Abans del llançament de la sonda de dilluns a la Agència Espacial Europea, mirem cap enrere en la centenària història de la recerca de vida a Mart
El llançament de l'Agència Espacial Europea de (ESA) nau espacial ExoMars traça Gas Orbiter dilluns 14 Març és un moment significatiu en l'exploració espacial. Això marca un nou començament en la recerca de vida a Mart.
L'interès per la vida a Mart es remunta segles. L'astrònom holandès Christiaan Huygens segle 17 va especular en el seu llibre Cosmotheoros sobre les condicions necessàries per a la vida. No veia cap raó per la qual Mart o els altres planetes no podien ser habitades.
Es diu 'Planetarians' dels habitants i es va lliurar a l'opinió que la seva alçada seria dictat per la grandària del planeta, de manera que fossin prou gran com per moure amb facilitat - com ho fem a la Terra.
Al segle 18 William Herschel va estudiar Mart, prenent nota de les brillants casquets polars i suposant que les marques fosques al planeta probablement eren mars. Es va pensar que la Terra i Mart eren alguna cosa similar, escrit en les Transaccions filosòfiques de la Royal Society que els habitants de Mart "probablement gaudeixen d'una situació similar a la nostra."
Un segle més tard, astrònoms pensaven alguna cosa diferent. Telescopis estan millorant tot el temps i els astrònoms estaven veient el que semblava ser rectes línies fosques que connecten els 'mars' foscos.
American astronomer Percival Lowell popularised the notion that these were canals. Mars was mostly desert, ell va pensar, and these canals were the last ditch efforts of a civilisation fighting to irrigate their dying world.
The idea provided inspiration for HG Wells and his novel The War of the Worlds, in which the Martians abandon their fight at home and invade Earth instead.
It is now thought that the ‘canals’ were optical illusions produced by slightly inferior telescopes. As soon as technology improved, the lines were never seen again.
By the 20th century, analysis of Mars’ atmosphere showed that there was hardly any water vapour present, and this put paid to the idea that there were large bodies of water there. The arrival of the first spacecraft in the 1960s showed that there had been water in the distant past and this eventually led to our current ideas that microbial life could have formed billions of years ago and that perhaps some is still clinging on.
In the late 1970s, Nasa’s two Viking missions touched down on the planet. Each lander contained a biological laboratory capable of performing four different experiments that could reveal life. Although the Labeled Release experiment gave initially positive results, it failed when repeated.
The other three experiments showed only negative results and so officially Nasa declared that no life was detected. Controversially, some scientists continue to claim that the initial success of the Labeled Release experiment should be treated as proof of life.
Regardless of such claims, Nasa have been moving away from looking for life a Mart. en comptes, they have concentrated on investigating the evidence that Mars was once more Earth-like with flowing water and a thicker atmosphere.
The latest twist began serendipitously in 2003. Esa’s Mars Express spacecraft made a tentative detection of methane in the planet’s atmosphere. Methane is a short-lived gas, and on Earth it is produced mainly by lifeforms.
En 2014, Nasa’s Curiosity rover also detected whiffs of the gas. This increased speculation that perhaps there were microbial communities still alive on Mars, producing the gas. The recent detection of running water on Mars also upped the stakes.
No obstant això, there is also the chance that the methane is produced by geological processes.
Esa’s ExoMars Trace Gas Orbiter is designed to find out which of these options is the most likely. It will look for the gas with unprecedented sensitivity and map its distribution across the planet over a number of years. If anywhere is particularly rich in methane production, that will be a natural target for further investigations.
On which note, Esa is sending the ExoMars rover to Mars’s surface a 2018. It will be equipped with instruments capable of detecting the signs of past and present microbial life.
The long search for life on Mars continues…
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