Context: Recently, the images captured by NASA’s OSIRIS-REx spacecraft have discovered that rocks on asteroid Bennu could crack as sunlight heats them up during the day and the rocks cool down at night.
Key Points

• For the first time evidence for this process called thermal fracturing has been definitively observed on an object without an atmosphere.
• The scientists involved in the study found features consistent with thermal fracturing using the spacecraft’s OSIRIS-REx Camera Suite, which can see features smaller than one centimeter.
• It can help in understanding what the surface used to be like and what it will be after millions of years from now. 

About Thermal Fracturing

• Like any weathering process, thermal fracturing causes the evolution of boulders and planetary surfaces over time.
• This ranges from changing the shape and size of individual boulders to producing pebbles or fine-grained regolith, to breaking down crater walls.
• It is to be noted that rocks expand during daytime when sunlight heats them and they contract at night, causing stress that forms cracks, which grow slowly over time.
• Thermal fracturing could be an important weathering process on asteroids, which are airless objects.
• For example: The daytime temperature on Bennu can touch as high as 127 degrees Celsius, and nighttime lows plummet to about minus 73 degrees Celsius.

About OSIRIS-Rex Mission

• The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS REx) is a planned NASA asteroid study and sample return mission.
• Aim: To study asteroid 101955 Bennu, a carbonaceous asteroid and return to Earth a sample for detailed analysis in 2023.

Why was Bennu chosen?

• Bennu was chosen as target asteroid for the mission as it was fit in the three criteria: accessibility, size and composition.
• Scientists at NASA need an asteroid that they can easily travel to, retrieve a sample from and return to Earth, all within a few years’ time.
• The closest asteroids are called near-Earth objects and they travel within 1.3 Astronomical Units (AU) of the sun.
• For a mission like OSIRIS-REx, the most accessible asteroids are somewhere between 0.08 – 1.6 AU.
• Further Bennu had similar orbit to Earth.
• Significance: Material returned is expected to enable scientists to learn more about the time before the formation and evolution of the Solar System, initial stages of planet formation, and the source of organic compounds which led to the formation of life.