Research press release




これまでの学説によれば、タルシス地域の大部分は、ノアキス紀(約41~37億年前)の末期に形成され、火星上の谷網の方向性に影響を与えたとされていた。今回、Sylvain Bouleyたちは、シミュレーションを行って、タルシス火山地域が形成される前の火星の地形を再現した。その結果、Bouleyたちは、観測された谷網の方向では、タルシスの火山的負荷が存在する必要がなく、熱帯での降水と谷の切り込み(生成)がタルシス地域の隆起の形成と同時に起こっていた可能性が高く、ヘスペリアン紀(約37~30億年前)に長期の火山活動があったことを明らかにした。


The early geological history of Mars is re-interpreted in light of new, topography-based evidence published online in Nature this week. Mars is home to the largest complex of volcanic rocks in the Solar System - the Tharsis region - which started forming more than 3.7 billion years ago and resulted in a prominent bulge on the surface of the planet. This event also induced a reorientation of Mars with respect to its spin axis (true polar wander), which is responsible for the present-day equatorial position of the volcanic region.

It has been suggested previously that the bulk of the Tharsis region had formed by the end of the Noachian period (about 4.1 to 3.7 billion years ago), and influenced the orientation of valley networks on the planet. Sylvain Bouley and colleagues performed simulations that allowed them to reconstruct the topography of Mars before the formation of the Tharsis volcanic region. They show that the observed directions of valley networks do not require the presence of the Tharsis volcanic load and that tropical precipitation and valley incision (creation) are likely to have taken place at the same time as the Tharsis bulge formation, with prolonged volcanic activity during the Hesperian period, about 3.7 to 3 billion years ago.

The authors conclude that rainfall or snowfall occurred during the formation of the Tharsis bulge, and propose that their topographic map provides a new framework within which to examine the first billion years of the geological history of Mars.

doi: 10.1038/nature17171

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