NASA to launch spacecraft to near-Earth asteroid

NASA is set to launch a new spacecraft in September that will travel to a near-Earth asteroid known as Bennu and bring back a sample of surface material which may contain building blocks of life. To identify the regions in which the building blocks of life may be found, the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) team equipped the spacecraft with an instrument

that will measure the spectral signatures of Bennu's mineralogical and molecular components.  Known as OVIRS (short for the OSIRIS-REx Visible and Infrared Spectrometer), the instrument will measure visible and near-infrared light reflected and emitted from the asteroid and split the light into its component wavelengths, much like a prism that splits sunlight into a rainbow. "OVIRS is key to our search for organics on Bennu. We will rely on it to find the areas of Bennu rich in organic molecules to identify possible sample sites of high science value, as well as the asteroid's general composition," said Dante Lauretta, principal investigator for the OSIRIS-REx mission at the University of Arizona in the US. OVIRS will work in tandem with another OSIRIS-REx instrument - the Thermal Emission Spectrometer, or OTES. While OVIRS maps the asteroid in the visible and near infrared, OTES picks up in the thermal infrared.  This allows the team to map the entire asteroid over a range of wavelengths that are most interesting to scientists searching for organics and water, and help them to select the best site for retrieving a sample. In the visible and infrared spectrum, minerals and other materials have unique signatures like fingerprints. These fingerprints allow scientists to identify various organic materials, as well as carbonates, silicates and absorbed water, on the surface of the asteroid. The data returned by OVIRS and OTES will actually allow scientists to make a map of the relative abundance of various materials across Bennu's surface. As the OSIRIS-REx spacecraft approaches Bennu, OVIRS will view one entire hemisphere at a time to measure how the spectrum changes as the asteroid rotates, allowing scientists to compare ground-based observations to those from the spacecraft. Once at the asteroid, OVIRS will gather spectral data and create detailed maps of the surface and help in the selection of a sample site. Using information gathered by OVIRS and OTES from the visible to the thermal infrared, the science team will also study the Yarkovsky Effect, or how Bennu's orbit is affected by surface heating and cooling throughout its day.

The asteroid is warmed by sunlight and re-emits thermal radiation in different directions as it rotates. 

This asymmetric thermal emission gives Bennu a small but steady push, thus changing its orbit over time. 

Understanding this effect will help scientists study Bennu's orbital path and improve our predictions of its influence on the orbits of other asteroids.