Phobos and Deimos are the two moons of the planet Mars. Scientists believe that they are captured asteroids. Their orbits are particularly interesting; on one hand, Phobos (top image) is slowly getting closer and closer to Mars and will eventually crash into the surface, while Deimos (bottom image) is orbiting further and further away and will eventually escape the planet’s gravity.

(image sources:,

The rotational center of the Milky Way galaxy, known as the galactic center, is located approximately 27000 light years from Earth. Scientists now know that there is a supermassive black hole there, with the mass of four million suns. The area where this black hole exists can be seen in the top two images, in the bright white area to the right of center. There is a large amount of interstellar dust blocking its view, making this part of our galaxy particularly difficult to study.

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These illustrations show HD 189733b, a huge gas giant that orbits very close to its host star HD 189733. The planet’s atmosphere is scorching with a temperature of over 1000 degrees Celsius, and it rains glass, sideways, in howling 7000 kilometre-per-hour winds.

(Image credit: NASA, ESA, M. Kornmesser)

With a distance of 4,553,946,490 km from the Sun, Neptune is the eighth planet and farthest away in our solar system. It has an orbital period of 164.79 Earth years. With an atmosphere of mostly hydrogen and helium, it is a gaseous planet with no physical surface; however, trace amounts of solid water, ammonia, and methane can be found which leads to its designation of an “ice giant.” Because of its great distance from the Sun, it is extremely cold. The temperature at the top of its clouds is approximately −218 °C.

Neptune exhibits interesting and unique weather patters. With wind speeds peaking at nearly 600 meters per second (1340mph) many extreme storms have been observed, such as its Great Dark Spots, anticyclones which can be as large as 13000x6600 km.


(image sources: Voyager II,

Venus is the second closest planet to the Sun and has the highest surface temperature of any planet in our solar system, with an orbital period of about 225 Earth days. Because of its similar gravity and size, it is sometimes known as Earth’s “sister planet.” However, besides these two aspects, the two planets have almost nothing in common. With the densest atmosphere on any terrestrial planet in the solar system, the surface pressure on Venus is about 92 times that of Earth; the same pressure one kilometer beneath Earth’s oceans.

Even though Venus is comparatively much further away from the Sun than Mercury, it is the hotter planet with a surface temperature of around 462 °C; this is because of its dense atmosphere of greenhouse gases such as carbon dioxide and sulfur dioxide. One remarkable aspect of the atmosphere of Venus is the precipitation of liquid sulfuric acid. The surface geology of the planet has been observed by NASA for over twenty years now, and it is seen that there is extensive and violent volcanism at the surface.

(image sources: NASA;,

The Sun is the closest star to the planet Earth, located at the center of our solar system. Consisting of approximately 99.9% of all the mass in the entire solar system, the Sun is the gravitational force holding it together. The Sun’s diameter is around 1,392,684 km, which is 109 times larger than Earth’s. It is estimated to have a mass of about 2.0 x 10^30 kg (2 x 10^27 metric tons), which is 330,000 times heavier than Earth. It is composed of mostly hydrogen (75%), with helium (24%) in considerable amounts as well.

The Sun is able to burn so brightly because of its mass; the center of the star is so compressed that hydrogen atoms actually collide into each other in a process called nuclear fusion, which generates a massive amount of energy and synthesizes larger elements such as helium. It has a measured surface temperature of approximately 5778K (5505 °C). It is expected to live on for another 5.5 billion years, at which point it will turn into a white dwarf; a very dense but small star that only gives off a small amount of energy.

(image sources: SDO:

Europa is Jupiter’s fourth largest moon and the sixth largest moon in the solar system. Based on observations of its smooth and icy surface, it is hypothesized that there could be an underground ocean of liquid water which may harbor life. At this distance from the sun it would be unlikely that any liquid water would form, but because of Europa’s slightly elliptical orbit around the very massive Jupiter, it is possible that tidal friction could occur and generate enough energy to melt ice below the surface. This is supported by the large craters on the surface which are filled with relatively fresh water ice and the geological activity of the planet, which is similar to Earth’s plate tectonics.

If there is in fact a sub-surface ocean on Europa, one hypothesis proposes that the ocean there is approximately twice the volume of Earth’s oceans and several kilometers below the surface ice. Another hypothesis proposes that the surface ice is even thinner. Astrobiologists are particularly interested in it because of the possibility of extraterrestrial life.

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Jupiter’s atmosphere is the largest in the solar system, consisting of mostly hydrogen and helium, which are the two lightest elements. There are trace amounts of methane, ammonia, hydrogen sulfide, and water as well. Being one of the gas giants, Jupiter has no solid surface aside from its relatively small rocky core, which is surrounded by a deep layer of liquid metallic hydrogen. Hydrogen exists in this phase because of the extreme atmospheric pressure that it is under.

The planet’s Great Red Spot is a massive anticyclonic storm with a diameter that is equivalent to two or three Earths on average (24-40000 km E-W, 12-14000 km N-S). Experimental observations have shown that the Great Red Spot is colder than most of the rest of the planet. Although the inner section of the storm is nearly stagnant, the outer edge has wind speeds of up to 432 km/h (120 m/s).

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Titan is the largest moon of the planet Saturn. It is the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid have been found. These bodies of liquid are composed of hydrocarbons; organic compounds such as methane and ethane. These compounds can exist on Titan in the liquid phase because the average surface temperature is approximately 94K (−179.2 °C). The moon is tidally locked in synchronous rotation with Saturn, and always shows one face to the planet. Because of this, there is a sub-Saturnian point on its surface, from which the planet would appear to hang directly overhead.

(images source: Cassini;

Saturn’s hexagon is a persisting hexagonal cloud pattern around the north pole of Saturn, located at about 78°N. The sides of the hexagon are about 13,800 km (8,600 mi) long, which is longer than the Earth’s diameter.

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