A NASA spacecraft, that will return a sample of a near-Earthasteroid named Bennu to Earth in 2023, has discovered plumes erupting from thecosmic body's surface — among a numerous other findings including evidence ofwater-bearing minerals.
Bennu also revealed itself to be more rugged than expected,challenging the mission team to alter its flight and sample collection plans,due to the rough terrain.
Bennu is the target of NASA's Origins, SpectralInterpretation, Resource Identification, Security-Regolith Explorer(OSIRIS-REx) mission, which began orbiting the asteroid on December 31 last year.
Bennu, which is onlyslightly wider than the height of the Empire State Building, may containunaltered material from the very beginning of our solar system.
"The discovery of plumes is one of the biggestsurprises of my scientific career," said Dante Lauretta, OSIRIS-RExprincipal investigator at the University of Arizona in the US.
"And the ruggedterrain went against all of our predictions. Bennu is already surprising us,and our exciting journey there is just getting started," Lauretta said.
Shortly after the discovery of the particle plumes onJanuary 6, the mission science team increased the frequency of observations,and subsequently detected additional particle plumes during the following twomonths.
Although many of theparticles were ejected clear of Bennu, the team tracked some particles thatorbited Bennu as satellites before returning to the asteroid's surface.
Scientists have also discovered evidence of abundantwater-bearing minerals on the surface of Bennu.
Using early spectral data from NASA's OSIRIS-REx spacecraftorbiting the asteroid, the team identified infrared properties similar to thosein a type of meteorite called carbonaceous chondrites.
"Scientists are interested in the composition of Bennubecause similar objects may have seeded the Earth with water and organicmaterials," said Victoria Hamilton, a mission co-investigator fromSouthwest Research Institute in the US.
"OSIRIS-REx data confirm previous ground-basedobservations pointing to aqueously altered, hydrated minerals on the surface ofthe asteroid," said Hamilton, lead author of the study published in thejournal Nature Astronomy.
OSIRIS-REx launched in 2016 to explore Bennu, which is thesmallest body ever orbited by spacecraft.
Studying Bennu will allow researchers to learn more aboutthe origins of our solar system, the sources of water and organic molecules onEarth, the resources in near-Earth space, as well as improve our understandingof asteroids that could impact Earth.
The OSIRIS-REx team also did not anticipate the number andsize of boulders on Bennu's surface.
From Earth-based observations, the team expected a generallysmooth surface with a few large boulders. Instead, it discovered Bennu's entiresurface is rough and dense with boulders.
The higher-than-expected density of boulders means that themission's plans for sample collection, also known as Touch-and-Go (TAG), needto be adjusted. The original mission design was based on a sample site that ishazard-free, with an 25-metre radius.
However, because ofthe unexpectedly rugged terrain, the team has not been able to identify a siteof that size on Bennu. Instead, it has begun to identify candidate sites thatare much smaller in radius.
The smaller sample site footprint and the greater number ofboulders will demand more accurate performance from the spacecraft during itsdescent to the surface than originally planned.
The mission team isdeveloping an updated approach, called Bullseye TAG, to accurately targetsmaller sample sites.
The OSIRIS-REx science team has made many other discoveriesabout Bennu in the three months since the spacecraft arrived at the asteroid,some of which were presented Tuesday at the 50th Lunar and Planetary Conferencein Houston and in a special collection of papers issued by the journal Nature.