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Lonar and its Martian namesake

In 2007,an impact crater on Mars was named Lonar,after the basaltic lake in Maharashtra that bears a strategic resemblance to the Red Planet’s geology. VIVEK DESHPANDE reports on the two Lonars and how they are similar to and different from each other

Written by Vivek Deshpande |
May 23, 2010 10:39:41 pm

Lonar Lake in Buldana district of Maharashtra,the only meteor-impact crater in the world in basaltic rock that contains salt water,is uniquely important for astrogeologists in that it serves as the best analog for them in their study of Martian geology. This was first reported by The Indian Express in 2005,when scientists connected to NASA had come to study the crater.

Not many,however,know that about three years ago,the analogy was taken further,when the International Astronomical Union (IAU) named an impact crater on Mars,Lonar.

The organisation has what is known as the Working Group on Planetary System Nomenclature,which invites suggestions for naming astral objects or their features and then publishes them after finalising a suitable name in the Gazetteer of Planetary Nomenclature.

The Martian Lonar,however,is much older—dating back by millions of years—and bigger—more than 11 km in diametre—compared to its namesake on the earth,which is just about 1.8 km wide and about 55,000 years old.

The only other crater on earth formed in basaltic rock is the 20-km-wide Logancha crater in Russia,on which scientists have little information.

Situated near the North Pole,the Martian Lonar is,like most other Martian craters,geologically similar to the Lonar on earth. It’s typically rimmed with ejecta material (material that is thrown outwards when the impact occurs),but has secondary craters near it,unlike in the Lonar in Maharashtra,a lone crater.

A 2008 paper by a group of American scientists led by JM Boyce revealed that the Martian Lonar has three ejecta layers around it. “Its feathery morphology is unlike any other Martian ejecta deposits and is reminiscent of turbulent flow in a low-density fluid,” the paper said. The scientists have proposed that the outer layer ejecta of the Martian Lonar consists of “fine-grain deposit cemented by ice”.

Scientists have been hopeful about finding water on Mars and the Lonar on earth is considered ideal for studying the possibility. Said American geologist Horton Newsom,who has done a pioneering study of Lonar from this angle,“The presence of calcite as the main late-stage mineral in the Lonar samples is consistent with the alterations by meteoric water and also supports the use of Lonar as an analog to Mars. Hydrothermal alterations (seepage of groundwater through fractures caused by the impact) at Lonar suggest Lonar-sized Martian craters may also have potential to form hydrothermal systems leading to such alterations if water is present there in some form,” he said. “With impact craters’ known ability to access shallow ground water,this could have become possible on Mars as well.”

Geologists’ interest in Lonar in Buldana grew multifold after the realisation that,geologically,it comes closest to Mars due to its basaltic base—Mars and moon have a basaltic crust. A meteor impact is believed to have caused it in the 65 million-year-old Deccan basalt trap.

Lonar was also in the news two years ago when a joint Indo-German team launched a unique experiment on the sediments there to gauge the environmental changes since the time the crater was formed,and most recently,for the presence of magnetotactic microbacteria.

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