Images captured by NASA’s OSIRIS-REx show the spacecraft’s sample head touching the surface of asteroid Bennu, which then became enveloped in a cloudy burst of dust and rock. The team now has to figure out how much surface material was collected, if any, but these images are being taken as a very positive sign.
On Tuesday, OSIRIS-REx made contact with Bennu, an 548.64 m-wide asteroid located 321 million kilometres from Earth, marking NASA’s first attempt at collecting an asteroid sample. Preliminary data from the probe pointed to a successful encounter, but new images released by NASA late yesterday are added proof.
Pictures snapped by the spacecraft’s SamCam imager show the 0.30 m-wide sampling head absolutely bathed in debris. Though I’m no expert, it would be hard to believe that nothing got scooped up by the collection system, known as Touch-and-Go, or TAG. But images can be deceiving, and the team, led by the University of Arizona, will spend the next week trying to figure out how much debris was collected.
Approximately one second after making touchdown, the probe fired a nitrogen gas bottle, which produced the debris cloud, according to a NASA statement. OSIRIS-REx arrived at a predetermined site called Nightingale and reached the surface during its first attempt. The round head at the end of the sampling arm, called TAGSAM, was the only part of the spacecraft that touched the asteroid’s surface. The TAG procedure was done autonomously with pre-programmed instructions from ground engineers.
Looking at the images, you can see the head crushing some of the porous rocks. Preliminary data suggests the head remained in contact with the surface for around six seconds, of which five seconds were spent collecting materials. NASA says the first three seconds are when the sampler likely collected most of the material. The probe was moving at 10 cm/sec when it reached the surface.
Its task complete, OSIRIS-REx then fired its reverse thrusters, which also kicked up surface material. The spacecraft, which backed away at 40 cm/sec, is once again orbiting Bennu, and it appears to be functioning normally.
As noted, the team is now trying to figure out if the sampler actually got anything. They’re hoping to collect around 60 grams, which is basically a chocolate bar’s worth of material. Eventually, OSIRIS-REx will return these samples to Earth for analysis, so the more material that’s collected the better.
The team will use a variety of techniques to make this determination. The first step will be to measure how much material was kicked up by the nitrogen blast. They’ll review images of the TAG procedure, including photos showing the amount of dust that accumulated around the sampling head. As a statement from the University of Arizona points out, the team will also try to weigh the collected material, which they’ll do with some fancy physics:
A couple of days after the SamCam images are analysed, the spacecraft will…measure the mass of the sample collected by determining the change in the spacecraft’s “moment of inertia,” a phrase that describes how mass is distributed and how it affects the rotation of the body around a central axis. This manoeuvre entails extending the TAGSAM arm out to the side of the spacecraft and slowly spinning the spacecraft about an axis perpendicular to the arm. This technique is analogous to a person spinning with their arm extended while holding a string with a ball attached to the end; the person can sense the mass of the ball by the tension in the string. Having done this manoeuvre before TAG, and now after, engineers can measure the change in the mass of the collection head as a result of the sample inside.
If the team determines that not enough material was collected, they’ll try again on January 12, 2021 at a site named Osprey. The TAG system has more nitrogen gas available, and the team is in no hot rush to get the job done, as OSIRIS-REx won’t be departing the asteroid until March 2021, when Earth and Bennu are in a favourable orbital alignment.
Once at Earth, the collected material will be studied by scientists for years to come. The surface of Bennu is thought to contain materials unchanged since the earliest days of the solar system, which could shed light on the role played by asteroids in delivering water, and possibly even the basic building blocks for life, to early Earth.