The Moons of Jupiter

    Jupiter is the biggest planet of the Solar System, it is more than 1000 times bigger than Earth. Its four bigger moons were discovered by Galileu Galilei in 1610, the are (in orbital order): Io, Europa, Ganimedes and Calisto. These moons are so big that if they had its own orbit around the Sun they would be consider as planets.

Galilean Moons, the Earth and the Moon (in scale).

Io

    Io is the closest moon to Jupiter, because of that it is highly influenced by the jovian gravity, just like the Earth is influenced by the Moon's gravity. Here, on Earth, the Moon's influence causes the tides in the sea. On Io instead of water, the tides are made of soil. Jupiter's influence is so hard that it changes Io's diameter in about 100 meters. This process generates heat inside Io and produces huge vulcanos around its surface. The yellow color of Io is due to the sulfur and sulfur dioxide produced by the vulcanic activity. See the images below:

Io with a huge red spot caused by an eruption.

Io's surface. The black dots are very big vulcanos.

Europa

    Europa is the most incredible moon of Jupiter, it is all covered by ice and because of Jupiter's gravity there's heat inside of it, the heat melt the ice and creates a "planetary" ocean underground. We can see the Jupiter's influence in the huge cracks of Europa's surface, some of than are more than one hundred miles long. Europa and Mars are the very best places to search for extraterrestrial life in our Solar System. In fact, there is two times more water on Europa then on Earth. See the images below:

Europa (image created with photos taken by the Galileo probe). 

Europa (photo taken by the Galileo probe).

Cracks on Europa's surface.

Cracks and details of Europa's surface.

Ganymede

    Ganymede is the biggest moon of Jupiter, it is bigger than the planet Mercury. Its surface is composed by water ice and dust. Although it is more distant from Jupiter, Ganymede is also influenced by Jupiter's gravity and probably it also has a big ocean underground.

Photo of Ganymede taken by the Voyager 1 probe.

Photo of Ganymede taken by the Galileu probe.

Calixto

    Calixto is the farther moon of Jupiter and the second largest. There is a lot of craters on its surface and, as Ganymede, it is composed by ice water and dust, and possibly there is liquid water on its subsoil.

Photo of Calixto taken by the Galileu probe. 

Photo of Calixto taken by the Voyager 1 probe.

Photos: Wikimedia (commons.wikimedia.org)

Enceladus, a Tiny Moon of Saturn

    Enceladus is a tiny moon of Saturn and one of the major targets for the search of extraterrestrial life. Enceladus is almost totally composed by ice and there are giant geysers in its south pole. The water vapor from the geysers go so high that it formed a ring around Saturn. It shows that there is liquid water on its interior and on Earth where there is water, there is life.

Photo of Enceladus taken by the Cassini probe. Source: NASA

Geysers on Enceladus. Source: Wikimedia

Comparison between Enceladus and the United Kingdom. Source: Wikimedia

Encélado

    Encélado é uma pequena lua de Saturno e um provável alvo para a procura de vida extra-terrestre. Encélado é quase totalmente feita de gelo e possui enormes gêiseres em seu polo sul, o vapor d'água proveniente deles alcança centenas de quilômetros de altura e acaba entrando em órbita de Saturno. Isso é uma evidência de que há água em estado líquido no interior de Encélado.

Foto de Encélado tirada pela sonda Cassini. Fonte: NASA

Comparação de tamanho entre Encélado e a Terra. Sua superfície é pouco maior do que o Reino Unido. Fonte: Wikimedia.

Gêiseres na superfície de Encélado. Fonte: Wikimedia.

Titan, the moon of Saturn

   Titan is the biggest moon of Saturn and it is the only other place in the Solar System besides Earth where there is lakes and rivers (which are made of methane). Recently JRehling ((http://www.unmannedspaceflight.com/index.php?showuser=321) made an incredibly map of Titan's surface:

    He used photos taken by the Cassini probe. I made a 3D version of it using Blender 3D:

   I also made a short video of it:

The Earth's Size

    The Earth's diameter is 12 756,2 kilometers (7 926.3 miles) and it is three times bigger than the Moon's diameter (which is 3474,8 Km or 2 159,14 miles), lsee the image below:

    Mars, the red planet, has about half of Earth's diameter (6792,4 Km or 4 220,6 miles), see the image below:

    The following video shows a size comparizon between planets, moons and stars in our galaxy:



Photos: Wikimedia (commons.wikimedia.org)

Veja a versão em português aqui: http://cosmonautax.blogspot.com.br/2012/10/tamanho-da-terra.html

Titã

   Titã é a maior lua de Saturno e é, também, o único corpo celeste no Sistema Solar, além da Terra, que contém lagos e rios (feitos de metano líquido). Recentemente JRehling (http://www.unmannedspaceflight.com/index.php?showuser=321) criou um incrível mapa da superfície de Titã:

    Ele utilizou imagens feitas pela sonda Cassini, que orbita Saturno e suas luas. Eu criei uma versão 3D de Titã utilizando o software Blender 3D e esse mapa:

   E, depois de apanhar um pouco do Blender, criei uma animação:

Rio Alienígena

        A sonda europeia/americana Cassini capturou fotos de um rio alienígena com 400 quilômetros de comprimento em Titã, a maior lua de Saturno. O curso do rio segue por falhas geológicas até o mar Kraken. Mas, diferente dos rios da Terra, não há água correndo nele, os rios, lagos e mares em Titã são de etano e metano líquidos. A chuva em Titã também é composta de etano e metano, os rios são formados pelo líquido da chuva que cai em regiões altas e escorrem para regiões mais baixas, onde formam lagoas, lagos e mares. Confira abaixo algumas imagens de radar dos rios e do mar de Kraken em Titã:

Rio em Titã desembocando no mar Kraken, à direita.

Imagem de radar do mar Kraken acima.

Imagens: http://commons.wikimedia.org