Earth

Our home and third planet from the Sun. Everyone knows this planet, but do you stop and think about the Earth from an astronomical perspective? Well, here you can!

Formation

After the Sun ignited hydrogen and began to supply energy to the Solar System, space around the Sun was immediately showered by a pressure wave of radiation, pushing the lighter gas and dust far out into the Solar System. Heavier rocky material was not affected, and over time collided to form larger planetesimals. These planetesimals fuel the planets’ formation as they fall under the gravitational pull of the increasing planetary mass, eventually forming Earth.

Structure

Like the other terrestrial planets, Earth has a silicate crust and a molten iron core. Earth is the densest planet in the Solar System. The crust spans for about 3 miles at the thinnest underneath the oceans, to 15 miles at the thickest on the continents. The lithosphere contains both the crust and the tectonic plates that are present for the continental shifts over millions of years. These plates are up to 38 miles deep with the major plates corresponding to the continents on the Surface. The mantle is divided into the upper mantle and the lower mantle. The upper mantle contains the bottom part of the tectonic plates, while the lower mantle contains solid rock. The outer core consists of a viscous mixture of rock thanks to the large pressure and heat generated by radioactive materials. The inner core consists of solid rock that is mostly composed of iron and nickel.

Surface

The surface of Earth is unique in the Solar system, the only one with liquid water. Oceans cover 71 percent of the surface of the Earth, with continental landmasses covering the rest. Unlike other terrestrial planets, Earth has ongoing geological activity and weathering, reducing the number of visible craters on the surface.

Atmosphere

Earth’s atmosphere is mostly composed of nitrogen at 78 percent, then oxygen at 20 percent, water at 1 percent, and trace amounts of carbon dioxide. The lowest section of the Earth’s atmosphere is the troposphere that contains life and stretches up to 11 miles above the surface of the Earth at the Equator. Without photosynthesis being performed by primitive ocean life, the current atmosphere would not have the large amount of oxygen, which also would not have formed the ozone layer, protecting land-based life from dangerous ultraviolet rays. The atmosphere also causes a greenhouse effect, allowing for raised temperatures on Earth compared to the temperature at which the Sun’s rays would directly heat the Earth. The difference between the two is 0 degrees Fahrenheit without the atmosphere compared to 60 degrees with the warming effect of the atmosphere.

Magnetic Field

Earth has the largest magnetic field of the terrestrial planets thanks to the kinetic movement of the Earth’s core. The poles of the magnetic field are located near the Earth’s poles, but are not in the same position. The Solar wind compresses the magnetic field on the side that faces the Sun while creating a large tail on the side of the magnetic field that does not face the Sun. The magnetic field helps to protect the Earth from Solar winds while giving magnificent light shows in the form of aurora borealis.

Satellites

Earth has around 4,500 satellites in orbit, with most in low Earth orbit for communications purposes. The satellites that are used to conduct science missions will be explained here.

The most famous of the Earth satellites is the International Space Station. As a collaboration between the US, Russia, Europe, Japan, and Canada, the ISS is the longest continuously occupied human settlement in space, operating now for just over twenty years. The ISS allows experimentations to be conducted in a space that is in free fall, simulating a zero-gravity environment.

On the lesser known side, NASA has launched many satellites as a part of their Earth Observing System program. The Landsat satellites image the Earth, while the Cloudsat satellites image the atmosphere for cloud data. The AQUA satellite records sea levels, precipitation amount, ice cover, and surface temperatures. In order to measure soil moisture levels, NASA created the SMAP satellite. Terra was launched in order to observe the Earth’s climate on a global scale. AURA studies the Earth’s climate, air quality, and ozone layer.