Fly-by-night Rocks And Dustballs


A good near-Earth asteroid explainer after you get through the commercial

Looks like we all survived the whiz-by of two asteroids moving in unrelated orbits yesterday. 2010 RX30 is about 32-65 feet across and flew some 154,000 or 0.6 the distance of the moon from Earth, while the smaller 2010 RF12 ( 20-46 feet) passed even closer at just 49,000 miles. Despite their closeness, both were very faint objects visually with magnitudes around 15-16. Both were discovered on September 5 by the Catalina Sky Survey based near Tuscon, Arizona. I find it amazing that such tiny objects can be picked up at all. Scientists estimate there are something like 50 million house-sized asteroids orbiting the sun in the vicinity of our planet with an average of one a day passing between us and the moon. From this population, one every ten years would be expected to hit our atmosphere and possibly survive its plunge to the ground in the form of meteorites.

If you’ve got a couple minutes and want to find out what kind of destructive force asteroids of a particular size and consistency have, check out the Impact Calculator. The user-friendly interface lets you choose size, impact angle, speed and more, and then outputs the crater size, depth and magnitude of the quake created. It’s a good way to get to know the dark side of these seemingly innocent star-like objects we watch creep across the night sky with our telescopes.

Comet Hartley 2 photographed through an 8-inch telescope this past weekend. The comet is currently in the evening sky in Andromeda and visible in 6-inch and larger telescopes. By early next month it will be bright enough to see in binoculars. Credit: Michael Jaeger

As long as we’re on the topic of flying rocks, NASA’s Deep Impact probe, the one that flung an 815-lb. hunk of copper into the Comet Tempel 1 on July 4, 2005 in order to study to study the aftermath of the impact, has begun a new mission to study Comet Hartley 2. Like Tempel 1, Hartley 2 is a periodic comet, one that goes around the sun in a relatively short period of time. Hartley, discovered by Malcolm Hartley in 1986, completes an orbit in 6 1/2 years; this fall it will pass near the Earth and become as bright as 5th magnitude during late October and early November, making it an easy binocular comet. Cross your fingers – it might be bright enough to see with the naked eye.

Artist's view of Deep Impact at Tempel 1 in 2005. Comet Hartley 2's core or nucleus is small by cometary standards, measuring only about 1/2 mile across. Comets are small bodies like asteroids but composed of a mixture of dust and ice. Credit: NASA

Since 2005, Deep Impact has been on an extended mission called EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation), and its target for the next 79 days is Hartley 2. Last Sunday it beamed its first photo of the comet to Earth, one of more than 64,000 pictures the probe will take during the mission. The flyby and closest approach to the comet will occur on November 4 which turns out to be the same time it’s best viewed here on Earth. We can look forward to seeing closeups of the what’s at the center of all that cometary fuzziness while at the same time following it in our binoculars. Very cool. Scientists will use the craft’s two camera-equipped telescopes for photography and an infrared spectrometer to study the comet’s makeup. In the coming weeks, I’ll provide easy-to-use maps so you can find Comet Hartley 2 for yourself. Read more about the comet HERE.

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