How Asteroid Bennu Caught NASA’s OSIRIS-REx mission By Surprise And Nearly Destroyed It 

NASA’s OSIRIS-Rex mission has been on a mission to collect asteroid samples and return them safely to Earth. However, as the space probe reached the asteroid Bennu region, it discovered a celestial body that appeared and behaved differently from what researchers earlier suggested. Hence, the OSIRI-REx mission was nearly caught by surprise by the space rock.

As NASA commenced with the planning of its first mission to collect an asteroid, JAXA was already on its way to conduct an asteroid mission named Japan’s Hayabusa. After flying through space to obtain samples from the space rock, the Hayabusa spacecraft successfully delivered the first fragment of an asteroid called Itokawa to Earth in 2010.

The Japanese spacecraft had triumphantly mapped the entire Itokawa a few years earlier. This mapping showed the landscape strewn accompanied with boulders. It also revealed that the space rock possesses smooth beach-like plains of gravel and sand. NASA designed and built its OSIRIS-REx mission based on these images of Itokawa. However, the asteroid that OSIRI-REx was meant to study was totally different. Hence, NASA almost lost its spacecraft because of this difference.

“The strategy for planning with OSIRIS-REx was to take Itokawa and all of the observations of asteroid Bennu that we had made of it before,” Kevin Walsh, a planetary scientist at Southwest Research Institute and lead scientist of the Regolith Development Working Group of the OSIRIS-REx mission, told “So we would look at the different way [the two asteroids] reflect light and the different way they reflected radar, and every indication was that Bennu would have more ponds of fine grains than Itokawa.”

Why NASA’s OSIRIS-REx Mission Was Nearly Destroyed By Asteroid Bennu

A stereoscopic photo of a rocky outcrop on the surface of asteroid Bennu. (Image credit: The University of Arizona Press/London Stereoscopic Company)

In 2016, NASA launched its OSIRIS-REx mission from Kennedy Space Center at Cape Canaveral to obtain asteroid samples and possibly return them to Earth. However, when the spacecraft arrived at asteroid Bennu in 2018, the team behind the launch realized that their earlier assumptions about space were “totally wrong,” Walsh revealed to

The spacecraft’s cameras showed a “boulder hellscape” instead of the earlier anticipated wide plains of sand and gravel interspersed with accumulations of boulders. The scientists behind the launch felt disappointed as there was no smooth open region and they hoped that the OSIRIS-REx would land to collect its sample.

“When we designed the spacecraft, we had a design targeting accuracy [for the landing] of about 50 meters [164 feet],” Laur The mission’s chief scientist Dante Lauretta told during an earlier interview that the team had concerning why the sample collection might not be possible at all. “The thermal properties, also the radar properties [of Bennu], really looked like a smooth surface. So when I first saw that [the surface was completely different], I really thought we might be in trouble there.”

Hence, the team debated on the safety of landing the spacecraft in towering bounders that stood against Bennu’s feeble gravity into heights that hid itself from Earth.

Suggestions To Safely Land The Spacecraft

Sir Brian May, a Legendary guitarist and popular astronomer contacted Lauretta to share his view about the mission. May holds a PhD in astronomy which he obtained after a 30-year hiatus mandated by Queen’s rise to fame in the 1970s. He also possesses the skill of stereoscopic imaging. May suggested to Lauretta that he could use his skill to assist the OSIRIS-REx team struggling to identify a boulder-free region to safely land the spacecraft on the asteroid Bennu.

“Once you have a stereo image of that particular potential landing site, you can really make that instinctive judgment as to whether things are going to work out,” May told in an earlier interview. “You see that there is this boulder, how much slope there is, how dangerous it is to get on and to get off.”

May’s assistance helped the OSIRI-REx team discover an obstacle-free crater to land the spacecraft and obtain some samples. However, the scientists remotely reprogrammed the spacecraft to execute the smooth landing without issue. The envisioned landing site should be about 164 feet wide (50 m). However, NASA’s team squeezed the van-size space probe to land into a smaller space of about 33-foot-wide (10 m) Nightingale Crater.

“When we launched, we planned to use a laser altimeter for the guidance down to the asteroid because we were expecting these big smooth areas,” Lauretta said. “We just thought that we would need to know that we were coming down at the right rate towards the surface. Instead, we had to completely change the strategy, using the onboard cameras and performing an extensive mapping campaign, sometimes mapping features as small as a couple of centimeters to put into the spacecraft’s memory so that it could make real decisions and guide itself down to the safe location.”

How NASA’s OSIRIS-REx Mission Obtained The Sample After Attaining the Smooth Landing Milestone

Despite the initial challenge encountered while making the touchdown, the team still achieved a smooth descent of the spacecraft. After the smooth landing, the OSIRIS-REx mission commenced with its sample collection by pressing down a device into the asteroid’s surface. Scientists expected the surface of the space rock to behave nearly like a swamp. But the OSIRIS-REx’s sample collection device sank 19 inches (50 cm) deep into Bennu within a few seconds.

As soon as the device sucked in the sample, the spacecraft reignited its thrusters. The firing of the thrusters made a huge wall of debris rise from the crater covering the ascending space probe. The OSIRIS-REx team only realized what actually happened when images from onboard cameras reached Earth.

The scientists later revealed that the gravel that engulfed the spacecraft during its ascent could have destroyed some of its components. The team also miscalculated the density of asteroid Bennu just like they wrongly estimated its hostile surface. The surface of the asteroid behaves more like water than terrestrial material.

“When we did our calculations, initially we were taking the density of all of Bennu, which is 1.1 grams per cubic centimeter,” said Walsh. “But our models showed afterward that to be able to compress the surface so much and drive the tag head so deep into the surface, the surface density would have to be like 0.4 grams per cubic centimeter. And so it was less than half as dense as the entire body.”

Why is Bennu’s surface WaterLike?

The team is still struggling to tell why the surface of asteroid Bennu possesses water-like quality. Walsh suggests that tiny sand-like particles may have filtered via the gaps between larger rock fragments and moved into the inner part of the asteroid, thereby creating massive empty space on the surface layer of the asteroid. This suggestion might explain the strange low density discovered on the asteroid’s surface. However, the overall density of the space rock seems to be extremely higher than that of its surface.

Walsh described the smooth landing as “scientifically interesting, although operationally challenging.” The challenges experienced by the OSIRI-REx asteroid never stopped it from accomplishing its mission goals on Bennu. In fact, the spacecraft is currently on its way back to Earth and will drop off its cargo on Sunday, September 24. Lauretta hopes to reveal the outcome of the first scientific results obtained from the sample analysis towards the end of the year.

“When we did our calculations, initially we were taking the density of all of Bennu, which is 1.1 grams per cubic centimeter,” said Walsh. “But our models showed afterward that to be able to compress the surface so much and drive the tag head so deep into the surface, the surface density would have to be like 0.4 grams per cubic centimeter. And so it was less than half as dense as the entire body.”


On the course of landing safely on the surface of asteroid Bennu, NASA’s OSIRIS REx mission was nearly destroyed. Despite the challenges, the spacecraft successfully obtained the asteroid sample and is currently on its way to deliver the obtained samples to Earth. This is truly one of the most interesting space missions of our time. What do you think about this historic mission? Check out these fascinating space gifts for your loved ones.

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