The water on Mars vanished. This might be where it went

L’eau sur Mars a disparu : où est-elle donc passée ?

Les canyons désertiques de la Planète rouge étaient auparavant remplis par les flots de ses rivières et océans. Aujourd'hui où est passée l'eau sur Mars ? Comment a-t-elle disparu ? Une nouvelle recherche apporte une réponse surprenante...

Mars was once wet, with an ocean’s worth of water on its surface. Today, most of Mars is as dry as a desert except for ice deposits in its polar regions. Where did the rest of the water go?

2. Some of it disappeared into space. Water molecules, pummeled by particles of solar wind, broke apart into hydrogen and oxygen atoms, and those, sped out of the atmosphere, lost to outer space. 3. But most of the water, a new study concludes, went down, sucked into the red planet’s rocks. And there it remains, trapped within minerals and salts. Indeed, as much as 99% of the water that once flowed on Mars could still be there, the researchers estimated in a paper published this week in the journal Science.

4. Data from the past two decades of robotic missions to Mars, including NASA’s Curiosity rover and the Mars Reconnaissance Orbiter,

showed a wide distribution of what geologists call hydrated minerals. “It became very, very clear that it was common and not rare to find evidence of water alteration,” said Bethany Ehlmann, a professor of planetary science at the California Institute of Technology and one of the authors of the paper.

5. Ehlmann, speaking at a news briefing Tuesday at the Lunar and Planetary Science conference, said that as the rocks are altered by liquid water, water molecules become incorporated into minerals like clays. “Water is effectively trapped into the crust,” she said.

6. To get a sense of the amount of water, planetary scientists talk about a “global equivalent layer” — that is, if Mars were smoothed out into a uniform, featureless ball, how deep would the water have been? The scientists estimated that the depth would have been 100 to 1,500 meters. The most likely depth was about 2,000 feet, they said, or roughly one-fourth as much water as is in the Atlantic Ocean. 7. The data and simulations also indicated that the water was almost all gone by 3 billion years ago, around the time on Earth when life consisted of single-cell microbes in the oceans. “This means that Mars has been dry for quite a long time,” said Eva Scheller, a Caltech graduate student who was the lead author of the Science paper.

8. Today, there is still water equivalent to a global ocean 65 to 130 feet deep, but that is mostly frozen in the polar ice caps.

3 BILLION YEARS AGO...

9. Planetary scientists have long marveled at ancient evidence of flowing water carved in the Martian surface — gigantic canyons, tendrils of winding river channels and deltas where the rivers disgorged sediments into lakes. NASA’s latest robotic Mars explorer, Perseverance, will be headed to a river delta at its edge in hopes of finding signs of past life.

10. Without a time machine, there is no way to observe directly how much water was on a younger Mars more than 3 billion years

ago. But the hydrogen atoms floating today in the atmosphere of Mars preserve a ghostly hint of the ancient ocean. That led to the new research concluding that a great majority of water went into the rocks.

11. “This is a very interesting new study in which many processes are combined to provide alternative scenarios for the fate of water on Mars,” Geronimo Villanueva, one of the NASA scientists who performed the earlier deuterium measurements, wrote in an email. “This opens the possibility for an even wetter past, and that rocks on Mars now hold more water than we initially thought.”

1. once ici, jadis, autrefois, à une époque / to be wet être mouillé; ici, Mars was [...] wet il y avait de l'eau sur Mars / worth ici, équivalent / dry sec; ici, aride.

2. to pummel frapper (à répétition) / to break, broke, broken apart (se) dissocier / to speed, speeded or sped, speeded or sped out of quitter (précipitamment) / (outer) space espace.

3. to suck aspirer, pomper / rock rocher, pierre / to remain rester, être encore / to trap piéger, retenir / indeed en fait / as much as jusqu'à / to flow couler; ici, exister / still encore / paper ici, étude / journal revue spécialisée (scientifique).

4. data données, informations / decade décennie / rover astromobile /

wide large, généralisé / distribution répartition, présence / common courant / evidence (inv.) preuves, signes, traces. 5. clay argile / crust croûte.

6. sense ici, idée / amount quantité, volume / global equivalent layer hauteur équivalente d'eau recouvrant la planète/d'un océan global qui occuperait le même volume, équivalence d'une couche d'eau globale / that is à savoir, c'est-à-dire / to smooth out lisser, uniformiser, ôter toute imperfection (ici, relief) / featureless uniforme, plat, sans relief / how deep de quelle profondeur / likely vraisemblable, probable / about (d') environ / foot pied (30,48 cm) / roughly environ.

7. to be almost all gone avoir presque entièrement disparu / billion milliard / around the time [...] when... plus ou moins à l'époque où... / single-cell unicellulaire / for quite a long time depuis pas mal de temps/ici, (très) longtemps / graduate student étudiant de deuxième/troisième cycle / lead principal, en chef.

8. ice cap calotte glaciaire.

9. long ici, depuis longtemps / to marvel at s'émerveiller devant / ancient très ancien / to carve creuser, sculpter / tendril boucle / winding qui serpente / to disgorge dégorger, déverser / latest dernier (en date), plus récent / to be headed to ici, être envoyé à/dirigé vers / edge bord.

10. time machine machine à explorer/voyager dans / ici, remonter le temps / way façon / to float flotter, être en suspension / [they] preserve a ghostly hint of [ils] témoignent de l'existence de. 11. to provide fournir; ici, permettre d'imaginer / fate sort, destinée / to perform effectuer / earlier précédent (early premier) / to open ici, offrir, laisser supposer / even ici, encore.