Two Pieces of a Cosmic Puzzle: Hayabusa2 and OSIRIS-REx

By Christine Hoekenga

June 22, 2018 -

It began with dust. Before there were asteroids, or planets, or people – about 4.6 billion years ago – a cloud of dust and gas swirled in the cosmos. At the center, a star began to form.

With heat and shock waves, clumps of this ancient dust coalesced into droplets of molten rock called chondrules. These chondrules and dust became the building blocks of the Solar System. Eventually, chunks of material as large as asteroids, and even planets, formed from this cloud and organized according to the laws of physics around a newly born star: our Sun.

Scientists believe one of these chunks became a protoplanet that eventually broke apart in a collision, giving rise to an asteroid that humans would one-day dub Bennu. Another (or perhaps the same) chunk produced another asteroid that would become known as Ryugu. Long before humans were around to give them names or contemplate their origins, both asteroids migrated from the asteroid belt between Mars and Jupiter into near-Earth space and settled into new orbits.

It wasn’t until hundreds of millions of years later, in the 1800s, that human astronomers trained their telescopes on the sky and began identifying and studying asteroids. Fast forward to 1999. That year, the Lincoln Near-Earth Asteroid Research (LINEAR) survey discovered two near-Earth asteroids that would go on to become the targets for two robotic sample return missions: NASA’s OSIRIS-REx, launched in 2016 to study asteroid Bennu, and the Japanese Aerospace Exploration Agency’s Hayabusa2, launched in 2014 to study Ryugu.

Even though humans have intently studied asteroids for centuries, we have had very few opportunities to get our hands on material directly from these cosmic time capsules. Meteorites, which are pieces of asteroids that have fallen to Earth, provide important clues about the early days of the Solar System, but they have two major limitations. First, scientists aren’t certain which parent bodies (asteroids) gave rise to most of them. Second, they are not clean, unaltered samples. After withstanding the heat of atmospheric entry, they land on the ground, where they become contaminated with materials from Earth and immediately begin to corrode.

The only sample humanity has ever collected directly from an asteroid came back with JAXA’s Hayabusa Mission in 2010. That sample contains less than a milligram of particles from Itokowa, a “stony” asteroid with high silica content.

Soon, though, we’ll have two new opportunities to study pristine asteroid material. This time the samples will come from the carbon-rich asteroids Bennu and Ryugu. These asteroids are of particular interest because they contain the very oldest material from the stellar nursery – and because carbon-bearing compounds are the basis of life as we know it. These samples, and the organic molecules they contain, will help shed light on some of humanity’s grand mysteries: Where did we come from? How did life develop on Earth?

Both spacecraft will reach their respective destinations during 2018 – Hayabusa2 in June and OSIRIS-REx in December – and the missions fit together like two adjoining pieces of a cosmic puzzle. In combination, the data and discoveries from these two asteroid explorers will reveal a long-shrouded portion of the Solar System’s portrait.

Mapping, navigating around, and collecting samples from small Solar System bodies are all relatively new endeavors for humanity, and the two mission teams have already been sharing ideas, data, and lessons learned for several years as part of a major partnership between NASA and JAXA. This exchange will continue as the two spacecraft operate in close proximity to their target asteroids. The OSIRIS-REx team will host Japanese scientists in the Science Operations Center at the University of Arizona, and OSIRIS-REx team members will travel to JAXA during Hayabusa2’s operations. They will share software, data, techniques for analysis, and aspects of each other’s cultural systems in the process. Ultimately, the two agencies will exchange portions of the returned samples as well.

However, the two missions’ strategies for exploration are quite different. For starters, OSIRIS-REx will go into orbit around Bennu during two separate phases of asteroid operations. All told, the NASA spacecraft will spend more than a year and a half imaging and mapping Bennu with its suite of remote sensing instruments (cameras, spectrometers, and a laser altimeter) – a plan based partially on lessons learned from JAXA’s first Hayabusa mission. All of this data will be used to select a single sample site with high scientific interest and low risk to the spacecraft. After carefully rehearsing, OSIRIS-REx will move in close, extend its sampling arm, and touch the asteroid’s surface for just five seconds, using nitrogen gas to stir up and collect at least 60 grams of loose material.

By contrast, Hayabusa2 will not actually orbit Ryugu. In fact, the JAXA spacecraft will spend only about three months mapping before it begins the process of collecting three separate, but smaller, samples from different geographic locations on Ryugu. In addition to remote sensing, Hayabusa2 will deploy a lander (called MASCOT) and two rovers (called MINERVA-II 1 and 2) and will use a projectile and small explosive during one sampling process to collect material from beneath the asteroid’s surface.

Despite the differences, there are shared challenges, and both teams’ learning curves will be steep. Until now, neither asteroid has been seen up close, and they will likely have some surprises in store. The predictions made from the ground about their shapes, sizes, and compositions could turn out to be wrong. Ryugu is expected to be about 80 percent larger than Bennu (approximately 900 meters in diameter versus 500 meters in diameter), but both asteroids are much smaller than the planets and most other bodies that have been orbited or landed on by spacecraft. The small size and microgravity environment makes navigation and sampling that much more challenging.

Both spacecraft are venturing into far-away and unknown territory and attempting feats that are new to humanity. For the most part, they will be on their own on the asteroid frontier, but the value of running complementary missions cannot be overstated. The scientific and cultural returns from the two missions combined is far more than double the value of each individual mission. The ability to make comparisons during planning, operations, and after the samples are returned reduces risk and make both missions exponentially better.

And, like any expedition, the chances for success increase when there are two friendly explorers forging similar paths and learning side-by-side.

Media Contact

Office of Communications
University of Arizona