NEO News (03/07/09) Newsworthy NEAs: 2009DD45 & 2008TN166

From Dave Morrison.

NEO News (03/07/09) Newsworthy NEAs: 2009DD45 & 2008TN166

The past week has seen lots of news coverage of 2009DD45, a 30m NEA that passed within about 70,000 km of Earth. Something this large comes this close only once every few years. Of greater interest to NEO scientists is 2008TN166, the largest NEA discovered in the past 8 years (with a mass a million times greater than DD45).

I also note the following interesting blogs from the New York Times and Discovery on the asteroid impact issue, stimulated by the close pass by DD45:

http://roomfordebate.blogs.nytimes.com/2009/03/06/the-lure-of-rocks-from-outer-space/

http://blogs.discovermagazine.com/badastronomy/2009/03/08/why-do-killer-asteroids-fascinate-us/

David Morrison

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2009DD45

Following are several news reports on the close pass of DD45. It such cases the main press speculation is how much damage it would have caused had it hit the Earth. At the lower end of its estimated size, a diameter of about 20m, it would likely have disintegrated too high to do any ground damage, but at the upper end of the estimated size it would have been comparable to the Tunguska 10-megaton blast in Siberia a century ago. We can expect about 100 NEAs this large to pass this close to Earth for every one that hits. The discovery of this one is another testimony to the continuing success of the Spaceguard survey, even though it is much smaller than the Spaceguard target population of NEAs larger than 1 km. Because it is so small, DD45 was found only two days before its fly-by of Earth on Monday March 2. Following is some press coverage of this event.

DM

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SPACE ROCK 2009DD45 BUZZES EARTH
Sky & Telescope on-line (March 1)

Late word out of the IAU's Minor Planet Center: a small asteroid will pass close to Earth tomorrow (March 2nd) at 13:44 Universal Time. How close? The MPC's Timothy Spahr calculates that it'll be 0.00047 astronomical unit from Earth's center. That's only about 40,000 miles (63,500 km) up - well inside the Moon's orbit and roughly twice the altitude of most communications satellites!

This little cosmic surprise, designated 2009DD45, turned up two days ago as a 19th-magnitude blip in images taken by Rob McNaught at Siding Spring Observatory in Australia. It was already within 1_ million miles of Earth and closing fast.

Thankfully, the news media have become less sensationalistic when it comes to these asteroidal close calls - especially since one actually struck our planet last October 7th, at night, and the impact went virtually unnoticed.

So why post this? Well, we figured someone might want to watch it zip by at up to a half degree per minute! Even though it's small, likely no more than 100 feet (30 meters) across, it'll brighten to magnitude 10_ at its closest - easily within reach of an 8-inch backyard telescope.

By the way, this isn't the closest "near-miss" asteroidal fragment on record. According to the MPC, tiny 2004FU162 skirted just 4,000 miles from us on March 31, 2004.

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SURPRISE ASTEROID BUZZED EARTH MONDAY
Victoria Jaggard, National Geographic News
March 2, 2009

Sky-watchers in Asia, Australia, and the Pacific islands welcomed a surprise guest Monday: an asteroid that passed just 41,010 miles (66,000 kilometers) above Earth. Discovered only days ago, asteroid 2009DD45 zipped between our planet and the Moon at 13:44 universal time (8:44 a.m. ET). The asteroid was moving at about 12 miles (20 kilometers) a second when it was closest to Earth.

"We get objects passing fairly close, or closer than this, every few months," Timothy Spahr, director of the International Astronomical Union's Minor Planet Center in Massachusetts, said in an email. "Also, though, note these are only the ones that are discovered. Many more pass this close undetected"-as asteroid 2009DD45 nearly did. Astronomers didn't notice the oncoming asteroid until February 28, when it showed up as a faint dot in pictures taken at the Siding Spring Observatory in Australia. At that point the asteroid was already a mere 1.5 million miles (2.4 million kilometers) from Earth, and closing in fast.

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ASTEROID PASSES CLOSE TO EARTH
By Alan Duke, CNN

You had a close encounter with a 40-yard-wide asteroid this week, but the astronomer who first spotted the large rock said it's nothing to worry about. Asteroid 2009DD45 on Monday passed within 38,000 miles of Earth, less than twice the height of the geostationary satellites we depend on for communications, according to Robert McNaught of the Australian National University.

McNaught, who watches for asteroids with his telescope 250 miles northwest of Sydney, Australia, discovered the approaching rock last week. "It's not something to worry about, but something to be aware of," he said.

While a direct hit on Earth could be a devastating natural disaster, McNaught said keeping track of asteroids can make a hit "potentially preventable. There is the possibility of pushing it off course, if you have decades of advance warning," McNaught said. "If you have only a few days, you can evacuate the area of impact, but there's not a great deal [else] you can do."

The 2009 DD45 asteroid circles the sun every 18 months, but its path will not threaten this planet at least for the next century, he said.

The number of "potentially harmful asteroids" discovered each year has grown dramatically over the past decade as "systematic programs" to scan the skies have been put in place, McNaught said. Nearly 100 new ones have been found in each of the past several years, he said.

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SPACE ROCK MAKES CLOSE APPROACH
BBC

An asteroid which may be as big as a ten-storey building has passed close by the Earth, astronomers say. The object, known as 2009DD45, thought to be 21-47m (68-152ft) across, raced by our planet at 1344 GMT on Monday. The gap was just 72,000 km (44,750 miles); a fifth of the distance between our planet and the Moon. It is in the same size range as a rock which exploded over Siberia in 1908 with the force of 1,000 atomic bombs. The object was first reported on Saturday by the Siding Spring Survey, a near-Earth object search programme in Australia.

It was confirmed by the International Astronomical Union's Minor Planet Centre (MPC), which catalogues Solar System objects. The closest recent flyby listed by the MPC is 2004FU162, a small asteroid about 6m (20ft) across which came within about 6,500km (4,000 miles) of our planet in March 2004.

"There is still a lot of debate over how big the Tunguska object was," Professor Alan Fitzsimmons, an astronomer at Queens University Belfast, told BBC News. "It was always thought to be 50 or 70m across. But some recent calculations have implied it may have been even smaller than that - maybe down to 30m in size. There's a large uncertainty there, but it puts (this object) in the same ballpark."

A United Nations working group on near-Earth objects (NEOs) met last month to discuss drafting international procedures for handling the asteroid threat. Dr Richard Crowther, chair of the UN Working Group on Near-Earth Objects, commented: "Although we will meet formally again in June of this year to advance our work on this important issue, I am sure we will discuss the implications of the 2009DD45 close approach informally before then.

He told BBC News: "Such unanticipated near-misses - at least in astronomical terms - demonstrate the need for the global community to establish the means to mitigate this impact threat."

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Among the worst coverage was a report on Fox News, showing the asteroid with a tail like a comet grazing the atmosphere and making a swishing sound, while a female reporter giggled in the background.

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2008TN166

An asteroid discovered in late 2008 turns out to be the brightest (and presumably largest) new NEA since 2001. Its diameter is apparently between 3 and 4 km. Alan Harris (of the Space Science Institute) notes that we have discovered about 82 objects 3 km or larger. He estimates the Spaceguard Survey is at least 95% complete in that size range, so he guesses there are only about 4 more to find, most likely in rather unusual long-period orbits.

The asteroid, 2008TN166, has a relatively long period of about 6 years. It was 4.27 AU from the Sun when it was discovered, nearly as far away as Jupiter. Such asteroids are sometimes referred to as NEAs with comet-like orbits. It was at perihelion in 2001 and 2007. Such large NEAs can still be detected fairly far from the Sun. It was discovered by the Mount Lemmon Survey, which detects objects down to magnitude 22. TN166 was favorably placed for observing in 2007 when it was much closer, but apparently nobody happened to be looking at the right place at the right time then.
DM (with help from Don Gennery and Al Harris)

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