Ask A Scientist
Could you walk on Neptune?
Asked by: Duncan Corey
School: Vestal Hill Elementary School
Teacher: Mrs. Morgan
Hobbies/Interests: Hobbies: Playing video games
Career Interest: Small Business Owner
Answer from Parag Vasekar
Solar energy, thin films, materials science
Florida Solar Energy Center (University of Florida), Orlando
Neptune is called a gas planet as it doesn't have a solid surface, but its composition is very close to ice. If one were able to walk on the surface of Neptune, also referred to as the 'ice giant', you would probably sink right in. Besides the temperature of Neptune is sub-zero. But let's just assume for a moment that Neptune has conditions like earth and one decides to walk on Neptune, will it be possible? The answer is yes. To understand this completely, we need to understand the concepts of mass, weight and gravity. We all have seen pictures and video footage of astronauts walking on the surface of the moon and know that it feels very light on the moon as compared to on the earth.
Mass is simply the amount of materials that an object is made of. Mass will remain the same whether we are on the earth, moon or Neptune. Now suppose one were to jump into the air. They wouldn't fly, but instead fall and land on the ground. There is a force which pulls you to the ground. This force is called gravity. The Earth makes gravity, so every time that you jump, you will land on Earth again, because the Earth's gravity pulls you. To make gravity, an object must have a very large number for mass. Earth has mass thousands of times more as compared to humans walking on its surface, so humans feel this gravitational force. The weight of a human or any object on Earth is its mass multiplied by force of gravity. It is this weight which makes us feel 'heavier' or 'lighter' on the surface of any planet.
Gravitational force on Neptune’s surface is 1.14 times that of Earth. So if you weigh 100 pounds on Earth, it is the equivalent of 114 pounds on Neptune and only 16.5 pounds on moon. So you will feel only a little heavier on Neptune and probably can walk comfortably. At the same time since you feel a lot lighter on the moon, you will be almost jumping and floating while walking on moon.
Neptune has much more mass (17 times) than Earth. But the diameter of Neptune is 3.8 times the diameter of the Earth. This makes the gravity on Neptune just 1.14 times the gravity of Earth.