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International Asteroid Day: the importance of Lonar and near earth objects

  • While asteroids do pose significant threats to Earth, they can answer plenty of questions about the solar system

An artist's impression of asteroids passing earth
An artist's impression of asteroids passing earth (ESA/Pierre Carril)

On 30 June, 1908, roughly more than 112 years ago, a large cosmic event shook the Podkamennaya Tunguska river area in Siberia, Russia. In what is believed to be the largest impact event on Earth in recorded history, it left "little evidence of its origin except flattening 500,000 acres of uninhabited forest, scorching the land, creating 'glowing clouds' and producing shock waves that were detected around the world," a recent Nasa feature recalls. Years later, the reason was revealed to be a "stony body", either an asteroid or comet, that exploded in the air.

The Tunguska Event, as it is now officially known, is the reason that four years ago the United Nations declared 30 June as International Asteroid Day. The aim? To raise public awareness about asteroid impact hazard. As an official release from the Asteroid Foundation explains, every year Asteroid Day presents the global public with a snap-shot of "cutting-edge asteroid research from the largest telescopes on Earth to some of the most ambitious space missions". This year, the topics under discussion include the acceleration in the rate of asteroid discoveries, the arrival of samples from asteroid Ryugu and Bennu (through the Hayabusa2 and OSIRIS-REx spacecraft missions, respectively), and preparations for a joint Nasa-ESA mission to binary asteroid Didymos, among other things.

While near earth objects, like asteroids, do present a significant threat to Earth, they are also supremely intriguing objects that can answer many questions about the solar system’s creation and journey. They are, as Nasa describes them, airless remnants and ancient rubble left over from the early formation of our solar system some 4.6 billion years ago. “Just like the earth, asteroids are objects moving around the sun on their own orbit paths. They are constantly tracked and there are specific asteroids that have been studied regularly. We have also visited some and collected samples, which help us understand the history of the solar system," says Siddharth Pandey, head of the Centre for Excellence in Astrobiology, Amity University, Mumbai.

What makes Maharashtra's Lonar lake unique

When an asteroid survives atmospheric entry and strikes the surface of a planet or a moon, it becomes what we call a meteorite. Meteorites often leave behind impact craters, which become a crucial evidence for space agencies and researchers. Since February 2019, Pandey has been conducting research at one such unique impact crater — the Lonar lake crater in Maharashtra. According to Nasa, Lonar was formed 35,000 to 50,000 years ago,and it is the only “fresh" impact structure in basalt on Earth, making it an important analog for impact craters on the surface of the Moon.

The Lonar lake as seen through Nasa Earth Observatory
The Lonar lake as seen through Nasa Earth Observatory ( Lauren Dauphin)

Pandey explains how meteorites of various shapes and sizes enter the earth's atmosphere almost on a daily basis. "What you see in Lonar was caused by an object that was roughly a kilometre wide. As soon as an object hits the surface at high velocity, it creates a massive cavity. The remnants of that cavity get displaced and deposited around the crater in the form of a ejecta ring," he says. "Lonar has been studied from different points of views by everyone from astronomers to astrodynamic researchers." From the point of view of astrobiology, the Lonar crater and lake are so unique because of the type of rock: basalt. "It is a very hard form of rock, that is dark and blackish. Craters in basalt take a long time to erode and that's why it is well-preserved," says Pandey.

A 2007 paper by researchers at Princeton University, Harvard University, the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution describes how Lonar has ejecta features similar to Martian impact craters. Pandey says this similarity could be key in the quest to find life on Mars. "A crater that has water flowing into it would have deposited organics and possible proof of past life in sediments. At Lonar, we are studying how microbial life lives preserved inside the rocks and the cracks inside the crater," he adds.

The crater also made headlines earlier in June when the water inside the lake turned from green to a striking pink. Pandey says while this phenomena has puzzled many, there’s actually a very simple explanation behind it. "It is a very well understood phenomena, which involves a certain type of an algae that lives in very salty water bodies. Whenever there is an increased rate of evaporation, the salinity increases because the water concentration drops," he says. "This increased salinity causes the algae to release a pink pigment. That's why the entire colour of the lake changed." Pandey adds that this process is often visible in salt pans and lakes around the world. "It's not a mystery at all."

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