An amazing image showing both the Earth and Moon. The distance between our planet and its satellite is actually much more than many would conceptualize. It is 384,400 kilometers (about 239,000 miles) on average, but as usual, our brains cannot deal with such large numbers. Only seeing that distance makes us realize how far even the closest body in the solar system to us – and gives some clues about how big is our Solar system actually. What’s more, we’ve actually been there, the humanity managed to cover that vast distance and walked on the moon!

Earth and Moon as seen by OSIRIS-REx. October 2, 2017.
 Earth and Moon as seen by OSIRIS-REx. October 2, 2017.

This composite image of the Earth and Moon above is made from data captured by NASA’s OSIRIS-REx’s MapCam instrument on October 2, 2017. The spacecraft was approximately 3 million miles (5 million kilometers) from Earth when the photos were taken. That distance is about 13 times the distance between the Earth and Moon. Three images (different color wavelengths) were combined and color-corrected to make the composite, and the Moon was brightened to make it more easily visible.

The purpose of OSIRIS-REx spacecraft (an acronym for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is to study, map and return samples for detailed analysis from asteroid 101955 Bennu, a carbon-rich hunk of rock that might contain organic materials or molecular precursors to life. It was launched on September 8, 2016, and the expected return date is September 24, 2023. If successful, OSIRIS-REx will be the first NASA spacecraft to return samples from an asteroid.

OSIRIS-REx spacecraft descending towards asteroid Bennu
This illustration shows NASA’s OSIRIS-REx spacecraft descending towards asteroid Bennu to collect a sample of the asteroid’s surface. Credits: NASA/Goddard/University of Arizona

101955 Bennu

101955 Bennu was discovered on September 11, 1999, by the Lincoln Near-Earth Asteroid Research (LINEAR) project, a collaboration of the United States Air Force, NASA, and MIT’s Lincoln Laboratory for the systematic detection and tracking of near-Earth objects.

It makes one orbit around the Sun every 1.2 years and makes one full rotation on its axis every 4.3 hours. Its average orbital distance from the Sun is about 105 million miles (168 million kilometers), which is only slightly farther than Earth’s average orbital distance of 93 million miles (150 million kilometers).​

Asteroid Bennu
This image of Bennu was taken by the OSIRIS-REx spacecraft from a distance of around 50 miles (80 km). Credits: NASA/Goddard/University of Arizona

101955 Bennu is a potential Earth impactor. It makes a close approach to Earth every six years, although its exact distance from Earth during these approaches varies. Its orbital path is tilted about 5 degrees relative to Earth’s. It has a 1-in-2,700 chance of impacting Earth in the late 22nd century. With a mean diameter of approximately 492 meters (1,614 ft; 0.306 mi), it can wipe out our civilization if it impacts our planet.

The carbonaceous material that composes asteroid Bennu originally came from dying stars such as red giants and supernovae. According to the accretion theory (see notes 1), this material came together 4.5 billion years ago during the birth of the Solar System. Its basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System’s formation, where the carbonaceous material underwent some geologic heating and chemical transformation into more complex minerals. So it’s pretty old, and by studying the asteroid, we can learn many things about the early solar system. NASA concludes:

“OSIRIS-REx is a mission to figure out where we came from, as asteroids are remnants from the formation of our solar system. But while the spacecraft might tell us some things about where we have been and where we are headed, it also can remind us of where we are right now.”

Notes

  1. In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes.

Sources

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