EARTH SCIENCES – Mars and the gi­ant tsunami

Once upon a time, mas­sive ti­dal waves carved the cliffs of the Red Planet, RICHARD A. LOVETT re­veals.

Cosmos - - Digest -

Sci­en­tists study­ing a re­gion of Mars known as Ara­bia Terra think they have iden­ti­fied the source of a tsunami that might have crashed into its shore bil­lions of years ago.

The idea of a Mar­tian ocean dates to the 1990s, when Ti­mothy Parker, now at NASA’S Jet Propul­sion Lab­o­ra­tory in Pasadena, Cal­i­for­nia, used Vik­ing images to iden­tify what ap­pears to be an an­cient shore­line along the edges of ter­rain sep­a­rat­ing the planet’s north­ern low­lands from its south­ern high­lands.

Sci­en­tists later con­cluded that if an as­ter­oid crashed into that ocean, a tsunami was a likely re­sult.

Now, in re­search pub­lished in the Jour­nal of Geo­physics Re­search: Plan­ets, a team led by Fran­cois Costard, a plan­e­tary ge­o­mor­phol­o­gist from the Univer­sité Paris Sud in France, be­lieves it has iden­ti­fied the pos­si­ble sources of one or per­haps two Mar­tian ti­dal waves.

Costard and col­leagues be­gan by look­ing for craters that might re­veal the lo­ca­tions of tsunami-pro­duc­ing im­pacts. Then they mod­elled how such waves would prop­a­gate, us­ing what were de­scribed as “well-ver­i­fied ter­res­trial mod­els”.

Tsunami pro­cesses on Mars would not be ex­actly the same as on Earth. To be­gin with the planet’s lower grav­ity should in­crease the amount of sed­i­ment the wave could carry. That means that for any given­size tsunami, the re­sult­ing de­posits would be rel­a­tively thicker.

Also, a tsunami gen­er­ated by an as­ter­oid im­pact of the size ex­am­ined by Costard’s team would have been huge – un­like any­thing hu­mans have ever wit­nessed.

Ac­cord­ing to the mod­el­ling, the waves near the im­pact point would have been 300 me­tres high. By the time they hit the coast they would still have reached 75 or 80 me­tres.

The most prob­a­ble source of the tsunami, the sci­en­tists con­cluded, is a 60-kilo­me­tre-wide crater about 1,000 kilo­me­tres off the pu­ta­tive coast. But it is also pos­si­ble that the de­posits could have been pro­duced by the com­bined re­sults of two in­de­pen­dent im­pacts, rep­re­sented by smaller craters closer to the shore.

The re­search also ex­plains bizarre fea­tures on the sea­ward ends of some of the tsunami de­posits. Com­posed of curv­ing, con­cen­tric ridges 10 to 20 me­tres high, these look just like the ridges in a thumbprint.

The ex­pla­na­tion starts with the fact that the tsunami would have come in two pulses.

The first would have been pro­duced when the as­ter­oid hit, shov­ing tremen­dous amounts of wa­ter out of its way. The sec­ond would have oc­curred when wa­ter rushed back into the re­sult­ing de­pres­sion.

The wa­ter pulses would have crashed to­gether in the cen­tre of the im­pact zone in a gi­ant splash, re­bound­ing out­ward in a sec­ond tsunami even larger than the first.

And that’s just the be­gin­ning of the story. When the first wave, a few min­utes ahead of the sec­ond, hit the shore­line, part of it would have been re­flected back to sea. There it would have met the on­com­ing sec­ond wave, caus­ing sed­i­ment to be dropped in pat­terns ex­actly like the enig­matic thumbprint ter­rains.

The pri­mary value of the study, how­ever, may not lie so much in lo­cal­is­ing the source of the tsunami as in con­firm­ing the the­ory that Mars may once have had an ocean ca­pa­ble of pro­duc­ing one.

“AC­CORD­ING TO THE MOD­EL­LING, THE WAVES NEAR THE IM­PACT POINT WOULD HAVE BEEN 300 ME­TRES HIGH.”

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