Fem af de bedste opdagelser ombord på NASAs Curiosity-rover på Mars

At afsløre det potentielt beboelige klima på oldtidens Mars er en vigtig del af NASAs mission om at udforske og forstå det ukendte, at inspirere og gavne menneskeheden - og i 10 år har Curiosity-roveren været på sagen på den røde planet.

For at markere lejligheden er her fem af de mest betydningsfulde opdagelser, som forskere har gjort ved hjælp af Curiosity's Sample Analysis at Mars (SAM) instrumentsuite. SAM er et af NASAs mest kraftfulde astrobiologiske instrumenter på Mars. Designet og bygget på NASAs Goddard Space Flight Center i Greenbelt, Maryland, søger og måler SAM organiske molekyler og lette elementer, som er vigtige for livet, som vi kender det. For at fuldføre denne opgave bærer SAM komponenter, som videnskabsmænd bruger eksternt til at teste prøver fra Mars.

1. Påvisning af organiske forbindelser på Mars

Charles Malespin og Amy McAdam, SAM's hoved- og stedfortrædende hovedefterforskere hos Goddard, er meget enige om SAMs mest betydningsfulde fund:SAM påviste organiske molekyler i stenprøver indsamlet fra Mars' Gale Crater. Organiske molekyler (dem der indeholder kulstof) kunne bruges som byggesten og "føde" for livet. Deres tilstedeværelse på Mars tyder på, at planeten engang kunne have understøttet liv, hvis det nogensinde var til stede.

Mens isotoperne i kuldioxid og metan målt under nogle SAM-prøveanalyser kunne være i overensstemmelse med ældgammel biologisk aktivitet, der producerer de observerede organiske stoffer, er der vigtigt også ikke-livsbaserede forklaringer - for eksempel kan dette isotopiske signal være et resultat af en interaktion mellem ultraviolet lys fra solen og kuldioxid i Mars atmosfære, der producerer organiske stoffer, der falder til overfladen, der kræves ikke liv.

Samlet set motiverer disse resultater igangværende og fremtidige undersøgelser med SAM og hele Curiosity-pakken af ​​instrumenter, såvel som andre planetariske missioner, der søger efter beviser for beboelige miljøer og liv uden for Jorden.

2. Metanvariabilitet

Ved hjælp af SAM's Tunable Laser Spectrometer, udviklet ved NASA's Jet Propulsion Laboratory i det sydlige Californien, har forskere opdaget udsving i overfloden af ​​metan i den nære overflade atmosfære, hvor Curiosity samler prøver. På Jorden kommer det meste af den metan, der er til stede i atmosfæren, dertil takket være processer fra livet og varierer som følge af ændringer i biologiske processer, men vi ved ikke, om det er tilfældet på Mars.

Nysgerrighed er ikke udstyret til at afgøre, om den metan, den har opdaget, stammer fra biologiske processer, men værten af ​​Red Planet-missioner fortsætter med at sammensætte det fristende puslespil.

3. Stendannelse og eksponeringsalder i Gale Crater

Curiosity had only been on Mars for a bit more than a year when, thanks to SAM, scientists determined both the formation age and the exposure age of a rock on the surface of another planet for the first time.

The rocks around the rim of Gale Crater were formed about 4 billion years ago, then transported as sediments to Yellowknife Bay. "Here they were buried and became sedimentary rocks," McAdam said. From there, weathering and erosion slowly broke down and exposed the rocks to surface radiation about 70 million years ago. Apart from providing insight into Mars's erosion rates, knowing how long a sample was exposed enables scientists to consider possible radiation-induced changes to organic compounds which could affect the ability to identify potential biosignatures.

"The age dating experiment was not planned before launch," McAdam said. "But flexibility in the design and operation of SAM, and dedication of a team of scientists and engineers, enabled it to be successfully carried out."

4. Homing in on the history of water on Mars

SAM has also shed light on Mars's wetter past and how the planet has dried out. Water is vitally important to life as we know it, and "multiple lines of evidence indicate that the rocks of Gale Crater record a rich history of water," Malespin said. Part of that evidence is the presence of jarosite, a ruddy-yellow mineral only formed in watery environments, McAdam said. An age-dating experiment with SAM and another Curiosity instrument (APXS) found jarosite hundreds of millions of years younger than expected.

This finding suggests that even as much of the surface of Mars was becoming dry, some liquid water remained below the surface in the Gale Crater environment, extending the period of habitability for any Martian microbes that might have existed.

In addition, analyses by SAM provided insight into the loss of Mars's atmosphere that led its long-term evolution from the early warm and wet state to the current cold and arid state. Water, H₂ O, contains two hydrogen atoms and one oxygen atom. The hydrogen can be swapped for a heavier form of itself, called deuterium. Through measuring the deuterium-to-hydrogen ratio in its samples, Curiosity uncovered evidence of a history of hydrogen escape and water loss on Mars.

5. Biologically useful nitrogen

On Earth, nitrogen is an essential ingredient in the recipe for life—but not just any nitrogen will do. For most biological processes to make use of it, the nitrogen atoms must first be "fixed":freed from their strong tendency to interact only with themselves. "Fixed nitrogen is required for the synthesis of DNA, RNA, and proteins," Malespin said. "These are the building blocks of life as we know it."

SAM detected fixed nitrogen in the form of nitrate in rock samples it analyzed in 2015. The finding indicated that biologically and chemically usable nitrogen was present on Mars 3.5 billion years ago.

"While this nitrate could have been produced early in Martian history by thermal shocks from meteor impacts," McAdam said, "it is possible that some could be forming in the Martian atmosphere today."

No finding from SAM or Curiosity's other instruments can offer proof positive for past life on Mars, but importantly, these discoveries don't rule it out. Earlier this year, NASA extended Curiosity's mission at least into 2025, allowing the rover and its mobile SAM chemistry lab to stay focused on the tantalizing matter of Mars's habitability. + Udforsk yderligere

Curiosity rover takes inventory of key life ingredient on Mars