Academic journal article Science Scope

Return to Sender (Part 2)

Academic journal article Science Scope

Return to Sender (Part 2)

Article excerpt

In August, NASA's OSIRIS-Rex mission will begin its route to Bennu, a carbonaceous near-Earth asteroid that is a member of the Apollo asteroid group (see last month's column for more info on this group of asteroids [Riddle 2018]). Mission plans call for a sample return of Bennu to arrive back on Earth in 2023. Asteroid Bennu has an aphelion (farthest from the Sun) distance of 1.3 astronomical units (AU) and a perihelion (closest to the Sun) distance of .89 AU, which brings it across the Earth's orbit. (Note: One AU equals 150,000,000 km, or 93,000,000 mi.). The surface of Bennu has a loose covering of weathered asteroid material and regolith, pebble-size pieces of the asteroid resulting from collisions with other objects in the asteroid belt.

OSIRIS-Rex launched into Earth's orbit in September 2016. To reach Bennu, the spacecraft orbited the Sun for one year and used Earth as a gravity assist during September 2017. The gravity assist not only increased the spacecraft's speed, but it also changed the spacecraft's trajectory, placing the spacecraft at the same orbital inclination as asteroid Bennu (see Figure 1).

During the next five months, the spacecraft will approach the asteroid and then make its first encounter in December. The mission is designed to have three encounters where the spacecraft will brush against the asteroid. As it approaches the asteroid, the spacecraft will extend a sampling arm that will first send a short blast of nitrogen gas at the surface to dislodge any loose material, and then it will scoop up the material with its sampler. In addition, OSIRIS-Rex will study the asteroid for the next three years while they travel together around the Sun. During the spring of 2021, the spacecraft will embark on a two-year trip back to Earth. When it enters Earth's orbit, the spacecraft will release a sample package that is expected to land in Utah, where it will be collected and brought to labs for analysis.

Like other NASA missions, OSIRIS-Rex is an acronym for its mission objectives. OSIRIS-Rex stands for Origins; Spectral Interpretations; Resource Identification; Security; Regolith Explorer. Asteroid Bennu is named after a Heron-like bird from Egyptian mythology. According to myth, Bennu was involved with the creation of the world--an appropriate name for a mission that in part studies the origins of our solar system.

Exploring with automated telescopes

Asteroid Bennu was one of the many asteroids discovered by LINEAR, the Lincoln Near-Earth Asteroid Research project, a series of automated telescopes designed to detect and observe near-Earth asteroids. Since 1998, LINEAR has discovered close to 250,000 small solar system bodies, including several thousand near-Earth asteroids (NEOs). The LINEAR project is operated by the Lincoln Laboratories at the Massachusetts Institute of Technology. The project has detected about one-third of the known NEOs and potentially hazardous asteroids and nearly one-half of the larger NEOs.

At the Observing With NASA website (see Resources), students are able to request black-and-white and color images of a variety of celestial objects taken by two automated telescopes, located in Arizona and Massachusetts, respectively. Students can request images of planets, the Sun, the Moon, galaxies, nebulae, asteroids, and more. Image choices are based on exposure length and field of view. A brief questionnaire, collected for usage statistics, will appear at the end of the request process. An e-mail address is required to receive the image, and you should expect to receive the requested pictures typically within a day or two.

Both of the automated telescopes are reflecting telescopes equipped with a six-inch mirror and a small CCD detector, an electronic chip similar to those found in digital cameras. Pictures are returned as .GIF and .FITS files. The latter are data collected by the CCD chip and can be opened in the image processing program JS9-4L at the Observing With NASA website (see Resources). …

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