Eyes on the skies! Astrogeologist explains why space rocks are so important

Meteorites and asteroids are not all rock and roll.
Deena Theresa
Professor Gretchen Benedix holding a sample of the Bunburra Rockhole meteorite.Space Science and Technology Centre - Johan63/iStock

From the get-go, I asked Professor Gretchen Benedix how she would describe her job to a child.

"I study rocks from space - I try to understand where we come from by looking at compositions of rocks from space," she says.

As an astrogeologist and cosmic mineralogist, Benedix has the privilege to get up close and personal with meteorites. 

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Though a handful of well-documented meteorites are known to have originated from the Moon and Mars, most of the meteorites found on Earth have been shown to have originated from asteroids. Studying them would open a treasure trove of information - from their initial composition to their subsequent processes involved in their chemical evolution. They could provide vital clues about the pre-planet forming stages of the solar system.

Currently, a professor at the School of Earth and Planetary Sciences at Curtin University, Perth, Benedix is also the lead on the initial Mineralogy/Petrology of the meteorites found by the Australian Desert Fireball Network (DFN). This interdisciplinary research group is working to 'uncover the mysteries' surrounding solar system formation.

The digital observatories monitor 1,158,306 square miles (3 million square km) of the night sky - a third of Australian skies, all night, every night. Using an automated data reduction pipeline, intelligent imaging systems, real-time server-side triangulation, and a supercomputer data management system, the DFN images and studies the paths of fireballs in the sky, their trajectories, and orbits.

It gets cooler.

Asteroid 6579 was renamed Benedix in 2006 by the International Astronomical Union for Gretchen Benedix's contributions to planetary science.

In an interview with IE, she tells us about her work with the DFN and how it impacts the world. 

Excerpts.

Interesting Engineering: Why are hunting and retrieving meteorites so important?

Professor Gretchen Benedix: We have a really good, broad knowledge of the overall solar system, but we have a few holes in our understanding. So, the more samples we get, the bigger the picture is. Until the DFN, we had a bunch of samples that we knew the orbits for, but we didn't have much information. As a geologist, you want to know where your rocks come from - their composition and distribution. Trying to mesh those two is kind of the holy grail - figuring out what the solar system is really like.

If you can track a rock, where it came from in space to where it landed on Earth, that opens up the whole idea of context. And if we can start building up this map, it helps us try to figure out where we want to go next and the most important thing that we want to find out.

IE: How close or far are we from creating this map?

So, we've had camera networks to track meteorites since the 1950s. One is based in Europe, one in the US, which no longer exists, and another in Canada. Between those three, they saw four meteorites fall. And then there were a couple of others that were accidentally recorded. In total, we had eight meteorites and their orbits figured, which helped put things in perspective. Now, after 10 years of running the DFN, its expanded version, the Global Fireball Observatory, and a few others that have popped up [France, the UK, and the original one in Eastern Europe], we've 45 meteorites and their orbits.

The interesting thing is if we can get the rock on the ground, it opens up a door for a whole lot of information we need. That gives us great context. On top of that, we have this fantastic observational data where you get fireballs all the time, but they don't necessarily have enough material and hit the ground. But you still get all that orbital information. So, with 10 years' worth of this data, you have this amazing knowledge - such as the area of space that the Earth is traveling through - which is crucial because we could hit these rocks anytime.

One of our students was looking at some of the data, which showed that a rock came into the atmosphere and kind of skipped back out again. It was a close pass - it was affected by the Earth but didn't hit the planet. So there's all this kind of debris kind of hanging out there. From that perspective, it's a slow process, and many coincidences have to happen to get a rock from space to the Earth. It needs to be the right size and composition, should have the right speed and direction, and must hit the atmosphere at the right angle. Over time, it's going to keep getting better. 

Eyes on the skies! Astrogeologist explains why space rocks are so important
An image of the expanse of Australian outback near Maree, in South Australia, where a team had gone to search for a meteorite seen on the Desert Fireball Network Cameras. Source: Prof. Gretchen Benedix

IE: What are the procedures you're most involved in?

My part is primarily the classification of the meteorites when they come to the lab. I have a team - and we have a whole consortium of scientists around the world that we interact with. Everybody gets a little piece of this rock, and we do a very thorough classification.

IE: Tell us about the different types of meteorites and how they're grouped.

There are primitive and evolved meteorites - and different types within them. Among the evolved, we have rocks ranging from those that come from Mars and the Moon, asteroids that have experienced a level of melting, to metallic cores. On the primitive side, we've got extraordinarily primitive meteorites, those that have been heated and those that have interacted with water or ice in space. We have this full range, and they have different basic compositions. 

Matching different groups to asteroids is a very interesting thing to do. We have observed how sunlight reflects off different asteroids. We then perform the same kind of experiment in the lab [Reflectance spectroscopy is particularly useful for studying the composition and structure of meteorites. A sample is illuminated with narrow beams of visible and infrared light, and the spectrum of the reflected light is analyzed for absorption lines that reveal the chemical composition of the object] with the rocks we have. Then we start to try and match them up.

The more samples we get on the ground with an orbit, the more we can measure the sunlight reflected off them and compare the data with the stuff we've collected from asteroids. 

Japan and the US have gone to asteroids and collected materials - changing the depth of what we can understand. Sending a spacecraft to orbit an asteroid has taught us so much - when we look at it through a telescope, it's a point of light. So we assumed it was a sphere, like a planet. They're not like that at all. And the more we see, the more we learn.

IE: Is it common to have these meteors originating from the same location on the Moon or Mars, or the same asteroid?

No. So the other area of research that I'm heavily involved in right now is the study of Mars' surface. I'm trying to understand the surface of Mars using machine learning to extract and count all the craters because we want to figure out where the meteorites we have come from. We don't think they've all come from one spot on Mars. We've created a machine learning method that allows us to extract the information we need because counting craters by hand is way too tedious. We've counted all the craters that are 100 meters and larger, and we've found the source crater for two types of meteorites on the surface of Mars. We can then take everything we know about this type of meteorite and apply it to that area of Mars.

There was a certain space mission [The Dawn space mission] that orbited asteroid Vesta. Before that mission, we had meteorites in our collection that matched spectrally to Vesta - through reflectance. So that's one example of asteroid meteorite grouping.

We don't always know the source or the parent body of everything else, so we have to guess. We do have a lot of spectroscopy, but it's impossible to determine the reflectance of every single body in the asteroid belt because there are millions of them. And some of them are very, very small. And so, all we can do is watch for the ones that might be coming close. We can take a good picture of it and keep an eye on what's happening out there. When we find a bunch that is in a weird orbit - we do these reflectance studies to get compositional information. 

IE: You mentioned machine learning. How has it particularly helped the DFM?

One of our students incorporated a machine learning algorithm into a drone. And so, the drone can go up high and map an area very quickly, which has largely helped with searching for meteorites. We then apply the algorithm to the imagery that the drone has collected. The algorithm has been trained to identify the difference between a meteorite and general stuff like other rocks.

This works well in the Outback [of Australia, which is sparsely populated] because the base ground is a very light-colored rock. Though the meteorites are pretty dark, the shadows of plants are an issue. The drone has already found two or three meteorites. That's just one aspect - We have a whole range of things happening with machine learning.

IE: How does it feel to hold a sample?

Every single time I hold a meteorite - and I've been doing it for a long time - it's a thrill. I've been to Antarctica a couple of times to search for meteorites. And the first time I went was the first time I'd ever really done any kind of geology fieldwork. Because I didn't do earth-based geology - all I ever did was stuff in the lab. Being in the field was so much fun. I've also worked at a couple of museums where I was like a kid in the candy store. Because you can open a drawer, and it's like, 'Oh, here's the piece of the Moon. Or here's a piece of the oldest rock you'll ever hold in your entire life. This is from the beginning of the solar system'. That kind of thing is quite nice. 

Eyes on the skies! Astrogeologist explains why space rocks are so important
Prof. Gretchen Benedix standing next to the Mundrabilla Iron meteorite outside the Western Australia Museum in 2006. Source: Prof. Gretchen Benedix

IE: Do you have a favorite meteorite?

I think it's the Mundrabilla iron [One of the largest meteorites found near Mundrabila, an area located along the southern portion of the Nullarbor Plain in Western Australia.] It was discovered in 1966. It sits outside the Western Australia Museum in Perth. The sample is 12.4 tonnes because it is entirely metallic, mostly iron and nickel. One of the rocks I looked at in my Ph.D. was the Mundrabilla. It's such an interesting meteorite - when it came tumbling through the atmosphere, it lost a bunch of sulfides. You can cut through the meteorite and get a slice of it, which looks very beautiful. It may contain molten metal that crystallized instantly to a solid. It's a strange rock, but I love it.

IE: How does your work impact the world/society?

Just the quest to understand how the Earth fits into the broader solar system scheme is a good question. The whole thing is a system that works together. And I think understanding and tackling it, and having different people look at other pieces of that puzzle, will build the whole picture. The quest for that basic knowledge is something that society with an 'I need to get stuff done right now' perspective may not appreciate yet. But in the long run, all the things we've learned over time have just helped us better understand how we affect things and how things affect us.