After almost two and a half years together NASA’s OSIRIS-REx spacecraft said goodbye to the asteroid Bennu and began its journey back to Earth.
The spacecraft is packing a precious cargo for Earth, which should return in September 2023: a piece of asteroid that could reveal the story of the origin of the solar system and life on Earth itself.
On Wednesday, OSIRIS-REx performed Bennu’s last overflight before launching from the side of the asteroid. In that last encounter, the spacecraft filmed Bennu for 5.9 hours, just over the full period of the asteroid’s rotation, at a distance of 3.5 kilometers. This is the closest to the Bennu spacecraft since the sampling event.
Amy Simon is a planetary scientist at NASA’s Goddard Space Flight Center. She explains Inverse that the main purpose of the final overflight was to look at the sampling site for the last time.
“When we did the sample collection and retreated, there was so much garbage and dust that we couldn’t actually see the surface,” Simon says. Inverse.
“The main thing is that we can see what has changed if we have left the crater or there is some new composition that has somehow been discovered. “
OSIRIS-REx collected 4 gigabytes of data during its final overflight. But scientists on Earth must wait until the spacecraft can send all this data to Earth, which will happen on April 13 at the earliest.
The spacecraft communicates with Earth control on Earth via a deep space network, a string used by NASA to communicate with a multitude of space missions, including the Perseverance rover on Mars. OSIRIS-REx gets between four and six hours of outgoing connection per day and transmits back at 412 kilobits per second – about 186 megabytes per hour. As a result, it will take several days for new data from OSIRIS-REx to come into our earthly hands.
Here’s the background – OSIRIS-REx has been orbiting the asteroid Bennu since December 2018. Its mission was to collect a sample of this ancient body and return it to Earth for analysis. On October 20, 2020, the spacecraft successfully touched an asteroid and captured a sample from the space rock of a “pile of rubble” using a robotic arm Touch-and-Go sample collection mechanism – which acted somewhat like a vacuum for loose materials on Bennu.
What did we learn about the asteroid Benn?
Prior to returning with the invested samples, OSIRIS-REx had already fed scientists with an abundance of new knowledge about the asteroid – and all other asteroids that had set out to come close to Earth.
“We actually learned a lot during the mission,” says Simon. “We had a few main goals besides obviously collecting samples.”
One of the other goals of the mission was to determine how much the asteroid’s orbit changes over time as a result of its interaction with the Sun and to learn about the composition of the asteroid.
When OSIRIS-REx reached Bennu, the asteroid actually moved 185 kilometers from where the ground mission team thought it would be, Simon admits.
“Its orbit changes over time, which is really interesting and such information is important for understanding the likelihood that these close terrestrial objects will affect the Earth,” Simon says.
Based on the vessel’s observations, the team also determined that the rotation of the asteroid is gradually accelerating – at a speed of one second every 100 years. Although this may seem rather insignificant, it indicates that the asteroid is just a “rubber pile” consisting of pieces of dust and rock held together by gravity, not a solid mass.
Images taken with OSIRIS-REx also represent the first evidence of thermal refraction on an object without an atmosphere. Scientists can use heat fracture measurements to determine the age of asteroids.
Thermal fracture takes place on Earth. On our planet, rocks baked in the sun break all day long at night as it cools. As rocks expand and contract, the accumulation of stress causes them to crack and eventually disintegrate into smaller pieces.
Similar to the rocks on Earth, the rocks on Bennu have differences in day and night temperatures. Daily highs on Bennu can reach almost 127 degrees Celsius (260 degrees Fahrenheit), and nighttime lows fall to about minus 73 degrees Celsius (minus 99 degrees Fahrenheit)
Scientists believed that thermal refraction could occur on asteroids like Bennu – but they never had any evidence of this until OSIRIS-REx.
When will OSIRIS-REx leave Benna?
OSIRIS-REx will launch from Bennu’s orbit on May 10 and embark on a two-year journey back to Earth. Bennu has an orbit that intersects with Earth’s orbital path, so the return trip is less expendable than it could be from other asteroids that are within our reach.
“Getting out of Bennu’s vicinity in May brings us to a‘ sweet spot ’, when the departure maneuver will consume the least amount of spacecraft on board,” Michael Moreau, deputy manager of OSIRIS-REx at NASA’s Goddard Space Flight Center in Greenbelt , Maryland, the statement said.
The spacecraft will remain in loose orbit until it leaves Bennu’s side, awaiting its planned departure.
Mission objectives OSIRIS-REx
OSIRIS-REx was launched from Earth on September 8, 2016, carrying six instruments designed to map asteroids, document sample locations, and other Bennu observations.
The mission marked NASA’s first attempt to land on an asteroid and return a sample of one of these curious bodies back to Earth. Two similar missions – Genesis and Stardust – have visited comets in the past and brought samples. Genesis, however, suffered a parachute crash, damaging part of the aircraft’s payload.
Why does OSIRIS-REx return asteroid samples?
Most of what we know about asteroids comes from meteorites, which are fragments that fall to Earth as their parent bodies pass by our planet. Meteors can be significantly altered by these journeys through the Earth’s atmosphere.
Unaltered asteroid patterns are crucial to understanding our origins. Scientists believe that asteroids are made of the same ancient material that formed the solar system billions of years ago. Studying asteroids gives us clues as to how planets, including Earth, existed.
Bennu orbits the Sun every 436.6 days. It is a type B asteroid – the most primitive type of asteroid. Bennu has barely changed since it was created 4 billion years ago, and contains relatively large amounts of carbon, organic molecules and amino acids – which are considered the building blocks of life.
By studying samples of asteroids in the laboratory, scientists will better understand its composition and the material that makes up these space bodies.
While observing asteroids or any other body in space through the eyes of a spacecraft, scientists are limited by the instruments found on the ship and cannot break them down to the exact minerals that are on the surface.
As a result, studying samples in the lab is a completely different ball game.
“Yeah, it’s going to be a lot of fun,” Simon says. “We’ll learn more about the actual materials that are there and how easily they break down, how heavy they are, with different compositions.”
“I think a lot of interesting things are going to come out of this,” she adds.
The mission is not just an attempt to find our origin – it is also a good way to protect the Earth.
Bennu comes to only 0.002 astronomical units on Earth every six years and there is very little chance that it will collide with our planet in approximately 150 years. By studying Bennu’s orbit and the small forces that affect its orbit, scientists can create better models of asteroid orbits and more accurately calculate the chances that they could collide with Earth.
When does OSIRIS-REx return to Earth?
OSIRIS-REx is scheduled to return to Earth on September 24, 2023 with a higher payload than expected.
Mission members suspect that OSIRIS-REx grabbed a significant amount of material from Bennu’s surface, presumably exceeding the mission’s original two-ounce request.
“We don’t have an absolute estimate, but we knew we had a lot,” Simon says.
After taking samples in 2020, NASA noticed a leak of material coming from the craft’s robotic arm. He collected much more than was needed, and the head of the collector could not be closed. Fortunately, the samples were eventually successfully stored on the spacecraft.
The OSIRIS-REx travel capsule will travel the Earth’s atmosphere and land by parachute at the Utah test and training ground.
After the capsule recovers, team members will transport it to a curative facility at NASA’s Johnson Space Center in Houston.
The agency will then distribute the sample to laboratories around the world, so that a large group of international scientists can study the creation of the solar system and our home planet at the same time.