OSIRIS-REx has launched and is on its way to 101955 Bennu to...
This is from Osiris-Rex's Wikipedia page:
...asteroid Bennu is a threatening Earth impactor capable of causing vast destruction and death
What is the chance that Bennu will impact Earth?
What is the potential for damage if it does hit?
How will information from Osiris-Rex affect an impact mitigation mission?
Bonus question: When will Bennu (potentially) impact with Earth?
Can OSIRIS-REx save us? No. I found no evidence that diverting the asteroid is a mission objective. The spacecraft is not equipped to influence the asteroid in any meaningful way.
From the Wikipedia article you quoted:
The science objectives of the mission are:
- Return and analyze a sample of pristine carbonaceous asteroid regolith in an amount sufficient to study the nature, history, and distribution of its constituent minerals and organic material.
- Map the global properties, chemistry, and mineralogy of a primitive carbonaceous asteroid to characterize its geologic and dynamic history and provide context for the returned samples.
- Document the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site in situ at scales down to millimeters.
- Measure the Yarkovsky effect (a thermal force on the object) on a potentially hazardous asteroid and constrain the asteroid properties that contribute to this effect.
- Characterize the integrated global properties of a primitive carbonaceous asteroid to allow for direct comparison with ground-based telescopic data of the entire asteroid population.
Does Bennu pose a risk to Earth?: recent calculations produced a cumulative probability of 1 in 1410 (or 0.071%) of impact with Earth in the period 2169 to 2199.
The first mission that will try to move an asteroid is the Asteroid Redirect Mission.
Relative to the third part of your question, OSIRIS-Rex will provide new data that may be helpful in more accurately estimating the future path of potentially hazardous asteroids by characterizing the Yarkovsky effect.
The idea of the Yarkovsky effect is a body in space absorbs light from the sun. This absorbed energy is re-emitted as infrared radiation. If the body is spinning or tumbling, this re-emitted radiation is in a different direction. Although this photon pressure (think light sails) is extremely small, it doesn't go away. So over several decades, an asteroid that we calculate (without taking the effect into account) will miss Earth by, say, 30,000 miles, might not miss at all!
Bennu (aka RQ36) was chosen partly because it is so black. It has an extremely low albedo, reflecting only about 4%, meaning it will absorb about 96% of the Sun's light. This provides a worst case that OSIRIS-Rex can observe, providing useful experimental data.
