In a planetary defense test, a NASA probe seeks to modify the trajectory of an asteroid.

A small NASA spacecraft approached a tiny asteroid on Monday, heading for a deadly 14,000 mph head-on collision. This was the first actual test of humanity's capacity to veer a dangerous object away from Earth before it collides with it.

Dimorphos, a 500-foot-wide asteroid, is a moon that orbits Didymos, a Didymos-sized asteroid that is 2,500 feet wide. Both are not dangerous to Earth, either before or after the 1,260-pound DART mission from NASA collides with one of them.

In a planetary defense test, a NASA probe seeks to modify the trajectory of an asteroid.
A rendering of NASA's DART probe approaching a tiny, 525-foot-wide asteroid called Dimorphos at 14,000 mph. The asteroid is actually a small moon circling Didymos, a bigger asteroid. The $330 million project is a trial run for a method of deflecting an asteroid or comet heading toward Earth. Image Credit : NASA

The $330 million DART project can evaluate the consequences of the probe's impact from Earth by accurately measuring how the moonlet's orbital period around Didymos changes as a result of the collision. However, the double-asteroid system presents an excellent target for the mission.

The DART probe should provide scientists with an exciting inside look as the spacecraft rushes toward its quarry, showing the target becoming larger and larger until it fills the whole field of vision seconds before impact. The probe will be sending back photographs of Dimorphos once per second.

Elena Adams, a DART mission systems engineer at the Johns Hopkins University Applied Physics Laboratory, said that two and a half minutes prior to impact, SMART Nav, the autonomous algorithms that have led us to that point, will shut off and we'll simply point the camera and take the most incredible pictures of this asteroid.

NASA intends to chronicle the mission beginning at 6 p.m. EDT by live-streaming the photographs on YouTube. The collision is anticipated to occur at 7:14 p.m., with streaming, one-per-second photos from the spacecraft beginning earlier.

In a planetary defense test, a NASA probe seeks to modify the trajectory of an asteroid.
Scale model of Didymos and Dimorphos using well-known Earthly locations. Image 
credit : NASA

Dimorphos has never been directly spotted and won't be distinguished from Didymos by DART's camera until an hour prior to impact, at a distance of around 15,000 miles. It will then appear as a tiny 1.4 pixel wide point of light. However, it will soon expand to 21 pixels in size by the time it travels 1,000 miles and is just 4 minutes away from impact.

According to Adams, "our final photograph will likely be from around 2.5 seconds before impact." So this lovely image of Dimorphos will actually occupy the whole field of vision of the DRACO (camera).

The moment of collision will mark the end of transmissions. The final few photographs, though, will take about 45 seconds to traverse the gulf, make it into computers, and appear on NASA's live stream because the crash will occur at a distance of 7 million miles from Earth.

According to Edward Reynolds, the DART project manager at APL, "you're going to hear that we've lost radio communication, but there are still going to be visuals coming in and being displayed once per second for around eight seconds."

"Those are pictures that are circling the planet. Even if they've fallen to the ground and we've lost radio contact, those photographs are still moving through the pipeline and being shown."

The impact and the debris launched back into orbit will be captured on camera by the little Italian hitchhiker spacecraft known as LICIACube, which was released from DART earlier this month. These pictures will be kept on board and eventually connected to Earth.

Due to the moonlet's orbit, which places it directly in front of Didymos as seen from Earth before passing behind it, the Didymos-Dimorphos double asteroid system makes for an excellent planetary defense test bed. This arrangement enables researchers on Earth to precisely measure small variations in the combined reflected light from both asteroids.

In a planetary defense test, a NASA probe seeks to modify the trajectory of an asteroid.
The blue line depicts how the orbit may be affected by the force of the DART spacecraft's 14,000 mph impact, while the white trace depicts the target asteroid Dimorphos' present 11 hours and 55 minute orbit. According to researchers, the impact may cause an orbital period reduction of around ten minutes. Image Credit : NASA

Dimorphos has an orbital period of 11 hours and 55 minutes, as determined by measuring the light's dimming and brightening, and post-impact measurements will let scientists ascertain whether DART had any influence.

Researchers anticipate that the collision will reduce the asteroid's orbital period by around 10 minutes, although it may take several days to a few weeks for observations to be made by space and terrestrial telescopes, such as the Hubble and James Webb satellite observatories.

Tom Statler, a DART program scientist, stressed that the double asteroid redirection test was just that—a test. We are performing this test on an asteroid that is not a threat because we can, just in case we ever need to and find an asteroid that is a threat.

A test of "our capacity to design an autonomously guided spacecraft that will really achieve the kinetic collision with the asteroid" is the first of the DART mission's two main goals, according to him.

The second experiment tests how the real asteroid reacts to the kinetic collision, he explained. The fundamental issue is, "How successfully did we move the asteroid, and can this technique of kinetic impact be applied in the future, if we ever needed to?"

DART's objective is far more straightforward and significantly less deadly than that of Hollywood movies like "Armageddon" and "Deep Impact," which envisioned piloted aircraft carrying nuclear weapons to divert or destroy their targets.

In some near-future Armageddon-class event, nuclear weapons may be the final line of defense, but the objective would still be deflection rather than annihilation.

Before DART's launch in November of last year, Lindley Johnson, NASA's "planetary defense" officer, told CBS News that "you simply don't want to blow it up, since it doesn't affect the path of all the stuff." "Even if it's buckshot rather than a rifle ball, it's still coming at you."

"What you want to do is just slow down this entire process a little bit. That will cause the asteroid's orbit and location to fluctuate over time.

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