Key Facts 

• A day on Venus is longer than a year! It takes 243 Earth days to complete 1 rotation while it orbits around the Sun in 225 Earth days. 

• We can experience the same pressure on the surface of Venus by diving about 1 km into oceans here on Earth.

Place around Jupiter 

Europa is the 6th closest moon of planet Jupiter at an average distance of 5.2 astronomical units from the Sun. It orbits Jupiter every 3.5 Earth days and only one side of Europa faces the planet due to gravitational lock.

The innermost 3 satellites of the Jovian system are in an orbital resonance. For every one orbit of Ganymede, Europa Orbits twice and Io orbits four times. This also means, sometimes all these moons align, with Io and Europa aligning most frequently.  

Europa’s orbit is not exactly circular and hence, as Europa approaches closer to Jupiter, the gravitational attraction elongates the moon in the direction towards the planet and away from it. And as it reaches the farthest point from Jupiter, Europa relaxes back into a more spherical shape.  

The Surface of Europa

The icy surface of Europa is filled with long and dark ridges and cracks known as ‘Lineae’. This is believed to occur due to the active glaciers sliding on the surface. These patterns and features of shifting Icy tectonic plates are a result of Jupiter’s Gravity tugging and pulling the Europa’s Surface causing friction and melting in the ice plates. Not all surface patterns are explained due to this phenomenon, some sections of the surface have rotated at certain angles as if the surface is floating above a liquid beneath. 

A subsurface ocean? How?

Instruments onboard Galileo spacecraft during its mission, detected a magnetic field generated by Europa. This Magnetic field appeared to be shifted during subsequent flybys. Scientists explain this anomaly by understanding that the Europa behaves like a conductor with a special induced magnetic field around it. Which is believed to be caused by an electrically conductive fluid present between the crust and mantle (Salt Water). 

Galileo spacecraft was also able to fly through the plumes of water-rich material ejected from Europa’s surface. Much like Saturn’s moons: Enceladus and Triton, further strengthening the hypothesis of the subsurface ocean.

Furthermore, scientists have also been pointing Hubble Space Telescope towards the moon. It has also detected the presence of water-rich plumes at the south pole of the Europa by taking ultraviolet images of Europa as it was passing in front of Jupiter. 

Fun Facts

• Europa is 5 times more reflective than our moon due to its surface of water ice.

• Europa’s mass exceeds the combined mass of all the smaller moons in the Solar System. 

• Europa has the smoothest surface compared to any other known body in the solar system. 

• Radiation levels per day on the surface of Europa are 1800 times the average annual dose of a human here on Earth.

A planetary system is a general term used for describing the system of planets and a host star around which these planets orbit. Our Sun is named ‘Sol’ from the Latin word: solis and anything related to it is ‘solar’, Hence the: Solar System. 

Our Planetary system consists of our host star, the Sun, and planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. It also has a number of dwarf planets like pluto, many moons, and millions of asteroids and meteoroids.

The question is: how big is our planetary system? Where can we plot the boundaries and declare that outside is not in our solar system? How far the Voyager 1 and Voyager 2 have to travel to finally be outside the solar system?

Solar Winds

The Sun generates a wind of ionized particles and magnetic field that stream millions of miles into space. This is known as ‘Solar Wind’ which defines the boundaries of the solar system. This can be imagined as a bubble-like region of space created and inflated by our Sun’s plasma(Heliosphere). 

Termination shock

The particles from the sun are emitted at about 400 km/hour. But, as we move farther away from the Sun, the pressure of the solar wind drops as a square of that distance. And eventually, the solar wind can no longer maintain the supersonic flow against the interstellar medium. Here, the wind slows down to subsonic speeds causing compression, heating, and change in the magnetic field known as ‘Termination shock’. It is believed to be 75 to 90 Astronomical units from our Sun.  

Heliosheath

The wind flow is not yet stopped but slowed down due to interaction with the interstellar medium. Outside of the termination shock is the region called ‘heliosheath’ where the flow of ionized particles is turbulent. This region is believed to be at approximately 80 to 100 astronomical units from the Sun.

Heliopause

The outer edge of the heliosheath is known as ‘Heliopause’ where the solar wind does not possess enough strength to counteract the cosmic galactic wind. The protons from the Sun become rare, approaching the Heliopause. This is the theoretical boundary of the solar system where stellar winds from the surrounding stars dominate the region of space. 

A bit of History 

Discovered by William Herschel on August 28, 1789, its name comes from Greek mythology(Giant Enceladus). Not a lot was known until Voyager 1 and Voyager 2 spacecraft passed nearby the planet in 1980 and 1981. Later in 2005, the Cassini spacecraft discovered the presence of water and captured some incredible pictures of the coldest satellite of Saturn.

Place around Saturn

From the total of 82 moons of Saturn, Enceladus is the 6th largest moon of the planet. 2nd closest major moon(There are some objects in Saturn’s rings which may or may not be considered as moons) to Saturn after Mimas. It orbits Saturn every 32.9 hours, fast enough to be observed in a single night. 

It is in a 2:1 orbital resonance with the moon: Dione(fourth closest major moon of Saturn). This orbital resonance means Enceladus completes 2 revolutions around Saturn for every 1 Revolution of Dione around the planet. This plays a major role in the orbit of the Enceladus, forcing it to be non-circular (eccentricity = 0.0047). This results in Tidal forces which heat up the interior of the moon.

Cryovolcanism on Enceladus

The moon is located at 9.5 Astronomical Units from our star. A major reason why water cannot exist in the liquid state on its surface. But the Tidal forces acting on the moon heats up the core, melting the innermost layer of ice and forms a subsurface ocean (Process known as ‘Tidal Heating’). This water then erupts from the weakest parts of the crust with a speed of about 1200 km/hr. This exceeds the escape velocity on Enceladus. With no gravitational influence of the moon on this material, it adds the water crystals to the E-Ring of Saturn. Some water crystals gravitate back towards the surface of Enceladus, renewing it continuously.  

During the Cassini Mission, the spacecraft was able to pass through the plumes of the volcanoes. And with the help of Cosmic Dust Analyzer on-board, it was able to detect the presence of amino acids, carbon dioxide, methane, nitrogen, and water in the plumes, contributing to the possibility of life beneath the surface of Enceladus.

Fun Facts

• The icy surface on the active south pole is constantly stretching and buckling due to gravitational forces. 

• Enceladus has the whitest, most reflective surface in the solar system.

• Enceladus sprays geysers of water ice, creating a ring of its own around Saturn(E Ring).

• Enceladus is small enough to fit into the length of the United Kingdom.