Why NASA Put Its DART Spacecraft on a Collision Course With an Asteroid?

On September 26th, we'll find out whether NASA'S tiny DART spacecraft can move an orbit of an 11 billion lb asteroid. Could this technology someday help save Earth from a planet-killer asteroid?
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Mark September 26 in your calendar – an exciting experiment will happen in outer space that day, one that has likely been paid for, in the main, by taxes given to NASA each year. This event will teach scientists a great deal about how to defend the planet from asteroids. Mission scientist Andy Rivkin, at Johns Hopkins University in Maryland, will watch how the DART spacecraft collides with an asteroid exceptionally closely.

About 6.8 million miles away from Earth is an asteroid object called Dimorphos. Dimorphos is one of the smallest astronomical objects in outer space that has been given a permanent name. It only has a diameter of 560 ft (170 meters), and it is for a particular reason that it has been named. At only 560 ft, if Dimorphos were just any piece of space rock floating about, scientists would have no reason to name it. Under nomenclature rules for naming outer space, in most cases, geographic features that are less than one hundred meters will not be given official names unless there is a very special reason.

But Dimorphos isn’t just any piece of space rock. It is a 560-ft piece of rock at the center of one of NASA’s most expensive experiments and tests in planetary defense. NASA is sending its 1102-lbs/500-kilogram DART spacecraft to deliberately collide with Dimorphos (estimated to be around 11 billion lbs/5 billion kilograms) and deflect it from its path.

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Dimorphos artists impression
Dimorphos artist’s impression by NASA

If these odds don’t interest you in space, on Earth, the equivalent might be going to your local zoo and watching an ant collide with an Elephant and seeing if the elephant changes course.

Can a 1102-lbs DART spacecraft change the orbit of an asteroid 10 million times than itself?

Can an 1102-lbs spacecraft change the orbit of an asteroid 10 million times than itself? This is the 324.5 million dollar question. So far, there has been a total expenditure of $308 million for the development of the DART spacecraft, $68.8 million for launch services, and an anticipated cost of $16.5 million for operations and data analysis.

Dart image 3
DART construction by NASA/Johns Hopkins APL/Ed Whitman

DART was launched on November 24, 2021, and has steadily been making its way to impact with Dimorphos on September 26.

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How will we know if NASA has been successful? 

Dimorphos isn’t just floating about aimlessly. Dimorphos is a minor-planet moon of a synchronous binary system with 65803 Didymos as the primary asteroid. In Layman’s terms, Dimorphos orbits around an even bigger asteroid called Didymos, which is 390 meters.

dart orbit
Double Asteroid Redirection Test (DART) by NASA

If DART’s impact, which will occur at a speed of approximately 4.1 miles per second / 14760 miles per hour, alters the length of Dimorphos’ orbit by at least 73 seconds, give or take 10 percent, the researchers will consider the mission a success; however, they believe that the actual diversion could be closer to approximately 10 minutes.

Even though the DART spacecraft is equipped with a camera, it will be destroyed upon impact. LICIACube, a sister spacecraft from the Italian Space Agency that split off from DART on September 11, will be relied on by the team instead to take detailed observations.

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LICIACube, 34 miles from the impact crater, will use two cameras to record data and capture collision images. It will also measure the kinetic impact of the collision on Dimorphos as well as any plume that may result from the crash site.

There will also be many other ground-based telescopes and space observatories, such as Hubble and James Webb, watching this expensive spectacle and taking measurements of Didymos’ orbit period and comparing them with observations made in the past. 

The European Space Agency has plans to launch a spacecraft known as Hera in 2024 to record the aftermath of the impact in greater detail.

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So it looks like more money will be spent by other space agencies observing the results of NASA’s 324.5 million dollar question for years to come.

Measuring the effect of the impact on Dimorphos’ orbit won’t necessarily be instantaneous

Rivkin states that although observations of the impact itself will be transmitted to Earth shortly after it happens, it will take weeks or even months to measure the effect of the impact on Dimorphos’ orbit to a high degree of precision and thus reveal whether or not the mission was successful. 

What do astronomers expect to happen?

According to Rivkin, when Dimorphos moves in front of Didymos, there is a noticeable decrease in brightness due to the shadow. We will be able to determine the time it takes for Dimorphos to go around Didymos if we measure the increase and decrease in brightness that we are currently observing.

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Is a noticeable decrease in brightness worth all that science, expense, and effort? One day the answers may help us to pioneer the technology that will save the planet from the fate of the dinosaurs.


Featured image credit: NASA’s DART Mission by NASA