An artist's concept of an asteroid belt around a Sun-like star beyond an Earth-like planet

An artist's concept of a near-Earth asteroid. It isn't known where the Mukundpura meteorite began its journey. It may have come from an asteroid at the edge of the solar system - but an origin point closer to Earth is also possibile. Image: NASA/JPL-Caltech via NASA Image Library

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Rare meteorite from the edge of the solar system falls in farmer's field

At around 4.5 billion years old, the Mukundpura meteorite could have secrets locked within its stony form.

Museum scientists have been loaned a small fragment and are planning to use it to study water and organics in the early solar system. 

The Mukundpura meteorite may have formed as part of an asteroid in the farthest reaches of our solar system, before making an exceptionally long journey to Earth. It landed in India in June 2017.

According to the Meteoritical Bulletin Database and local media reports, the two-kilogramme meteorite landed in the soft soil of an agricultural field near Jaipur. A local villager reported having observed a bright object fall with a thundering sound about 100 metres from his house.

A small piece of this fall has now been loaned to the Museum by Arizona State University. Scientists will endeavour to find out what it can tell us about water and organic materials in the early solar system.

The Sun's reflection

There are approximately 60,000 meteorites held in official repositories around the world. But only around 500 of them are like Mukundpura.

The piece of the Mukundpura meteorite that the Museum has on loan from Arizona State University

Most meteorites were once part of asteroids that formed around 4.5 billion years ago, and Mukundpura's origin is likely the same. But unlike the majority, the 2017 arrival is what is known as a CM carbonaceous chondrite.

This type of meteorite is non-metallic, but does contain water and organics - although only experts know how to find them.

Dr Ashley King, a planetary scientist at the Museum explains, 'It isn't liquid sloshing around, but there is water locked up in the minerals.

'CM carbonaceous chondrites come from asteroids where there was water and organic materials. Most of this rock is made up of phyllosilicate materials. These are hydrated silicates, so things with water in them.'

Although it hasn't been analysed yet, Ashley estimates that Mukundpura is around 70% phyllosilicates.

CM chondrites like Mukundpura have a bulk chemistry that although altered by water is similar to what is in the Sun.

The Museum's Ivuna meteorite specimen is an exceptionally rare CI carbonaceous chondrite. Like CMs, it is fragile and soft to the touch and is stored in a nitrogen rich environment to preserve it.

'They're kind of a reflection of what was going on in the solar nebula 4.5 billion years ago - what materials there were and how these things stuck together. Meteorites tell us how we go from having this big cloud of gas and dust to having a Sun, eight planets, an asteroid belt and comets.'

Extraterrestrial water

Water-rich asteroids formed in the cold outer regions of our solar system. They are a collection of ice, silicate and simple organic materials.

Earth formed close to the Sun and scientists think it is difficult for all of its water to have originated here. But these outer asteroids colliding with a young Earth could be one way that water initially arrived on our planet.

There is evidence to suggest that water also occurred on the Moon and on the other terrestrial planets (Mercury, Venus and Mars) at some point in the solar system's history.

'They all formed in a region where you have rocky materials but you don't have icy materials,' says Ashley. 'But one of the ways that you can bring water is by kicking it in from the outer solar system.' 

An artist's concept of the OSIRIS-REx spacecraft collecting samples from the near-Earth asteroid Bennu. Scientists believe that this asteroid is similar in composition to Mukundpura and other carbonaceous chondrites. Image: NASA's Goddard Space Flight Centre/ Wikimedia Commons

Turning ice into water required some heating, likely caused by the radioactivity in the early solar system. The icy asteroids were heated from the inside by radioactive decay, and the resulting water reacted with the silicate materials to create phyllosilicates.  

Studying Mukundpura

Mukundpura may have travelled here from the edge of our solar system - although an origin point closer to Earth is also a possibility.  

The meteorite was collected almost immediately after its fall near Mukundpura Village in Rajasthan. The sample loaned to the Museum is around 0.4 grams in weight. Scientists will likely CT scan it for a non-invasive look at the meteorite's internal structure.

'We might also do some electron microscope work. So we'll map the chemistry and the distribution of the elements on the surface. We'll also look at the mineralogy so we can see what minerals are in there and how much there is of them. '

X-ray diffraction will be used to allow the scientists to look at the phyllosilicates. Different types of phyllosilicates form under specific conditions. The types found can tell experts about the chemical and physical conditions of the asteroid it came from, such as the water content and the temperatures it may have been heated to.

A rare fall

The majority of meteorites that fall to Earth end up in oceans or uninhabited regions and are never found. But those collected are assigned into two categories: finds and falls.

Meteorites can last for tens of thousands of years on Earth's surface if they land in a dry environment - such as Antarctica. Image: Nancy Lanza Via NASA Johnson Flickr (CC BY-NC 2.0)

'Meteorites can land anywhere but usually nobody sees it happening. They just sit on the surface until somebody stumbles across it - that's what we call a find,' explains Ashley.

'Nearly all meteorites are finds and almost all of them come from deserts - hot deserts, but also Antarctica. Because it's dry, they can survive there for tens of thousands of years, relatively unaltered.'

Mukundpura is special, however. It is one of less than 5% of CM chondrites have had their descent to Earth' surface observed. This means that it is categorised as a fall - making the already rare meteorite even more extraordinary.