Date: October 31st, 2012

Title: Monthly News Roundup – A New Neighbor

Podcaster: Morgan Rehnberg


Alpha Centauri Bb:

Hubble’s Constant:


Saturn’s moons:

Bio: Morgan Rehnberg is a graduate student at the University of Colorado – Boulder, where he studies the rings of Saturn under the direction of Dr. Larry Esposito. Morgan received his B.S. in Physics from Beloit College and is the developer of the PhAst software package for the viewing and manipulating of astronomical images

Description: In this episode of the Monthly News Roundup, Earth gets a new neighbor and the Universe gets a more accurate age.  Astronomers discover a new heating mechanism in space and suggest a new formation model for Saturn’s moons.

Bio: Morgan Rehnberg is a graduate student at the University of Colorado – Boulder, where he studies the rings of Saturn under the direction of Dr. Larry Esposito. Morgan received his B.S. in Physics from Beloit College and is the developer of the PhAst software package for the viewing and manipulating of astronomical images

Today’s Sponsor: This episode of 365 days of Astronomy is sponsored by – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.



Welcome to the 365 Days of Astronomy Podcast for October 31st, 2012.  I’m Morgan Rehnberg and this is the Monthly New Roundup.  Happy Halloween!  This episode was recorded October 27th from Boulder, Colorado.


Our top story this month is the discovery of the closest ever extra-solar planet.  The planet, named Alpha Centauri Bb, was found in the triple-star system Alpha Centauri, the closest star system to Earth.  With a mass believed to be only slightly larger than that of Earth’s, it is also the smallest-ever planet discovered outside our solar system.

The discovery was made by a team of European astronomers using the 140-inch telescope at the European Southern Observatory and announced this month in the journal Nature.

The team used the radial-velocity method to detect Alpha Centauri Bb.  This technique relies on the fact that an orbiting planet tugs its host star around a bit as it circles.  When the planet is closest to us, it tugs the star towards the Earth a tiny bit; the opposite effect occurs when the planet is at its farthest point.  When the star moves towards us, the light it emits looks slightly bluer than normal. When it’s moving away from us, the light looks a bit redder.  Astronomers use an instrument called a spectrograph to measure these changes and relate them to the size of the planet.  In this case, the star was moving towards and away from us at an excruciatingly slow pace of about 50 centimeters per second.  Such a measurement was only possible because of how nearby the planet and star are.

Sadly, Alpha Centauri Bb would be a pretty unpleasant place to visit.  With a year that lasts just three Earth days, the planet bakes in the heat of its star, reaching temperatures of over 1000 degrees.  If a habitable planet does exist around this star, however, it won’t take a very large advance in technology to detect it and we’ll hopefully know in the coming years.

What will probably have to wait more than a few years is the launch of a mission to directly study Alpha Centauri Bb.  At more than 4 lightyears away, it would take our fastest spacecraft tens of thousands of years to reach the star.  The good news, however, is that the speeds needed to reach the planet on human timescales are not only physically plausible, but an active field of research today.


From the local, let’s turn to the cosmic.  Scientists this month announced the most precise measurements of Hubble’s constant yet obtained.  These observations place stricter limits on the age and size of the Universe and continue the process of narrowing down this notoriously difficult-to-measure parameter.

Hubble’s constant gives the rate of expansion of the Universe.  It’s new value, 74.3 plus or minus 2.1 km/s/kpc means that a galaxy observed 1 kiloparsec, or about three million lightyears, away will be moving away from us at a rate of 74.3 kilometers per second.  Objects even farther away recede even faster, sometimes even faster than the speed of light.  To determine the age of the Universe, astronomers can take this expansion, run time backwards, and calculate how long it takes the Universe to collapse back to the Big Bang.

The parameter was first discovered theoretically in 1927 by Georges Lemaître (“Lament”) who derived it from Einstein’s theory of general relativity.  It’s named, however, for Edwin Hubble, who confirmed this expansion observationally two years later at the newly-constructed 100-inch telescope at the Mount Wilson Observatory.

But Hubble’s constant, it turns out, is not so constant after all.  In the late 1990’s, observations began to show that the rate of expansion is actually accelerating.  This is contrary to our current understanding of physics.  On scales as large as the Universe, gravity is the only force through which interactions occur and it should be working to pull the things closer together, slowing the pace of expansion.  Something must be overpowering gravity, and cosmologists call this mystery force dark energy.  Not to be confused with the unrelated dark matter, dark energy remains one of the most important open questions in physics today.


Supernova remnants are some of the most beautiful objects in the galaxy.  These hot pockets of material seem to be glowing from within as they expand out into space.  But what powers this glow?  A group of Russian astronomers publishing this month in the journal Nature have detected titanium-44, believed to be one of the key fuel sources for supernova remnants.

Titanium-44 is a radioactive version of titanium which decays with a half-life of 60 years into the element scandium. This process releases energy which then heats up the surrounding material and causes the beautiful glows.  These new observations show that the supernova 1987a released an amount of titanium-44 equal to about 100 times the mass of the Earth, more than scientists were expecting.

Supernovae occur at the end of the life of a giant star.  Stars about the same size as our Sun end their lives by collapsing to a tiny, hot star known as a white dwarf.  When much larger stars run out of fuel, however, they explode in an event that temporarily shines more brightly than an entire galaxy. During this time, extra-heavy elements are forged and spewed out into space.  While hot, these elements lack any source of continuous energy.  This is where radioactive elements like titanium-44 come into play.  They briefly power the supernova remnant as it slowly starts to fade away.

Fortunately for us, all known supernovae have occurred far from the Earth.  The closest star to us which has a chance to go supernova is the star Betelgeuse, which lies about 650 lightyears away.  If Betelgeuse were to explode, it would be visible during the day for a few weeks before fading from view forever.


We end this month with a return to our solar system for a peek into the formation of Saturn’s moons.  Saturn hosts 62 moons which vary greatly in both size and composition.  From giant Titan with its lakes of liquid methane to tiny Anthe’s almost pearl-like icy exterior, Saturn’s moons are a diverse bunch.  Scientists presenting this month at the Division for Planetary Sciences meeting of the American Astronomical Society have put forth a new mechanism for the formation of these varied bodies.

They postulate that Saturn once had a family of giant moons, much like Jupiter does today.  Unlike Jupiter’s Galilean moons, however, these moons were on unstable orbits which eventually led them to collide with one another.  These powerful collisions broke the moons into chunks of ice and rock.  Most of this debris reformed into the even larger Titan that we see today, but some went on to form the myriad smaller moons which are mostly constructed of ice.

Lest you think such titanic interactions were confined to the outer solar system, Earth’s moon is also believed to have been the result of an even more violent impact.  Astronomers at the same meeting put forth several new theories which try to account for the substantial amount of Earth-based materials which make up our moon.

Thanks for listening to this episode of the Monthly News Roundup.  As always, I welcome your comments and corrections.  You can contact me at  See you next month!

End of podcast:

365 Days of Astronomy
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