Illustration of the OSIRIS-REx sample return capsule passing through Earth’s atmosphere
NASA Goddard Space Flight Center/CI Lab
Bits of the asteroid Bennu are set to return to Earth. NASA’s OSIRIS-REx spacecraft collected samples of the asteroid in 2020 and is scheduled to deliver them on 24 September.
Launched in 2016, OSIRIS-REx entered orbit around Bennu in 2018. Bennu was chosen as a target because of its relatively close distance to Earth – at the time of launch, it was about 225 million kilometres away, and it got as close as 50 million kilometres from Earth in the following years.
Bennu is classified as a near-Earth object (NEO) due to its regular close approaches to our planet. While there is a 0.057 per cent chance of a collision with Earth in the next 300 years, it is not expected to impact us in the near future. However, if it were to collide, its 490 metre size would cause significant damage.
The primary reasons for studying Bennu are to understand how to protect Earth from similar asteroids and to explore its primitive nature. According to Anjani Polit at the University of Arizona, part of the OSIRIS-REx team, asteroids like Bennu are remnants from the early solar system and serve as time capsules. Bennu contains large concentrations of carbon, which are the main building blocks of organic molecules and potentially crucial for the formation of life on Earth.
Japan’s Hayabusa2 spacecraft has already returned samples from the asteroid Ryugu. Comparing the dust samples from Bennu and Ryugu will aid researchers in understanding the history of the solar system.
On 24 September, the OSIRIS-REx team will carefully decide whether it is safe to release the sample capsule. If approved, the capsule will be launched towards Earth from a distance of about 102,000 kilometres, equivalent to over a quarter of the distance to the moon. After a four-hour journey, it will enter the Earth’s atmosphere at a speed of approximately 44,000 kilometres per hour. During descent, it will be protected by a heat shield and parachutes until it lands in the Utah desert.
If the capsule cannot be released on 24 September, researchers will have to wait two more years for another opportunity. If successful, the OSIRIS-REx spacecraft will continue on a mission to the asteroid Apophis. Meanwhile, scientists on Earth will immediately begin analyzing the samples from Bennu.
