Podcaster: Morgan Rehnberg

Title:   Monthly News Roundup – A Record Setting Month

Link :

Einstein planet:
Gamma-ray burst:
Moon impact:

Description: Two of the largest ever blasts are observed.  Kepler may be ending, but could a new exoplanet discovery method take over?

Bio: Morgan Rehnberg is a graduate student in astrophysics and planetary science at the University of Colorado – Boulder.  When not studying the rings of Saturn, he develops software to help search for asteroids that might hit the Earth.  He blogs and podcasts about astronomy and space science at

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2013, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at



You’re listening to the 365 Days of Astronomy Podcast for May 26, 2013. I’m Morgan Rehnberg and this is the Monthly News Roundup. This episode was produced by Cosmic Chatter and recorded May 23rd in Boulder, Colorado.


We start this month with the likely end of NASA’s planet hunting mission. The Kepler spacecraft, which is operated by my employer, the Laboratory for Atmospheric and Space Physics, suffered a mechanical breakdown this month. With the loss of its second reaction wheel, Kepler can probably no longer maintain the precise aim required to make accurate observations.

Reaction wheels are used to control the orientation of virtually all modern spacecraft. They work by leveraging a principle called the conservation of angular momentum. Like anything rotating, these spinning metal disks have angular momentum. Changing how fast they spin alters the amount of momentum the disk has. But, since this momentum is conserved, changing how the disk rotates also causes Kepler itself to rotate. Since we live in a three-dimensional world, we need three reaction wheels, one for each axis on which the spacecraft must rotate.

Reaction wheels have a couple of distinct advantages over maneuvering thrusters. They can be controlled using electric motors powered by Kepler’s solar panels. This saves valuable fuel, which is very heavy. These motors can also be controlled more finely than thrusters, allowing smaller, more precise adjustments to be made.

Unfortunately, reaction wheels also have a downside. Because they are constantly in motion for the duration of a mission, reaction wheels are a common point of mechanical failure. Because of this, Kepler carried a backup wheel for just this kind of situation. The problem is, this isn’t the first reaction wheel to fail. The backup was put into service last year to replace the first malfunctioning wheel. Now, with a second wheel damaged, there are not enough left to position the spacecraft.

Mission controllers are considering a couple of possible fixes, including using a single maneuvering thruster to replace the missing reaction wheel and trying to restart last year’s broken wheel. In reality, though, this breakdown likely will mark the end of the Kepler mission.

Even if Kepler has, in fact, made its final observation, its legacy in astronomy is already assured. Over the last three and a half years, the mission has resulted in the discovery of thousands of new planets. Prior to Kepler, we knew of only a few celestial neighbors. Now, the sky just seems full of them.


The news for planet hunters wasn’t all bad this month. A team of researchers using data from Kepler successfully demonstrated a new technique for discovering exoplanets. This method makes use of Einstein’s theory of special relativity and the planet, formally known as Kepler-76b, has been nicknamed Einstein’s planet.

The theory of special relativity is among the most important in physics. It postulates, among other things, that space and time are linked and that the speed of light is constant for all observers in the universe. One of the interesting consequence of these ideas is the so-called “headlight effect.” The headlight effect says that objects emitting light appear brighter in the direction they are moving and dimmer elsewhere.

Since an orbiting planet causes a star to move back and forth, the star should appear to brighten and dim slightly during the course of the planet’s orbit. This stellar wobbling is the same effect utilized by the popular Doppler shift method of planet discovery. In that method, the star changes color as it moves back and forth.

By measuring how drastically the star changes in brightness, astronomers can infer how quickly it must be wobbling. This is directly connected to the mass of the orbiting planet, revealing a piece of information not typically available about Kepler-discovered planets.

This effect is very slight, meaning that extremely accurate observations are required. This might limit the ultimate utility of this technique, but it could provide a nice complement to Kepler-like transit observations when such accuracy is present. Either way, it’s one more tool in the belt for planet searchers.


May also marked another far-out event: the brightest-ever recorded gamma-ray burst. The burst, which was observed by multiple space- and ground-based observatories, was also the longest-ever observed event. Because it was detectable for nearly a day, an unprecedented amount of data could be collected.

Gamma-rays are the highest-frequency, most energetic form of light. A typical gamma-ray has more than a billion times more energy than a ray of light emitted by the Sun. Because of this, they are extremely difficult to detect. It also takes an event with an incredible amount of energy to generate them. Most gamma-ray bursts are associated with supernovae, the most powerful explosions in the Universe. When these giants stars collapse, they form black holes. Material which doesn’t fall into the black hole is ejected at nearly the speed of light. Along with this material are gamma-rays.

This burst, named GRB 130427A, smashed all previous records. One detected photon was more than three times as energetic as any other photon ever observed. First detected by NASA’s SWIFT and Fermi space telescopes, many ground-based observatories soon joined in. Because of their high energies, special types of telescopes must be used to observe gamma-rays.

Although gamma-rays are extremely hazardous to living organisms, the Earth’s atmosphere largely protects us from them. Lower-energy gamma rays can be emitted here on Earth through radioactive decay and are one of the most hazardous forms of radiation.

Astronomers will keep their eyes peeled for any signs of the supernova which likely caused this event. The incredible energies released in this particular blast will make such an explosion a fascinating source of study.


A smaller, yet still-record-setting blast occurred closer to home this month. Automated telescopes monitoring the Moon observed the largest impact ever observed on that body. The resulting flash was ten times brighter than anything seen previously. Had you happened to be looking at the Moon at just the right time, it would have been easily visible to the naked eye.

The object which created the blast was quite small – less than half a meter in diameter. Yet it created a crater nearly twenty meters across. How is this possible? The meteorite was travelling more than 90,000 kilometers per hour when it struck the lunar surface. The tremendous kinetic energy of the projectile vaporized nearby surface material and blasted the rest out of the crater.

Scary as it sounds, such impacts are quite common on the Earth. Unlike the Moon, however, the Earth has a protective atmosphere and such space rocks burn up as beautiful shooting stars. Friction from the air in our atmosphere heats them up until they explode harmlessly far above the surface.

Although this blast may be the largest ever recorded, it’s far from the largest the Moon has ever suffered. Many craters on the Moon are tens or even hundred of kilometers across. The largest, Aitken basin, would cover nearly half the United States.

Impactors like the one observed this month are too small to be reliably detected by telescopes looking for Earth-impact asteroids. But the random and unpredictable nature of these impacts highlights the importance of keeping a watchful eye for these incoming visitors.


Thanks for listening to this episode of the 365 Days of Astronomy Podcast. For more astronomy news and commentary, visit or follow cosmic_chatter on Twitter. You can send comments and corrections to See you in June!


End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at In the new year the 365 Days of Astronomy project will be something different than before….Until then…goodbye.