Today's Asteroid Research: Japan-U.S. Sample Exchange, Collision Experiments to Protect Humanity...The Challenge Continues

Numerous mysteries remain unaddressed in the solar system— How did planets and other planetary bodies evolve to what they are today, how did life originate on Earth, among many others. Asteroids, which are less remarkable celestial bodies than the sun and planets, are said to hold the key to unlocking these mysteries, and they are the focus of intense interest among researchers. Japan has succeeded twice in recovering samples from asteroids using spacecraft (sample return), and research collaboration between Japan and the U.S. that has followed will continue. Research on asteroids is also gaining momentum in the field of "defense" to protect humans from the impact of celestial bodies on Earth. There are several new exploration missions, and Japan is actively involved in them. The following is a summary of 2024's most interesting developments surrounding asteroids.

Japan and the U.S. "enhance each other's capabilities" through large sample recovery

In August, the Japan Aerospace Exploration Agency (JAXA) received some samples that were brought back to Earth from an asteroid by the "OSIRIS-REx" spacecraft, which is also known as the "American version of Hayabusa." As part of a cooperation with the National Aeronautics and Space Administration (NASA), samples collected by JAXA's "Hayabusa 2" were exchanged with the samples brought back by the OSIRIS-REx spacecraft for analysis. Classification and observation work then continued at JAXA's dedicated facility.

In 2010, the first Hayabusa mission brought back samples of an asteroid to Earth for the first time in history. This was followed by Hayabusa 2's exploration of the asteroid "Ryugu" and OSIRIS-REx's exploration of "Bennu." The collected stone and sand samples were brought back to Earth in December 2020 and September 2023, respectively. The sample amount brought back by Hayabusa 2 was 5.4 g, far exceeding the expected minimum amount of 100 mg, and OSIRIS-REx also doubled its target of 60 g to 121.6 g, both achieving large sample recovery.

Under a memorandum of understanding for the mutual support of research and exploration, JAXA delivered 10% of the Ryugu's samples (∼0.5 g) to NASA in November 2021. On August 21, 2024, three NASA representatives visited the JAXA Institute of Space and Astronautical Science (ISAS) in Sagamihara City and presented 0.66 g of their samples. The samples to be shared must exhibit the overall characteristics of color, shape, and size and be without any damage or contamination.

Kathleen Vander Kaaden, Chief Scientist for Astromaterials Curation at NASA Headquarters, who delivered the samples to ISAS, shared her thoughts at the press conference as follows. "We value our continued collaboration with JAXA on asteroid sample return missions to both increase our science return and reduce risk on these and other missions. JAXA has extensive curation capabilities, and we look forward to what we will learn from the shared analysis of the OSIRIS-REx samples."

Mars satellites, lunar exploration... Technology ahead of its time for the future

The samples from Bennu were received at the ISAS facility called the Extraterrestrial Sample Curation Center. This facility has already handled samples from Ryugu. Curation means to collect and identify materials and information from a specific viewpoint to ascertain their value.

The facility has a clean room where dust and dirt are removed and temperature, humidity, and air pressure are kept at a constant level. The room is equipped with hermetically sealed containers for handling samples without contaminating them and devices that shine infrared light on samples to identify substances and measure their quantities. It includes a device developed by a French research institute.

This is where the "initial description process" was performed on the Bennu sample to ascertain its basic information. Samples will then be selected and distributed to national and international research groups by the end of the year. There are two main categories of distribution frameworks: (1) "strategic and priority allocation" to promote comparative research with Ryugaku samples and to improve analytical techniques and (2) "general open call" to support research proposing open and free ideas.

Professor Tomohiro Usui, manager of the Astromaterials Science Research Group at ISAS, told the press in June 2024, "It's not just a comparison of Ryugu and Bennu. In the future, there is the JAXA's "MMX" plan to recover samples from Phobos, a satellite of Mars, and the "Artemis Project" (international lunar exploration) will bring samples from the Moon. It is also important to anticipate the curation technologies of 2030s and 40s."

A super first-class sample with history locked in

Ryugu, which Hayabusa 2 visited, is a carbonaceous asteroid, an example of a "C-type asteroid," a type that contains organic matter and water and is considered to preserve the conditions of the early solar system well. It is believed that these bodies collided with the prehistoric Earth, bringing raw materials for life and seawater. A key objective of Hayabusa 2 is to investigate the origin of life by verifying this hypothesis. Meanwhile, Bennu is also C-type asteroid, which is classified as a "type B" in the fine classification.

Hayabusa 2 landed on Ryugu twice to collect the surface and subsurface samples, which it brought back to Earth. Each of these engineering achievements was widely reported. By contrast, scientific results are steadily accumulated over many years via carefully examining samples and comparing the results with observational data and theory. Therefore, it is difficult for these results to receive impactful publicity. Following an initial analysis, the Ryugu samples are being distributed inside and outside Japan in response to suggestions from scientists. The results obtained so far can be explained, for example, by the following.

(1) The elemental composition and isotopic ratios of Ryugu are similar to those of "Ivuna-type carbonaceous meteorites," which are believed to retain the conditions existed when the solar system was formed. This type of meteorite has been regarded by researchers as a standard sample that provides insights for understanding the history of the solar system. In other words, Hayabusa 2 collected samples similar to materials present in the planets existed in the early solar system. This means that humans were able to acquire a fresh, super first-class sample as meteorites found on Earth are altered by the Earth's environment.

(2) Numerous "hydrous minerals" were found, which were formed when water was present. These minerals seemed to be formed when ice melted to form water and reacted with minerals. Researchers found that a slight amount of liquid water was trapped in iron sulfide crystals. The current Ryugu, however, is small in size and cannot produce liquid water; therefore, it must have originally been a larger celestial body (the parent body). Furthermore, water contained carbon dioxide, but for carbon dioxide to be incorporated into water, it must have been in the solid state at low temperatures. The isotopic composition of hydrogen and nitrogen in some samples also suggests that the Ryugu's origin is a cold place in the far reaches of the solar system. Radioisotope studies also revealed that hydrous minerals were formed 5 million years after the birth of the solar system, i.e., 4.6 billion years ago.

At the time of the Hayabusa 2's observations from above, Ryugu was considered to be made of dehydrated rocks, but the samples brought back were still rich in hydrous minerals. Only its surfaces were dehydrated. These facts also show the significance of exploration to recover real samples.

3D amino acid structure, Difference with Earth's organisms

(3) Organic matter was found in abundance in the samples and contained amino acids that are essential for life. However, these amino acids are different from those found in Earth organisms. Even though amino acids have the same atomic configurations, there are differences in their 3D molecular structures as if they are mirrored, like the right hand and left hand. They are optical (mirror image) isomers, which you learn in high-school chemistry. Most amino acids in the Earth organisms are left-handed type. By contrast, equal numbers of right- and left-handed amino acids were found in the Ryugu samples. If asteroidal amino acids were also predominantly left-handed, it would support a hypothesis that the raw materials for life were carried by celestial bodies. However, the obtained result turned this issue into something "that must be studied further."

The results obtained so far have revealed a history of Ryugu that gives us a sense of solar system development. Initially, in the far reaches of the early solar system, many microplanets, which are parts of planets, were formed. One of them was the Ryugu's parent body, which was several tens of kilometers in diameter. After colliding with another celestial body and being shattered, this parent body seemed to have partially re-assembled to become the present-day Ryugu, about 900 m in diameter, and moved close enough to the Earth for the probe to reach it.

On November 21, 2024, a research group from Kyoto University and other universities announced that they discovered salt crystals in the Ryugu samples. Salt water in the parent body was considered to evaporate or freeze and then precipitate out. They showed the process by which liquid water disappeared on Ryugu, and this result is considered a significant achievement related to the history of water in the solar system.

Ryugu is probably only one example of a time capsule-like celestial body filled with the details of the history of the solar system. One can see how various materials have been transported on moving celestial bodies. What are the origins of organic matter and water that have provided the basis for life on Earth? The writer looks forward to seeing how science continues to tackle these questions.

Two samples... Interests in similarities and differences

Meanwhile, existing papers on the Bennu samples indicate their similarities with the Ryugu samples. Professor Shogo Tachibana of the Graduate School of Science at the University of Tokyo, (Specially appointed Professor at ISAS) said, "Their elemental compositions are very similar, and they show a special pattern not seen in meteorites fallen to Earth. Several organic molecules are found in both samples. Meanwhile, we are beginning to see differences, such as the possibility that Bennu has slightly higher levels of carbon and nitrogen."

Similarities between both samples reflect what generally happened in the solar system, while differences reflect the unique history of each asteroid. Tachibana enthusiastically said, "It is important to compare elements, isotopes, minerals, organic matter, and so on from multiple perspectives. We want to elucidate the beginning of the solar system and process by which organic matter and water arrived on Earth."

Observation of that comet Hayabusa 2, still going strong

Now, a little more than 3,600 days after its launch in December 2014, Hayabusa 2 is at 257 million km away from Earth and is on its way to its second destination, the asteroid "1998KY26." In the summer of 2024, its onboard camera observed "Tsuchinshan-ATLAS Comet" as the comet approached the sun. To digress, while this comet was expected to be visible to the naked eye from the ground, it had attracted attention when U.S. researchers pessimistically predicted that it would disintegrate before becoming visible to the naked eye. In the end, it did not collapse, and many people observed it with the naked eye. I barely managed to capture its faint appearance in a photograph in Tokyo, but what about you readers?

Hayabusa 2 will now approach the asteroid "Torifune" in July 2026 and accelerate using its gravitational force while observing it. It will approach Earth in December 2027 and June 2028, and arrive at 1998KY26 in July 2031. Meanwhile, OSIRIS-REx was renamed "OSIRIS-APEX" and will arrive at the next asteroid, "Apophis," in 2029. Both spacecrafts are on one-way journeys, and although we will miss them, they will not be coming back to Earth.

Attention also focused on Earth "defense" research

Asteroids are also the focus of "planetary defense" research aiming to protect human beings living on Earth from celestial collisions. It is known that 66 million years ago, at the end of the Cretaceous Period, a celestial body that is 10 km in diameter hit Earth, and this collision was a major cause of the extinction of dinosaurs. Other celestial bodies, large and small, have continued to collide with the Earth, including but not limited to this event. If a celestial body threatens humanity in the future, we will be forced to respond.

The U.S. and Europe therefore embarked on a full-scale study. Through this they studied the shift in the orbit of a celestial when it is hit by a spacecraft. For this purpose, a double asteroid comprising the asteroid "Didymos (diameter: 780 m)" and its satellite "Dimorphos (diameter: 160 m)" was selected. First, NASA's spacecraft "Dart" hit Dimorphos in September 2022 at about 6 km/s. As a result, its orbital period was successfully shortened by 32 min. The extent of the shift surprised researchers as it far exceeded their expectations of about 10 min. Note that the double asteroid does not pose an actual risk of impact with Earth.

The European Space Agency's (ESA) "Hera" was subsequently launched from the U.S. on October 7, 2024 toward this double asteroid. It will arrive in 2026 to study in detail changes in the orbit and rotation caused by the Dart's impact as well as craters created by the impact.

Japan equipped Hera with a thermal infrared camera and will also participate in its scientific research. Associate Professor Tatsuaki Okada, head of the Hera project team at ISAS, explained, "To determine the effect of hitting an asteroid with a spacecraft, it is necessary to study the weight and hardness of the asteroid in detail, and Hera will provide that information. This is not an easy task because we also have to consider the scattered material."

According to Associate Professor Makoto Yoshikawa, who heads the Planetary Defense team at JAXA, research in this field began in earnest in 1990s, and discussions have been particularly active in recent years at the United Nations and space agencies of various countries. A total of 1.4 million asteroids has already been discovered in the solar system. Of these, about 36,000, such as Ryugu and Bennu, is approaching Earth; however, we know that they will not collide for the next 100 years or so. It is believed that all asteroids within a diameter of over 10 km are found, and there is no concern about a collision on the scale that wiped out dinosaurs. However, the number of asteroid discoveries, especially those within a dimeter of <1 km, continues to increase, indicating that there are many undiscovered celestial bodies.

In 2013, a meteorite with a diameter of 17 m fell in Chelyabinsk Oblast, Russia, causing serious damage. Detecting such celestial bodies before impact and limiting their damage through evacuation and other measures are important, along with developing technologies to deflect the orbit of a body with a diameter of dozens to hundreds of meters by hitting it with a spacecraft, as is done with Dart. Planetary defense can be considered a field of disaster prevention, which will also require social science initiatives and comprehensive knowledge that transcends disciplinary boundaries.

Departure using a Japanese Rocket

Note that Apophis, which OSIRIS-APEX aims to reach, will only be 32,000 km from Earth by April 2029. Its diameter is 340 m. At one point, it was suggested that this giant body might collide with Earth, but this suggestion was later ruled out. A distance of 32,000 km is closer to the ground than the geostationary orbit of a satellite (altitude: 36,000 km). The ESA says that "such a large object comes this close to Earth only once every 5,000-10,000 years"; therefore, this is a valuable opportunity for observation. In response, the United Nations has designated the year 2029 as the "International Year of Asteroid Awareness and Planetary Defense."

In July 2024, the ESA revealed its plans for "Ramses," a probe to examine Apophis. The ESA Board of Directors will make a formal decision November 2025 on whether or not to approve the proposed plan. If approved, it will be launched in April 2028 and arrive in February 2029, two months before Apophis comes closest to Earth. On November 20, 2024, JAXA and the ESA issued a joint statement that included the consideration of cooperating with this plan. Specifically, in addition to offering thermal infrared cameras and solar panels by Japan, they considered providing "launch opportunities." It is becoming possible that the Japan's large "H3" rocket will be used for the Ramses' departure from Earth.

There were other developments involving Japan in 2024 regarding asteroids. JAXA is planning a deep-space exploration technology demonstrator, "Destiny Plus," to explore "Phaeton," an active asteroid continuously emitting matter. The original plan was to launch Destiny Plus by the end of March 2024 using Epsilon S, a small rocket under development. However, due to an explosion that occurred during a test of Epsilon S in July 2023, it will be launched in fiscal year 2028 using a different rocket. On October 9, 2024, ISAS reported to a subcommittee of the government's Space Policy Committee. According to the Space Basic Plan timetable, which was revised on December 24, 2024, future discussions and arrangements will be made based on the premise of using the H3 rocket.

The United Arab Emirates (UAE) Space Agency's MBR Explorer asteroid probe will be launched with H3, the Agency and Mitsubishi Heavy Industries announced on October 11, 2024. According to their documents, the launch is scheduled for March 2028. After performing a "flyby" of six stars in the asteroid belt between Mars and Jupiter to observe them as they pass one by one, the probe will finally land on the seventh star, "Justitia." What an ambitious plan!

If you allow me to take this opportunity to get little personal, the asteroid Kusaka (1992HL) in the asteroid belt is named after a relative of mine (of the author, deceased). Regardless of which country's probe you are, please stop by if you are in the neighborhood.

When we think of the solar system, we imagine sun shining brilliantly in the center and planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune in a row. However, since the latter half of 2020s, the exploration and research of "supporting players," such as asteroids, comets, "outer solar system objects" outside Neptune, and the satellites of each planet, are clearly increasing. Throughout history, these have influenced the existence of the main planets, and they may help solve the mystery of the existence of life. There is even a possibility for finding evidence for extraterrestrial life on the satellites of Jupiter and other planets. I will enjoy the news that these supporting players will be in the spotlight in the future.