astronomy@iowa

At 13:40 UT (that’s 7:40 a.m. CST) on March 2, the near-Earth asteroid 2009 DD45 zipped past Earth at a distance of only 0.00048 A.U. Considering that the average Earth-Sun distance is 1 Astronomical Unit, 0.00048 A.U. works out to be a mere 45,000 miles! That’s a close shave by anyone’s standards. The Moon’s average distance is 240,000 miles and the geosynchronous satellites monitoring our weather and blanketing Earth with a global positioning and communication network orbit the earth at 23,000 miles. Having an Apollo group asteroid careen past the planet at twice the distance of the geosynchronous satellites is certainly something to note.

This kind of celestial fly-by is not entirely unprecedented, however. In 1972 a small asteroid (or meteoroid, if you prefer) skimmed through Earth’s upper atmosphere as if it were a stone skipping off a pond. That object entered the atmosphere over the Northwest United States and exited somewhere over Canada. Estimated to be about the size of an SUV, an impact or airburst of an rock this size would have been very impressive. Not the kind of event that would spell doom for civilization, but enough to get your attention. The most recent event of this type was the Tunguska blast over a remote area of Siberia in 1908 when a loose-aggregate meteoroid, or perhaps a comet fragment, entered the atmosphere and exploded in the upper atmosphere. Trees were stripped of branches and felled for many square miles around the spot directly below the blast. On a bit larger scale, anyone standing in the desert Southwest 50,000 years ago might have been in for a shock when a 100-foot meteoroid slammed into the ground (becoming a meteorite in the process) and created the Barringer meteor crater. At over 3/4 mile in diameter and nearly 600 feet deep, Barringer crater is the best preserved example of what happens when big rocks cross Earth’s orbit.

Thought to be about the same size as the Tunguska event’s object and just  bit smaller than the meteorite responsible for the Barringer crater, 2009 DD45 is over 100 feet in size and could have potentially unleashed many dozens of times the explosive force of the atomic bombs used at the end of World War II. Sleep well.

For further information: 2009 DD45 orbital parameters from NASA’s Jet Propulsion Laboratory (JPL) and a movie on YouTube showing the asteroid’s fly-by.

On September 17, the International Astronomical Union announced that 2003 EL61 would be classified as the fifth named dwarf planet and officially designated Haumea. The name was chosen after meetings of the IAU’s Committee on Small Body Nomenclature and the Working Group for Planetary System Nomenclature. The number of dwarf planets is now five: Ceres, Eris, Haumea, Makemake and Pluto.

The 2,200 km ellipsoidal body—deformed due to a four-hour rotation period—is just beyond the orbit of Pluto and has two satellites. Orbiting among the Trans-Neptunian objects, Haumea is currently 50 astronomical units from the Sun but can get as close as 35 A.U. The astronomical unit is the average Earth-Sun distance and a standard measure of distance within the solar system.

In Hawaiian mythology, Haumea is the goddess of childbirth and fertility.

Two years ago the International Astronomical Union (IAU) angered a lot of people when the Solar System’s ninth planet Pluto was demoted and designated a “dwarf planet” along with the asteroid Ceres and the recently discovered trans-neptunian object Eris. Well, the IAU has now come up with an official designation for Pluto and Eris that is almost guaranteed to upset people all over again. While some may think it’s a silly exercise to spend so much energy coming up with classification schemes (years ago the physicist Enrico Fermi complained about the number of sub-atomic particles saying “If I could remember the names of all these particles, I’d be a botanist.”), it is important for scientists to make classifications of the objects they study. The Greeks used the term “planetes astrum” to describe the wandering stars—as opposed to the “fixed” stars—but that definition did not really distinguish the actual planets from the Moon and Sun. But “Plutoid?”

The IAU Committee on Small Body Nomenclature defines a plutoid as “celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit.” For naming purposes, any body that meets these criteria and have an absolute magnitude brighter than H = +1 where H is the magnitude of the planet, asteroid, comet, etc. at one Astronomical Unit from the Sun.

In the above image, Pluto and its three moons are shown on the left while Eris is on the right.

Image Credit: IAU, NASA/ESA Hubble Space Telescope, H. Weaver (JHU/APL), A. Stern (SwRI), the HST Pluto Companion Search Team and M. Brown.