International Asteroid Day: A look at NASA's first planetary defense mission
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International Asteroid Day: A look at NASA's first planetary defense mission

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International Asteroid Day: A look at NASA's first planetary defense mission

June 30, 2020 is International Asteroid Day, commemorating the Earth's largest recorded asteroid impact while focusing on the real danger of asteroids that could collide with Earth.

In two years, NASA will demonstrate its asteroid deflection technology on the newly named Dimorphos, a moon orbiting the near-Earth asteroid Didymos. This will be the agency's first full-scale demonstration of this type of technology on behalf of planetary defense.

Dimorphos received its name last week, just in time for a reflection on the importance of understanding the threat of near-Earth asteroids. Near-Earth objects are asteroids and comets whose orbits place them within 30 million miles of Earth.

Tuesday is International Asteroid Day, commemorating the Earth's largest recorded asteroid impact while focusing on the real danger of asteroids that could collide with Earth.

In 1908, a powerful asteroid struck the Podkamennaya Tunguska River in a remote Siberian forest of Russia. The event leveled trees and destroyed forests across 770 square miles, which is equal to the size of three-quarters of the US state of Rhode Island. The impact threw people to the ground in a town 40 miles away.

In 2013, an asteroid entered Earth's atmosphere over Chelyabinsk, Russia. It exploded in the air, releasing 20 to 30 times more energy than that of the first atomic bombs, generating brightness greater than the sun, exuding heat, damaging more than 7,000 buildings and injuring more than 1,000 people. The shock wave broke windows 58 miles away. It went undetected because the asteroid came from the same direction and path as the sun.

And it explains why astronomers and the Asteroid Day group want people to be aware. Detecting the threat of near-Earth objects, or NEOs, that could potentially cause grave harm is a primary focus of NASA and other space organizations around the world.

And in 2022, NASA will test its asteroid deflection technology to see how it impacts the motion of a near-Earth asteroid in space.

Didymos and Dimorphos

Two decades ago, a binary system involving a near-Earth asteroid was found to have a moon orbiting it, dubbed Didymos. In Greek, Didymos means "twin," which was used to describe how the larger asteroid, which is nearly half a mile across, is orbited by a smaller moon that is 525 feet in diameter. At the time, the moon was known as Didymos b.

But when the binary system became the target of NASA's 2022 Double Asteroid Redirection Test mission, or DART, it was time for the moon to get an official name.

Last week, the International Astronomical Union officially named the moon Dimorphos. Kleomenis Tsiganis, a planetary scientist at the Aristotle University of Thessaloniki and a member of the DART team, suggested the name.

"Dimorphos, which means 'two forms,' reflects the status of this object as the first celestial body to have the 'form' of its orbit significantly changed by humanity — in this case, by the DART impact," said Tsiganis. "As such, it will be the first object to be known to humans by two, very different forms, the one seen by DART before impact and the other seen by the European Space Agency's Hera, a few years later."

In late 2022, Didymos and Dimorphos will be relatively close to Earth and within 6,835,083 miles of our planet — the perfect time for the DART mission to occur.

DART will deliberately crash into Dimorphos to change the asteroid's motion in space, according to NASA. This collision will be recorded by LICIACube, a companion CubeSat or cube satellite provided by the Italian Space Agency. The CubeSat will travel on DART and then be deployed from it prior to impact so it can record what happens.

"Astronomers will be able to compare observations from Earth-based telescopes before and after DART's kinetic impact to determine how much the orbital period of Dimorphos changed," said Tom Statler, DART program scientist at NASA Headquarters, in a statement. "That's the key measurement that will tell us how the asteroid responded to our deflection effort."

A few years after the impact, the European Space Agency's Hera mission will conduct a follow-up investigation of Didymos and Dimorphos.

While the DART mission was developed for NASA Planetary Defense Coordination Office and managed by the Johns Hopkins University Applied Physics Laboratory, the mission's team will work with the Hero mission team under an international collaboration known as the Asteroid Impact and Deflection Assessment, or AIDA.

"DART is a first step in testing methods for hazardous asteroid deflection," said Andrea Riley, DART program executive at NASA Headquarters, in a statement. "Potentially hazardous asteroids are a global concern, and we are excited to be working with our Italian and European colleagues to collect the most accurate data possible from this kinetic impact deflection demonstration."

A mission of firsts

Dimorphos was chosen for this mission because its size is relative to asteroids that could pose a threat to Earth.

DART will crash into Dimorphos moving at 14,763.8 miles per hour. A camera on DART, called DRACO, and autonomous navigation software will help the spacecraft detect and collide with Dimorphos.

This fast impact will only change Dimorphos' speed as it orbits Didymos by 1%, which doesn't sound like a lot, but it will change the moon's orbital period by several minutes. That change can be observed and measured from ground-based telescopes on Earth. It will also be the first time humans have altered the dynamics of a solar system body in a measurable way, according to the European Space Agency.

The launch window for DART opens in July 2021 with the impact expected in 2022.

Three years after the impact, Hera will arrive to study Dimorphos in detail, measuring physical properties of the moon, studying the DART impact and study its orbit.

This may sound like a long time to wait between the impact and follow-up, but it's based on lessons learned in the past.

In July 2005, NASA's Deep Impact spacecraft launched a 815-pound copper impact into a comet, Tempel 1. But the spacecraft was not able to see the crater that resulted because the impact released tons of dust and ice. However, NASA's Stardust mission in 2011 was able to characterize the impact — a 492-foot gash.

Together, the valuable data collected by DART and Hero will contribute to planetary defense strategies, especially understanding what kind of force is needed to shift the orbit of a near-Earth asteroid that may collide with our planet.

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