Looking a Gift Horse in the Mouth: NRAO & Asteroid YU55

Posted on November 7, 2011


Artist's impression of TW Hydrae

Tumbling asteroids in a planet-forming disc around a young star, here depicted by NRAO artist, Bill Saxton.

Space really is aptly named. There’s a lot of nothing between bits of stuff out in space. Even here in our Solar System, where billions of particles orbit the Sun along with the planets, asteroids, and comets, the distances between them all are still measured in many thousands of miles. Space is that big.

However, that doesn’t mean that there isn’t the occasional house call, such as this week when mini-asteroid YU55 scoots through Earth’s backyard on its eccentric path around the Sun.

Thanks to the messiness of making a Solar System from a clumpy pile of swirling gas and dust, some asteroids are rogues, mavericks of convention. Those that are not happily orbiting in the main asteroid belt have been kicked out into non-conforming, eccentric, tilted orbits around the Sun that let them nyah-nyah the near-circular, regular orbits of the rest of their neighbors. Sometimes, their wheeling about turns into a snooker match that ends with an asteroid getting pocketed by Jupiter. But, most of the time, like this time, the rocky bohemian gets away with it.

The Gift Horse

YU55 is only about 1,300 feet across, discovered in 2005 by the SPACEWATCH program funded by NASA out of the University of Arizona, Tucson. Through an optical telescope, it is blacker than charcoal, because it is a carbonaceous-type asteroid, meaning that its rock is made up of silicates, organic material, and water — the earliest bits of the Solar System. Observing this little guy during this rare, close approach means observing a chunk of cosmic Lego that built our planetary neighborhood. What a gift! You are probably not surprised to learn that the NRAO plans to aim everything we’ve got at it to learn more! :)

Although many folks are hearing about this plucky little asteroid for the very first time, it also buzzed us last year – but millions of miles away. During that previous pass, NSF’s 1000-foot Arecibo telescope in Puerto Rico bounced radio waves off of it to construct a rough picture of its surface and to clock its rotation. The image Arecibo pieced together is of a roughly spherical object that spins once every 18 hours. The latest images from NASA’s latest observations reveal some lumpiness on YU55.

All Eyes on Target

This pass of YU55 will bring it to within 201,700 miles of planet Earth, closer to us than our own Moon. As it zips by, several optical, infrared, and radio telescopes around the world — including those of citizen astronomers (see below) — will help us gather data about this little block of proto-Solar System. The expected detail will be enough that boulders on the surface of YU55, if they are present, will easily be imaged by the largest of the ‘scopes in action. NASA is saying that this pass gives astronomers an equal to or better imaging opportunity than had they sent a space probe. Wow.

GBT in Autumn

The Green Bank Telescope, the world’s largest fully-steerable telescope, preparing to collect radio waves bounced off of YU55.

In addition to NASA’s Deep Space Network radio telescopes and its Infrared Telescope Facility, the National Radio Astronomy Observatory (NRAO) will aim three of its world-famous radio telescopes at this passing asteroid: the largest fully-steerable dish, the Green Bank Telescope (GBT), with a dish 330 feet across; the largest radio telescope array dedicated to full time, long baseline interferometry, the Very Long Baseline Array (VLBA); and the most flexible centimeter-wavelength interferometer, the Very Large Array (VLA).

The Observations

Starting on November 8th at 1:30 pm EST, the GBT will begin picking up radio waves that have been aimed at YU55 from Arecibo. The incredible details the GBT picks up will let us map the surface to see features about 7.5 meters across.

Later on the 8th, the GBT and EVLA will probe for any temperature changes of YU55 on its surface and down a few feet into the rocky asteroid.

On Thursday, the VLBA will begin observing and pinpoint the exact spin axis of asteroid YU55. Using the radar data of surface features collected by the other telescopes, the VLBA will let us accurately determine YU55’s spin.

Also, this close approach to Earth is expected to shift YU55’s spin. A comparison of the asteroid’s spin seen in 2010 with the one clocked by the VLBA this week will let astronomers measure how much the Earth altered YU55’s spin when it passed. Awesome.

Radar of YU55

Asteroid YU55 as imaged in 2010 by radar with the NSF’s 1000-ft Arecibo Telescope.

We Love This Stuff

Leading the charge is Dr. Michael Busch, one of NRAO’s talented Jansky Fellows, working out of UCLA. He is one of the world’s experts on using radio telescopes, especially long baseline interferometry, to observe and measure asteroids. A great communicator and an enthusiastic, brilliant scientist, Michael will be here on Wednesday to talk about his work. I am looking forward to chatting with him and sharing what I learn.

Personally, I find these moments to be thrilling, when we use our incredible telescopes to join in a fast-paced, live opportunity to search for the origins of our cosmic neighborhood and beyond. And thanks to the asteroid’s close flyby, it doesn’t take an incredible telescope to participate in this incredible exploration. If you have a telescope larger than 6-inches aperture (new link to Sky & Telescope) or a radio antenna of at least one square meter, you should be able to pick up this asteroid yourself. I may even lug out my Dob and see if I can catch this ancient guy swinging by. I hope you get to observe it, too.

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Posted in: Green Bank, VLBA