Where Is Bennu?

While reading the news, a story about an asteroid caught my eye. The next I knew, I was doing some research and learning a lot I did not know about asteroids. I am sharing what I learned in this post. I hope you enjoy it.

Asteroids are irregularly shaped rock fragments left over from the formation of the solar system about 4.6 billion years ago when a big cloud of gas and dust collapsed. After the collapse, most of the material fell to the center of the cloud and formed the sun. Much like planets although smaller, asteroids orbit the sun in a belt between Mars and Jupiter. Scientists think there are probably millions of asteroids, ranging in size from hundreds of miles across to as small as pebbles.

Although the Moon, Mars, and the International Space Station make the most headlines, NASA has done some amazing things with numerous spacecraft to learn what asteroids look like, what they are made of, and what orbital paths they take. One thing NASA has learned is no two asteroids are alike. Asteroids are not round like planets. They are jagged and have very odd shapes, some are square or rectangular.

The current known asteroid count is 1,081,163. Scientists study them, categorize them based on their composition, and even give them names, in addition to a number. The International Astronomical Union’s Committee on Small Body Nomenclature controls the naming. Most of the names are based on mythology but there are some exceptions. One giant space rock orbiting the sun was named for Mr. Spock and another is named after rock musician Frank Zappa. Some names are somber tributes such as seven asteroids named after the crew of the Space Shuttle Columbia who died in 2003. The Harvard Smithsonian Center for Astrophysics keeps a fairly current list of the names. A few well known ones include Ceres, Eros, Geographos, Hathor, Hermes, Icarus, Pallas, and Vesta. Asteroids which have been imaged in great detail by NASA spacecraft include Mathilde, Gaspra, and Ida.

One reason asteroids are of interest is they are believed to contain metals such as nickel and iron. We may find out they also have rare minerals which are scarce and in high demand on Earth. This reminds me of a great novel by Michael Suzrez. The bestselling author of Daemon wrote Delta-V, a near-future technological thriller in which a charismatic billionaire recruits a team of adventurers to launch the first deep space mining operation. The plot was for the mission to alter the trajectory of human civilization. A great read.

There is a lot to be learned from asteroids. Since asteroids formed at the same time as other objects in our solar system, the space rocks can give scientists lots of information about the history of planets and the sun. Until now, scientists have had to learn about asteroids by studying meteorites, the small bits of asteroids which have flown through our atmosphere and landed on Earth’s surface. The next step is to actually land on an asteroid and get a sample not contaminated by having fallen through Earth’s atmosphere.

The recent activity on Mars is quite impressive but, in some ways, I find project OSIRIS-REx, which stands for Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer, likewise impressive. The project began in 2016 when NASA launched the OSIRIS-REx spacecraft to study an asteroid near Earth named Bennu and bring a sample of the asteroid back to Earth.
Bennu, asteroid #101955, is a carbon-rich asteroid in the Apollo group. It was discovered in 1999. In addition to being scientifically interesting, Bennu is potentially hazardous to Earth and is listed on the Sentry Risk Table, a list of asteroids with the potential to crash into Earth. Bennu has a radius of 861 feet. (See picture at top of the article). The mass of the asteroid is estimated at 172 billion pounds. Bennu is orbiting the sun at 63,000 mph and passes close to Earth every six years. Scientists have calculated there is a 1 in 2,700 chance the asteroid will crash into Earth sometime between 2175 and 2199. Not a worry for us or our children or grandchildren and, by the time it is a real risk, I am sure a method to deflect asteroids will have been invested.

Bennu was selected for OSIRIS-REx because of its ideal proximity to Earth, its size, and its composition. The asteroid contains organic molecules, volatiles, and amino acids which may have been the precursors to life on Earth. The NASA spacecraft took off from Earth in September 2016 and arrived at Bennu in December 2018. On October 20, 2020, the spacecraft made a precision but brief landing on the surface of Bennu. It extended a foot-like appendage which punched the surface and then released a blast of nitrogen to stir up the surface. It then captured the debris in a capsule, closed the lid of the capsule, and headed back into orbit. On Monday, May 10, 2021, the spacecraft turned on its thrusters for seven minutes to begin its journey toward Earth. 

Because of various orbital complexities I don’t understand, the spacecraft will have to make two laps around the Sun and then, if all goes as planned, the spacecraft will travel more than a billion miles and return to Earth after more than two years of travel. When the spacecraft gets within about 6,000 miles from Earth, it will eject the capsule carrying two ounces of invaluable samples. When close to Earth, the capsule will release parachutes which will allow for a smooth landing. NASA expects the capsule will land in the desert in Utah on September 24, 2023. The precious samples will then head to a NASA laboratory in Texas where scientists are eagerly awaiting to begin research which could unlock secrets of the early solar system. If you are interested to see a short and interesting video explaining the OSIRIS-REx mission click here.