The Rocket Equation
The Tsiolkovsky Rocket Equation, or Ideal Rocket Equation, describes the motion of vehicles that follow the basic principle of a rocket: a device that can apply acceleration to itself (a thrust) by expelling part of its mass with high speed and thereby move due to the conservation of momentum. There are two forms of the equation that we use regularly for calculations.
Europa - A Moon of Jupiter
Europa is the fourth largest moon of Jupiter next to Ganymede, Callisto, and Io. These four moons are known as the Galilean moons because they were discovered in 1610 by Galileo. Galileo was looking through his telescope and saw what looked like a mini solar system inside our solar system. He saw the largest planet in our solar system, Jupiter, with these four moons orbiting around it like it was a star and planets. This changed the way of thinking of our place in the universe from Aristotle's "humans are the center of the universe" train of thought.
Europa has an ice-crust estimated to be between 3-30 km thick and underneath that is a liquid water ocean. Europa is about the size of Earth's moon, but it may contain up to twice the volume of water! Earth's oceans average of depth of 4 km, where Europa's average estimate is 100 km.
Europa is of much interest to NASA and the science community because it has the best potential to find life outside of Earth in our solar system. From life here on Earth we believe we need three ingredients for habitability: Water, Chemistry, and Energy.
Water: From life on Earth, we usually find life when we have water. Europa has a liquid water ocean so check that box!
Chemistry: We need the building blocks of life, the stuff you find in rocks, carbon and other elements from the periodic table. These could potentially come from the thought to be rocky core of Europa. Chemistry and Energy go together in this case.
Energy: On Earth we have the Sun for our energy, Earth is in the "Habitable Zone" of the solar system to receive enough energy from the Sun to power life. However since Europa is orbiting Jupiter, it is way too far away from the Sun to receive enough energy for harboring life, so we need a different source here. At Jupiter there is something called Tidal Heating. Tidal Heating is where the gravitational fields of Jupiter and the other large moons cause Europa to flex, squishing it and elongating it. This flexing is mechanical energy that gets translated to friction creating heat inside of Europa to help maintain the liquid water ocean. This flexing could potentially create environments like hydro-thermal vents that we here on Earth releasing salts & minerals into the ocean.
With the combination of these three ingredients for habitability, it gives Europa significant astrobiological potential. NASA is headed to Europa to confirm this environment and to look for microbial life in the ocean, or what I like to call #SpaceFish!
Why is Pluto not a Planet Anymore?
Growing up Pluto was definitely my favorite planet. In third grade I picked Pluto as the topic of my science report for the Solar System section. I even made a model of Pluto! But Pluto got downgraded to a Dwarf Planet after the discovery of several more objects like it which reside in what is called the Kuiper Belt.
For an object to be a planet, it needs to meet three requirements defined by the International Astronomical Union (IAU):
It needs to be in orbit around the Sun – Check! So Pluto is 1-for-1!
It needs to have enough gravity to pull itself into a spherical shape – Check! So Pluto is now 2-for-2!!
It needs to have “cleared the neighborhood” of its orbit – ......Nope....Pluto is only 2-for-3....Pluto is not a planet.
Alright so what does "cleared the neighborhood" actually mean and why doesn't Pluto check this box? This means that Pluto has to be the dominant gravitational body in its orbit. To be the dominant gravitational body in one's orbit means that when they interact with other smaller objects they either consume them or sling them away with their gravity. The other objects in Pluto's orbit are much larger in terms of mass. Pluto only has about 7% of the mass of other objects in it's orbit. So sadly this is the reason why Pluto is only a Dwarf Planet and not a regular Planet. :(