add_planet method" do
+    new_sol = SolarSystem.new("New Sol")
+    it "will take a planet and return an array of planets" do
+      pluto = Planet.new("Pluto", "pink", 56, 87, "pet-friendly")
+      expect(new_sol.add_planet(pluto)).must_be_instance_of Array
+    end
+
+    it "will take the parameter as a planet" do
+      pluto = "Pluto"
+      # note to me: when using curly braces, the code inside runs before expect
+      # when using with .must_raise
+      expect { new_sol.add_planet(pluto) }.must_raise ArgumentError
+    end
+  end
+
+  describe "list_planets method" do
+    new_sol = SolarSystem.new("New Sol")
+    pluto = Planet.new("Pluto", "pink", 56, 87, "pet-friendly")
+    new_sol.add_planet(pluto)
+    it "will return true if the list is an instance of a string" do
+      expect(new_sol.list_planets).must_be_instance_of String
+    end
+  end
+
+  describe "find_planet_by_name method" do
+    new_sol = SolarSystem.new("New Sol")
+    pluto = Planet.new("Pluto", "pink", 56, 87, "pet-friendly")
+    new_sol.add_planet(pluto)
+    it "will return an instance of Planet" do
+      expect(new_sol.find_planet_by_name("Pluto")).must_be_instance_of Planet
+    end
+  end
+
+  describe "distance_between method" do
+    it "will return the distance between two planets" do
+      new_sol = SolarSystem.new("New_Sol")
+      pluto = Planet.new("Pluto", "pink", 56, 87, "pet-friendly")
+      puffer = Planet.new("Puffer", "yellow", 78, 89, "not a planet")
+      new_sol.add_planet(pluto)
+      new_sol.add_planet(puffer)
+      expect(new_sol.distance_between(pluto.name, puffer.name)).must_equal 2
+    end
+  end
+end