When Worlds Collide

A particularly bright fireball was observed earlier today over a wide area in Russia. Of even greater significance was the very strong sonic boom associated with the passage of the meteor through Earth’s atmosphere.

News out of Russia is reporting that ‘hundreds’ of casualties resulted from people being hit by falling glass, caused by the breaking of windows by the pressure wave associated with the sonic boom. Meteors are quite common around the Earth, but one of this magnitude is fortunately a rare event. The light of the meteor trail that we see in the sky is caused by friction between the incoming fragments and Earth’s atmosphere, which rapidly heats the surface of the fragments to the point that they give off visible light. The intensity of the light is a complex interplay between the speed of the object and the increasing density of the atmosphere as it moves lower into the atmosphere. The sonic boom is a clear indication that the fragments are moving much faster than the speed of sound, and just like jets that exceed the speed of sound, it is the inability of the air molecules to move fast enough to get out of the way of the fast object that generates the shock wave that we hear as a sonic boom. If the shock wave is intense enough, it can break panes of glass, which appears to have been the case today over a large area in Russia.

On June 30, 1908, a rock estimated to about 100 meters (328 feet) in diameter exploded (because of the rapid build-up of pressure as the object got lower into the atmosphere) above the Tunguska region of Siberia, which flattened trees over 2000 square kilometers (800 square miles) and produced a shock wave that knocked people to the ground at a distance of tens of kilometers (tens of miles) from the detonation point.

This image is from the Leonid Kulik expedition in 1927.

Today’s incoming rock likely was quite a bit smaller than the Tunguska rock, although it will take time for Russian scientists to assess what damage has taken place. NASA scientists are confident that the close passage of an asteroid to Earth later today and the trajectory (the flight path) of the Russia meteor were very different, so the two events are not connected, even though they will occur within hours of each other. Both the Russia meteor and the close flyby of an asteroid are reminders that space is not completely empty; whenever Earth happens to cross the path of some solid material in space, whether the size of a sand grain or a large building, the fast-moving objects are going to interact strongly with our atmosphere.

Jim Zimbelman is a geologist in the National Air and Space Museum’s Center for Earth and Planetery Studies

Minor Planet 4262 DeVorkin

David DeVorkin

David DeVorkin is a curator in the Space History Department of the National Air and Space Museum.

On  6 April 2012, the following notice appeared in the Minor Planet Circular, under the category “Names of New Minor Planets”:

(4262) DeVorkin = 1989 CO
Discovered 1989 Feb. 5 by M. Arai and H. Mori at Yorii.
David H. DeVorkin (b. 1944) Chair of the Historical Astronomy Division of the American Astronomical Society (1997-1999), wrote the definitive biography of astronomer Henry Norris Russell. DeVorkin has been Curator at the Smithsonian National Air and Space Museum since 1981.

How did a “minor planet”—colloquially and better known as an asteroid—come to be named after our own David DeVorkin? The story goes back to the retirement party at NASA Headquarters of Steven J. Dick, then Chief Historian of NASA, and before that, the historian of the Naval Observatory in Washington, D.C., for many years. At the party the honoree was delighted by the announcement of a new asteroid name, 6544 Stevendick. I was happy for him, and thought that it would be great if we could the same thing some day for David, who had made so many contributions to the Museum and to the history of astronomy. The idea sat in the back of my mind for a couple of years, as I really wasn’t sure how to go about it. I decided to postpone it until Steve arrived as the Charles A. Lindbergh Chair in Aerospace History in mid-2011 (a one-year fellowship for senior scholars with distinguished publication records).

After he arrived, Steve and I talked about whether we could time a naming for some event, such as a birthday, but the timing could not be reliably controlled. That indeed turned out to be the case, as the first time we submitted a nomination, someone lost Steve’s e-mail and we had to do it all over again in early 2012. The naming process is to submit a short nomination paragraph  (often a capsule biography) to the International Astronomical Union’s Committee for Small-Body Nomenclature via the Minor Planet Center, a body of the IAU run by the Smithsonian Astrophysical Observatory in Cambridge, Mass.

We fashioned the biography above to fit the strict criteria for brevity and included details that might appeal to the astronomers on the committee. Then we waited for something to happen, such as an e-mail. Of course we couldn’t take it for granted that the nomination would be accepted, although it appeared likely. Steve was also concerned that the news would leak after the name came out, based on David’s close contacts with the astronomical community. But nothing happened. Last April Steve finally suggested that we check the Minor Planet Circular, which is the official publication of record and comes out each month around full Moon, and there it was. At least we managed to surprise David.

Comets are named after their first discoverers, a convention that arose in the early twentieth century, but that rule applies to almost nothing else in the sky. When astronomers found the first four asteroids, Ceres, Pallas, Vesta and Juno, at the beginning of the nineteenth century, they treated them as planets, naming them for Roman gods to continue the tradition. As Caltech astronomer Mike Brown notes in his eminently readable memoir How I Killed Pluto, And Why It Had It Coming  (2010), for some time there were 11 or 12 planets, including  those four and in 1846, the newly discovered Neptune. But the proliferation of asteroid discoveries in the late nineteenth century, combined with their small size, resulted in their demotion to minor planethood—sending the number of major planets back to eight, then nine when Clyde Tombaugh discovered  Pluto in 1930, and back to eight when the IAU demoted it to “dwarf planet” in 2006. (Brown discovered the erstwhile tenth planet, Eris, in 2005, but actually favored the reduction to eight, based on the fact that Pluto turned out to only one of a number of rather small “Kuiper Belt objects.”)

As the number of asteroid names grew, a Greco-Roman naming convention became less and less feasible and was eventually dropped for Main Belt objects between Mars and Jupiter—570,355 on the day I write this, and growing by the day, although many have not been assigned formal numbers yet. As the rules in the above link reveal, there are several special classes of minor planets that do retain classical or mythological naming conventions, many of them in special orbits like the Earth-crossers we are increasingly worried about. But Main Belt asteroids can be named almost anything credible by their discoverers for ten years after the object receives an official number—but as the rules say, not for one’s dog, or for political figure who hasn’t been dead for a century. After the decade is up, unnamed asteroids are left to the discretion of the IAU Committee. Rightly or wrongly, Steve and I take the assignment of the relatively low number of 4262 to David DeVorkin as a sign of the appreciation of the committee for the importance of his work (only one with a lower number was named in the 6 April Circular).

What do we know about 4262 DeVorkin? Not very much. Discovered by two Japanese astronomers, it is a small rock, only a few kilometers across, orbiting in the Main Belt. The only pictures of it that have been taken show just a moving pinpoint of light. But perhaps in this or some future century, one of our spacecraft, crewed or robotic, might pass by and take some pictures. Someone will ask: who was DeVorkin anyway? The official description on some future version of the web will be one way he or she could find out.

Michael J. Neufeld is a curator in the Space History Department of the National Air and Space Museum. He is the author of  Von Braun: Dreamer of Space, Engineer of War (2007).