Europa orbits Jupiter at an average speed of 13.7 km/s. At the same time Jupiter orbits the Sun at a speed of 13.1 km/s. This means that Europa has an orbital speed relative to the Sun of 26.8 km/s when it is in the shadow behind Jupiter once every 85 hours.
Earth's orbital speed is 29.8 km/s which is only 3.0 km/s different from Europa's max solar orbital speed. Compared with Mars which has an orbital speed of 24.0 km/s which is 5.8 km/s different form Earth's.
- Does this mean that it is easier to land a spacecraft on Europa, than it is to land on Mars?
- Io with 17.3 km/s around Jupiter gives it a max of 13.1 + 17.3 = 30.4 km/s around the Sun when in shadow once every 43 hours. Just a 0.6 km/s difference, our own Luna orbits us at 1.0 km/s. Does any sizable object have a more similar speed to Earth than Io does?
And considering that Europa has no atmosphere and just about 1/3 of Mars' surface gravity, it looks like an easy target to go to! According to a table on this page (which refers to a calculator by Erik Max Francis) a Hohmann transfer from Earth to Jupiter takes 2 years and 9 months. That's pretty quick compared to many of the current missions which travel even 10 years.
Shouldn't also radiation problems be smaller for a lander than for an orbiter (either of Europa itself or an orbiter around Jupiter which makes repeated close Europa fly bys) because the moon covers half of the radiating source. And even more in a deep crack. And sensitive electronics might perhaps be drilled/melted down a few meters into the ice to get complete shielding.
Is there a monster factor in the Jupiter system which makes it much harder to land on Europa (or Io) than I've made it look here? Harder than to land on Mars.