Japan’s Hayabusa 2 spacecraft has successfully landed on the surface of the asteroid Ryugu, a historic moment in space exploration that could provide fascinating details on the origins of life on Earth.
At 7:49 am local time in Japan the spacecraft touched down on Ryugu, having descended from a stable orbit about 20 kilometers above the surface. Taking place some 310 million kilometers from Earth—well past the point where even communication at light-speed is too slow for real-time control—the entire descent was automated, and took about 23 hours. As it gently contacted the surface, the Hayabusa 2 spacecraft should have had a closing speed of just seven centimeters per second. If all proceeded according to plan, a meter-long sampling arm successfully fired a bulletlike projectile into the surface, causing up to 0.1 gram of material to be collected in a sample capsule to be transported back to Earth in late 2020.
The spacecraft took images before, during and after the attempted sample collection, which will be the only way to know whether the mechanism has been successful. After leaving the surface, Hayabusa 2 took about half a day to return to its home position above the asteroid. “This is really exciting, because this is the first time in history that we [may have] got a sample of a carbonaceous asteroid,” says Patrick Michel from the Côte d'Azur Observatory in France, a co-investigator on the mission.
Hayabusa 2 was launched in December 2014 by the Japan Aerospace Exploration Agency (JAXA), arriving in June 2018 at Ryugu, a primitive C-type (carbonaceous) asteroid. Ryugu is scarcely a kilometer across but is believed to contain an immense scientific treasure: pristine material left over from the primordial solar system of 4.6 billion years ago, an epoch preceding the coalescence of the sun’s retinue of planets. To study this science-rich rock, Hayabusa 2 has already created global maps from its orbital perch and also sent three small rovers down to the surface in late 2018. A fourth rover will be deployed later this year. But the mission’s foremost goal has always been to directly gather samples from the surface, using similar equipment first deployed on a predecessor mission, Hayabusa 1. The only previous asteroid sample-return mission, Hayabusa 1, returned dust grains from the S-type (or stony) asteroid Itokawa in June 2010, a less-pristine object thought to have formed considerably later than Ryugu in the solar system’s history.
Hayabusa 1’s sample-collecting mechanism did not work as planned, however, with the projectile failing to fire into the surface—although the spacecraft’s thrusters did kick dust up into its collector. Hayabusa 2’s scientists and engineers are hopeful they have addressed any issues this time around—if it has worked successfully, the payoff could be huge. “This time we think we can get organic matter,” says JAXA’s Makoto Yoshikawa, the mission manager for Hayabusa 2, referring to carbon-rich compounds that, along with water and sunlight are the fundamental basis of life on Earth. “In Hayabusa 1’s case at Itokawa we did not find organic matter. But this time at Asteroid Ryugu, we think we can get organic matter and water in the sample. So this is our main target.”
After the spacecraft arrived at the asteroid the team began studying images to find a suitable landing site to collect a sample. It quickly became apparent the material on the surface was not as fine as expected, instead comprising rubblelike rocks and boulders that could easily scuttle an errant sample-collecting attempt. So to increase the chance of success, the spacecraft dropped target markers onto Ryugu in October 2018—thin sheets of reflective material to serve as mirrors for range-finding lasers that can accurately measure the distance to the surface.
The original plan called for three separate landings and sample collections, returning material from different locations. Concerns over the rough terrain, however, mean only one more landing is likely to be attempted, one which will be even more ambitious. No earlier than April the spacecraft will shoot an impactor weighing one kilogram toward the surface at a speed of two kilometers per second, excavating a small crater some two to three meters across. The team will then decide whether to descend and attempt to collect a sample from within this crater, scooping up material from inside the asteroid itself—something that has never been done before.
NASA scientists involved in OSIRIS-REx, another asteroid sample-return effort coincidentally happening at the same time, will be watching Hayabusa 2’s work at Ryugu with bated breath. OSIRIS-Rex’s mission calls for collecting up to two kilograms of material from the asteroid Bennu, also a C-type asteroid, in late 2020. A strong collaboration between Japan and the U.S. has seen the two teams sharing information, and the OSIRIS-REx team will learn invaluable data from Hayabusa 2’s attempted landings. “We’re very interested in what happens during their sampling attempt,” says Dante Lauretta, principal investigator on OSIRIS-REx and a co-investigator on Hayabusa 2. “We’re going to set up a meeting [with JAXA] to go through the lessons learned.”
Peering back in time via the remote-sensing data and direct samples gathered by these spacecraft, researchers hope to learn just how asteroids—and maybe comets, too—first seeded Earth with water and other key ingredients for life. If and when the pristine samples of these primordial asteroids are returned, global teams of scientists will scour them for organic materials such as amino acids, which may provide new clues to our beginnings. Analyzing the isotopic composition of the samples will also reveal precisely how old each asteroid is, firming up the chronology of our solar system’s becoming. “We want to verify whether these bodies have organic material,” Michel says, “and also analyze this material in order to understand the role of asteroids in the emergence of life on Earth. One scenario could be that all the elements needed for the emergence of life, including water and maybe other prebiotic materials, were brought by these small bodies.”
Hayabusa 2 is set to depart Ryugu in late 2019, and in late 2020 it will arrive at Earth, dropping off its capsule filled with precious cargo from the solar system’s dawn. Together with OSIRIS-REx, this intrepid interplanetary mission might just tell us more about our own world’s origins than ever before.