History was made yesterday as NASA’s OSIRIS-REx became the first U.S. spacecraft to successfully retrieve a sample of rock and dust from an asteroid, which will be later returned to Earth.
It is a remarkable achievement, and scientists hope the sample will contain some clues as to how life originated on Earth. The asteroid, called Bennu, contains carbon, and there is also now evidence for organic molecules, the kind that life as we know it is based on. Asteroids like Bennu are thought to have delivered many of these necessary molecules to the early Earth, helping life to get started here.
Bennu is ancient, but well-preserved, making it an ideal target for collecting such samples, which provide a window into what the early Solar System was like.
OSIRIS-REx – Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer – briefly “touched” Bennu on Tuesday, October 20, to perform the Touch-And-Go (TAG) maneuver. The TAG attempt was successful, and the sample will now be stowed away for the return trip to Earth, which will begin in March 2021. Although scientists know that the TAG worked as intended, they also now need to make sure that enough material was collected. If not, then another attempt will be made in January.
“This amazing first for NASA demonstrates how an incredible team from across the country came together and persevered through incredible challenges to expand the boundaries of knowledge,” said NASA Administrator Jim Bridenstine. “Our industry, academic, and international partners have made it possible to hold a piece of the most ancient Solar System in our hands.”
So just how did OSIRIS-REx attempt to obtain the sample from Bennu?
First, the spacecraft left its orbit around Bennu at 1:50 PM EDT and started descending toward the asteroid. The 11-foot (3.35-meter) sampling arm, known as the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), was extended during this time. The descent lasted about four hours until the spacecraft was 410 feet (125 meters) above the surface.
At that point, OSIRIS-REx performed a Checkpoint burn of its thrusters, which put it in the exact location needed at the sampling site, called Nightingale.
A second burn ten minutes later, Matchpoint, slowed down the spacecraft to match the speed of Bennu’s rotation. The spacecraft touched down at Nightingale 11 minutes later, after navigating past a huge two-story tall boulder called Mount Doom.
Nightingale is one of the few smooth areas on Bennu, covered in sand, about the size of a small parking lot. Most of the asteroid is covered in rocky regolith and boulders.
“This was an incredible feat – and today we’ve advanced both science and engineering and our prospects for future missions to study these mysterious ancient storytellers of the Solar System,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “A piece of primordial rock that has witnessed our Solar System’s entire history may now be ready to come home for generations of scientific discovery, and we can’t wait to see what comes next.”
Telemetry from OSIRIS-REx indicated that the sampling procedure went as planned, but it will now take a week to determine if the sample was large enough, ideally at least 60 grams. How do they do that? First, by comparing images of the Nightingale site before and after TAG to see how much surface material moved around in response to the burst of nitrogen gas from the thrusters.
“After over a decade of planning, the team is overjoyed at the success of today’s sampling attempt,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson. “Even though we have some work ahead of us to determine the outcome of the event – the successful contact, the TAGSAM gas firing, and back-away from Bennu are major accomplishments for the team. I look forward to analyzing the data to determine the mass of sample collected.”
“It’s hard to put into words how exciting it was to receive confirmation that the spacecraft successfully touched the surface and fired one of the gas bottles,” said Michael Moreau, OSIRIS-REx deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The team can’t wait to receive the imagery from the TAG event late tonight and see how the surface of Bennu responded to the TAG event.”
“Our first indication of whether we were successful in collecting a sample will come on October 21 when we downlink the back-away movie from the spacecraft,” Moreau said. “If TAG made a significant disturbance of the surface, we likely collected a lot of material.”
Then, the team will take photos of the TAGSAM head with a camera known as SamCam. That will show how much dust collected around the sample collector head. Other photos will also be attempted to look directly into the sampling head itself to see how much material is inside it.
The team will also try to measure the mass of the sample, by determining the change in the spacecraft’s “moment of inertia,” or how mass is distributed and how it affects the rotation of the body around a central axis. The TAGSAM arm will be extended while the spacecraft slowly spins on an axis perpendicular to the arm. This way, the change in the mass of the collection head as a result of the sample inside it can be measured by the engineers.
“We will use the combination of data from TAG and the post-TAG images and mass measurement to assess our confidence that we have collected at least 60 grams of sample,” said Rich Burns, OSIRIS-REx project manager at Goddard. “If our confidence is high, we’ll make the decision to stow the sample on October 30.”
The sampling procedure was brief, and the spacecraft then fired its thrusters again to back away from the asteroid.
“Today’s TAG maneuver was historic,” said Lori Glaze, Planetary Science Division director at NASA Headquarters in Washington. “The fact that we safely and successfully touched the surface of Bennu, in addition to all the other milestones this mission has already achieved, is a testament to the living spirit of exploration that continues to uncover the secrets of the solar system.”
Since Bennu is far away, 200 million miles (321 million kilometers) from Earth, the TAG maneuver was performed autonomously, using pre-programmed instructions.
So what happens if it turns out that no material, or not enough material, was actually collected? In that case, another attempt will be made on Jan. 12, 2021 at another similar location called Osprey.
Once it is confirmed that enough sample has been collected, the sample will need to be stored for its return to Earth. The spacecraft’s robotic arm will place sample collector head into the Sample Return Capsule (SRC). After the SRC closes up tight, the robotic arm will retract and OSIRIS-REx will begin its journey home. It will depart Bennu in March 2021 and arrive back at Earth on Sept. 24, 2023. It will land using a parachute in Utah’s west desert.
Bennu, about 0.306 miles (492 meters) across, is a near-Earth asteroid, which makes it more easier to get to, in less time, than asteroids in the main asteroid belt between Mars and Jupiter. There is a slim chance that Bennu could eventually hit Earth, but the odds are currently only 1-in-2,700 of an impact sometime between 2175 and 2199.
Last year, scientists also found that Bennu has plumes of tiny particles erupting from its surface, as seen in images from OSIRIS-REx. The particle plumes were discovered on Jan. 6, 2019, and observed multiple times during the next couple months. Some of the particles even orbited Bennu as tiny “satellites” before settling back on the surface again.
OSIRIS-REx also found water-bearing minerals on Bennu, similar to those in carbonaceous chondrite meteorites, as well as carbonate mineral veins in some boulders, evidence for previous hydrothermal activity on the ancient parent rocky body that Bennu broke off from billions of years ago.
The study of Bennu and similar asteroids like Ryugu will provide valuable clues as to how they, and the early Solar System as a whole, formed billions of years ago. And if the scientists are right, new insights into how life first arose on ancient Earth.
OSIRIS-REx was launched aboard a ULA Atlas V 411 rocket from Cape Canaveral Air Force Station in Florida on Sept. 8, 2016.
More information about OSIRIS-REx is available on the mission website.