[meteorite-list] Close Encounter of the Rocky Kind (Asteroid 2005 YU55)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 7 Nov 2011 14:48:34 -0800 (PST)
Message-ID: <201111072248.pA7MmYvX021580_at_zagami.jpl.nasa.gov>

FOR IMMEDIATE RELEASE
FROM THE UNIVERSITY OF ARIZONA

Nov. 7, 2011

This story and photos are online at: http://uanews.org/node/43045

Contact information follows this story.

Close Encounter of the Rocky Kind

Discovered by a University of Arizona astronomer six years ago, a
city-block-sized space rock will race past the Earth closer than the moon
in what will be the closest encounter of an object of this size in more
than 60 years.

When an asteroid the size of a city block zips past the Earth about 29,000
miles per hour on Nov. 8, it will seem like an encounter with an old
acquaintance to Univeristy of Arizona astronomer Robert McMillan.

Six years ago, McMillan was taking images of the night sky with an
83-year-old telescope on Kitt Peak searching for asteroids, chunks of rock
that weren't swept up into one of the nascent planets during the formation
of our solar system and have traveled around the sun ever since. That is
how he discovered 2005 YU55.

"2005 YU55 is one of the potentially hazardous asteroids that make close
approaches from time to time because their orbits either approach or
intersect the orbit of the Earth," said McMillan, who is an associate
research scientist with the UA's Lunar and Planetary Laboratory with a
joint appointment in the UA's Steward Observatory.

The asteroid ? or more correctly, minor planet ? will approach the Earth
within about 202,000 miles, closer than the distance to the moon. No
object of comparable size has come this close since 1976, and none is
going to until 2028, when another asteroid dubbed 2001 WN5 will pass about
halfway between the moon and the Earth.

Although 2005 YU55's orbit takes it into Earth's neighborhood every once
in a while, there is no chance of it hitting our planet for at least
another 100 years. However, because asteroids' trajectories change over
time, there is a slight chance it may do so at some point in the future.

Enter SPACEWATCH and the Catalina Sky Survey, two research programs at the
UA's Lunar and Planetary Laboratory dedicated to the study of small
objects like asteroids and comets. Founded in 1980 by the late Tom Gehrels
and McMillan, who is now its principal investigator, SPACEWATCH aims to
find objects that might pose a hazard to Earth and gain a better
understanding of how the solar system came to be.

Begun by LPL senior staff scientist Steve Larson and now led by senior
staff scientist Ed Beshore, the Catalina Sky Survey is a NASA-supported
project to discover and catalog Earth-approaching and potentially
hazardous asteroids.

"We complement each other in what we focus on," McMillan said. "With
SPACEWATCH, we spend a lot of our time doing follow-ups on objects that
have already been discovered through other programs. Because we can go
after fainter and dimmer objects, we can chase them longer after their
time of discovery as they are hurtling out deeper into space."

SPACEWATCH was the first program dedicated to the discovery and tracking
of asteroids that made use of charge-coupled devices, or CCDs, which are
now found in many digital cameras, instead of photographic plates to scan
the skies. The 0.9-meter telescope, built in 1921, was the first telescope
the UA's Steward Observatory ordered. Originally housed on campus, it was
moved to Kitt Peak in 1962, where it has been in operation ever since.

The search for asteroids is challenging and tedious.

"When you look through a telescope, asteroids don't look any different
from stars," McMillan explained. "The only difference is that they're
moving, and to detect that motion we have to take a series of images.
Usually we take three images spaced 20 or 30 minutes apart."

Next, the observers run specialized software to examine those images for
any star-like images that are moving from one image to the next. The
software compiles them into a list of candidates that is presented to the
observer for their approval.

"We have to double-check the images, because the software is not perfect
and sometimes picks up things that aren't really asteroids," McMillan said.

Objects that pass the review are then forwarded to the Minor Planet
Center, or MPC, at the Smithsonian Astrophysical Observatory in Cambridge,
Mass.

In determining which ones could potentially slam into Earth, asteroid
hunters look for those that are traveling faster than the more common Main
Belt Asteroids, which orbit the sun between the orbits of Mars and Jupiter
and do not pose a threat. Objects meeting those criteria are sent to the
MPC separately with special designations as candidates for Near Earth
Objects, or NEOs. The MPC reviews them and decides which ones should be
designated as NEOs.

That is how 2005 YU55 went from being a faint speck of light to a
Potentially Hazardous Asteroid.

"The MPC posted it on their confirmation page, which is monitored by
everybody who follows up newly discovered Near Earth Objects," McMillan
said. "So we followed it up on subsequent nights and over the following
month. Over time, we refined its orbit to the point that NASA's Jet
Propulsion Laboratory listed a large number of potential close encounters
with the Earth."

"Now, after 767 observations by ground-based observers, we have the orbit
of that asteroid really nailed down, so we know it's not going to hit the
Earth on Nov. 8."

In addition to observation with optical telescopes, radar measurements
revealed 2005 YU55's distance, velocity and size. The coal-black asteroid,
which is almost spherical in shape and measures about 1,300 feet in
diameter, slowly spins as it travels through space, completing a rotation
every 18 hours.

According to McMillan, the gravity of other planets, as well as the
pressure of sunlight affect the paths of asteroids. In addition, a
phenomenon known as the Yarkovsky Effect ? slight asymmetries in heat
distribution that arise as the object soaks up sunlight and radiates it
back into space as it turns ? plays a role. Those asymmetries exert forces
that add up over time to cause the asteroid to veer off its orbit ever so
slightly.

"We now know that 2005 YU55 is a carbonaceous chondrite asteroid that is
relatively dark and contains carbon," McMillan said, "But long-range
trajectories are very difficult to predict when you don't know the exact
physical properties of the asteroid."

To better understand the properties of Potentially Hazardous Asteroids,
the Lunar and Planetary Laboratory is leading the OSIRIS-REx mission, an
$800 million NASA-funded mission to visit another carbonaceous chondrite,
1999 RQ36.

The OSIRIS-REx spacecraft will study the asteroid for a year, then scoop
up a sample and bring it back to Earth in 2023.
By that time, 2005 YU55 will have long passed our planet and continue on
its lonely journey through the cold, black void of the outer fringes of
the solar system.

###

CONTACTS:

Robert S. McMillan (520-621-6968; bob at lpl.arizona.edu)

Daniel Stolte, University Communications (520-626-4402;
stolte at email.arizona.edu)


LINKS:

UA Lunar and Planetary Laboratory and department of planetary sciences:
http://www.lpl.arizona.edu

SPACEWATCH project: http://spacewatch.lpl.arizona.edu

Catalina Sky Survey: http://www.lpl.arizona.edu/css

OSIRIS-REx mission:
http://www.nasa.gov/topics/solarsystem/features/osiris-rex.html
Received on Mon 07 Nov 2011 05:48:34 PM PST