Seek Advanced Materials from Asteroids and Comets

The discovery of graphene, the thinnest possible slice of graphite, in small solar system bodies by an Indian scientist has stimulated tremendous interest in space-based industries

Editor’s Note: Dr Chaitanya Giri’s discovery of graphene in meteorites is considered a stepping stone in the history of carbon-focusing cosmochemistry. On our request, the scientist, who is also an eminent contributor to Science India where he helms the Science Diplomacy column every month, explains in the following write-up the story of this vital discovery as well as its significance.

The global economy is not only materialistic but materials-driven. The ever-growing need for electric cars, hydrogen fuel, bendable electronics, internet-of-things (IoT) devices, lightweight structural materials for automobiles and infrastructure will come from reserves of new-age materials. But where will these materials come from? Outer space?

Our knowledge of meteorites, the most accessible extraterrestrial rocks, is not too old. But, we are by no means new to meteorites either. Humans have made weapons and tools of them, and have carved meteorites into idols of gods for millennia. However, it was only after analytical chemistry and mineralogy began advancing in the 20th century. Of course, with the concurrent ability to venture into outer space, this knowledge has seen tremendous growth.

Asteroids, broadly categorised as stony (those predominantly stone-like), iron-nickel, and carbonaceous (for their high carbon content), have been studied for where they originated from, how they evolved, and what forces of nature have they endured in outer space. Of the three broad categories, carbonaceous meteorites have generated the most significant interest. Carbonaceous meteorites contain amino acids and other prebiotic molecules that are of immense importance in the biochemistry of life. These discoveries paved the way for new inquiries into the origin of life on Earth and the habitability factors that make Earth the only known planet, for now, to harbour life as we know it. Carbonaceous meteorites are central to such a crucial human quest and led to numerous space missions visiting comets and carbonaceous asteroids.

Europe's Giotto (1985) spacecraft to Comet Halley and Rosetta (2004) to Comet Churyumov-Gerasimenko; United States’ Stardust (2004) spacecraft to Comet Wild-2 and OSIRIS-REX (2016) to asteroid Bennu; and Japan’s Hayabusa-1 (2003) to asteroid Itokawa and Hayabusa-2 (2014) to asteroid Ryugu all went to carbonaceous small solar system bodies (SSSBs).

While all this was happening, I got an opportunity to work as an independent early-career scientist at the Earth-Life Science Institute (ELSI), a brand-new institution built by the Japanese government’s science ministry at the Tokyo Institute of Technology. I moved to ELSI with a five-year professional experience, including my ‘professional’ doctorate and first post-doctoral position, at Germany’s prestigious Max Planck Institute for Solar System Research. During those five years, I studied the surface organic geochemistry of comets, which was the topic of my thesis and a requirement for the then ongoing European Space Agency’s Rosetta mission, which was approaching its celestial target, the comet 67P/Churyumov-Gerasimenko. Having studied geological sampling of comets while I was a co-investigator of a gas chromatography-mass spectrometry payload ‘COSAC’ on Rosetta’s lander Philae, I naturally developed an inclination to study asteroids in a similar vein. COSAC’s reportage of four molecules that I was part of, methyl isocyanate, acetone, propionaldehyde, and acetamide, which were never earlier detected astronomically on any comet, only pushed my inclination into a purpose.

ELSI accepted my proposal to explore the asteroid’s carbonaceous composition; however, I was not directly associated with any asteroid sampling mission. This small research project was running independently. Japanese Hayabusa-2 and US’ OSIRIS-REX were preparing to bring samples from two different carbonaceous asteroids during the same period. Although ELSI offered me a unique opportunity to work distantly with teams associated with both the missions, I travelled between ELSI and the Carnegie Institution of Washington (CIW) in the national capital of the US.

My collaborator and friend Andrew Steele from CIW, who I was visiting, and his colleague Marc Fries from NASA Johnson Space Center, had already made a startling discovery in 2008. They found graphite whiskers in ancient fragments of two meteorites, namely Allende and QUE 94366.

A whisker is a rolled-up two-dimensional sheet of carbon atoms bound to each other in hexagonal configuration. Their discovery validated crucial conjectures made in the 1970s and 1980s by renowned astrophysicists Jayant Narlikar and NC Rana from India and Fred Hoyle and Chandra Wickramasinghe from the United Kingdom. Back then, they had expounded that graphite needles, if present in the intergalactic medium, could be the causal factor for absorbing the cosmic microwave background, temperature, the remnant radiation of Big Bang measured at 3 Kelvin (-270 °C) across the universe. Steele and Fries’ discovery did not confirm whether graphite whiskers could do that, but they certainly found out that needle-like graphite whiskers are indeed present in outer space.

Moving a step ahead, when I joined CIW as a visiting scientist, we decided to explore whether we could find the non-rolled two-dimensional sheets of carbon in the same fragments that showed them graphite whiskers. We found Raman signatures of single-layer and multi-layer graphene, the two-dimensional carbon allotrope in Allende and QUE 94366. The graphene and graphite whiskers are present in mineral fragments, known as calcium-aluminum-rich inclusions, which form at temperatures over 2000°C, extremely close to the proto-Sun, and well before the formation of the eight planets in our Solar System.

SSSBs, like asteroids and comets, were long known to be rich in water, organics, and rare-earth minerals. With the timely discovery of graphite whiskers, graphene, and other allotropes of carbon, these bodies can also be viewed as a treasure trove of carbon materials, making them attractive targets for extraterrestrial minerals and material prospection subsequently mining.

And are space agencies attracted to these prospects? Certainly yes. In the recently concluded International Astronautical Congress held in October 2021 in Dubai, UAE’s national leadership announced its goal to land on an asteroid by 2033. In October 2021, NASA will launch its LUCY spacecraft that will fly by several asteroids in the Main Asteroid Belt and those present along Jupiter’s orbit, between 2025 and 2033. Japan is currently building two spacecrafts aimed at small bodies for launch in 2024. They are DESTINY+ and Mars Moon eXploration (MMX). DESTINY+ aims for asteroid 3200 Phaeton, which is the source of Geminids meteor shower that is witnessed every December in the Northern Hemisphere. At the same time, MMX is aiming to study the two asteroidal moons of Mars, Phobos, and Deimos. The ambitions for SSSBs don’t stop there.

The European Space Agency and the government of Luxembourg have been quite bullish on technology capacity building for extraterrestrial mining. Towards that end, they established the European Space Resources Innovation Centre (ESRIC) in Luxembourg in 2020. ESRIC and similar research institutions in the coming years will become bright hotspots of the academia-start-ups-industry interface, much needed for extraterrestrial mining capabilities. Such hotspots will be crucial for retrieving materials of immense importance to the material needs of the global economy of the near future.

Since I began working on Rosetta, I had always felt the Indian government and institutions are capable of making forays in this niche domain. Indeed, such missions cannot happen overnight, but their preparation needs to begin well in advance. My experience of being party to discoveries like the four molecules of comet 67P and graphene in meteorites confide me that the exploration of SSSBs will definitely excite scientists, entrepreneurs, industrialists and the wider masses of India. In the coming months, India, too may soon start preparing for such missions. I will be ecstatic to roll up my sleeves and be part of a gung-ho team committed to such undertakings.

This blog was published in the October 2021 edition of Science India magazine published by Vijnana Bharati.