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Neve de gelo seco em Marte

Por Wailã de Souza Cruz – Astrônomo da Fundação Planetário

Mais uma notícia interessante acaba de ser divulgada pela Nasa sobre Marte, e não foi o Curiosity (outro robozinho que posou recentemente no planeta vermelho) que a trouxe. Desta vez foi a sonda espacial Mars Reconnaissance Orbiter. Baseado nos dados coletados pela sonda, cientistas concluíram que pode nevar dióxido de carbono (CO2) nos polos de Marte durante o inverno. Isso nunca havia sido observado em nenhum outro lugar do Sistema Solar.

Marte também tem ciclos climáticos como na Terra. Seu eixo é inclinado cerca de 25º (o da Terra é de 23,5º), o que faz com que, em determinadas épocas, um hemisfério fique mais iluminado que o outro. Mas nesse planeta a instabilidade dos ciclos climáticos e do tempo são surpreendentes. Aqui na Terra os oceanos e as chuvas ajudam a manter o clima.

Sua atmosfera composta por dióxido de carbono, hidrogênio, argônio, pouquíssimo vapor d´água e oxigênio, é muito rarefeita, o que faz com que a temperatura oscile em mais de 100ºC. Essa oscilação torna sua atmosfera bastante dinâmica.

Por isso não chega ser surpreendente que a sonda tenha encontrado neve de CO2 no polo sul durante os invernos de 2006 e 2007. Para se ter gelo seco (como é mais conhecido) as temperaturas devem estar abaixo dos -125ºC. Ainda restam dúvidas se é neve que caiu naquela região, que se estende por mais de 500km de diâmetro, ou se o congelamento aconteceu já na superfície como uma geada. Mas é fato que as partículas de gelo de CO2 observadas são realmente grandes para cair como neve. 

A sonda Mars Reconnaissance Orbiter foi lançada em agosto de 2005 e entrou na órbita de Marte em maio de 2006. Sua principal missão é encontrar evidências da existência de água e estudar seu clima.

Um artigo completo sobre esta descoberta será publicado no Journal of Geophysical Research.

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