Monthly Archives: March 2009

2009 dd45, asteroid

Revisiting the Celestial Drive-by

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More Data Yields Better Information

Remember that near-Earth asteroid that whizzed by us last week and caused a flurry of excitement? There was a lot of speculation about how much damage 2009 DD45 would have caused if it had hit our planet. Several of us wrote about that in a special New York Times blog discussion and there were numerous press reports about “‘Roid Rage” and so forth.

Well, with the passage of time and continuing observations of this tiny interloper, astronomers have been able to tighten up the size estimates on 2009 DD45. In a short note to subscribers of the NEO News listserv, scientist David Morrison reported:

Rick Binzel and colleagues observed DD45 in the infrared from Mauna Kea and reported as follows to the Central Bureau for Astronomical Telegrams: R. P. Binzel, M. Birlan, and F. E. DeMeo, Paris Observatory, made 0.8- to 2.5-micron spectroscopic measurements on Mar. 2.6 UT using the NASA Infrared Telescope Facility 3-m reflector on Mauna Kea. Absorption bands revealed at 1 and 2 microns show the characteristics of the S-type class of asteroids. Using the average albedo value of 0.36 for small NEAs in this class and based on its observed brightness, the diameter is estimated to be 19 +/- 4 m. This is near the lower size limit and, together with the stony composition, suggests that this object would likely have disintegrated too high to do any ground damage. Knowing the size also allows us to revise the estimate of how often a NEA of this size passes this close to Earth, to roughly once per year.

Asteroid Eros is a good example of a S-type asteroid; the chunk of rock that wandered past Earth last week is also an S-type asteroid. Courtesy NASA (click to embiggen).
Asteroid Eros is a good example of a S-type asteroid; the chunk of rock that wandered past Earth last week is also an S-type asteroid. Courtesy NASA (click to embiggen).

So, essentially what happened is that observers figured out what this object is made of — a stony mix of silicates and other rocky materials. We know how much light such materials can reflect (what their brightness, or albedo, is), and based on the observed brightnesses, astronomers were able to figure out a size of somewhere between 15-23 meters (roughly  50 to 75 feet) in diameter. That’s not large enough to make it safely through the atmosphere — this object would have burned up had it been on a collision course with Earth.

This illustrates the value of continuing observations of asteroids, or any celestial object for that matter. The more you observe, the more you learn and the more you ultimately know about an object.  No doubt continued observations of DD45 will refine its orbital parameters, its spin, and other factors about this piece of rock that orbits the Sun and occasionally comes close to Earth.

exoplanets, extrasolar planets, Keck Observatory, Kepler mission

About Those Exoplanets

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How Will We Know What Kepler’s Finding?

The galaxy neighborhood that Kepler will search for exoplanets. Courtesy Kepler Mission, painting by Jon Lomberg. (Click to embiggen.)
The galaxy neighborhood that Kepler will search for exoplanets. Courtesy Kepler Mission, painting by Jon Lomberg. (Click to embiggen.)

Now that the Kepler mission is on its way to final orbit and commissioning, astronomers are excited about the possibilities for new planets to be found “out there” in the nearest 3,000 light-years of space.  It’s worth remembering, however, that the Kepler spacecraft will be identifying planetary “possibilities” — that is, it will study star fields over time; in its data will be stars that appear to flicker.

The Kepler folk have a very cool interactive page that helps you understand how the spacecraft does its search (note, the link leads to a Flash-activated site), but essentially it looks for those flickers of star light and then relays that information to scientists for further study. There are thousands of stars to look at, so once Kepler commences on its official search mission, the datasets could be quite large. And who knows what we’ll find out there?

There are several possibilities about what causes stars to flicker, and only one of them is a planetary system.  A star could flicker because it’s variable – that is, it has some intrinsic (exclusive to itself) mechanism that causes its luminosity to brighten and dim on a regular schedule. All those stars will be of great interest to folks who study variables — including the American Association of Variable Star Observers.

Another possibility might be gravitational lensing events.  These occur when something  massive passes between us and a more distant object. Of course we’re familiar with gravitational lensing by distant galaxy clusters, but it can happen that something will do the same thing to a star in our own galaxy, causing its light output to appear to flicker. The late scientist Bohdan Paczy?ski was quite interested in such events, and the OGLE survey (among others) does real time studies of such events in our galaxy.

The Keck telescopes on Mauna Kea are used for planet-hunting. The Kepler mission findings will keep it busy searching out exoplanets. (Photo by Laurie Hatch, used by permission; click to embiggen.)
The Keck telescopes on Mauna Kea are used for planet-hunting. The Kepler mission findings will keep it busy searching out exoplanets. (Photo by Laurie Hatch, used by permission; click to embiggen.)

So, before Kepler scientists can confidently state that they’ve found a planet around another star, they have to take into account those other possibilities.

Once they think they’ve got a candidate, that’s when people like Geoff Marcy (of the University of California at Berkeley) step in and observe those stars using observatories such as the W.M. Keck telescopes in Hawai’i.

They essentially look for planets that are “transiting” the disks of the stars — that is, they pass in front of the star from our point of  view. That transit causes the flicker of starlight that betrays the existence of a planet.

The Keck team, headed by Marcy, will start looking for planetary candidates using Kepler data starting in late July of this year.  So, keep your eyes open for news from the exoplanet front. It’s bound to be interesting!