The Arecibo Observatory sent a powerful radio signal to space in 1974. Assume there is an alien civilization located on a planet around Alpha Centauri (distance 4.2 light-years from Earth) and they detect this transmission. They immediately send an invasion force that travels at 10% of the speed of light. What year ON EARTH will the alien invasion force arrive

The invasion will arrive in the year 2020

Explanation:

Detailed explanation and calculation is shown in the image below

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.