Getting the right spin on a close-passing asteroid

Feb 11, 2013 by Dave Finley
How the Yarkovsky Effect slows an asteroid's orbital motion; opposite rotation direction would speed up the orbital motion. Credit: Alexandra Bolling, NRAO/AUI/NSF

(Phys.org)—The record-setting close approach of an asteroid on Feb. 15 is an exciting opportunity for scientists, and a research team will use National Radio Astronomy Observatory (NRAO) and NASA telescopes to gain a key clue that will help them predict the future path of this nearby cosmic neighbor.

A 150-foot-wide asteroid called 2012 DA14, discovered just a year ago, will pass only 17,200 miles above the Earth on Feb. 15. That's closer than the geosynchronous communication and . While the object definitely will not strike the Earth, this is a record close approach for an object of this size. Astronomers around the world are preparing to take advantage of the event to study the asteroid.

A team including NRAO astronomer Michael Busch will use a novel observing technique to determine which way the space rock is spinning as it speeds on its orbit through the Solar System. The direction of its spin is an important factor in predicting how the object's orbit will change over time.

"Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years," Busch said.

Busch's team will use the Karl G. Jansky (VLA) and the Very Long Baseline Array (VLBA) antennas at Pie Town and Los Alamos, New Mexico, along with a Solar System radar on NASA's 230-foot antenna at Goldstone, California. The Goldstone antenna will transmit a powerful beam of toward the asteroid, and NRAO's New Mexico antennas will receive the waves reflected from the asteroid's surface.

Because of the asteroid's uneven surface and the different reflectivity of portions of the surface, the reflected radar signal will have a characteristic signature, or "speckles," as observed from Earth. By measuring which antenna in a widely-separated pair receives the speckle pattern first, the astronomers can learn which way the asteroid is spinning. This way of using the telescopes is significantly different than their normal astronomical observing, and the research team has developed special techniques for processing the data.

How does this tell anything about the asteroid's orbital changes? Just as the afternoon is the warmest part of the day on Earth, the space rock develops a warm region that radiates infrared light in its maximum amount during "afternoon" on the asteroid. That outgoing infrared radiation provides a gentle but firm jet-like push to the asteroid. The direction of the asteroid's spin determines whether "afternoon" is either forward or rearward of its direction of motion.

If the hot spot is forward of the direction of motion, the infrared push will slow the asteroid's orbital speed, and if the hot spot is rearward of the direction of motion, it will speed up the orbital motion. This effect, over time, can make a significant change in the orbit. This is called the Yarkovsky Effect, after the engineer who first identified it.

"When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time," Busch said.

The Goldstone-VLA-VLBA observations will be made on Feb. 16, when the 's South-to-North motion in the sky makes it readily visible to those antennas.

Explore further: SDO captures images of two mid-level flares

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User comments : 6

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Kaymen
1.7 / 5 (7) Feb 11, 2013
Why are we not tagging these asteroids that come so close? A simple radio transponder would work without affecting the orbit significantly. Wouldn't it give us a better understanding of their orbits and increase the likelihood of detecting others in similar orbits?
Parsec
5 / 5 (2) Feb 11, 2013
Matching orbits with this asteroid would be difficult to do with the kind of advance notice astronomers had to get ready. While it may seem like the distance from earth is the biggest issue, and because its close, tagging would be easy, the real issue is the delta-v required to get up close to it. That's more a function of how fast its going relative to the earth at closest approach.
Q-Star
1.9 / 5 (9) Feb 11, 2013
Why are we not tagging these asteroids that come so close? A simple radio transponder would work without affecting the orbit significantly. Wouldn't it give us a better understanding of their orbits and increase the likelihood of detecting others in similar orbits?


"Tagging" won't provide us with any additional information. We know it's orbital parameters, can predict where it's going to be forever.

The only thing that could change our predictions is if it has an encounter with some unknown object,,, but we'll know that, because all we have to do when we're curious as to what it's up to,,, is look. It's the ones we don't already know about that anyone needs to lose sleep over.
Jeddy_Mctedder
1 / 5 (6) Feb 11, 2013
the yarkovsky effect is a second if not third order effect dependent upon a MYRIAD of factors for the actual result and cannot be accurately predicted. it is fantasy to think an asteroid can be nudged into a spin through inertial pushing, let alone, coated in massive quantities of paint to alter the reflectivity of the heat , (sinking or reflecting more of the radiation) .

you want to move an asteroid over time, it will be done with raw inertia---which can be implemented MANY different ways, even some tricky ones. but this yarkovsky speculation has been around forever. mere speculation. we need to go to the asteroids and start experimenting with every possible instrument package as a first baby step to learning the process of deflecting these things and protecting ourselves from them. privatising the asteroid visitations is fine by me. profiteable scams notwithstanding.
http://transhuman...l-enterp
antialias_physorg
3 / 5 (4) Feb 11, 2013
Why are we not tagging these asteroids that come so close?


1) You have to match speed with this thing to put anything on it. These suckers are moving with 10s of kilometers PER SECOND relative to Earth. Just putting something in its way would be like parking your car in the way of an aircraft carrier that goes from New York to Los Angeles in under a minute. I think I don't have to draw you a picture of what that would do to your paintjob.

2) How long do you think such a beacon would remain active? And for what purpose? It's not like we can't track them or predict their course once they passed us by. Stuff tends to move in space rather predictably.
Maggnus
3.7 / 5 (3) Feb 12, 2013
the yarkovsky effect is a second if not third order effect dependent upon a MYRIAD of factors for the actual result and cannot be accurately predicted.


A small but measurable effect. Enough that over time, it can move an object substancially.

but this yarkovsky speculation has been around forever. mere speculation.


No, it hasn't been around forever, it's barely 100 years old. No, it is a real effect, not speculation.

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