OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security Regolith Explorer) is a NASA mission that will visit the 500m diameter near-Earth asteroid, 1999 RQ36. This asteroid has been chosen as the mission's target for two main reasons. Firstly, it is the most accessible carbonaceous asteroid, meaning it is rich in carbon and volatiles (chemical species that have a low boiling point). It will come within 350,000km of Earth in the year 2135.1 This class of primitive (subject to little processing since formation) asteroids are thought to be direct remnants of the terrestrial planets' building blocks and they contain complex organic molecules. As such, detailed knowledge of this asteroid is fundamental to understanding planet formation and, potentially, the origin of life. Secondly, this is one of the most potentially hazardous asteroids known.1 Recent calculations based on observations of the asteroid's orbit predict a 1 in 1800 chance of impact with Earth in the year 2182.
Mission launch is scheduled for September 2016 and after its circuitous, 654-million-kilometer journey, OSIRIS-REx will reach the asteroid by October 2018. We will study the asteroid remotely during a 505 day rendezvous, before a brief maneuver to collect samples (60g or more) is performed. The spacecraft, with asteroid samples, will return to Earth after a 512-million-kilometer trip in 2023.
The OSIRIS-REx mission name is an acronym that captures its five objectives, which are as follows: Origins—return to Earth and analyze a pristine sample from the asteroid to discover the origin of its volatile elements and organic molecules, which may have led to life on Earth. Spectral Interpretation—perform detailed global mapping of the asteroid to provide geologic context for the returned samples and high-fidelity comparisons with ground-based and space observations of carbonaceous asteroids. Resource Identification—identify carbonaceous asteroid resources that may be used in human exploration. Security—quantify the asteroid's Yarkovsky effect (a very subtle force created when an asteroid absorbs sunlight and re-emits it as heat, causing the body to drift) on this potentially hazardous asteroid, to potentially help protect the Earth from future asteroid impacts. Regolith Explorer—explore and study the regolith (layer of loose material that covers solid rock on many planetary bodies, including the Moon and asteroids) at the sampling site in situ, down to sub-centimeter scales.
Figure 1. Illustrating the touch-and-go sample acquisition mechanism, through which asteroid regolith samples will be collected.
Members of the OSIRIS-REx team have measured the size, shape, and rotation state of the target asteroid using Arecibo and Goldstone planetary radar observations.2 IR observations from numerous telescopes, including the Spitzer Space Telescope were also made.3, 4 From the results, we infer that the asteroid is covered by large amounts of loose regolith consisting of sub-centimeter size particles that are coarser than moon dust. These regolith characteristics are ideal for the novel sample-collection strategy that we will employ.
The asteroid regolith samples will be collected using the 3m long touch-and-go sample acquisition mechanism (see Figure 1). During this process OSIRIS-REx will use two high-pressure gas jets to agitate surface material and blow it into a collector, which resembles a car air filter. The collector also features 24 sticky pads (2cm in diameter) onto which dust grains (of a millimeter or smaller size) will adhere. The collector, or sampler head, will be deployed from and stowed in the spacecraft by an articulated arm.
The spacecraft payload includes five other instruments. The OSIRIS-REx Camera Suite (OCAMS) will be built by University of Arizona researchers. It consists of three separate cameras and will image the asteroid from long range down to a few meters from the surface. The Canadian Space Agency will provide the OSIRIS-REx Laser Altimeter (OLA) for high-resolution global topographic mapping, including candidate sample sites. Mapping of surface minerals and organic compounds, at 0.08–2m resolution, will be conducted using the OSIRIS-REx Visible and IR Spectrometer (OVIRS), to be built by the NASA Goddard Space Flight Center. The OSIRIS-REx Thermal Emission Spectrometer (OTES) will be built at Arizona State University and will be used to characterize the thermal environment of the asteroid and to map its mineralogy through the collection of thermal IR data. Finally, students at Massachusetts Institute of Technology and Harvard University will build the Regolith X-Ray Imaging Spectrometer (REXIS) for mapping the distribution of chemical elements over the asteroid's surface, including potential sampling sites.
NASA selected the OSIRIS-REx mission for its New Frontiers program in May 2011. The Lunar and Planetary Laboratory at the University of Arizona in Tucson leads the science mission and NASA's Goddard Space Flight Center is responsible for the overall mission management. Lockheed Martin will build and operate the spacecraft. For more information concerning the mission, visit the website: www.osiris-rex.lpl.arizona.edu.
Dante S. Lauretta
University of Arizona
Tucson, United States
Dante Lauretta is a professor of planetary science at the University of Arizona's Lunar and Planetary Laboratory.
1. A. Milani, S. R. Chesley, M. E. Sansaturio, F. Bernardi, G. B. Valsecchi, O. Arratia, Long term impact risk for (101955) 1999 RQ36, Icarus
203(2), p. 460-471, 2009. doi:10.1016/j.icarus.2009.05.029
2. M. C. Nolan, C. Magri, S. J. Ostro, L. A. Benner, J. D. Giorgini, E. S. Howell, R. S. Hudson, The shape and spin of 101955 (1999 RQ36) from Arecibo and Goldstone radar imaging, Bull. Am. Astron. Soc. 39(3), p. 433, 2008.
3. C. W. Hergenrother, D. J. Scheeres, M. Nolan, C. D'Aubigny, M. A. Barucci, B. E. Clark, E. Dotto, Lightcurve and phase function photometry of the OSIRIS-REx target (101955) 1999 RQ36, 43rd Lunar Planetary Sci. Conf. 43, p. abstract 2219, 2012.
4. J. P. Emery, Y. R. Fernández, M. S. Kelley, C. Hergenrother, J. Ziffer, D. S. Lauretta, M. J. Drake, H. Campins, Thermophysical characterization of potential spacecraft target (101955) 1999 RQ36, 41st Lunar Planetary Sci. Conf. 41, p. abstract 2282, 2010.