A sample of the asteroid Ryugu brought back to Earth gets a close-up


The Hayabusa2 spacecraft took this image of the asteroid Ryugu from a distance of 40 kilometers as it approached the asteroid in 2018. Credit: JAXA

Brown’s scientists are analyzing a small piece of the asteroid Ryugu in an attempt to better understand the history of the solar system.

In December 2020, the Japanese spacecraft Hayabusa2 flew above Earth to deposit a cache of rock samples taken from a near-Earth asteroid called Ryugu. Asteroids like Ryugu are believed to represent the ancient building blocks of the solar system, and scientists are eager to take a closer look at the returned samples.

Last week, the Japan Aerospace Exploration Agency shipped one of the samples – a millimeter-sized fragment of the asteroid’s surface – to Brown University planetologist Ralph Milliken’s lab for analysis. . Milliken’s lab is one of the first in the United States to examine a sample from Ryugu so far.

Milliken and Takahiro Hiroi, Principal Investigator at Brown, are members of the Hayabusa2 mission science team. They are interested in investigating evidence of mineral aquifers on the asteroid, and they already have published research on the subject based on the remote sensing equipment of the spacecraft. Now that they have a returned sample, Milliken and Hiroi are eager to compare their measurements from a distance with the close-up observations in the lab.

Milliken discussed the work in progress in an interview.

Q: Why was Brown selected as one of the labs to analyze a sample from Ryugu?

Ralph milliken

Ralph Milliken looks at a small piece of the asteroid Ryugu. Credit: Brown University

First of all, we’re really excited to be a part of what is an incredible international mission, and it’s a great honor to be able to analyze this sample so early in the process. I think there are several reasons why we were chosen. One is the presence of our colleague, Takahiro Hiroi, who is an expert in working with meteor samples and asteroid science in general, and he also worked on the first Hayabusa mission. There are other relationships with Brown in the mission as well, including Professor Seiji Sugita of the University of Tokyo, who holds a Ph.D. Brown. graduate who is the main scientist of the main camera of the spacecraft.

Another reason is that Brown operates a ">Nasa facility called RELAB, the reflectance experimentation laboratory. RELAB has a long history – for 30 years now – of working with alien samples dating back to the Apollo missions to the Moon, as well as the Soviet Luna missions. So we have a lot of expertise in making high precision measurements, working with colleagues to interpret this data, and then combining these results with other observations to fully understand these samples and what they mean for the processes. taking place beyond Earth.

Q: Can you describe the sample itself in a little more detail?

It’s quite small – only about 1 millimeter by 0.5 millimeter. It comes from the outer surface of Ryugu. The Hayabusa2 spacecraft made two hits on Ryugu. The first, it touched the undisturbed surface and grabbed some of that material. Then, for the second landing, the spacecraft sampled a location where a man-made impact crater had been created on the surface in hopes that it would produce deeper material. The idea is to compare this surface material with the “cooler” material below which has been somewhat more protected from the effects of space weathering which can alter the uppermost undisturbed surface. The sample we examined came from the first touchdown on the surface.

Q: What are you looking specifically for in your analysis?

The Hayabusa2 mission has a large science team, and each of these experts has a different question they are pursuing. Our group is very interested in minerals formed by water and organic compounds. Are they present in these samples, and if so, what is their chemistry and what do they tell us about the role of water in the first million years of our solar system? Our initial data from the remote sensing instruments on the spacecraft suggested that Ryugu may not be as water rich as expected. One hypothesis is that the original asteroid was weathered by water, resulting in the formation of aquifer clay and possibly other minerals, but at some point the asteroid was then heated to the point of become partially dehydrated. Now that we have the samples in hand, we can take a closer look and see if this assumption was correct.

Q: What form does analysis take?

Small sample of asteroid Ryugu

Small sample of the asteroid Ryugu. Credit: Brown University

To begin with, we do what’s called near and mid infrared reflectance spectroscopy, which analyzes light reflected from the sample at wavelengths longer than what the human eye can see but tells us about. the minerals present. There are similar instruments on the spacecraft that analyzed the surface of the asteroid on a scale of several meters to a few centimeters. But in the lab, we look at the micrometric scale. Thus, we can examine the individual small grains, the complexity of the minerals and their chemistry, and understand if and how the aqueous minerals are present in the sample. Once we have this detailed information, we can go back and look at the data from our larger-scale spacecraft and ask: were the assumptions we made based on that data correct or do we need to revise. our interpretations? Having data from remote sensing spacecraft and then having samples in hand to do detailed lab analyzes really helps us learn to bridge those spatial scales.

Q: Why is it important to study asteroids like Ryugu?

We believe that asteroids like Ryugu represent the primordial building blocks of the solar system. So, by learning more about Ryugu, we may be able to learn more about how the solar system was formed and how it evolved to be as it is today.

Additionally, Takahiro and I are co-investigators of the NASA study. OSIRIS-REx mission that is currently on its way back to Earth to bring back samples from the asteroid Bennu and which spacecraft data has shown is home to aqueous minerals and organic compounds. We are also looking forward to measuring samples from this mission, so this analysis of Ryugu’s samples will also help us prepare for these future measurements.

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